Electrode assembly and secondary battery

Abstract

The utility model provides an electrode assembly and a secondary battery. The electrode assembly comprises a positive pole piece, a negative pole piece and a diaphragm structure arranged between the positive pole piece and the negative pole piece, the positive pole piece is provided with first equal-thickness parts, the negative pole piece is provided with second equal-thickness parts, the compaction density of the first parts of the first equal-thickness parts is larger than that of the second parts, the number of the first parts is two, and the number of the second parts is two. The second part is located between the two first parts in the width direction of the electrode assembly; and / or the compaction density of the fourth part of the second equal-thickness part is larger than that of the third parts, and the fourth part is located between the two third parts in the width direction; and / or the ionic conductivity of the first region of the diaphragm structure is smaller than that of the second regions, and the first region is located between the two second regions in the width direction. According to the utility model, the problem that the capacity of the secondary battery is reduced due to the lithium precipitation phenomenon of the secondary battery in the prior art is solved.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and more specifically, to an electrode assembly and a secondary battery. Background Technology

[0002] A rechargeable battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after being discharged, allowing the active materials to be reactivated and reused. Lithium-ion batteries, as a representative of rechargeable batteries, are characterized by high energy density and long cycle life. The following section uses lithium-ion batteries as an example to illustrate this.

[0003] During the cycling process of a secondary battery, capacity decay inevitably occurs. This decay can be categorized into reversible and irreversible capacity decay. Lithium plating on the surface of the negative electrode is a representative example of irreversible capacity decay. In current technologies, to achieve high energy density in secondary batteries, the ratio of active material capacity per unit area of ​​the positive and negative electrodes is designed to be relatively extreme. This leads to lithium plating easily occurring in the central region of the negative electrode during cycling, resulting in a reduction in battery capacity.

[0004] Therefore, existing technologies suffer from the problem that secondary batteries are prone to lithium plating, which leads to a reduction in battery capacity. Utility Model Content

[0005] The main objective of this invention is to provide an electrode assembly and a secondary battery to solve the problem that lithium plating easily occurs in existing secondary batteries, leading to a reduction in battery capacity.

[0006] To achieve the above objectives, according to one aspect of the present invention, an electrode assembly is provided, comprising a positive electrode, a negative electrode, and a separator structure disposed between the positive and negative electrode. The positive electrode has a first equal-thickness portion, and the negative electrode has a second equal-thickness portion, wherein: the compaction density of a first portion of the first equal-thickness portion is greater than the compaction density of the second portion; there are two first portions, and the second portion is located between the two first portions along the width direction of the electrode assembly; and / or the compaction density of a fourth portion of the second equal-thickness portion is greater than the compaction density of a third portion; there are two third portions, and the fourth portion is located between the two third portions along the width direction; and / or the ionic conductivity of a first region of the separator structure is less than the ionic conductivity of a second region; there are two second regions, and the first region is located between the two second regions along the width direction.

[0007] Furthermore, the first equal-thickness portion has a first center line extending along the length direction of the electrode assembly, the first center line passing through the second portion, and the second portion being symmetrically arranged about the first center line, and the two first portions being symmetrically arranged about the first center line; and / or the second equal-thickness portion has a second center line extending along the length direction, the second center line passing through the fourth portion, and the fourth portion being symmetrically arranged about the second center line, and the two third portions being symmetrically arranged about the second center line; and / or the diaphragm structure has a third center line extending along the length direction, the third center line passing through the first region, and the first region being symmetrically arranged about the third center line, and the two second regions being symmetrically arranged about the third center line.

[0008] Furthermore, the width of the second part is 40-50% of the width of the first equal-thickness part; and / or the width of the fourth part is 40-50% of the width of the second equal-thickness part; and / or the width of the first region is 40-50% of the width of the diaphragm structure.

[0009] Furthermore, the second part has a first transition portion at the connection between it and the two first parts, and the compaction density of the first transition portion gradually decreases in the direction away from the first part; and / or the fourth part has a second transition portion at the connection between it and the two third parts, and the compaction density of the second transition portion gradually increases in the direction away from the third part.

[0010] Furthermore, the thickness of the second region of the diaphragm structure is less than the thickness of the first region.

[0011] Furthermore, the diaphragm structure includes: a first diaphragm and a second diaphragm stacked together, the width of the first diaphragm being smaller than that of the second diaphragm, the overlapping portion of the first diaphragm and the second diaphragm forming a first region, and the portion of the second diaphragm not covered by the first diaphragm forming a second region.

[0012] Furthermore, the thickness difference between the first region and the second region is less than or equal to 7 micrometers; or the thickness difference between the first region and the second region is less than 5% of the thickness of the positive electrode sheet; or the thickness difference between the first region and the second region is less than 5% of the thickness of the negative electrode sheet.

[0013] Furthermore, the diaphragm structure includes a substrate and a coating layer disposed on the substrate, wherein the thickness of the coating layer in the second region is less than the thickness of the coating layer in the first region; and / or the thickness of the substrate in the second region is less than the thickness of the substrate in the first region.

[0014] Furthermore, the porosity of the second region of the membrane structure is greater than that of the first region.

[0015] According to another aspect of the present invention, a secondary battery is provided, including the electrode assembly described above.

[0016] Applying the technical solution of this utility model, the electrode assembly in this application includes a positive electrode sheet, a negative electrode sheet, and a separator structure disposed between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet has a first equal-thickness portion, and the negative electrode sheet has a second equal-thickness portion, wherein: the compaction density of the first portion of the first equal-thickness portion is greater than the compaction density of the second portion, there are two first portions, and the second portion is located between the two first portions along the width direction of the electrode assembly; and / or the compaction density of the fourth portion of the second equal-thickness portion is greater than the compaction density of the third portion, there are two third portions, and the fourth portion is located between the two third portions along the width direction; and / or the ionic conductivity of the first region of the separator structure is less than the ionic conductivity of the second region, there are two second regions, and the first region is located between the two second regions along the width direction.

[0017] When using the electrode assembly of this application, by setting the compaction density of the first portion of the first equal-thickness portion of the positive electrode sheet to be greater than the compaction density of the second portion of the first equal-thickness portion, and setting the compaction density of the fourth portion of the second equal-thickness portion of the negative electrode sheet to be greater than the compaction density of the third portion of the second equal-thickness portion, the CB value (the ratio of negative electrode material capacity per unit area to positive electrode material capacity per unit area) between the second and fourth portions can be increased, thereby effectively reducing lithium deposition. Furthermore, setting the ionic conductivity of the first region of the separator structure to be less than the ionic conductivity of the second region of the separator structure can effectively reduce the electrochemical reaction rate of the positive and negative electrodes in the first region, thereby reducing lithium intercalation in the negative electrode sheet, and thus also effectively reducing lithium deposition. Therefore, the electrode assembly of this application effectively solves the problem of lithium deposition in existing secondary batteries, which easily leads to a reduction in battery capacity. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an undue limitation of the present invention. In the drawings:

[0019] Figure 1 A schematic diagram of the structure of an electrode assembly according to a specific embodiment of the present invention is shown;

[0020] Figure 2 This shows a front view of the first equal-thickness portion of the positive electrode sheet of the electrode assembly in this application before rolling;

[0021] Figure 3 It shows Figure 2 A side view of the first uniform thickness portion of the positive electrode sheet before rolling;

[0022] Figure 4 It shows Figure 2A top view of the first uniform thickness portion of the positive electrode sheet before rolling;

[0023] Figure 5 A schematic diagram of the structure of the positive electrode sheet according to a specific embodiment of this application is shown;

[0024] Figure 6 A schematic diagram of the structure of the negative electrode sheet according to a specific embodiment of this application is shown;

[0025] Figure 7 This shows a front view of the second equal-thickness portion of the negative electrode sheet of the electrode assembly in this application before rolling;

[0026] Figure 8 It shows Figure 7 Side view of the second equal-thickness portion of the negative electrode sheet before rolling;

[0027] Figure 9 It shows Figure 7 A top view of the second equal-thickness portion of the negative electrode sheet before rolling.

[0028] The above figures include the following reference numerals:

[0029] 10. Positive electrode sheet; 11. First equal thickness portion; 111. First part; 112. Second part; 113. First transition portion; 12. First thinning region; 13. Positive current collector; 20. Negative electrode sheet; 21. Second equal thickness portion; 211. Third part; 212. Fourth part; 213. Second transition portion; 22. Second thinning region; 23. Negative current collector; 30. Membrane structure; 31. First membrane; 32. Second membrane. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0032] In this utility model, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction of the component itself; similarly, for ease of understanding and description, "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not used to limit this utility model.

[0033] To address the problem that lithium plating easily occurs in existing secondary batteries, leading to a reduction in battery capacity, this application provides an electrode assembly and a secondary battery.

[0034] Furthermore, the secondary battery in this application has the following electrode assembly.

[0035] like Figures 1 to 9 As shown, the electrode assembly in this application includes a positive electrode 10, a negative electrode 20, and a separator structure 30 disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10 has a first equal-thickness portion 11, and the negative electrode 20 has a second equal-thickness portion 21, wherein: at least a portion of the first equal-thickness portion 11 has a compaction density greater than at least another portion of the first equal-thickness portion 11; and / or at least a portion of the second equal-thickness portion 21 has a compaction density greater than at least another portion of the first equal-thickness portion 11; and / or at least a portion of the separator structure 30 has an ionic conductivity less than at least another portion of the separator structure 30. Specifically, the first equal-thickness portion 11 includes a first part 111 and a second part 112. The compaction density of the first part 111 of the first equal-thickness portion 11 is greater than that of the second part 112. There are two first parts 111, and the second part 112 is located between the two first parts 111 along the width direction of the electrode assembly. And / or the second equal-thickness portion 21 includes a third part 211 and a fourth part 212. The compaction density of the fourth part 212 of the second equal-thickness portion 21 is greater than that of the third part 211. There are two third parts 211, and the fourth part 212 is located between the two third parts 211 along the width direction. And / or the membrane structure 30 includes a first region and a second region. The ionic conductivity of the first region of the membrane structure 30 is less than that of the second region. There are two second regions, and the first region is located between the two second regions along the width direction. As can be seen from the above, for the electrode assembly in this application, different compaction density regions can be set only for the first uniform thickness portion 11 of the positive electrode 10, or only for the second uniform thickness portion 21 of the negative electrode 20, or only for the membrane structure 30, with different ionic conductivity settings. Of course, these three settings can also be combined in pairs, or all three can be set simultaneously. In this case, correspondingly, the second portion 112, the fourth portion 212, and the first region are set in pairs or all three relative to each other. It should be noted that the width direction in this application is... Figure 1 The vertical direction in this application is the length direction. Figure 1 The left and right directions in the middle.

[0036] When using the electrode assembly of this application, by setting the compaction density of the first portion 111 of the first equal-thickness portion 11 of the positive electrode 10 to be greater than the compaction density of other regions of the second portion 112, and by setting the compaction density of the fourth portion 212 of the second equal-thickness portion 21 of the negative electrode 20 to be greater than the compaction density of the third portion 211 of the second equal-thickness portion 21, the CB value (the ratio of negative electrode material capacity per unit area to positive electrode material capacity per unit area) between the second portion 112 and the fourth portion can be increased, thereby effectively reducing lithium deposition. Furthermore, by setting the ionic conductivity of the first region of the separator structure 30 to be less than the ionic conductivity of the second region of the separator structure 30, the electrochemical reaction rate of the positive electrode 10 and the negative electrode 20 in the first region can be effectively reduced, thereby reducing lithium intercalation in the negative electrode 20 and effectively reducing lithium deposition. Therefore, the electrode assembly of this application effectively solves the problem in the prior art where lithium deposition easily occurs in secondary batteries, leading to a reduction in secondary battery capacity.

[0037] Optionally, in one specific embodiment of this application, the first equal-thickness portion 11 has a first center line L1 extending along the length direction of the electrode assembly, the first center line L1 passes through the second portion 112, and the second portion 112 is symmetrically arranged about the first center line L1, and the two first portions 111 are symmetrically arranged about the first center line L1; and / or the second equal-thickness portion 21 has a second center line L2 extending along the length direction, the second center line L2 passes through the fourth portion 212, and the fourth portion 212 is symmetrically arranged about the second center line L2, and the two third portions 211 are symmetrically arranged about the second center line L2; and / or the diaphragm structure 30 has a third center line extending along the length direction, the third center line passes through the first region, and the first region is symmetrically arranged about the third center line, and the two second regions are symmetrically arranged about the third center line. In other words, in this embodiment, the two first portions 111 are symmetrically arranged about the second portion 112, and the second portion 112 is symmetrically arranged about the first center line L1 extending along the length direction of the first equal-thickness portion 11; the two third portions 211 are symmetrically arranged about the fourth portion 212, and the fourth portion 212 is symmetrically arranged about the second center line L2 extending along the length direction of the second equal-thickness portion 21; the two second regions are symmetrically arranged about the first region, and the first region is symmetrically arranged about the third center line along the length direction of the separator structure 30. This effectively reduces lithium plating in the middle region of the negative electrode sheet.

[0038] Optionally, the width of the second portion 112 is 40-50% of the width of the first equal-thickness portion; and / or, the width of the fourth portion 212 is 40-50% of the width of the second equal-thickness portion; and / or, the width of the first region is 40-50% of the width of the diaphragm structure 30. In one specific embodiment of this application, the sum of the widths of the two first portions 111 is equal to the width of the second portion 112; the sum of the widths of the two third portions 211 is equal to the width of the fourth portion 212; and the sum of the widths of the two second regions is equal to the width of the first region. That is, the width of the second portion 112 is half the width of the first equal-thickness portion 11, while the width of the first portion 111 is one-quarter of the width of the first equal-thickness portion 11; the width of the fourth portion 212 is half the width of the second equal-thickness portion 21, while the width of the third portion 211 is one-quarter of the width of the second equal-thickness portion 21; the width of the first region is half the width of the diaphragm structure 30, while the width of the second region is one-quarter of the width of the diaphragm structure.

[0039] Optionally, the second part 112 has a first transition portion 113 at the connection with the two first parts 111, and the compaction density of the first transition portion 113 gradually decreases in the direction away from the first part 111; the fourth part 212 has a second transition portion 213 at the connection with the two third parts 211, and the compaction density of the second transition portion 213 gradually increases in the direction away from the third parts 211.

[0040] Regarding the formation of the different compaction densities of the first equal-thickness portion 11 and the second equal-thickness portion 21 in this application, during the fabrication of the coatings for the first equal-thickness portion 11 and the second equal-thickness portion 21, the portion with higher compaction density corresponds to a thicker coating, while the portion with lower compaction density corresponds to a thinner coating. Therefore, after rolling the coatings of the first equal-thickness portion 11 and the second equal-thickness portion 21, the thicker coating can form a region with high compaction density, while the thinner coating can form a region with low compaction density. For the first equal-thickness portion 11 and the second equal-thickness portion 21 before rolling, the coating thickness corresponding to the two first portions 111 is greater than the coating thickness corresponding to the second portion 112, while the coating thickness corresponding to the two third portions 211 is less than the coating thickness corresponding to the fourth portion 212. Therefore, the coatings of the two first portions 111 and the coating of the second portion 112 can form a concave shape, while the coatings of the two third portions 211 and the coating of the fourth portion 212 can form a convex shape. Specifically, the ratio of the coating thickness of the first part 111 to the coating thickness of the second part 112 can be 1.01-1.05, and the ratio of the coating thickness of the fourth part 212 to the coating thickness of the third part 211 can also be 1.01-1.05. Of course, the above ratio parameters can be adjusted adaptively according to actual usage requirements, while also avoiding over-pressure on the coatings of the first part 111 and the fourth part 212 during the rolling process. Furthermore, for the junctions of the coatings of the first part 111 and the second part 112, and the junctions of the coatings of the third part 211 and the fourth part 212, if the junction is an inclined transition before rolling, the inclined portion will be formed as either the first transition portion 113 or the second transition portion 213 after rolling.

[0041] Of course, in this application, for the positive electrode 10 and the negative electrode 20, such as Figure 5 As shown, the positive electrode 10 also includes a positive current collector 13 and a first thinning region 12, the first thinning region 12 and the first equal-thickness portion 11 being disposed on at least one surface of the positive current collector 13; as Figure 6 As shown, the negative electrode sheet also includes a negative electrode current collector 23 and a second thinning region 22, wherein the second thinning region 22 and the second equal thickness portion 21 are disposed on at least one surface of the negative electrode current collector 23.

[0042] Optionally, the thickness of the second region of the membrane structure 30 is less than the thickness of the first region, so that the ionic conductivity of the first region of the membrane structure 30 is less than the ionic conductivity of the second region.

[0043] In one specific embodiment of this application, such as Figure 1As shown, the diaphragm structure 30 includes a first diaphragm 31 and a second diaphragm 32 stacked together. The width of the first diaphragm 31 is smaller than that of the second diaphragm 32. The overlapping portion of the first diaphragm 31 and the second diaphragm 32 forms a first region, and the portion of the second diaphragm not covered by the first diaphragm 31 forms a second region, thereby achieving a thickness of the second region that is less than the thickness of the first region. That is, the second diaphragm 32 is disposed between the positive electrode 10 and the negative electrode 20, corresponding to the first equal-thickness portion 11 and the second equal-thickness portion 21; the first diaphragm 31 is disposed on the side of the second diaphragm 32 facing the second portion 112, corresponding to the second portion 112; or the first diaphragm 31 is disposed on the side of the second diaphragm 32 facing the fourth portion 212, corresponding to the fourth portion 212. In other words, in this embodiment, the first diaphragm 31 can be disposed facing the positive electrode 10 or the negative electrode 20. Furthermore, it should be noted that for... Figure 1 In fact, it is a structural schematic diagram after partial cross-section of the electrode assembly, so as to make it easier to understand the positional relationship between the positive electrode 10, the negative electrode 20 and the diaphragm structure 30.

[0044] In one specific embodiment of this application, the thickness difference between the first region and the second region is less than or equal to 7 micrometers; or the thickness difference between the first region and the second region is less than 5% of the thickness of the positive electrode 10; or the thickness difference between the first region and the second region is less than 5% of the thickness of the negative electrode 20. This avoids the thickness difference between the first region and the second region being too large, which would affect the overall flatness of the electrode assembly. Specifically, the thickness of the second separator 32 is less than or equal to 7 micrometers; or the thickness of the second separator 32 is less than 5% of the thickness of the positive electrode 10; or the thickness of the second separator 32 is less than 5% of the thickness of the negative electrode 20. Of course, in this application, the specific thickness of the second separator 32 can also be adaptively adjusted according to the actual usage.

[0045] In this application, to achieve a difference in thickness between the first and second regions, besides using two stacked diaphragms of different areas, a single diaphragm can also be used, with regions of different thicknesses on the diaphragm. Specifically, the diaphragm structure 30 includes a substrate and a coating layer disposed on the substrate, wherein the thickness of the coating layer in the second region is less than the thickness of the coating layer in the first region; and / or the thickness of the substrate in the second region is less than the thickness of the substrate in the first region. The coating layer of the diaphragm structure 30 can be a ceramic coating, etc.

[0046] Of course, in addition to the above-mentioned implementation methods, in this application, the porosity of the second region of the diaphragm structure 30 can also be made greater than that of the first region, so that the ionic conductivity of the first region of the diaphragm structure 30 is less than that of the second region. The different porosities of the first and second regions can be achieved by separately hot-pressing the first region of the diaphragm structure 30. Specifically, the manufacturing process of the electrode assembly includes a hot-pressing process. Based on the conventional hot-pressing process, a secondary hot-pressing can be performed on the middle part of the electrode assembly corresponding to the first region to reduce the porosity of the first region. Alternatively, the first and second regions with different porosities can be formed by improving the manufacturing process of the diaphragm structure 30.

[0047] As can be seen from the above description, the embodiments of this utility model achieve the following technical effects:

[0048] 1. Effectively solves the problem that lithium plating easily occurs in existing secondary batteries, leading to a reduction in battery capacity.

[0049] Obviously, the embodiments described above are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of this utility model.

[0050] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0051] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0052] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. An electrode assembly, characterized by, The device includes a positive electrode (10), a negative electrode (20), and a separator structure (30) disposed between the positive electrode (10) and the negative electrode (20). The positive electrode (10) has a first equal-thickness portion (11), and the negative electrode (20) has a second equal-thickness portion (21), wherein: The compaction density of the first portion (111) of the first equal-thickness portion (11) is greater than the compaction density of the second portion (112). There are two first portions (111) along the width direction of the electrode assembly, and the second portion (112) is located between the two first portions (111); and / or The compaction density of the fourth portion (212) of the second equal-thickness portion (21) is greater than the compaction density of the third portion (211), wherein there are two third portions (211), and the fourth portion (212) is located between the two third portions (211) along the width direction; and / or The ionic conductivity of the first region of the membrane structure (30) is less than that of the second region. There are two second regions, and the first region is located between the two second regions along the width direction.

2. The electrode assembly according to claim 1, characterized in that, The first equal-thickness portion (11) has a first center line extending along the length direction of the electrode assembly, the first center line passing through the second portion (112), and the second portion (112) being symmetrically arranged about the first center line; and the two first portions (111) being symmetrically arranged about the first center line; and / or The second equal-thickness portion (21) has a second centerline extending along the length direction, the second centerline passing through the fourth portion (212), and the fourth portion (212) is symmetrically arranged about the second centerline; the two third portions (211) are symmetrically arranged about the second centerline; and / or The diaphragm structure (30) has a third centerline extending along the length direction, the third centerline passing through the first region, and the first region is symmetrically arranged about the third centerline, and two second regions are symmetrically arranged about the third centerline.

3. The electrode assembly according to claim 1, characterized in that, The width of the second portion (112) is 40-50% of the width of the first equal-thickness portion (11); and / or The width of the fourth portion (212) is 40-50% of the width of the second equal-thickness portion (21); and / or The ratio of the width of the first region to the width of the diaphragm structure (30) is 40-50%.

4. The electrode assembly according to claim 1, characterized in that, The second part (112) has a first transition portion (113) at the connection with the two first parts (111), the compaction density of the first transition portion (113) gradually decreasing in the direction away from the first part (111); and / or The fourth part (212) has a second transition portion (213) at the connection with the two third parts (211), and the compaction density of the second transition portion (213) gradually increases in the direction away from the third part (211).

5. The electrode assembly according to claim 1, characterized in that, The thickness of the second region of the diaphragm structure (30) is less than the thickness of the first region.

6. The electrode assembly of claim 5, wherein, The diaphragm structure (30) includes: A first diaphragm (31) and a second diaphragm (32) are stacked, wherein the width of the first diaphragm (31) is smaller than that of the second diaphragm (32), the portion of the first diaphragm (31) and the second diaphragm (32) that overlaps forms the first region, and the portion of the second diaphragm that is not covered by the first diaphragm (31) forms the second region.

7. The electrode assembly according to claim 5, characterized in that, The thickness difference between the first region and the second region is less than or equal to 7 micrometers; or The thickness difference between the first region and the second region is less than 5% of the thickness of the positive electrode sheet (10); or The thickness difference between the first region and the second region is less than 5% of the thickness of the negative electrode sheet (20).

8. The electrode assembly according to claim 5, characterized in that, The diaphragm structure (30) includes a substrate and a coating layer disposed on the substrate, wherein the thickness of the coating layer in the second region is less than the thickness of the coating layer in the first region; and / or The thickness of the substrate in the second region is less than the thickness of the substrate in the first region.

9. The electrode assembly according to claim 1, characterized in that, The porosity of the second region of the membrane structure (30) is greater than that of the first region.

10. A secondary battery characterized by comprising: The electrode assembly includes any one of claims 1 to 9.

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