Diaphragm, electrode assembly and battery monomer

Abstract

The utility model provides a diaphragm, an electrode assembly and a battery monomer. The diaphragm comprises a main body part and a reinforcing part arranged on at least one side of the main body part, and the reinforcing part extends in the length direction of the main body part; and the reinforcing part is in a wave shape. The diaphragm prepared by the utility model can provide good heat resistance and higher liquid absorption capacity, ensures the safety of the diaphragm at higher temperature, reduces the risk of contact short circuit of positive and negative pole pieces caused by diaphragm shrinkage at high temperature, and can meet the requirements of high power and high energy density at the present stage.

Description

Technical Field

[0001] The utility model belongs to the technical field of batteries, and in particular relates to a diaphragm, an electrode assembly and a battery monomer. Background Art

[0002] With the rapid development of the new energy industry, lithium-ion batteries, perovskite batteries and other solar cells have been widely used in various fields of life. Among them, the safety of lithium-ion batteries has always been a key issue in the industry. In the actual use of batteries, it is difficult to avoid abuse. Overcharging, hot boxes, external shorts, etc. cause the electrode components to accumulate a lot of heat, causing the diaphragm to shrink and cause thermal runaway.

[0003] Usually, people increase the thickness of the diaphragm to reduce the thermal shrinkage rate of the diaphragm and improve the safety of the electrode assembly under heat. However, the increase in the thickness of the diaphragm will lead to a series of disadvantages such as increased DC internal resistance of the electrode assembly, increased material costs, and reduced energy density, which cannot meet the current needs of high power and high energy density. The diaphragm coating method can also effectively improve the heat shrinkage resistance of the diaphragm, but it also faces the same problem.

[0004] Therefore, how to optimize the diaphragm to improve its resistance to heat shrinkage and meet the current demand for high power and high energy density has become an urgent problem that technicians in this field need to solve. Utility Model Content

[0005] In view of the shortcomings of the prior art, the purpose of the utility model is to provide a diaphragm, an electrode assembly and a battery cell. The diaphragm prepared by the utility model can provide good heat resistance and high liquid absorption capacity, ensure the safety of the diaphragm at high temperatures, reduce the risk of short circuit of positive and negative electrode sheets due to diaphragm shrinkage at high temperatures, and meet the current needs of high power and high energy density.

[0006] To achieve this purpose, the utility model adopts the following technical solutions:

[0007] In a first aspect, the utility model provides a diaphragm, the diaphragm comprising a main body, and a reinforcing portion arranged on at least one side in a width direction of the main body, the reinforcing portion extending along a length direction of the main body;

[0008] The reinforcement portion is in a wave shape.

[0009] The diaphragm prepared by the utility model can provide good heat resistance and high liquid absorption capacity, ensure the safety of the diaphragm at high temperatures, reduce the risk of short circuit between positive and negative electrodes due to shrinkage of the diaphragm at high temperatures, and meet the current needs of high power and high energy density.

[0010] As a preferred technical solution of the utility model, the width of the reinforcement portion is denoted as W1, and W1≥2mm.

[0011] As a preferred technical solution of the utility model, the reinforcing portion includes concave portions and convex portions that are alternately and periodically arranged, and the center distance between adjacent convex portions and / or concave portions is denoted as W2.

[0012] Preferably, W2 satisfies the following condition: 0.5≤W2≤10mm.

[0013] As a preferred technical solution of the utility model, the height of the reinforcement portion is 0.1-5 mm, for example, it can be 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm or 5 mm.

[0014] As a preferred technical solution of the utility model, the cross-sectional shape of the reinforcement portion along a direction perpendicular to its own extension direction includes a trapezoid and / or a semicircle.

[0015] As a preferred technical solution of the utility model, the diaphragm includes a polymer film or a composite film.

[0016] Preferably, the polymer film comprises a polyethylene film and / or a polypropylene film.

[0017] Preferably, the composite film comprises a base layer and a modified layer disposed on at least one surface of the base layer.

[0018] Preferably, the base layer comprises a polyethylene film and / or a polypropylene film.

[0019] As a preferred technical solution of the utility model, the material of the modified layer is any one of aluminum oxide, boehmite or silicon dioxide.

[0020] In a second aspect, the utility model provides an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet and the separator as described in the first aspect.

[0021] As a preferred technical solution of the utility model, when the area of ​​the positive electrode sheet is larger than the area of ​​the negative electrode sheet, the overlap width W3 of the non-ear area of ​​the positive electrode sheet and the reinforcement portion of the diaphragm satisfies the following conditions: 0.2≤W3≤10mm; or,

[0022] When the area of ​​the negative electrode sheet is greater than that of the positive electrode sheet, the width W3 of the overlapping area between the non-tab area of ​​the negative electrode sheet and the reinforcement portion of the separator satisfies the following condition: 0.2≤W3≤10 mm.

[0023] In a third aspect, the utility model provides a battery cell, wherein the battery cell comprises the electrode assembly as described in the second aspect.

[0024] In a fourth aspect, the utility model provides a battery, comprising the battery cell as described in the third aspect.

[0025] In a fifth aspect, the utility model provides an electrical device, wherein the electrical device comprises the battery as described in the fourth aspect.

[0026] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0027] Compared with the prior art, the beneficial effects of the utility model are:

[0028] (1) The utility model adopts a design that is simple in structure and easy to implement, which can improve the lateral physical strength of the diaphragm and is easy to industrialize.

[0029] (2) The diaphragm prepared by the utility model can provide good heat resistance and high liquid absorption capacity, ensure the safety of the diaphragm at high temperatures, reduce the risk of short circuit between positive and negative electrodes due to shrinkage of the diaphragm at high temperatures, and meet the current demand for high power and high energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the preparation of the reinforcement part in the preparation method provided in Example 1 of the present utility model.

[0031] Figure 2 This is a schematic diagram of the structure of the diaphragm prepared in Example 1 of the present utility model.

[0032] Figure 3 This is a cross-sectional view of the trapezoidal reinforcement portion in the diaphragm prepared in Example 1 of the present invention.

[0033] Figure 4 This is a cross-sectional view of the triangular reinforcement portion of the diaphragm prepared in comparative example 2 of the present invention.

[0034] Figure 5 This is a cross-sectional view of the triangular reinforcement portion of the diaphragm prepared in comparative example 2 of the present invention after hot pressing.

[0035] Among them, 1-main body; 2-reinforcement part; 3-positive electrode sheet. DETAILED DESCRIPTION

[0036] It should be understood that, in the description of the present utility model, the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present utility model and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present utility model. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present utility model, unless otherwise specified, "multiple" means two or more.

[0037] It should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0038] Those skilled in the art should understand that the present invention necessarily includes necessary pipelines, conventional valves and general pump equipment for realizing a complete process, but the above content does not constitute the main innovation of the present invention. Those skilled in the art can add layouts on their own based on the process flow and equipment structure selection, and the present invention does not make special requirements or specific limitations on this.

[0039] The technical solution of the utility model is further explained below with reference to the accompanying drawings and through specific implementation methods.

[0040] In a specific embodiment, the utility model provides a diaphragm, the diaphragm comprising a main body, and a reinforcing portion arranged on at least one side in the width direction of the main body, the reinforcing portion extending along the length direction of the main body;

[0041] The reinforcement portion is in a wave shape.

[0042] It should be noted that the reinforcement portion may be a depression, a protrusion or a combination of the two relative to the plane of the main body portion.

[0043] The diaphragm prepared by the utility model can provide good heat resistance and high liquid absorption capacity, ensure the safety of the diaphragm at high temperatures, reduce the risk of short circuit between positive and negative electrodes due to shrinkage of the diaphragm at high temperatures, and meet the current needs of high power and high energy density.

[0044] Further, the width of the reinforcement portion is recorded as W1, W1 ≥ 2 mm, for example, it can be 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm or 10 mm, etc. However, it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0045] In the present invention, the width W1 of the reinforcement part is ≥2 mm, which can ensure the mechanical strength of the reinforcement part. If W1 is less than 2 mm, the mechanical strength of the reinforcement part of the diaphragm cannot be met.

[0046] It should be noted that, when the reinforcement portion is provided on both sides of the body portion in the width direction, W1 is the width of the reinforcement portion of the single-side diaphragm.

[0047] Furthermore, the reinforcing portion includes concave portions and convex portions that are alternately and periodically arranged, and the center distance between adjacent convex portions and / or concave portions is denoted as W2.

[0048] It should be noted that the center distance refers to the horizontal distance between the center axes of adjacent convex parts, or the horizontal distance between the center axes of adjacent concave parts.

[0049] Further, W2 satisfies the following condition: 0.5≤W2≤10 mm, for example, it can be 0.5 mm, 1 mm, 3 mm, 5 mm, 7 mm, 9 mm or 10 mm, etc. However, it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0050] In the present invention, if W2 is less than 0.5 mm, wrinkles are easily generated during hot pressing, affecting the wetting effect of the electrode piece and the performance of the electrode assembly. If W2 is greater than 10 mm, the mechanical strength provided by the reinforcement is insufficient and cannot play a role in preventing thermal shrinkage of the diaphragm.

[0051] Furthermore, the height of the reinforcement portion is 0.1-5 mm, for example, it can be 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm or 5 mm.

[0052] In the present invention, if the height is less than 0.1 mm, sufficient mechanical strength cannot be provided, and if the height is greater than 5 mm, wrinkles are easily generated after hot pressing, which affects the electrode sheet wetting effect and the performance of the electrode assembly.

[0053] Furthermore, the cross-sectional shape of the reinforcement portion along a direction perpendicular to its own extension direction includes a trapezoid and / or a semicircle.

[0054] In the utility model, the trapezoidal and / or semicircular cross-sectional shape will not cause the appearance of an irregular shape of the diaphragm after hot pressing.

[0055] Furthermore, the separator includes a polymer membrane or a composite membrane.

[0056] Furthermore, the polymer film includes a polyethylene film and / or a polypropylene film.

[0057] Furthermore, the composite film includes a base layer and a modified layer disposed on at least one side surface of the base layer.

[0058] Furthermore, the base layer includes a polyethylene film and / or a polypropylene film.

[0059] Furthermore, the material of the modified layer is any one of aluminum oxide, boehmite or silicon dioxide.

[0060] It should be noted that the reinforcing part on the diaphragm can be used in conjunction with the modified layer to significantly enhance the heat shrinkage resistance. The main component of the modified layer includes at least one of alumina, boehmite and silicon dioxide, and other ceramic materials can also be used, not limited to the materials provided above.

[0061] In another specific embodiment, the utility model provides an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet and the separator as described above.

[0062] Further, when the area of ​​the positive electrode sheet is larger than that of the negative electrode sheet, the overlap width W3 of the non-ear area of ​​the positive electrode sheet and the reinforcement portion of the diaphragm satisfies the following conditions: 0.2≤W3≤10mm, for example, it can be 0.2mm, 0.5mm, 1mm, 3mm, 5mm, 7mm, 9mm or 10mm, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; or,

[0063] When the area of ​​the negative electrode sheet is larger than that of the positive electrode sheet, the overlapped area width W3 of the non-ear area of ​​the negative electrode sheet and the reinforcing portion of the separator satisfies the following condition: 0.2≤W3≤10mm, for example, it can be 0.2mm, 0.5mm, 1mm, 3mm, 5mm, 7mm, 9mm or 10mm, etc. However, it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0064] In the present invention, if W3 is less than 0.2 mm, it cannot provide sufficient support and cannot improve the wettability of the electrode sheet after hot pressing of the electrode assembly; if W3 is greater than 10 mm, it will affect the fit between the positive and negative electrode sheets and the diaphragm and affect the transmission of lithium ions.

[0065] It should be noted that when the reinforcement portion is provided on both sides of the main body in the width direction, W3 is the width of the overlapping area between the non-ear area of ​​the single-side pole piece and the reinforcement portion of the diaphragm.

[0066] In another specific embodiment, the utility model provides a battery cell, wherein the battery cell includes the electrode assembly as described above.

[0067] In another specific embodiment, the utility model provides a battery, which includes the battery cell as described above.

[0068] In another specific embodiment, the utility model provides an electrical device, wherein the electrical device comprises the battery as described above.

[0069] The following are specific examples.

[0070] Example 1

[0071] This embodiment provides a diaphragm, and its structural schematic diagram is as follows Figure 2 As shown, the diaphragm includes a main body 1 and reinforcement parts 2 arranged on both sides of the main body 1 in the width direction, and the reinforcement parts 2 extend along the length direction of the main body 1; the reinforcement parts 2 are wavy in shape;

[0072] The width of the reinforcement portion 2 on one side is recorded as W1, W1 = 4 mm;

[0073] The reinforcing portion 2 includes concave portions and convex portions that are alternately and periodically arranged, and the center distance between adjacent convex portions is denoted as W2, W2=3mm;

[0074] The height of the reinforcement part 2 is 0.1 mm;

[0075] The cross-sectional shape of the reinforcing portion 2 along a direction perpendicular to its own extension direction includes a periodically arranged trapezoid;

[0076] The separator is a polyethylene film.

[0077] Figure 3 The cross-sectional view of the trapezoidal reinforcement portion in the diaphragm prepared in this embodiment is shown. As can be seen from the figure, the cross-sectional shape of the reinforcement portion 2 includes periodically arranged trapezoids.

[0078] This embodiment also provides a method for preparing a diaphragm, the method comprising the following steps:

[0079] Will be like Figure 1 The embossing roller shown is installed on the membrane side of the winder, and then the membrane is prepared into a continuous roll and installed on the conveying roller of the membrane. Subsequently, the height of the reinforcement part of the membrane when winding is controlled by adjusting the pressure of the embossing roller to obtain the membrane.

[0080] This embodiment also provides an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet 3 and the separator as described above;

[0081] The area of ​​the negative electrode sheet 3 is larger than that of the positive electrode sheet, and the width W3 of the overlapping area between the non-tab area of ​​the negative electrode sheet 3 and the reinforcing portion 2 of the separator meets the following condition: W3=2 mm.

[0082] Example 2

[0083] The difference between this embodiment and the first embodiment is that the height of the reinforcement portion is 0.5 mm.

[0084] The remaining parameters and steps are consistent with those in Example 1.

[0085] Example 3

[0086] The difference between this embodiment and the first embodiment is that the height of the reinforcement portion is 1 mm.

[0087] The remaining parameters and steps are consistent with those in Example 1.

[0088] Example 4

[0089] The difference between this embodiment and the first embodiment is that the height of the reinforcement portion is 2 mm.

[0090] The remaining parameters and steps are consistent with those in Example 1.

[0091] Example 5

[0092] The difference between this embodiment and embodiment 1 is that the height of the reinforcement portion is 3 mm.

[0093] The remaining parameters and steps are consistent with those in Example 1.

[0094] Example 6

[0095] The difference between this embodiment and the first embodiment is that the height of the reinforcement portion is 5 mm.

[0096] The remaining parameters and steps are consistent with those in Example 1.

[0097] Example 7

[0098] The difference between this embodiment and embodiment 1 is that the height of the reinforcement portion is 3 mm, the width of the reinforcement portion is 2 mm, and the width of the overlapped area is 1.5 mm.

[0099] The remaining parameters and steps are consistent with those in Example 1.

[0100] Example 8

[0101] The difference between this embodiment and embodiment 1 is that the height of the reinforcement portion is 3 mm, and the center distance between adjacent protrusions is 0.5 mm.

[0102] The remaining parameters and steps are consistent with those in Example 1.

[0103] Example 9

[0104] The difference between this embodiment and embodiment 1 is that the height of the reinforcement portion is 3 mm, and the center distance between adjacent protrusions is 10 mm.

[0105] The remaining parameters and steps are consistent with those in Example 1.

[0106] Example 10

[0107] The difference between this embodiment and embodiment 1 is that the height of the reinforcement portion is 3 mm, and the width of the overlapping area between the non-ear area of ​​the negative electrode sheet and the reinforcement portion of the separator is 0.2 mm.

[0108] The remaining parameters and steps are consistent with those in Example 1.

[0109] Embodiment 11

[0110] The difference between this embodiment and embodiment 1 is that the width of the reinforcement portion is 12 mm, the height of the reinforcement portion is 3 mm, and the width of the overlapping area between the non-tab area of ​​the negative electrode sheet and the reinforcement portion of the separator is 10 mm.

[0111] The remaining parameters and steps are consistent with those in Example 1.

[0112] Example 12

[0113] The difference between this embodiment and Embodiment 7 is that the width of the reinforcement portion is 1.8 mm, and the width of the overlapping area between the non-tab area of ​​the negative electrode sheet and the reinforcement portion of the separator is 0.5 mm.

[0114] The remaining parameters and steps remain the same as those in Example 7.

[0115] Embodiment 13

[0116] The difference between this embodiment and the first embodiment is that the height of the reinforcement portion is 6 mm.

[0117] The remaining parameters and steps are consistent with those in Example 1.

[0118] Embodiment 14

[0119] The difference between this embodiment and Embodiment 5 is that the center distance between adjacent protrusions is 0.3 mm.

[0120] The remaining parameters and steps are consistent with those in Example 5.

[0121] Embodiment 15

[0122] The difference between this embodiment and Embodiment 5 is that the center distance between adjacent protrusions is 12 mm.

[0123] The remaining parameters and steps are consistent with those in Example 5.

[0124] Example 16

[0125] The difference between this embodiment and embodiment 1 is that the diaphragm includes a base layer (polyethylene film) and a modified layer disposed on one surface of the polyethylene film, and the material of the modified layer is aluminum oxide.

[0126] The remaining parameters and steps are consistent with those in Example 1.

[0127] Comparative Example 1

[0128] The difference between this comparative example and Example 1 is that the diaphragm is not provided with a reinforcement portion.

[0129] The remaining parameters and steps are consistent with those in Example 1.

[0130] Comparative Example 2

[0131] The difference between this comparative example and Example 1 is that the reinforcing portion includes concave portions and convex portions that are alternately and periodically arranged, the cross section of the convex portion is triangular, and the internal angle of the convex portion is less than 60°.

[0132] The remaining parameters and steps are consistent with those in Example 1.

[0133] Figure 4 A cross-sectional view of a triangular reinforcement portion in the diaphragm prepared in Comparative Example 2 is shown.

[0134] Figure 5 A cross-sectional view of the triangular reinforcement portion of the diaphragm prepared in Comparative Example 2 after hot pressing is shown. It can be seen from the figure that the reinforcement portion of this shape is prone to wrinkles after hot pressing. The reinforcement portion affects the transmission of lithium ions during the charge and discharge process, resulting in black spots and lithium deposition at the corresponding position.

[0135] Performance Testing

[0136] The electrode assemblies provided in the above embodiments and comparative examples are made into battery cells, and the specific steps include:

[0137] The lithium iron phosphate positive electrode sheet, the negative electrode sheet and the above-mentioned separator are wound into an electrode assembly by a circular winding needle.

[0138] The electrode assemblies are subjected to hot pressing, Hi-pot testing, X-ray, ultrasonic welding, laser welding, full welding, air tightness testing, liquid injection, formation, OCV testing, k-value testing, and finally capacity testing to obtain battery cells, which are then subjected to extreme hot box testing.

[0139] The process of the extreme hot box test includes:

[0140] The battery cell is fully charged to 100% SOC, heated to 130℃ in 5 minutes, kept warm for 30 minutes after the temperature is constant, and then heated at a gradient of 10℃ for 30 minutes each time the temperature rises by 10℃ until the battery cell fails. This temperature is defined as the ultimate hot box temperature of the battery cell.

[0141] The test results are shown in Table 1.

[0142] Table 1

[0143]

[0144]

[0145] analyze:

[0146] It can be seen from the above table that the diaphragm provided by the utility model can provide good heat resistance and high liquid absorption capacity, ensure the safety of the diaphragm at higher temperatures, reduce the risk of short circuit between the positive and negative electrodes due to shrinkage of the diaphragm at high temperatures, and meet the current needs of high power and high energy density.

[0147] It can be seen from Examples 1-16 and Comparative Example 1 that if the diaphragm is not provided with a reinforcement portion, the thermal shrinkage rate and the ultimate hot box temperature of the diaphragm are very low, and the heat shrinkage resistance of the diaphragm is poor.

[0148] It can be seen from Examples 7 and 12 that if the width of the reinforcement portion is too small, the mechanical strength cannot be satisfied and the reinforcement portion cannot be suppressed from thermal contraction of the separator.

[0149] It can be seen from Examples 1-11, Example 13 and Comparative Example 1 that if the height is too small, it cannot provide sufficient mechanical strength and cannot suppress thermal shrinkage of the diaphragm; if the height is too large, wrinkles are easily generated after hot pressing, affecting the electrode wetting effect and electrode assembly performance.

[0150] It can be seen from Examples 5 and 14-15 that if the center distance between adjacent protrusions is too small, wrinkles are likely to occur after hot pressing, affecting the electrode wetting effect and electrode assembly performance; if the center distance between adjacent protrusions is too large, the mechanical strength provided is insufficient and cannot play a role in preventing thermal shrinkage of the diaphragm.

[0151] It can be seen from Example 1 and Example 16 that if a modified layer is provided on the polyethylene film, the shrinkage resistance of the diaphragm is significantly enhanced.

[0152] It can be seen from Example 1 and Comparative Example 2 that if the cross-section of the convex portion in the reinforcement portion is set to be triangular, the reinforcement portion of this shape is prone to wrinkles after hot pressing. The reinforcement portion affects the transmission of lithium ions during the charge and discharge process, resulting in black spots and lithium deposition at the corresponding position, thereby destroying the performance of the battery cell.

[0153] The applicant declares that the above is only a specific implementation method of the present utility model, but the protection scope of the present utility model is not limited thereto. The technicians in the relevant technical field should understand that any changes or substitutions that can be easily thought of by the technicians in the relevant technical field within the technical scope disclosed in the present utility model fall within the protection scope and disclosure scope of the present utility model.

Claims

1. A diaphragm, characterized in that: The diaphragm includes a main body, and a reinforcing portion provided on at least one side in the width direction of the main body, wherein the reinforcing portion extends along the length direction of the main body; The reinforcement portion is in a wave shape.

2. The diaphragm according to claim 1, characterized in that The width of the reinforcement portion is denoted as W1, where W1≥2 mm.

3. The diaphragm according to claim 1, characterized in that The reinforcing portion includes concave portions and convex portions that are alternately and periodically arranged, and the center distance between adjacent convex portions and / or concave portions is denoted as W2; The W2 satisfies the following condition: 0.5≤W2≤10mm.

4. The diaphragm according to claim 1, characterized in that The height of the reinforcement portion is 0.1-5 mm.

5. The diaphragm according to any one of claims 1 to 4, characterized in that: The cross-sectional shape of the reinforcement portion along a direction perpendicular to the reinforcement portion's extension direction includes a trapezoid and / or a semicircle.

6. The diaphragm according to any one of claims 1 to 4, characterized in that: The diaphragm comprises a polymer film or a composite film; The composite film comprises a base layer and a modified layer arranged on at least one side surface of the base layer.

7. The diaphragm according to claim 6, characterized in that The material of the modified layer is any one of aluminum oxide, boehmite or silicon dioxide.

8. An electrode assembly, characterized in that: The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator as claimed in any one of claims 1 to 7.

9. The electrode assembly according to claim 8, characterized in that: When the area of ​​the positive electrode sheet is larger than that of the negative electrode sheet, the overlap width W3 of the non-tab area of ​​the positive electrode sheet and the reinforcement portion of the separator satisfies the following condition: 0.2≤W3≤10mm; or, When the area of ​​the negative electrode sheet is greater than that of the positive electrode sheet, the width W3 of the overlapping area between the non-tab area of ​​the negative electrode sheet and the reinforcement portion of the separator satisfies the following condition: 0.2≤W3≤10 mm.

10. A battery cell, characterized in that: The battery cell includes the electrode assembly according to claim 8 or 9.

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