Diaphragm, battery and electric equipment

Abstract

The utility model relates to a diaphragm, a battery and electric equipment, the diaphragm is in a trend of sinking from two ends to the middle on at least one main surface of the diaphragm along a first direction, and the first direction is perpendicular to the thickness direction of the diaphragm. When the diaphragm is used for the battery, a gap can be formed between the pole piece and the diaphragm, so that the diaphragm and the pole piece can be soaked in electrolyte, the soaking efficiency of the electrolyte is improved, and the battery performance is further improved.

Description

Technical Field

[0001] This disclosure relates to the field of battery technology, and more specifically, to a separator, a battery, and an electrical device. Background Technology

[0002] Currently, polyolefin separators are used in batteries, but these separators have poor wettability with electrolytes. Furthermore, stacked batteries require hot pressing to increase battery rigidity. After hot pressing, there is a strong adsorption force between the electrodes and the separator, which hinders the diffusion of the electrolyte through the separator to the positive and negative electrode surfaces and into the battery via capillary action. This results in low electrolyte wetting efficiency, affecting the battery manufacturing cycle time and the overall wetting effect. In short, existing separators have poor electrolyte wetting properties, leading to a decrease in battery performance. Utility Model Content

[0003] The purpose of this disclosure is to provide a separator, a battery, and an electrical device, wherein the separator can improve the wetting efficiency of the electrolyte, improve the uniformity of the wetting distribution, and improve battery performance.

[0004] To achieve the above objectives, a first aspect of this disclosure provides a diaphragm in which, along a first direction, on at least one main surface of the diaphragm, the diaphragm tends to be concave from both ends to the middle, the first direction being perpendicular to the thickness direction of the diaphragm.

[0005] Optionally, along the first direction, the diaphragm includes a recessed region and a first region and a second region disposed on both sides of the recessed region, wherein the average thickness of the first region and the second region is greater than the average thickness of the recessed region.

[0006] Optionally, along the first direction, the diaphragm tends to thin from both ends to the middle.

[0007] Optionally, the first direction is the length direction or the width direction of the diaphragm.

[0008] Optionally, the average depth of the recessed area along the thickness direction of the diaphragm is 0.15 μm to 4 μm.

[0009] Optionally, the recessed area is strip-shaped, and in the second direction, both ends of the recessed area extend to the edge of the diaphragm; the second direction is perpendicular to the thickness direction of the diaphragm, and the second direction is perpendicular to the first direction.

[0010] Optionally, on at least one main surface of the diaphragm, the first region and the second region have the same area.

[0011] Optionally, on at least one main surface of the diaphragm, the area of ​​the recessed region accounts for 8% to 50% of the total area of ​​the diaphragm.

[0012] Optionally, on at least one main surface of the diaphragm, the area of ​​the recessed region accounts for 11% to 33% of the total area of ​​the diaphragm.

[0013] Optionally, the diaphragm satisfies at least one of the following (a) to (c):

[0014] (a) The diaphragm has the same thickness in the first region;

[0015] (b) The diaphragm has the same thickness in the second region;

[0016] (c) The average thickness of the diaphragm in the first region is the same as the average thickness of the diaphragm in the second region.

[0017] Optionally, the first region is a strip extending along a second direction, the second direction being perpendicular to the thickness direction of the diaphragm and perpendicular to the first direction; the first region includes one or more first sub-regions sequentially arranged along the first direction, the average thickness of the plurality of first sub-regions increasing sequentially in a direction away from the recessed region; and / or,

[0018] The second region is a strip extending along a second direction, which is perpendicular to the thickness direction of the diaphragm and perpendicular to the first direction; the second region includes one or more second sub-regions arranged sequentially along the first direction, and the average thickness of the plurality of second sub-regions increases sequentially in the direction away from the recessed region.

[0019] Optionally, on at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent first sub-regions in the diaphragm thickness direction is 0.1 μm to 1.5 μm; and / or,

[0020] On at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent second sub-regions in the direction of diaphragm thickness is 0.1 μm to 1.5 μm.

[0021] Optionally, on at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent first sub-regions in the diaphragm thickness direction is 0.5 μm to 1 μm; and / or,

[0022] On at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent second sub-regions in the direction of diaphragm thickness is 0.5 μm to 1 μm.

[0023] Optionally, the diaphragm satisfies at least one of the following (d) to (f):

[0024] (d) The diaphragm has the same thickness within the same first sub-region;

[0025] (e) The diaphragm has the same thickness within the same second sub-region;

[0026] (f) The recessed area passes through the geometric center of at least one of the main surfaces, and the thickness of each sub-area is symmetrically distributed on both sides of the recessed area.

[0027] Optionally, the width directions of the first sub-region and the second sub-region are the same as the first direction, and the diaphragm satisfies at least one of the following (A) to (E):

[0028] (A) The average width of each of the first sub-regions is the same;

[0029] (B) The average width of each of the second sub-regions is the same;

[0030] (C) The recessed area passes through the geometric center of at least one of the main surfaces, and the widths of each sub-area are symmetrically distributed on both sides of the recessed area;

[0031] (D) The width of each of the first sub-regions is the same;

[0032] (E) The width of each of the second sub-regions is the same.

[0033] Optionally, the first region includes two first sub-regions, the width direction of the first sub-regions being the same as the first direction, the average width ratio of the first sub-region closer to the recessed region to the recessed region being 0.5~6:1; the average width ratio of the first sub-region farther from the recessed region to the recessed region being 0.5~6:1; and / or,

[0034] The second region includes two second sub-regions. The width direction of the second sub-regions is the same as that of the first region. The average width ratio of the second sub-region closer to the recessed region to the recessed region is 0.5 to 6:1. The average width ratio of the second sub-region farther from the recessed region to the recessed region is 0.5 to 6:1.

[0035] Optionally, the first region includes two first sub-regions, the width direction of the first sub-regions being the same as the first direction, the average width ratio of the first sub-region closer to the recessed region to the recessed region being 1~6:1; the average width ratio of the first sub-region farther from the recessed region to the recessed region being 1~6:1; and / or,

[0036] The second region includes two second sub-regions. The width direction of the second sub-regions is the same as that of the first region. The average width ratio of the second sub-region closer to the recessed region to the recessed region is 1 to 6:1. The average width ratio of the second sub-region farther from the recessed region to the recessed region is 1 to 6:1.

[0037] Optionally, the diaphragm includes a base film and an inorganic coating covering at least one side of the base film in the thickness direction; the base film in the recessed region, the first region, and the second region has the same average thickness; on at least one side of the base film in the thickness direction, the average thickness of the inorganic coating in the recessed region is less than the average thickness of the inorganic coating in the first region and the average thickness of the inorganic coating in the second region.

[0038] Optionally, the first region includes two first sub-regions, wherein the ratio of the average thickness of the inorganic coating in the first sub-region closer to the recessed region to the recessed region is 1.2 to 6:1; and the ratio of the average thickness of the inorganic coating in the first sub-region farther from the recessed region to the recessed region is 1.4 to 9:1; and / or,

[0039] The second region includes two second sub-regions. The ratio of the average thickness of the inorganic coating in the second sub-region closer to the recessed region to the recessed region is 1.2 to 6:1; the ratio of the average thickness of the inorganic coating in the second sub-region farther from the recessed region to the recessed region is 1.4 to 9:1.

[0040] Optionally, the diaphragm satisfies at least one of the following conditions:

[0041] (I) The average thickness of the base film is 5 μm to 25 μm;

[0042] (II) The inorganic coating comprises ceramic particles, which include aluminum oxide, hydrated aluminum oxide, silicon nitride, silicon dioxide, zirconium oxide or titanium dioxide.

[0043] Optionally, the average thickness of the inorganic coating in the recessed area is 0.5 μm to 2 μm, the average thickness of the inorganic coating in the first area is 1.15 μm to 4.5 μm, and the average thickness of the inorganic coating in the second area is 1.15 μm to 4.5 μm; and / or,

[0044] The average thickness of the inorganic coating in the first sub-region is 1.1 μm to 5 μm, and the average thickness of the inorganic coating in the second sub-region is 1.1 μm to 5 μm.

[0045] A second aspect of this disclosure provides a battery including electrodes and a separator as described in the first aspect of this disclosure, the separator having a concave tendency from both ends to the middle such that a gap is formed between the separator and at least one electrode.

[0046] Optionally, the battery is a wound battery, and the separator includes a recessed area and a first area and a second area disposed on both sides of the recessed area. The first area, the recessed area and the second area of ​​the separator are arranged sequentially along the extension direction of the winding of the battery.

[0047] Optionally, the battery is a stacked battery, the stacked battery includes tabs, the separator includes a recessed region and a first region and a second region disposed on both sides of the recessed region, and the tabs are disposed at at least one end in the first direction.

[0048] A third aspect of this disclosure provides an electrical device including the battery described in the second aspect of this disclosure.

[0049] Through the above technical solution, the separator disclosed herein can form a gap between the central region of the electrode and the separator in the battery, which helps the separator and the electrode to be wetted with electrolyte, improves the wetting efficiency of electrolyte, and thus improves battery performance.

[0050] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0051] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0052] Figure 1 This is a cross-sectional view of the membrane prepared in the thickness direction according to Embodiment 1 of this disclosure.

[0053] Figure 2 This is a schematic diagram of the negative electrode plate site tested in Test Example 2 of this disclosure.

[0054] Figure 3 This is a schematic diagram of the orientation of a wound battery and a recessed area in this disclosure.

[0055] Figure 4 This is a schematic diagram of a stacked battery and the orientation of the recessed area in this disclosure.

[0056] Explanation of reference numerals in the attached figures

[0057] 1: First region; 1a: First sub-region; 1b: First sub-region; 2: Second region; 2a: Second sub-region; 2b: Second sub-region; 3: Recessed region; 4: Inorganic coating; 5: Base film; 6: Roll; 7: Tab; 8: Separator; H: Average distance between surfaces; W: Average width; A, B, C, D, and E are negative electrode sites. Detailed Implementation

[0058] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0059] The first aspect of this disclosure provides a diaphragm in which, along a first direction, on at least one main surface of the diaphragm, the diaphragm tends to be concave from both ends to the middle, and the first direction is perpendicular to the thickness direction of the diaphragm.

[0060] In this disclosure, "middle" and "two ends" are relative terms. "Two ends" refers to the adjacent positions on the outer edges of the diaphragm, while "middle" is relative to "two ends." The diaphragm structure has a concave tendency from both ends to the middle. This can be either a gradual inward concavity from both ends to the middle, or a stepped inward concavity from both ends to the middle, as shown below. Figure 1 As shown, the diaphragm as a whole forms a shape with a single recessed area. For example, in an embodiment where the cross-section of the diaphragm perpendicular to the thickness direction is square, the two ends can refer to the edge regions adjacent to a set of opposite sides of the square; in an embodiment where the cross-section of the diaphragm perpendicular to the thickness direction is circular, the two ends can refer to the edge regions distributed at both ends of a diameter of the circle and adjacent to the circumference.

[0061] When the diaphragm is rectangular in shape, it has length, width, and thickness (length ≥ width > thickness), and the first direction can be either the length direction or the width direction of the diaphragm. When the first direction is the length direction of the diaphragm, along the first direction, on at least one main surface of the diaphragm, the diaphragm tends to be concave from both ends to the middle, that is, on at least one main surface of the diaphragm, the middle region of the diaphragm in the length direction is concave compared to the two ends.

[0062] In this disclosure, the main surface of the diaphragm refers to the two opposing surfaces with relatively large diaphragm areas, for example... Figure 1 The upper and lower surfaces of the diaphragm are the two main surfaces of the diaphragm, and the average distance between the two main surfaces is the thickness of the diaphragm. In one embodiment, the diaphragm is stepped inward from both ends to the middle. In this embodiment, the main surfaces do not include the interface of the stepped change that is parallel to the thickness direction.

[0063] This disclosure presents a design with a recessed middle section in the separator. When the separator is used in a battery, a gap is formed between the middle region of the separator and the electrode. This gap allows space for the electrolyte, which is beneficial for the electrolyte to wet the middle region of the separator or electrode, thereby improving the electrolyte wetting efficiency and enhancing the battery's cycle performance, power performance, fast charging performance, and rate performance.

[0064] According to one embodiment of this disclosure, a recessed region is formed on at least one main surface of the diaphragm along a first direction. In this disclosure, along the first direction, on at least one main surface of the diaphragm, the diaphragm tends to be concave from both ends to the middle to form the recessed region. The shape of the recessed region is not particularly limited; for example, the cross-section of the recessed region perpendicular or parallel to the thickness direction of the diaphragm can be square, circular, trapezoidal, or irregular in shape. For example, the recessed region can correspond to... Figure 1The location corresponding to the recessed area 3 is concave compared to the surfaces of the two sides 1a and 1b, forming a recessed area. The cross-section of the recessed area perpendicular to the thickness direction of the diaphragm is square.

[0065] The presence of the recessed area can create a gap between the middle region of the separator and the electrode when the separator is applied in the battery. This gap can reserve space for the electrolyte, improve the electrolyte wetting efficiency, help the electrolyte to fully wet, and improve battery performance.

[0066] According to one embodiment of this disclosure, the separator thins from both ends to the middle along a first direction. This embodiment allows a gap to be formed between the separator and the electrode, providing space for the electrolyte, improving electrolyte wetting efficiency, facilitating full electrolyte wetting, and enhancing battery performance.

[0067] According to one embodiment of this disclosure, along a first direction, the diaphragm includes a recessed region and a first region and a second region disposed on both sides of the recessed region, wherein the average thickness of the first region and the second region is greater than the average thickness of the recessed region. For example, when the diaphragm is in the shape of a cuboid, the diaphragm has a length, a width, and a thickness (length ≥ width > thickness). In this case, the first region, the recessed region, and the second region may be arranged sequentially along the length direction of the diaphragm, or the first region, the recessed region, and the second region may be arranged sequentially along the width direction of the diaphragm.

[0068] According to one embodiment of this disclosure, the first direction is the length direction or the width direction of the diaphragm.

[0069] The separator of this disclosure is divided into a recessed region 3 and a first region 1 and a second region 2 located on both sides of the recessed region. The thickness of the regions on both sides is greater than the thickness of the recessed region. The first region 1 and the second region 2 on both sides provide support for the electrode in contact with the separator. The thickness difference between the recessed region and the two sides of the separator creates a gap between the electrode and the separator in the middle region of the battery, which is far from the edge of the separator after the battery is formed. This facilitates the electrolyte to wet the middle region of the battery, improves the wetting efficiency of the separator, improves the uniformity of the wetting distribution, and thus improves the battery performance.

[0070] In this disclosure, the recessed region is a region further away from the edge of the diaphragm than the first region and the second region, and the recessed region may or may not include the center of the main surface of the diaphragm.

[0071] In this disclosure, the test method for "average thickness" can be to randomly select more than 10 locations within the corresponding area and measure the average value of the membrane thickness.

[0072] In this disclosure, the average depth refers to the average distance between the recessed area and the surfaces of the first and second areas on the same main surface of the diaphragm, i.e., the distance between the two surfaces in the thickness direction. It is the average of the distances measured at more than 10 randomly selected locations. The testing method is the stylus method (probe method), and the testing instruments are an atomic force microscope (AFM) and a profilometer. The stylus method (probe method) employs a contact surface topography measurement technique. The tip of the probe contacts the sample surface, and the probe moves on the workpiece. A detector connected to the probe can detect the change in the contact force between the two surfaces during this process and record the electrical signal. Through this test, the surface undulation data of the sample along the probe's movement path can be obtained. When the stylus sweeps across the step, the height difference between the top and bottom of the step can be displayed by a displacement sensor, which is the distance between the two surfaces in the thickness direction.

[0073] In this disclosure, battery performance includes cycle performance, power performance, fast charging performance, and rate performance. Cycle performance refers to the battery's ability to maintain its performance during charging and discharging; cycle performance affects the battery's lifespan and reliability. Power performance refers to the battery's ability to output energy within a certain time period. Rate performance refers to the current required for the battery to discharge its rated capacity within a specified time, expressed as a multiple of the rated capacity. Fast charging performance refers to the battery being charged to the charging cutoff voltage using a specific fast charging strategy, then discharged to the discharge cutoff voltage using standard methods, cycling a certain number of times, and its fast charging performance is determined by the capacity retention rate.

[0074] According to one embodiment of this disclosure, the average depth of the recessed area along the thickness direction of the diaphragm is 0.15 μm to 4 μm, preferably 0.4 μm to 3 μm. For example... Figure 1 As shown, the average depth of the recessed area refers to: on at least one main surface of the diaphragm, the average distance H between the surface of the first region 1 and the surface of the recessed region 3 in the diaphragm thickness direction is 0.15 μm to 4 μm, preferably 0.4 μm to 3 μm; and / or, on at least one main surface of the diaphragm, the average distance H between the surface of the second region 2 and the surface of the recessed region 3 in the diaphragm thickness direction is 0.15 μm to 4 μm, preferably 0.4 μm to 3 μm.

[0075] In other words, when a recessed area is formed on one side of the diaphragm thickness direction (i.e., one main surface of the diaphragm), for that side, the average height difference between the surface of the first region 1 and the surface of the recessed region 3 along the diaphragm thickness direction is 0.15 μm to 4 μm, preferably 0.4 μm to 3 μm; and / or, on at least one surface of the diaphragm thickness direction, the average height difference between the surface of the second region 2 and the surface of the recessed region 3 along the diaphragm thickness direction is 0.15 μm to 4 μm, preferably 0.4 μm to 3 μm. When recessed areas are formed on both sides of the diaphragm thickness direction, for one or both sides: along the diaphragm thickness direction, the average distance H between the surface of the first region 1 and the surface of the recessed region 3 on the same side is 0.15 μm to 4 μm, preferably 0.4 μm to 3 μm; and / or, along the diaphragm thickness direction, the average distance H between the surface of the second region 2 and the surface of the recessed region 3 is 0.15 μm to 4 μm, preferably 0.15 μm to 3 μm. The above-described embodiments facilitate the formation of a suitable gap between the electrode and the separator in the central region of the battery, which is located away from the edge of the separator. This allows the electrolyte to penetrate into the central region of the battery, improving the electrolyte wetting efficiency, enhancing the uniformity of electrolyte distribution, and ultimately improving battery performance. In this application, "and / or" can be understood as satisfying one or both of the preceding and following conditions.

[0076] According to one embodiment of this disclosure, the recessed region 3 is formed in the shape of a strip, and in a second direction, both ends of the recessed region 3 extend to the edge of the separator; the second direction is perpendicular to the thickness direction of the separator and perpendicular to the first direction. For example, in an embodiment where the surface of the separator perpendicular to its thickness direction is rectangular, the first direction can be the length direction or the width direction of the rectangle, and both ends of the strip-shaped recessed region can extend to a set of opposite sides of the rectangle parallel to the length direction or the width direction. The above embodiment is beneficial for saving production costs, improving production line efficiency and the economic benefits of enterprises. In a further embodiment, the strip-shaped recessed region can pass through the geometric center of the main surface of the separator. Since the electrolyte diffusion path is long at the center of the battery, which is prone to insufficient wetting, passing through the geometric center can further promote the wetting of the electrolyte at the center of the battery.

[0077] In a further embodiment, the cross-section of the strip-shaped recessed area 3 extending in the direction of extension can be formed as a rectangle, trapezoid, parallelogram, or as a strip with wavy edges, serrated edges, or irregular edges.

[0078] According to one embodiment of the present disclosure, on at least one main surface of the diaphragm, the first region 1 and the second region 2 have the same area, and further, the first region and the second region have the same shape.

[0079] In one specific embodiment, on at least one main surface of the diaphragm, the area of ​​the recessed region accounts for 8% to 50% of the total area of ​​the diaphragm, preferably 11% to 33%; that is, on one side surface in the thickness direction of the diaphragm, the area of ​​the recessed region accounts for 8% to 50% of the total area of ​​the diaphragm, preferably 11% to 33%. See details... Figure 1 The surface perpendicular to the diaphragm thickness direction should be parallel to... Figure 1 The left and right directions in the middle, perpendicular to Figure 1 The above-described implementation method allows for increased gaps between the electrode and the separator in the central region of the battery, away from the separator edge, while maintaining good thermal stability. This enables more electrolyte to be wetted in the central region of the battery, improving electrolyte wetting efficiency, enhancing the uniformity of wetting distribution, and ultimately improving battery performance.

[0080] According to one embodiment of this disclosure, the separator has a uniform thickness within the first region 1. That is, the thickness is the same throughout the first region 1. This simplifies the manufacturing process and facilitates the production of batteries with regular shapes.

[0081] According to one embodiment of this disclosure, the separator has a uniform thickness within the second region 2. That is, the thickness is the same throughout the second region 2. This simplifies the manufacturing process and facilitates the production of batteries with regular shapes.

[0082] According to one embodiment of this disclosure, the average thickness of the diaphragm in the first region 1 is the same as the average thickness of the diaphragm in the second region 2. That is, the average thickness of the first region 1 and the second region 2 is the same. Thus, the overall shape of the first region 1 and the second region 2 is relatively regular after they come into contact with the electrodes on opposite sides of the recessed region 3, and the manufacturing process is simple.

[0083] According to one embodiment of this disclosure, the first region is a strip extending along a second direction, which is perpendicular to the thickness direction of the diaphragm and also perpendicular to the first direction. The first region 1 includes one or more first sub-regions 1a / 1b sequentially arranged along the first direction. The average thickness of the plurality of first sub-regions 1a / 1b increases sequentially in the direction away from the recessed region 3, and the thickness of the first sub-regions 1a / 1b closer to the recessed region 3 is greater than the thickness of the recessed region 3. The sequential increase in the average thickness of the plurality of first sub-regions 1a / 1b in the direction away from the recessed region 3 means that, along the first direction, the average thickness of the first sub-region 1a relatively closer to the recessed region 3 is less than the average thickness of the first sub-region 1b relatively farther from the recessed region 3.

[0084] According to one embodiment of this disclosure, the second region is a strip extending along a second direction, which is perpendicular to the thickness direction of the diaphragm and also perpendicular to the first direction. The second region 2 includes one or more second sub-regions 2a / 2b sequentially arranged along the first direction. The average thickness of the plurality of second sub-regions 2a / 2b increases sequentially in the direction away from the recessed region 3, and the average thickness of the second sub-regions closer to the recessed region 3 is greater than the thickness of the recessed region. The sequential increase in the average thickness of the plurality of second sub-regions 2a / 2b in the direction away from the recessed region 3 means that, along the first direction, the average thickness of the second sub-region 2a relatively closer to the recessed region 3 is less than the average thickness of the second sub-region 2b relatively farther from the recessed region 3.

[0085] The thicknesses of the first sub-region 1a / 1b and / or the second sub-region 2a / 2b are set according to the above rules, which is conducive to forming such a Figure 1 The surface shown resembles a stepped separator. This embodiment allows for a gradual, stepped increase in the gap between the electrode and the separator in the central region of the battery, away from the separator edge. This enables more electrolyte to be wetted in the central region, improving electrolyte wetting efficiency, enhancing electrolyte distribution uniformity, and ultimately improving battery performance.

[0086] According to one embodiment of this disclosure, the surfaces of the first region, the recessed region, and the second region together constitute the main surface; on at least one main surface of the diaphragm, along the thickness direction of the diaphragm, the average distance H between the surfaces of two adjacent first sub-regions is 0.1 μm to 1.5 μm; and / or, on at least one main surface of the diaphragm, along the thickness direction of the diaphragm, the average distance H between the surfaces of two adjacent second sub-regions is 0.1 μm to 1.5 μm. Further, on at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent first sub-regions is 0.5 μm to 1 μm; and / or, on at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent second sub-regions is 0.5 μm to 1 μm.

[0087] The method for testing the average distance H between the surfaces of two adjacent first sub-regions and two adjacent second sub-regions can refer to the method for testing the average distance between the recessed area and the surfaces of the first and second regions described above. It should be noted that when the two sub-regions are distributed in a stepped manner, the test of the average distance H does not consider the vertical plane parallel to the direction of membrane thickness.

[0088] That is, on the same side of the separator, the average height difference between the surfaces of two adjacent first sub-regions is 0.1 μm to 1.5 μm, preferably 0.5 μm to 1 μm; and / or, on the same side of the separator, the average height difference between the surfaces of two adjacent second sub-regions is 0.1 μm to 1.5 μm, preferably 0.5 μm to 1 μm. The above embodiments are advantageous in preventing short circuits caused by direct contact between the positive and negative electrodes, and in providing impedance pores for storing the electrolyte and providing lithium-ion transport channels.

[0089] According to one embodiment of this disclosure, the separator has the same thickness within the same first sub-region; and / or, the separator has the same thickness within the same second sub-region. For example, the separator satisfies at least one of the following: the thickness is the same at all locations in the first sub-region 1a, or the thickness is the same at all locations in the first sub-region 1b, or the thickness is the same at all locations in the second sub-region 2a, or the thickness is the same at all locations in the second sub-region 2b. In the above embodiment, the thickness of the separator forms a stepped shape from the middle to both sides of the first and second sub-regions, gradually increasing the gap between the electrode and the separator in the central region of the battery, away from the edge, thereby improving the electrolyte wetting efficiency and allowing more electrolyte to be wetted into the central region of the battery. Simultaneously, the stepped thickness variation avoids affecting the mechanical properties of the separator, maintaining good mechanical properties and thermal stability, which is beneficial for improving the overall performance of the battery.

[0090] According to one embodiment of this disclosure, the recessed region passes through the geometric center of at least one main surface, and the thickness of each sub-region is symmetrically distributed on both sides of the recessed region. That is, on one side of the recessed region, the direction from near the recessed region to away from the recessed region includes first sub-regions 1a, 1b, 1c..., and on the other side of the recessed region, the direction from near the recessed region to away from the recessed region includes second sub-regions 2a, 2b, 2c..., where the thickness of 1a is equal to the thickness of 2a, the thickness of 1b is equal to the thickness of 2b, and the thickness of 1c is equal to the thickness of 2c. This facilitates improved regularity of the separator and battery, and also facilitates mass production.

[0091] According to one embodiment of this disclosure, the average width W of each first sub-region is the same, that is, the average width W of different first sub-regions is the same. For example, the average width W of first sub-region 1a and the average width W of first sub-region 1b are equal. In the above embodiment, the thickness of the separator changes smoothly in a stepped manner from the recessed area to both ends, which is beneficial to better fit the separator with the electrode, maintain good mechanical properties and thermal stability of the separator, and maintain good safety performance of the battery.

[0092] According to one embodiment of this disclosure, the average width W of each second sub-region is the same, that is, the average width W of different second sub-regions is the same. For example, the average width W of second sub-region 2a and second sub-region 2b is equal. In the above embodiment, the thickness of the separator changes smoothly in a stepped manner from the recessed area to both ends, which is beneficial to better adhesion between the separator and the electrode, maintain good mechanical properties and thermal stability of the separator, and maintain good safety performance of the battery.

[0093] According to one embodiment of this disclosure, the recessed region passes through the geometric center of at least one main surface, and the widths of each sub-region are symmetrically distributed on both sides of the recessed region. That is, on one side of the recessed region, the direction from near the recessed region to away from the recessed region includes first sub-regions 1a, 1b, 1c..., and on the other side of the recessed region, the direction from near the recessed region to away from the recessed region includes second sub-regions 2a, 2b, 2c..., where the width of 1a is equal to the width of 2a, the width of 1b is equal to the width of 2b, and the width of 1c is equal to the width of 2c. This facilitates the formation of the recessed region at the center of the diaphragm, improving the electrolyte wetting at the center of the diaphragm.

[0094] According to one embodiment of this disclosure, each first sub-region has the same width. That is, for a single first sub-region 1a / 1b, its width is consistent throughout. According to one embodiment of this disclosure, each second sub-region has the same width. That is, for a single second sub-region 2a / 2b, its width is consistent throughout. In this way, the diaphragm shape is relatively regular, and the manufacturing process is less difficult.

[0095] According to one embodiment of this disclosure, the first region includes two first sub-regions, wherein the average width ratio of the first sub-region closer to the recessed region to the recessed region is 0.5~6:1, preferably 1~6:1; and the width ratio of the first sub-region farther from the recessed region to the recessed region is 0.5~6:1, preferably 1~6:1; and / or, the second region includes two second sub-regions, wherein the average width ratio of the second sub-region closer to the recessed region to the recessed region is 0.5~6:1, preferably 1~6:1; and the average width ratio of the second sub-region farther from the recessed region to the recessed region is 0.5~6:1, preferably 1~6:1. The above embodiments facilitate better adhesion between the separator and the electrode, maintain good mechanical properties and thermal stability of the separator, and ensure good safety performance of the battery.

[0096] The width direction of the first sub-region and the second sub-region mentioned above is the same as that of the first direction.

[0097] According to one embodiment of this disclosure, the diaphragm includes a base membrane and an inorganic coating covering at least one side of the base membrane in the thickness direction. The thickness of the recessed region, the first region, and the second region of the diaphragm refers to the total thickness of the base membrane and the inorganic coating in each region.

[0098] Commonly used base membranes, such as polyolefin membranes, exhibit significant shrinkage at high temperatures. This inherent defect in the raw material results in poor thermal stability of ordinary base membranes, severely impacting the safety performance of power batteries. Coating the surface of the base membrane with an inorganic coating can improve the thermal stability and puncture resistance of polyolefin separators.

[0099] According to one embodiment of this disclosure, the thickness of the inorganic coating remains essentially constant, that is, the inorganic coating thicknesses of the recessed region, the first region, and the second region are approximately the same, and the base film thicknesses of the first region and the second region are respectively greater than the base film thickness of the recessed region.

[0100] According to another embodiment of this disclosure, the thickness of the base film remains substantially constant, that is, the average thickness of the base film in the recessed region, the first region, and the second region is approximately the same. On at least one side of the base film thickness direction, the average thickness of the inorganic coating in the recessed region is less than the average thickness of the inorganic coating in the first region and the average thickness of the inorganic coating in the second region. In this application, the average thickness of the inorganic coating refers to the average thickness of the inorganic coating on one side of the base film thickness direction.

[0101] In a further embodiment, the first region includes two first sub-regions, wherein the average thickness ratio of the inorganic coating of the first sub-region closer to the recessed region to the recessed region is 1.2 to 6:1; and the average thickness ratio of the inorganic coating of the first sub-region farther from the recessed region to the recessed region is 1.4 to 9:1; and / or, the second region includes two second sub-regions, wherein the average thickness ratio of the inorganic coating of the second sub-region closer to the recessed region to the recessed region is 1.2 to 6:1; and the average thickness ratio of the inorganic coating of the second sub-region farther from the recessed region to the recessed region is 1.4 to 9:1.

[0102] In a more specific embodiment, the recessed region, the first sub-region, and the second sub-region are respectively formed as strips, more preferably as strips with a rectangular surface shape. The first and second sub-regions are symmetrically arranged about the recessed region, that is, with the center line of the recessed region as the axis, the first and second sub-regions closer to the recessed region are symmetrically arranged, and the first and second sub-regions farther from the recessed region are symmetrically arranged. The symmetrically arranged sub-regions have the same surface shape and thickness. The average width ratio of the first sub-region to the recessed region is 0.5~6:1, and the average width ratio of the second sub-region to the recessed region is 0.5~6:1, more preferably the first and second sub-regions have the same width. The above embodiment, on the one hand, allows the separator and the electrode to fit better, maintains good thermal stability of the separator, and maintains good safety performance of the battery; on the other hand, it makes the gap between the electrode and the separator in the middle region of the battery away from the edge of the separator larger, allowing more electrolyte to be wetted in the middle region of the battery, improving the electrolyte wetting efficiency, and thus improving battery performance; it is also beneficial to production and preparation, improving the economics of separator products, increasing production line efficiency, and improving the economic benefits of enterprises.

[0103] In a further embodiment, the average thickness of the base film is 5 μm to 25 μm.

[0104] According to one embodiment of this disclosure, the average thickness of the inorganic coating in the recessed region is 0.5 μm to 2 μm, the average thickness of the inorganic coating in the first region is 1.15 μm to 4.5 μm, and the average thickness of the inorganic coating in the second region is 1.15 μm to 4.5 μm. This embodiment helps prevent short circuits caused by direct contact between the positive and negative electrodes, facilitates the provision of impedance pores for storing electrolyte, and provides lithium-ion transport channels.

[0105] According to one embodiment of this disclosure, the average thickness of the inorganic coating in the first sub-region is 1.1 μm to 5 μm, and the average thickness of the inorganic coating in the second sub-region is 1.1 μm to 5 μm. This embodiment is advantageous in preventing short circuits caused by direct contact between the positive and negative electrodes, and in providing impedance pores for storing electrolyte and providing lithium-ion transport channels.

[0106] According to one embodiment of this disclosure, the inorganic coating comprises ceramic particles and a binder. Based on the weight of the inorganic coating, the ceramic particles account for 30% to 50% by mass, preferably 35% to 48%, and the binder accounts for 2% to 15% by mass, preferably 4% to 10%. This embodiment helps the diaphragm maintain good thermal stability and prevents direct short circuits between the positive and negative electrodes caused by thermal shrinkage of the diaphragm at high temperatures.

[0107] In a further embodiment, the ceramic particles include aluminum oxide, hydrated aluminum oxide, silicon nitride, silicon dioxide, zirconium oxide, or titanium dioxide. The above embodiments help maintain good thermal stability of the separator and prevent direct short circuits between the positive and negative electrodes caused by thermal shrinkage of the separator at high temperatures.

[0108] According to one embodiment of this disclosure, the base membrane may be selected from one or more of polyethylene microporous membrane, polypropylene microporous membrane, polypropylene / polyethylene / polypropylene three-layer composite microporous membrane, polyvinylidene fluoride microporous membrane, polyvinylidene fluoride-hexafluoropropylene microporous membrane, polyimide microporous membrane, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyester nonwoven fabric, polyimide nonwoven fabric, aramid nonwoven fabric, and spandex nonwoven fabric; the adhesive is a conventional adhesive in the art, including but not limited to one or more of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polyimide (PI), polyacrylic acid (PAA), and carboxymethyl cellulose (CMC).

[0109] According to one embodiment of this disclosure, the diaphragm satisfies at least one of the following conditions: the areal density of the diaphragm is 7~9 g / m³. 2The air permeability is 95~130 s / 100ml; the transverse heat shrinkage rate of the diaphragm at 105℃ is 0.5%~2%, and the longitudinal heat shrinkage rate is 0.5%~2%. The diaphragm disclosed herein can maintain good thermal stability while relatively reducing the areal density and air permeability, thereby further improving the wetting effect of the electrolyte.

[0110] This disclosure provides a method for preparing a diaphragm, the method comprising: mixing ceramic particles, a binder and water to obtain a ceramic slurry; and coating the ceramic slurry onto a base membrane to form an inorganic coating.

[0111] According to one embodiment of the present disclosure, the mass ratio of ceramic particles, binder and water can be (2~25):1:(2~40), preferably (8~20):1:(10~30).

[0112] According to one embodiment of the present disclosure, the preparation method further includes dispersing the mixture obtained by mixing. The dispersion treatment can be selected from one or more of mechanical stirring, ultrasonic dispersion, high pressure dispersion, medium dispersion and high-speed shear emulsification.

[0113] According to one embodiment of this disclosure, coating can be done in a manner conventional in the art, such as one or more of micro-grooving roller coating, doctor blade coating, and slot extrusion coating.

[0114] A second aspect of this disclosure provides a battery including electrodes and a separator according to a first aspect of this disclosure. The separator tends to be concave from both ends to the middle, thereby forming a gap between the separator and at least one electrode. A recessed region is formed on at least one side surface in the thickness direction of the separator to form a gap between the electrode and the separator at a location away from the edge.

[0115] According to one embodiment of this disclosure, the battery is a wound battery, and the manufacturing process of the wound battery includes winding, such as... Figure 3 As shown, the winding causes the separator recessed area 3 to surround the winding shaft of the battery, and the first region, recessed area and second region of the separator are arranged sequentially along the extension direction of the winding shaft of the battery. The separator includes the recessed area 3 and the first region 1 and the second region 2 disposed on both sides of the recessed area. The recessed area 3 is formed on at least one side surface in the thickness direction of the separator.

[0116] According to another embodiment of this disclosure, the battery is a stacked battery, and the manufacturing process of the stacked battery includes stacking. In this embodiment, the stacked battery includes tabs 7, such as... Figure 4 As shown, the diaphragm includes a recessed region 3 and a first region 1 and a second region 2 disposed on both sides of the recessed region, and the tab is disposed at at least one end in the first direction.

[0117] A third aspect of this disclosure provides an electrical device, including the battery provided in the second aspect of this disclosure. The electrical device may be a vehicle, a portable electronic device, etc.

[0118] The present disclosure is described in further detail below with reference to the accompanying drawings, but the disclosure is not limited thereto.

[0119] In the following examples and comparative examples, the same base film was used: a PE base film with a porosity of 45%, a thickness of 7 μm, an air permeability of 90 s / 100 ml, a puncture strength of 0.35 kgf, and an areal density of 4.0 g / m³. 2 ;

[0120] The areal density of the diaphragm was tested on a vision analyzer of model JTMV-1210CNC.

[0121] The air permeability of the diaphragm was tested on a Wang Yan-type air permeability tester with model number EG01-55-1MR, and the test standard referred to GB / T 36363-2018 "Polyolefin diaphragms for lithium-ion batteries".

[0122] The thermal shrinkage rate of the diaphragm was tested on a Binder oven instrument under the condition of maintaining it at 105°C for 1 hour.

[0123] The VC content at site C of the electrode was tested using gas chromatography-mass spectrometry.

[0124] Thickness refers to the average thickness. The test method is to cut 10 diaphragms, stack them together, and use a micrometer to test them at certain intervals along the TD direction. The test result is divided by 10 to obtain the average thickness.

[0125] The average depth refers to the average distance between two surfaces, which is the difference between the average distances measured at 10 locations in each of the three sub-regions: the depression, the first sub-region, and the second sub-region. The test method is the step measurement method, and the test instruments are atomic force scanning microscope (AFM) and profilometer.

[0126] Example 1

[0127] Ceramic particles, binder and water are mixed in a mass ratio of 2:1:4. The slurry is then dispersed evenly using a grinding device to obtain a ceramic slurry. The ceramic slurry is then applied in a stepwise manner onto a base film, baked at 75°C and then wound up to obtain a diaphragm including an inorganic coating.

[0128] The diaphragm includes a base membrane 5 and an inorganic coating 4, the inorganic coating 4 being coated on the surface of the base membrane perpendicular to the thickness direction; along the first direction of the diaphragm, the diaphragm includes a recessed region 3 and a first region 1 and a second region 2 disposed on both sides of the recessed region 3; the thickness of the inorganic coating in the recessed region 3 is less than the thickness of the inorganic coating in the first region and the thickness of the inorganic coating in the second region, so that the thickness of the diaphragm gradually decreases from both sides to the middle, and the area of ​​the recessed region accounts for 11% of the total area of ​​the diaphragm; on the surface perpendicular to the thickness direction of the diaphragm, the areas of the first region 1 and the second region 2 are the same; the first region 1 is a strip extending along the second direction, and the first region 1 includes two first sub-regions 1a and 1b arranged sequentially along the first direction, the recessed region 3, the first sub-region 1a, and the second region 2. The average thickness of the first sub-region 1b increases sequentially in the direction away from the recessed region 3; the first region 1 and the second region 2 are symmetrically arranged on both sides of the recessed region 3; the second region 2 is a strip extending in the second direction, and the second region 2 includes two second sub-regions 2a and 2b arranged sequentially in the first direction, the average thickness of the recessed region 3, the second sub-region 2a, and the second sub-region 2b increases sequentially in the direction away from the recessed region 3; the first sub-region 1a and the second sub-region 2a are symmetrically arranged on both sides of the recessed region 3, and the average width W and the average thickness of the first sub-region 1a and the second sub-region 2a are the same; the first sub-region 1b and the second sub-region 2b are symmetrically arranged on both sides of the recessed region 3, and the average width W and the average thickness of the first sub-region 1b and the second sub-region 2b are the same.

[0129] The average thicknesses of the inorganic coatings in the first sub-region 1b, the first sub-region 1a, and the recessed region 3 are 3 μm, 2 μm, and 1 μm, respectively, with an average width ratio of 4:4:1. The average thickness ratio of the inorganic coatings in the first sub-region 1a, which is closer to the recessed region, to the recessed region is 2:1, and the average width ratio is 4:1. The average thickness ratio of the inorganic coatings in the first sub-region 1b, which is farther from the recessed region, to the recessed region is 3:1, and the average width ratio is 4:1. On one main surface of the diaphragm, the average distance H between the surfaces of the first sub-region 1a and the first sub-region 1b in the diaphragm thickness direction is 1 μm. On one main surface of the diaphragm, along the diaphragm thickness direction, the average distance H between the surface of the first region 1 and the surface of the recessed region 3 is 1.5 μm, that is, along the diaphragm thickness direction, the average depth of the recessed region 3 is 1.5 μm.

[0130] The inorganic coating thicknesses of the second sub-region 2b, the second sub-region 2a, and the recessed region 3 are 3 μm, 2 μm, and 1 μm, respectively, with a width ratio of 4:4:1. The average thickness ratio of the inorganic coating between the second sub-region 2a, which is closer to the recessed region, and the recessed region 3 is 2:1, and the average width ratio is 4:1. The average thickness ratio of the inorganic coating between the second sub-region 2b, which is farther from the recessed region, and the recessed region 3 is 3:1, and the average width ratio is 4:1. On one main surface of the diaphragm, the average distance H between the surfaces of the second sub-region 2a and the second sub-region 2b in the diaphragm thickness direction is 1 μm. On one main surface of the diaphragm, along the diaphragm thickness direction, the average distance H between the surface of the second region 2 and the surface of the recessed region 3 is 1.5 μm, that is, along the diaphragm thickness direction, the average depth of the recessed region 3 is 1.5 μm.

[0131] That is, the inorganic coatings of the first sub-region 1b and the second sub-region 2b, which are far from the depression region 3, have the same thickness and width; the inorganic coatings of the first sub-region 1a and the second sub-region 2a, which are close to the depression region 3, have the same thickness and width.

[0132] Examples 2-11

[0133] The preparation methods of the diaphragms in Examples 2 to 11 are the same as those in Example 1, except that the thickness or width of the inorganic coating in each sub-region is different, as shown in Table 1.

[0134] Table 1

[0135]

[0136] In Table 1, since the first sub-region 1b and the second sub-region 2b are symmetrically arranged, the average thickness and average width of the inorganic coating are the same; the first sub-region 1a and the second sub-region 2a are symmetrically arranged, and the average thickness and average width of the inorganic coating are the same. The average thickness, average thickness ratio and average width ratio of the inorganic coating in the second sub-region 2b, the second sub-region 2a and the recessed region 3 are omitted.

[0137] Comparative Example 1

[0138] The only difference between the preparation method of the diaphragm in Comparative Example 1 and Example 1 is that the thickness of the inorganic coating at different locations is the same, which is 3 μm.

[0139] Test Example 1

[0140] The physical properties of the diaphragms obtained in Examples 1-11 and Comparative Example 1 were tested, and the results are shown in Table 2.

[0141] Table 2

[0142]

[0143] According to the data in Table 2, the diaphragm disclosed herein can maintain good thermal stability while reducing the areal density and air permeability, thereby further improving the wetting effect of the electrolyte.

[0144] The separators from Examples 1-11 and Comparative Example 1 were assembled with positive and negative electrodes to form experimental batteries.

[0145] Positive electrode: The positive electrode active material lithium iron phosphate, conductive agent Ketjen black, and binder polyvinylidene fluoride (PVDF) are mixed evenly in N-methylpyrrolidone (NMP) solvent at a mass ratio of 96:2:2. The mixture is then coated on both sides of the positive electrode current collector aluminum foil. After drying and rolling, the positive electrode is obtained.

[0146] Negative electrode: Graphite material, SP conductive carbon black, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) are mixed and dispersed in a solvent (a mixed solvent of N-methylpyrrolidone and water) in a mass ratio of 100:1:1.5:1.5. The mixture is then coated on both sides of the negative electrode current collector copper foil and dried and rolled to obtain the negative electrode.

[0147] The diaphragm was made of polyethylene (PE) ceramic film as described in Examples 1-11 and Comparative Example 1.

[0148] Electrolyte: The lithium salt is lithium hexafluorophosphate (LiPF6), and the organic solvent includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). The electrolyte has a 5% VC content by mass. After injection, the electrolyte is soaked at 45°C for 36 h and 48 h, respectively.

[0149] Test Example 2

[0150] After disassembling the batteries prepared in Examples 1-11 and Comparative Example 1, five different positions on the negative electrode were marked as A, B, C, D, and E. The mass content (%) of vinylene carbonate (VC) in the electrolyte at position C in the recessed region was tested, and the results are shown in Table 3.

[0151] Test Example 3

[0152] The fast-charging performance of the batteries prepared in Examples 1-11 and Comparative Example 1 was tested. The test method was as follows: at room temperature, 2C charging to 65% SOC, 1.5C charging to 70% SOC, 1.2C charging to 80% SOC, 0.5C charging to 3.62V, 0.2C charging to 3.75V, resting for 30 minutes, 1C discharging to 2V, and resting for 30 minutes; 500 cycles were performed. The test results are shown in Table 3.

[0153] Table 3

[0154]

[0155] According to the data in Tables 1, 2 and 3, compared with the separator of Comparative Example 1, the electrolyte injection time of the separator of this disclosure can be reduced from 48h to 36h. The electrolyte injection volume in 36h is higher than the wetting effect of the separator of Comparative Example 1 in 48h, thus improving the fast charging performance of the battery.

[0156] By comparing Examples 3, 6, and 7, it can be seen that, under the condition that the average width ratio of the first sub-region and the recessed region of this disclosure is the same, when the average thickness ratio of the inorganic coating of the first sub-region and the recessed region of the separator is within a preferred range, the wetting effect of the separator is better, and the fast charging performance of the battery is better. Compared with Example 6, Example 3 has a better electrolyte wetting effect, a smaller thermal shrinkage rate, better thermal stability, and better safety and fast charging performance than Example 6. Compared with Example 7, Example 3 has a better electrolyte wetting effect, a smaller air permeability value, and better fast charging performance of the battery than Example 7.

[0157] By comparing Examples 1, 8, and 9, it can be seen that, under the condition of the same average thickness ratio of the inorganic coating, when the average width of the first sub-region and the recessed region is within the preferred range of this disclosure, the wetting effect of the separator is better, and the fast-charging performance of the battery is better. Compared with Example 8, Example 1 has a lower areal density, a lower air permeability value, and better fast-charging performance of the battery. Compared with Example 9, Example 1 has a better electrolyte wetting effect, a lower thermal shrinkage rate, better thermal stability, and better safety performance than Example 9.

[0158] By comparing Examples 3 and 11, it can be seen that, under the condition that the average width ratio of the first sub-region and the recessed region is the same, when the average distance between the surfaces of two adjacent first sub-regions is within the preferred range of this disclosure, the wetting effect of the separator is better, and the fast charging performance of the battery is better. Compared with Example 11, Example 3 has a better electrolyte wetting effect, lower areal density, lower air permeability, and better safety and fast charging performance than Example 11.

[0159] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0160] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0161] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A diaphragm, characterized in that, Along a first direction, on at least one main surface of the diaphragm, the diaphragm tends to be concave from both ends to the middle, and the first direction is perpendicular to the thickness direction of the diaphragm.

2. The diaphragm according to claim 1, characterized in that, Along the first direction, the diaphragm includes a recessed region and a first region and a second region disposed on both sides of the recessed region, wherein the average thickness of the first region and the second region is greater than the average thickness of the recessed region.

3. The diaphragm according to claim 1, characterized in that, Along the first direction, the diaphragm tends to thin from both ends to the middle.

4. The diaphragm according to claim 1, characterized in that, The first direction is the length direction or the width direction of the diaphragm.

5. The diaphragm according to claim 2, characterized in that, Along the thickness direction of the diaphragm, the average depth of the recessed area is 0.15μm~4μm.

6. The diaphragm according to claim 2, characterized in that, The recessed area is strip-shaped, and in the second direction, both ends of the recessed area extend to the edge of the diaphragm; the second direction is perpendicular to the thickness direction of the diaphragm, and the second direction is perpendicular to the first direction.

7. The diaphragm according to claim 2, characterized in that, On at least one main surface of the diaphragm, the first region and the second region have the same area.

8. The diaphragm according to claim 2, characterized in that, On at least one main surface of the diaphragm, the area of ​​the recessed region accounts for 8% to 50% of the total area of ​​the diaphragm.

9. The diaphragm according to claim 8, characterized in that, On at least one main surface of the diaphragm, the area of ​​the recessed region accounts for 11% to 33% of the total area of ​​the diaphragm.

10. The diaphragm according to any one of claims 2-9, characterized in that, The diaphragm satisfies at least one of the following (a) to (c): (a) The diaphragm has the same thickness in the first region; (b) The diaphragm has the same thickness in the second region; (c) The average thickness of the diaphragm in the first region is the same as the average thickness of the diaphragm in the second region.

11. The diaphragm according to claim 2, characterized in that, The first region is a strip extending along a second direction, which is perpendicular to the thickness direction of the diaphragm and also perpendicular to the first direction; the first region includes one or more first sub-regions sequentially arranged along the first direction, and the average thickness of the plurality of first sub-regions increases sequentially in a direction away from the recessed region; and / or, The second region is a strip extending along a second direction, which is perpendicular to the thickness direction of the diaphragm and perpendicular to the first direction; the second region includes one or more second sub-regions arranged sequentially along the first direction, and the average thickness of the plurality of second sub-regions increases sequentially in the direction away from the recessed region.

12. The diaphragm according to claim 11, characterized in that, On at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent first sub-regions in the direction of diaphragm thickness is 0.1 μm to 1.5 μm. And / or, On at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent second sub-regions in the direction of diaphragm thickness is 0.1 μm to 1.5 μm.

13. The diaphragm according to claim 12, characterized in that, On at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent first sub-regions in the direction of diaphragm thickness is 0.5 μm to 1 μm. And / or, On at least one main surface of the diaphragm, the average distance between the surfaces of two adjacent second sub-regions in the direction of diaphragm thickness is 0.5 μm to 1 μm.

14. The diaphragm according to any one of claims 11-13, characterized in that, The diaphragm satisfies at least one of the following (d) to (f): (d) The diaphragm has the same thickness within the same first sub-region; (e) The diaphragm has the same thickness within the same second sub-region; (f) The recessed area passes through the geometric center of at least one of the main surfaces, and the thickness of each sub-area is symmetrically distributed on both sides of the recessed area.

15. The diaphragm according to any one of claims 11-13, characterized in that, The width directions of the first sub-region and the second sub-region are the same as the first direction, and the diaphragm satisfies at least one of the following (A) to (E): (A) The average width of each of the first sub-regions is the same; (B) The average width of each of the second sub-regions is the same; (C) The recessed area passes through the geometric center of at least one of the main surfaces, and the widths of each sub-area are symmetrically distributed on both sides of the recessed area; (D) The width of each of the first sub-regions is the same; (E) The width of each of the second sub-regions is the same.

16. The diaphragm according to any one of claims 11-13, characterized in that, The first region includes two first sub-regions, the width direction of the first sub-regions being the same as the first direction. The average width ratio of the first sub-region closer to the recessed region to the recessed region is 0.5~6:1; the average width ratio of the first sub-region farther from the recessed region to the recessed region is 0.5~6:1; and / or, The second region includes two second sub-regions. The width direction of the second sub-regions is the same as that of the first region. The average width ratio of the second sub-region closer to the recessed region to the recessed region is 0.5 to 6:

1. The average width ratio of the second sub-region farther from the recessed region to the recessed region is 0.5 to 6:

1.

17. The diaphragm according to claim 16, characterized in that, The first region includes two first sub-regions, the width direction of the first sub-regions being the same as the first direction, the average width ratio of the first sub-region closer to the recessed region to the recessed region being 1~6:1; the average width ratio of the first sub-region farther from the recessed region to the recessed region being 1~6:1; and / or, The second region includes two second sub-regions. The width direction of the second sub-regions is the same as that of the first region. The average width ratio of the second sub-region closer to the recessed region to the recessed region is 1 to 6:

1. The average width ratio of the second sub-region farther from the recessed region to the recessed region is 1 to 6:

1.

18. The diaphragm according to any one of claims 2 to 10, characterized in that, The diaphragm includes a base film and an inorganic coating covering at least one side of the base film in the thickness direction; the base film in the recessed region, the first region, and the second region has the same average thickness; on at least one side of the base film in the thickness direction, the average thickness of the inorganic coating in the recessed region is less than the average thickness of the inorganic coating in the first region and the average thickness of the inorganic coating in the second region.

19. The diaphragm according to claim 18, characterized in that, The first region includes two first sub-regions, wherein the average thickness ratio of the inorganic coating of the first sub-region closer to the recessed region to the recessed region is 1.2 to 6:1; and the average thickness ratio of the inorganic coating of the first sub-region farther from the recessed region to the recessed region is 1.4 to 9:1; and / or, The second region includes two second sub-regions. The ratio of the average thickness of the inorganic coating in the second sub-region closer to the recessed region to the recessed region is 1.2 to 6:1; the ratio of the average thickness of the inorganic coating in the second sub-region farther from the recessed region to the recessed region is 1.4 to 9:

1.

20. The diaphragm according to claim 18, characterized in that, The diaphragm satisfies at least one of the following conditions: (I) The average thickness of the base film is 5 μm to 25 μm; (II) The inorganic coating comprises ceramic particles, which include aluminum oxide, hydrated aluminum oxide, silicon nitride, silicon dioxide, zirconium oxide or titanium dioxide.

21. The diaphragm according to claim 19, characterized in that, The average thickness of the inorganic coating in the recessed area is 0.5 μm to 2 μm, the average thickness of the inorganic coating in the first area is 1.15 μm to 4.5 μm, and the average thickness of the inorganic coating in the second area is 1.15 μm to 4.5 μm; and / or, The average thickness of the inorganic coating in the first sub-region is 1.1 μm to 5 μm, and the average thickness of the inorganic coating in the second sub-region is 1.1 μm to 5 μm.

22. A battery, characterized in that, The battery includes electrodes and a separator as described in any one of claims 1 to 21, wherein the separator tends to be concave from both ends to the middle such that a gap is formed between the separator and at least one electrode.

23. The battery according to claim 22, characterized in that, The battery is a wound battery, and the separator includes a recessed area and a first area and a second area disposed on both sides of the recessed area. The first area, the recessed area and the second area of ​​the separator are arranged sequentially along the extension direction of the winding of the battery.

24. The battery according to claim 22, characterized in that, The battery is a stacked battery, the stacked battery includes tabs, the separator includes a recessed area and a first area and a second area disposed on both sides of the recessed area, and the tabs are disposed at at least one end in the first direction.

25. An electrical device comprising the battery as described in any one of claims 22-24.

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