Electrode assembly and secondary battery

Abstract

The present invention provides an electrode assembly and a secondary battery. The secondary battery includes a shell, a top cover assembly and an electrode assembly. The shell has a accommodating chamber, the electrode assembly is accommodated in the accommodating chamber, and the top cover assembly is connected to the shell. The electrode assembly includes a first pole piece, a second pole piece and a diaphragm, and the diaphragm separates the first pole piece and the second pole piece. The first pole piece, the second pole piece and the diaphragm are wound into a flat structure, and the flat structure includes a main body area and a corner area, and the corner area is arranged at both ends of the main body area along the width direction. The first pole piece and the second pole piece are both wound into multiple turns. A gap is provided between two adjacent turns of the first pole piece, and the gap includes a first gap and a second gap. The first gap corresponds to the position of the corner area, the second gap corresponds to the position of the main body area, and the size of the first gap is larger than the size of the second gap.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to an electrode assembly and a secondary battery. Background Art

[0002] Existing secondary batteries usually use a wound electrode assembly, and the electrode assembly is wound by a positive electrode sheet, a negative electrode sheet and a separator. During the charge and discharge process of the secondary battery, the electrode sheet will expand in volume due to the de-lithiation or lithium insertion state of the active material. The expansion will cause expansion stress between the positive and negative electrode sheets. If the expansion stress is not effectively released, the wound electrode assembly will be twisted and deformed. In particular, in the corner area formed by the winding of the electrode assembly, the expansion stress is most concentrated, and the electrode assembly is more likely to twist and deform. In addition, in the later stage of the cycle, the expansion stress will also squeeze out the electrolyte between the positive and negative electrode sheets, resulting in poor wettability of the electrode assembly. Summary of the invention

[0003] In view of the problems existing in the background technology, the object of the present invention is to provide an electrode assembly and a secondary battery, which can release expansion stress, avoid electrode fracture, and ensure the consistency of dynamic performance.

[0004] In order to achieve the above objectives, the present invention provides an electrode assembly and a secondary battery.

[0005] The electrode assembly includes a first pole piece, a second pole piece and a diaphragm, and the diaphragm separates the first pole piece and the second pole piece. The first pole piece, the second pole piece and the diaphragm are wound into a flat structure, and the flat structure includes a main body area and a corner area, and the corner area is arranged at both ends of the main body area along the width direction. The first pole piece and the second pole piece are both wound into multiple turns. There is a gap between two adjacent turns of the first pole piece, and the gap includes a first gap and a second gap. The first gap corresponds to the position of the corner area, and the second gap corresponds to the position of the main body area. The size of the first gap is larger than the size of the second gap.

[0006] A ratio of the size of the first gap to the size of the second gap is less than 16.

[0007] The size of the first gap is 20 μm to 80 μm, and the size of the second gap is 5 μm to 20 μm.

[0008] The second pole piece is provided with a first protrusion and a second protrusion, the first protrusion corresponds to the corner area, the second protrusion corresponds to the main area, the first protrusion and the second protrusion protrude toward the same side of the second pole piece, and the height of the first protrusion is greater than the height of the second protrusion.

[0009] The diaphragm includes a first diaphragm and a second diaphragm, and the first diaphragm and the second diaphragm are respectively located on both sides of the second pole piece. The first protrusion and the second protrusion protrude toward the first diaphragm. In the corner area, a third gap is left between the second pole piece and the first diaphragm, and the size of the third gap is equal to the height of the first protrusion. In the main body area, a fourth gap is left between the second pole piece and the first diaphragm, and the size of the fourth gap is equal to the height of the second protrusion.

[0010] The second pole piece includes a first area and a second area, the first area corresponds to the corner area, and the second area extends from one end of the first area and corresponds to the main area. The first area is provided with a first protrusion, and the ratio of the area of ​​the first protrusion to the area of ​​the first area is 50%-90%. The second area is provided with a second protrusion, and the ratio of the area of ​​the second protrusion to the area of ​​the second area is 50%-90%.

[0011] The first pole piece is a negative pole piece, and the second pole piece is a positive pole piece.

[0012] The ratio of the width to the thickness of the main body region is 5-20.

[0013] In the main body region, the number of layers of the first pole piece is an even number, and the number of layers of the second pole piece is an even number.

[0014] The secondary battery comprises a shell, a top cover assembly and the electrode assembly. The shell has a receiving chamber, the electrode assembly is received in the receiving chamber, and the top cover assembly is connected to the shell.

[0015] The beneficial effects of the present invention are as follows: By setting the first gap and the second gap, the present application can reserve expansion space for the first pole piece and the second pole piece, thereby releasing the expansion stress and reducing the degree of deformation of the electrode assembly. At the same time, the electrolyte can also enter the interior of the electrode assembly through the first gap and the second gap, thereby improving the wettability and reducing the risk of lithium precipitation. Since the stress on the corner area is greater, the present application sets the size of the first gap to be larger than the size of the second gap, so that the volume of the electrolyte in the first gap before expansion is larger than the volume of the electrolyte in the second gap, thereby improving the difference in wettability between the main area and the corner area after expansion to a certain extent, and ensuring the consistency of the dynamic performance of the electrode assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. 4 is an exploded view of a secondary battery according to an embodiment of the present invention.

[0017] Figure 2 for Figure 1 Cross-sectional view of the electrode assembly.

[0018] Figure 3 for Figure 2 A schematic diagram of the second pole piece after unfolding.

[0019] Figure 4 for Figure 3 Cross-section taken along line AA.

[0020] Figure 5 for Figure 2 Another schematic diagram of the second pole piece after unfolding.

[0021] Figure 6 for Figure 2 Schematic diagram of the first pole piece during expansion.

[0022] The reference numerals are described as follows:

[0023] 1 Electrode assembly 3 Top cover assembly

[0024] 11 first pole piece 31 top cover plate

[0025] 12 second pole piece 32 electrode terminal

[0026] 121 First region 33 Insulating member

[0027] 122 Second region 34 Current collecting member

[0028] 13 Diaphragm G1 First gap

[0029] 131 First diaphragm G2 Second gap

[0030] 132 Second diaphragm G3 Third gap

[0031] 14 Main area G4 Fourth gap

[0032] 15 Corner area P1 First protrusion

[0033] 2 Shell P2 Second protrusion

[0034] 21 Accommodation chamber X Horizontal

[0035] 22 First side plate Y longitudinal

[0036] 23 Second side plate Z axis DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0038] In the description of this application, unless otherwise clearly specified and limited, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance; the term "plurality" refers to two or more; unless otherwise specified or explained, the terms "connected", "fixed", etc. should be understood in a broad sense, for example, "connected" can be a fixed connection, a detachable connection, an integral connection, an electrical connection, or a signal connection; "connected" can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0039] In the description of this specification, it should be understood that the directional words such as "upper" and "lower" described in the embodiments of the present application are described from the perspectives shown in the drawings and should not be understood as limiting the embodiments of the present application. The present application is further described in detail below through specific embodiments and in conjunction with the drawings.

[0040] Reference Figure 1 The secondary battery of the present application may be a prismatic lithium-ion battery. Specifically, the secondary battery includes an electrode assembly 1 , a shell 2 , and a top cover assembly 3 .

[0041] The housing 2 has a receiving chamber 21 formed inside to accommodate the electrode assembly 1 and the electrolyte. The housing 2 has an opening formed at one end along the axial direction Z, and the electrode assembly 1 can be placed in the housing 2 through the opening. The housing 2 can be made of a conductive metal material such as aluminum or aluminum alloy. The axial direction Z is parallel to the height direction of the secondary battery and perpendicular to the lateral direction X and longitudinal direction Y of the secondary battery.

[0042] The housing 2 may include a first side plate 22 and a second side plate 23, wherein the first side plates 22 are respectively located on both sides of the electrode assembly 1 along the longitudinal direction Y, and the second side plates 23 are respectively located on both sides of the electrode assembly 1 along the transverse direction X, and the first side plates 22 and the second side plates 23 are connected together to form a rectangular accommodating chamber 21. The area of ​​the first side plate 22 is greater than that of the second side plate 23.

[0043] There may be multiple electrode assemblies 1, and the multiple electrode assemblies 1 are stacked in sequence along the longitudinal direction Y. Figure 2 Each electrode assembly 1 includes a first electrode sheet 11 , a second electrode sheet 12 and a diaphragm 13 , and the diaphragm 13 separates the first electrode sheet 11 from the second electrode sheet 12 .

[0044] The top cover assembly 3 includes a top cover plate 31, an electrode terminal 32, an insulating member 33 and a current collecting member 34. The top cover plate 31 is connected to the shell 2 and covers the opening of the shell 2, so that the electrode assembly 1 is enclosed in the accommodating chamber 21 of the shell 2. The insulating member 33 is arranged on the inner side of the top cover plate 31 to separate the top cover plate 31 and the electrode assembly 1. The electrode terminal 32 is arranged on the top cover plate 31 and protrudes to the outside of the top cover plate 31. There are two electrode terminals 32 and two current collecting members 34, one current collecting member 34 connects the first pole piece 11 and one electrode terminal 32, and the other current collecting member 34 connects the second pole piece 12 and the other electrode terminal 32.

[0045] Reference Figure 2 , the first pole piece 11, the second pole piece 12 and the diaphragm 13 are wound into a flat structure, and the first pole piece 11, the second pole piece 12 and the diaphragm 13 are all wound into multiple turns. During molding, the first pole piece 11, the second pole piece 12 and the diaphragm 13 can be first fixed to a winding shaft, and the winding shaft is rotated to spirally wind the first pole piece 11, the second pole piece 12 and the diaphragm 13 to form a winding body; after winding and forming, the winding shaft is pulled out from the winding body; finally, the winding body is pressed into a flat shape.

[0046] The flat structure includes a main body area 14 and a corner area 15, and the corner area 15 is arranged at both ends of the main body area 14 along the width direction. In the present application, the width direction of the main body area 14 is parallel to the axial direction Z. The main body area 14 is opposite to the first side plate 22, and the corner area 15 is opposite to the second side plate 23.

[0047] In the main body region 14, the first pole piece 11 and the second pole piece 12 are divided into multiple layers along the thickness direction, and the thickness direction of the main body region 14 is parallel to the longitudinal direction Y of the secondary battery. Before expansion, each layer of the first pole piece 11 of the main body region 14 is substantially perpendicular to the longitudinal direction Y, and each layer of the second pole piece 12 of the main body region 14 is substantially perpendicular to the longitudinal direction Y.

[0048] In the corner area 15 , the first pole piece 11 and the second pole piece 12 are divided into multiple layers in a direction away from the winding center; each layer of the first pole piece 11 in the corner area 15 is generally arc-shaped, and each layer of the second pole piece 12 in the corner area 15 is generally arc-shaped.

[0049] During the charge and discharge process, the first pole piece 11 and the second pole piece 12 will expand in volume, which will cause expansion stress between the first pole piece 11 and the second pole piece 12. If the expansion stress is not effectively released, the electrode assembly 1 is prone to deformation. At the same time, the expansion stress will squeeze out the electrolyte between the first pole piece 11 and the second pole piece 12, causing the wettability of the electrode assembly 1 to deteriorate.

[0050] Preferably, the present application sets a gap between two adjacent circles of first pole pieces 11, and the gap includes a first gap G1 and a second gap G2. The first gap G1 corresponds to the position of the corner area 15, and the second gap G2 corresponds to the position of the main area 14. The size of the first gap G1 is larger than the size of the second gap G2.

[0051] By setting the first gap G1 and the second gap G2, the present application can reserve expansion space for the first pole piece 11 and the second pole piece 12, thereby releasing the expansion stress and reducing the deformation degree of the electrode assembly 1. At the same time, the electrolyte can also enter the interior of the electrode assembly 1 through the first gap G1 and the second gap G2, thereby improving the wettability and reducing the risk of lithium deposition.

[0052] In the corner area 15, the distance between two adjacent layers of the first pole pieces 11 is d1, and two layers of diaphragms 13 and one layer of the second pole piece 12 are arranged between the two layers of the first pole pieces 11. Therefore, the value obtained by subtracting the thickness of the two layers of diaphragms 13 and the thickness of the second pole piece 12 from d1 is the size of the first gap G1.

[0053] Similarly, in the main area 14, the spacing between two adjacent layers of the first pole pieces 11 is d2, and two layers of diaphragms 13 and one layer of the second pole piece 12 are arranged between the two layers of the first pole pieces 11, and the value obtained by subtracting the thickness of the two layers of diaphragms 13 and the thickness of the second pole piece 12 from d2 is the size of the second gap G2.

[0054] When the electrode assembly 1 expands, the stress in the corner area 15 is most concentrated and is most likely to deform. Figure 6 When expanding, the main body region 14 expands most severely in the middle region (line L1) along the axial direction Z; at the same time, the first pole piece 11 is stretched during expansion, so a certain tension is generated inside. At L1 where the expansion is most severe, the first pole piece 11 is subjected to the combined action of two tensions F1 and F4, which limit the expansion of the first pole piece 11 in the main body region 14. Taking F1 as an example, F1 is decomposed into two component forces F 11 and F 12 , F4 is decomposed into two components F 41 and F 42 , F 11 and F 41 cancel each other out, so F 12 and F 42 This will affect the deformation of the first pole piece 11 in the main region 14 .

[0055] Similarly, during expansion, the two ends of the first pole piece 11 in the corner area 15 will also be subjected to two tension forces, namely F2 and F3. 21 and the component force F of F3 31 The first pole piece 11 of the corner area 15 will be pulled along the axial direction Z, and the component force F of F222 and the component force F of F3 32 The first pole piece 11 of the corner area 15 will be pulled along the longitudinal direction Y; and since the first pole piece 11 of the corner area 15 is arc-shaped, F 22 and F 32 will not cancel each other out; under the combined action of F2 and F3, the first gap G1 will be severely reduced. Therefore, in the electrode assembly 1, the stress in the corner area 15 is more concentrated; at the same time, since the first pole piece 11 and the second pole piece 12 in the corner area 15 are arc-shaped, they are more likely to deform under the action of stress. When the stress is too large, the first pole piece 11 and the second pole piece 12 in the corner area 15 are prone to breakage.

[0056] Since the stress in the corner area 15 is more concentrated, if the size of the first gap G1 is equal to the size of the second gap G2, then when the electrode assembly 1 expands and deforms, the first gap G1 will shrink more than the second gap G2. That is to say, if the size of the first gap G1 is equal to the size of the second gap G2 at the beginning, then when the secondary battery cycles to a certain extent, the size of the first gap G1 will be smaller than the size of the second gap G2. At this time, the electrolyte in the main area 14 will be more than the electrolyte in the corner area 15, resulting in a difference in wettability between the main area 14 and the corner area 15, affecting the consistency of the dynamic performance of the electrode assembly 1.

[0057] Therefore, the present application preferably has a size of the first gap G1 that is larger than that of the second gap G2, so that the volume of the electrolyte in the first gap G1 before expansion is larger than the volume of the electrolyte in the second gap G2. The present application releases the stress of the corner area 15 in a timely manner by increasing the first gap G1, thereby avoiding the fracture of the first pole piece 11 and the second pole piece 12 in the corner area 15. In comparison, the size of the second gap G2 is smaller, and has less effect on the thickness of the secondary battery along the longitudinal direction Y. Since the stress on the corner area 15 is greater, when the secondary battery is cycled to a certain extent, the size of the first gap G1 will be roughly equal to the size of the second gap G2, so that the volume of the electrolyte in the first gap G1 after expansion is roughly equal to the volume of the electrolyte in the second gap, thereby improving the difference in wettability between the main area 14 and the corner area 15 to a certain extent, and ensuring the consistency of the dynamic performance of the electrode assembly 1.

[0058] In addition, when the main body area 14 expands to a certain extent, the main body area 14 will fit with the first side plate 22 of the shell 2, so even if the second gap G2 is small, the first side plate 22 can limit the deformation of the main body area 14. The corner area 15 is arc-shaped, and the second side plate 23 is flat, so the second side plate 23 cannot limit the distortion of the corner area 15, and the first gap G needs to have a larger size.

[0059] The ratio of the size of the first gap G1 to the size of the second gap G2 is less than 16. If the ratio of the size of the first gap G1 to the size of the second gap G2 is too large, there will be a large difference between the diameter of the corner area 15 and the thickness of the main area 14, resulting in obvious marks at the junction of the main area 14 and the corner area 15, affecting the flatness of the electrode assembly 1.

[0060] The size of the first gap G1 is 20 μm to 80 μm. If the size of the first gap G1 is less than 20 μm, the stress cannot be fully released, resulting in distortion of the corner area 15. If the size of the first gap G1 is greater than 80 μm, the lithium ion transmission path is too long, which is easy to cause lithium deposition.

[0061] The size of the second gap G2 is 5 μm to 20 μm. When the main body area 14 expands, it will squeeze the first side plate 22. Under the expansion stress and the reaction force of the first side plate 22, the second gap G2 is easy to disappear, causing the electrolyte to be squeezed out of the main body area 14, causing a cycle jump. If the size of the second gap G2 is greater than 20 μm, the thickness of the main body area 14 will be increased to a large extent, reducing the energy density of the secondary battery.

[0062] The second pole piece 12 is provided with a first protrusion P1 and a second protrusion P2, the first protrusion P1 corresponds to the corner area 15, and the second protrusion P2 corresponds to the main area 14. The first protrusion P1 and the second protrusion P2 protrude toward the same side of the second pole piece 12. The height h1 of the first protrusion P1 is greater than the height h2 of the second protrusion P2.

[0063] The first protrusion P1 and the second protrusion P2 may be formed by stamping the second pole piece 12. Figure 4 After stamping, recesses are formed inside the first protrusion P1 and the second protrusion P2.

[0064] The present application can increase the distance d1 between two adjacent first pole pieces 11 in the corner area 15 by providing the first protrusion P1 on the second pole piece 12, thereby forming a first gap G1 between two adjacent first pole pieces 11. The size of the first gap G1 can be adjusted by adjusting the value of h1.

[0065] Similarly, the present application can increase the distance d2 between the first pole pieces 11 of two adjacent layers in the main region 14 by providing the second protrusion P2 on the second pole piece 12, thereby forming a second gap G2 between the first pole pieces 11 of two adjacent layers. By adjusting the value of h2, the size of the second gap G2 can be adjusted.

[0066] The first protrusion P1 may be circular, strip-shaped, polygonal or elliptical. Figure 4, the first protrusion P1 is circular and is provided in a plurality, and the plurality of first protrusions P1 are arranged in an array; the second protrusion P2 is circular and is provided in a plurality, and the plurality of second protrusions P2 are arranged in an array. Alternatively, referring to Figure 6 The first protrusion P1 may also be in a strip shape and may be provided in a plurality, and the second protrusion P2 may also be in a strip shape and may be provided in a plurality.

[0067] The diaphragm 13 includes a first diaphragm 131 and a second diaphragm 132, which are respectively located on both sides of the second pole piece 12. The first diaphragm 131 and the second diaphragm 132 are both wound into multiple turns, and between two adjacent turns of the first pole piece 11, one turn of the first diaphragm 131 and one turn of the second diaphragm 132 are arranged.

[0068] The first protrusion P1 and the second protrusion P2 protrude toward the first diaphragm 131. Figure 2 In the corner area 15, a third gap G3 is left between the second pole piece 12 and the first diaphragm 131, and the size of the third gap G3 is equal to the height of the first protrusion P1; in other words, the first diaphragm 131 fits the top of the first protrusion P1. In the main body area 14, a fourth gap G4 is left between the second pole piece 12 and the first diaphragm 131, and the size of the fourth gap G4 is equal to the height of the second protrusion P2. In other words, the first diaphragm 131 fits the top of the second protrusion P2. The size of the third gap G3 is greater than the size of the fourth gap G4.

[0069] Reference Figure 2 and Figure 3 , the second pole piece 12 includes a first region 121 and a second region 122. The first region 121 corresponds to the corner region 15, in other words, the first region 121 is a layer of the second pole piece 12 of the corner region 15. The second region 122 extends from one end of the first region 121 and corresponds to the main body region 14, in other words, the second region 122 is a layer of the second pole piece 12 of the main body region 14.

[0070] The first region 121 is provided with a first protrusion P1, and the ratio of the area of ​​the first protrusion P1 to the area of ​​the first region 121 is 50%-90%. If the area ratio is greater than 90%, the density of the first protrusion P1 is too large, and it is easy to crush the second pole piece 12 during molding. If the area ratio is less than 50%, the overall strength of the first protrusion P1 is relatively weak, and it is easy to be flattened during the winding molding process.

[0071] Similarly, the second region 122 is provided with a second protrusion P2, and the ratio of the area of ​​the second protrusion P2 to the area of ​​the second region 122 is 50%-90%. If the area ratio is greater than 90%, the density of the second protrusion P2 is too large, and it is easy to crush the second pole piece 12 during molding. If the area ratio is less than 50%, the overall strength of the second protrusion P2 is weak, and it is easy to be flattened during the winding molding process.

[0072] The first pole piece 11 is a negative pole piece, and the first pole piece 11 includes a copper foil and a negative electrode active material coated on the surface of the copper foil, and the negative electrode active material includes graphite or silicon. Correspondingly, the second pole piece 12 is a positive pole piece, and the second pole piece 12 includes an aluminum foil and a positive electrode active material coated on the surface of the aluminum foil, and the positive electrode active material includes lithium manganese oxide or lithium iron phosphate. The material of the second pole piece 12 is relatively soft and has good elasticity, and it is easy to press out the first protrusion P1 and the second protrusion P2, and it is not easy to break.

[0073] The ratio of the width w of the main body region 14 in the axial direction Z to the thickness t in the longitudinal direction Y is 5 to 20. Figure 6 The larger the width of the main body area 14, the smaller the elongation during expansion deformation, and the smaller the tension on the first pole piece 11, thereby reducing the stress concentration in the corner area 15 and reducing the deformation of the corner area 15. Of course, if w / t is too large, for example, greater than 20, the electrode assembly 1 will be too flat and cannot meet the requirements for the shape of the secondary battery.

[0074] In the main body area 14, the number of layers of the first pole piece 11 is an even number, and the number of layers of the second pole piece 12 is an even number. That is to say, the first pole pieces 11 located on both sides of the winding center along the longitudinal direction Y are the same in number of layers, and the second pole pieces 12 located on both sides of the winding center along the longitudinal direction Y are the same in number of layers. The present application improves the symmetry of the main body area 14 about the winding center by setting the number of layers of the first pole piece 11 in the main body area 14 to an even number and the number of layers of the second pole piece 12 in the main body area 14 to an even number, so that the expansion forces on both sides of the winding center along the longitudinal direction Y are equal, thereby improving the uniformity of the expansion of the main body area 14, reducing the local deformation of the electrode assembly 1, and avoiding the fracture of the pole pieces.

Claims

1. An electrode assembly (1), comprising a first electrode sheet (11), a second electrode sheet (12) and a diaphragm (13), wherein the diaphragm (13) separates the first electrode sheet (11) from the second electrode sheet (12); the first electrode sheet (11) comprises a copper foil and a negative electrode active material coated on a surface of the copper foil, wherein the negative electrode active material comprises graphite or silicon; The first pole piece (11), the second pole piece (12) and the diaphragm (13) are wound into a flat structure, and the flat structure comprises a main body region (14) and a corner region (15), wherein the corner region (15) is arranged at both ends of the main body region (14) in a width direction; The first pole piece (11) and the second pole piece (12) are both wound into multiple turns; A gap is provided between two adjacent circles of first pole pieces (11), the gap comprising a first gap (G1) and a second gap (G2); The first gap (G1) corresponds to the position of the corner area (15), the second gap (G2) corresponds to the position of the main body area (14), and the size of the first gap (G1) is greater than the size of the second gap (G2); A ratio of a size of the first gap (G1) to a size of the second gap (G2) is less than 16; The ratio of the width to the thickness of the main body region (14) is 5 to 20; The size of the first gap (G1) is 20µm~80µm, and the size of the second gap (G2) is 5µm~20µm.

2. The electrode assembly (1) according to claim 1, characterized in that: The second pole piece (12) is provided with a first protrusion (P1) and a second protrusion (P2), the first protrusion (P1) corresponds to the position of the corner area (15), the second protrusion (P2) corresponds to the position of the main body area (14), and the first protrusion (P1) and the second protrusion (P2) protrude toward the same side of the second pole piece (12); The height of the first protrusion (P1) is greater than the height of the second protrusion (P2).

3. The electrode assembly (1) according to claim 2, characterized in that: The diaphragm (13) comprises a first diaphragm (131) and a second diaphragm (132), wherein the first diaphragm (131) and the second diaphragm (132) are respectively located on two sides of the second pole piece (12); The first protrusion (P1) and the second protrusion (P2) protrude toward the first diaphragm (131); In the corner area (15), a third gap (G3) is left between the second pole piece (12) and the first diaphragm (131), and the size of the third gap (G3) is equal to the height of the first protrusion (P1); in the main body area (14), a fourth gap (G4) is left between the second pole piece (12) and the first diaphragm (131), and the size of the fourth gap (G4) is equal to the height of the second protrusion (P2).

4. The electrode assembly (1) according to claim 2, characterized in that: The second pole piece (12) comprises a first region (121) and a second region (122), wherein the first region (121) corresponds to the position of the corner region (15), and the second region (122) extends from one end of the first region (121) and corresponds to the position of the main body region (14); The first region (121) is provided with a first protrusion (P1), and the ratio of the area of ​​the first protrusion (P1) to the area of ​​the first region (121) is 50%-90%; The second region (122) is provided with a second protrusion (P2), and the ratio of the area of ​​the second protrusion (P2) to the area of ​​the second region (122) is 50%-90%.

5. The electrode assembly (1) according to claim 2, characterized in that: The first pole piece (11) is a negative pole piece, and the second pole piece (12) is a positive pole piece.

6. The electrode assembly (1) according to claim 1, characterized in that: In the main body region (14), the number of layers of the first pole piece (11) is an even number, and the number of layers of the second pole piece (12) is an even number.

7. A secondary battery, comprising a housing (2), a top cover assembly (3), and an electrode assembly (1) according to any one of claims 1 to 6; The shell (2) has a containing chamber (21), the electrode assembly (1) is contained in the containing chamber (21), and the top cover assembly (3) is connected to the shell (2).

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