Cell, battery cell, and methods for preparing cell and battery cell

Abstract

The present disclosure provides a cell, a battery cell, and methods for preparing a cell and preparing a battery cell. The cell comprises: a first electrode sheet and a second electrode sheet; an isolation membrane disposed between the first electrode sheet and the second electrode sheet to isolate the first electrode sheet and the second electrode sheet from each other, and forming a winding structure together with the first electrode sheet and the second electrode sheet; along the winding direction of the cell, the innermost turn of the cell is provided with N layers of isolation membrane, the N layers of isolation membrane being wound to form a tubular structure having a through hole therein, and an end portion of the isolation membrane located within the through hole has an extension portion and a pressing portion connected to each other, wherein, as viewed along the axial direction of the through hole, the extension portion divides the through hole into two parts; and the pressing portion presses against the inner wall of the through hole and is bent toward one side along the inner wall of the through hole. The tubular structure formed by winding the isolation membrane directly abuts against the tab during welding, so as to replace the ejector pin.

Description

Battery cell, battery cell, method for preparing battery cell and battery cell Technical Field

[0001] This disclosure relates to the field of battery technology, and in particular to a battery cell, a battery cell, a method for preparing a battery cell, and a method for preparing a battery cell. Background Technology

[0002] The battery manufacturing process includes processes such as coating, sheet making, winding, assembly, and welding. Currently, in the process of welding the tabs to the battery casing and / or cover, a pin is used to pass through the through-hole formed by winding the separator film and hold the tab in place during welding, so that the tab can be effectively welded to the casing and cover.

[0003] To accommodate the ejector pins, the through-holes formed by the winding of the separator need to have a large inner diameter. However, these large-diameter through-holes also occupy a significant amount of space in the middle of the cell, resulting in a lower energy density. Therefore, improving the energy density of the cell has become an urgent technical problem to be solved. Summary of the Invention

[0004] To address at least one of the above-mentioned and other technical problems in the prior art, this disclosure provides a battery cell, a battery cell, a method for preparing a battery cell, and a method for preparing a battery cell.

[0005] This disclosure provides a battery cell comprising: a first electrode and a second electrode; a separator disposed between the first electrode and the second electrode to isolate the first electrode and the second electrode, and forming a wound structure with the first electrode and the second electrode; along the winding direction of the battery cell, the innermost ring of the battery cell is provided with N layers of separator, where N≥2, the N layers of separator are wound to form a cylindrical structure with an internal through hole, the end of the separator located in the through hole having a sequentially arranged extension portion and a pressing portion; wherein, viewed along the axial direction of the through hole, the extension portion divides the through hole into at least two parts; the pressing portion presses against the inner wall of the through hole.

[0006] According to embodiments of this disclosure, the extension and the pressing portion are each formed of at least one insulating membrane.

[0007] According to an embodiment of this disclosure, when viewed along the axial direction of the through hole, the extension is S-shaped.

[0008] According to embodiments of this disclosure, the diameter of the through-hole is configured to be greater than or equal to 0.6 mm and less than or equal to 2.3 mm. According to embodiments of this disclosure, the diameter of the through-hole is less than 2.0 mm.

[0009] According to embodiments of this disclosure, 8 ≥ N ≥ 5. According to embodiments of this disclosure, the thickness of the cylindrical structure is configured to be greater than or equal to 0.06 mm and less than or equal to 0.5 mm. According to embodiments of this disclosure, the thickness of the cylindrical structure is further configured to be greater than or equal to 0.1 mm and less than or equal to 0.2 mm. According to embodiments of this disclosure, the thickness of the separator is configured to be less than or equal to 11 micrometers. According to embodiments of this disclosure, the separator includes a substrate; or, the separator includes a substrate and a coating attached to at least one surface of the substrate. The substrate includes one of polyethylene, polypropylene, and polyvinylidene fluoride; the coating includes at least one of a ceramic coating, a nano-coating, and a silicone coating.

[0010] According to embodiments of this disclosure, a first electrode has a first current collector and a first active material layer disposed on the surface of the first current collector; a second electrode has a second current collector and a first active material layer disposed on the surface of the second current collector; the battery cell further includes at least one first tab and at least one second tab, the first tab being electrically connected to the first current collector and the second tab being electrically connected to the second current collector. In the height direction of the battery cell, the first tab abuts against one end of the cylindrical structure; and / or, the second tab abuts against the other end of the cylindrical structure. The first tab and / or the second tab abuts against the end of the cylindrical structure.

[0011] According to embodiments of this disclosure, in the projection of the cell in the height direction, the projection of the cylindrical structure is configured as one of a circular ring, an elliptical ring, or a polygonal ring. Embodiments of this disclosure also provide a battery cell, including a cell; a housing having an opening defining a receiving cavity, the cell being disposed within the receiving cavity; and a cover disposed at the opening to close the receiving cavity; wherein one of the housing and the cover is welded to a first tab of the cell, forming an electrical connection, and the other of the housing and the cover is welded to a second tab of the cell, forming an electrical connection. According to embodiments of this disclosure, a method for manufacturing a battery cell is also provided, comprising: holding a first electrode and a separator with a winding needle; in the length direction of the electrode, a third winding starting section of the separator extends from the first winding starting section of the first electrode; feeding a second electrode; winding the first electrode and the separator, such that the third winding starting section is wound to form a cylindrical structure with an internal through hole, wherein the extension portion of the separator located within the through hole extends from one side of the inner wall of the through hole to the opposite side, the pressing portion of the separator abuts against the inner wall of the through hole and bends to one side along the inner wall of the through hole, and in the winding direction, a second winding starting section of the second electrode extends beyond the first winding starting section to form an electrode assembly; and welding the electrode assembly to a first electrode tab and a second electrode tab to form a battery cell. According to embodiments of this disclosure, the wound separator protrudes from the first electrode in the width direction of the first electrode. The portion of the separator protruding from the first electrode outside the cylindrical structure is subjected to heat treatment.

[0012] According to an embodiment of the present disclosure, winding a third winding starting segment to form a cylindrical structure with a through hole includes: winding the third winding starting segment to form a cylindrical structure with at least two layers of insulating membrane.

[0013] According to an embodiment of the present disclosure, winding the third winding starting segment to form a multi-layered cylindrical structure includes: winding the third winding starting segment to form a cylindrical structure with a thickness of at least 0.06 mm and less than or equal to 0.5 mm.

[0014] According to embodiments of this disclosure, the method for preparing a battery cell further includes: removing the winding needles and hot-pressing the electrode assembly so that the cross-section of the electrode assembly along a first plane is approximately circular, the first plane being perpendicular to the winding axis of the electrode assembly.

[0015] According to embodiments of this disclosure, welding the electrode assembly to the first electrode tab and the second electrode tab includes: welding one end of the first electrode tab to the first current collector of the first electrode plate to form an electrical connection; and welding one end of the second electrode tab to the second current collector of the second electrode plate to form an electrical connection.

[0016] This disclosure also provides a method for preparing a battery cell, comprising: placing the cell in a receiving cavity formed by a housing; abutting a second tab of the cell against the end face of the cell away from the housing, and welding the second tab to the housing; assembling a cover into the opening of the housing to close the receiving cavity; and welding a first tab of the cell to the cover. The separator of the cell is wound into a cylindrical structure. When welding the cell to the housing and / or the cover, the cylindrical structure can be used to abut the tab instead of a ejector pin, which simplifies the welding process. Furthermore, since no ejector pin is required during welding, the outer diameter of the corresponding cylindrical structure can be wound smaller, thereby reducing the space occupied by the cylindrical structure in the middle of the cell and improving the energy density of the battery cell. Attached Figure Description

[0017] Figure 1 is a schematic cross-sectional view of a portion of a battery cell according to an exemplary embodiment of the present disclosure;

[0018] Figure 2 is a schematic diagram of a cylindrical structure according to an illustrative embodiment of the present disclosure;

[0019] Figure 3 is an exploded view of the battery cell shown in Figure 1;

[0020] Figure 4 is an exploded view of a battery cell according to an illustrative embodiment of the present disclosure;

[0021] Figure 5 is a flowchart of a method for preparing a battery cell according to an illustrative embodiment of the present disclosure;

[0022] Figure 6 is a flowchart of a method for preparing a battery cell according to an illustrative embodiment of the present disclosure.

[0023] In the accompanying drawings, the reference numerals have the following specific meanings: 1. Battery cell; 11. First electrode; 111. First winding start section; 12. Second electrode; 121. Second winding start section; 13. Separator; 131. First separator; 132. Second separator; 133. Third winding start section; 1331. Winding portion; 1332. Extension portion; 1333. Pressing portion; 14. First tab; 15. Second tab; 2. Shell cover; 3. Shell; 31. Liquid injection plug. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0026] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0027] When using expressions such as "at least one of A, B, and C," the meaning should generally be interpreted according to the understanding of someone skilled in the art. For example, "a system having at least one of A, B, and C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C. Similarly, when using expressions such as "at least one of A, B, or C," the meaning should generally be interpreted according to the understanding of someone skilled in the art. For example, "a system having at least one of A, B, or C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C.

[0028] The remote control device and mobile platform system of this disclosure will now be described in detail with reference to the accompanying drawings. Unless otherwise specified, the features of the following embodiments and implementations can be combined with each other.

[0029] Figure 1 is a schematic cross-sectional view of a battery cell according to an exemplary embodiment of the present disclosure.

[0030] According to the battery cell 1 provided in this disclosure, as shown in FIG1, it includes a first electrode 11, a second electrode 12, and a separator 13. The separator 13 is disposed between the first electrode 11 and the second electrode 12 to isolate the first electrode 11 and the second electrode 12, and the separator 13 forms a wound structure with the first electrode 11 and the second electrode 12. Along the winding direction of the battery cell 1, the innermost ring of the battery cell 1 is provided with N layers of separator 13, where N≥2. The N layers of separator 13 are wound to form a cylindrical structure with through holes inside. The end of the separator located in the through hole has an extension portion 1332 and a pressing portion 1333 connected to each other. (That is, it can be understood that the innermost ring of the battery cell has multiple layers of separator 13.) The extension portion 1332 extends from one side of the inner wall of the through hole to the opposite side, and when viewed along the axial direction of the through hole (as shown in FIG1), the extension portion 1332 divides the through hole into at least two parts. The pressing part 1333 presses against the inner wall of the through hole.

[0031] The winding of the separator 13 to form a cylindrical structure with at least two layers of separator 13 provides high structural strength. When welding the battery cell 1 to the outer casing 3 and / or cover 2, the cylindrical structure can directly abut the tabs, replacing the ejector pins. During welding, since there is no need to insert ejector pins into the through-holes for support, the inner diameter of the through-holes in the cylindrical structure formed by winding the separator 13 does not need to consider the size of the ejector pins. Consequently, the outer diameter of the cylindrical structure can be wound smaller, reducing the space occupied by the cylindrical structure in the middle of the battery cell 1 and thus increasing the energy density of the battery cell 1.

[0032] Based on the characteristic of the cylindrical structure having through holes, the portion of the separator 13 located within the through holes also forms an extension 1332 and a pressing portion 1333. The extension 1332 extends from one side of the inner wall of the through hole to the other, providing radial support to the cylindrical structure and compensating for its structural strength. Furthermore, when the cylindrical structure supports the electrode lugs, the extension 1332 also abuts against the lugs, thus dispersing the axial force on the cylindrical structure and helping to prevent collapse due to excessive stress. The pressing portion 1333 abuts against the inner wall of the through hole, and the friction between the pressing portion 1333 and the inner wall of the through hole restricts the extension 1332 from approaching one side of the inner wall of the through hole, keeping the extension 1332 approximately in the middle of the cylindrical structure.

[0033] In the above scheme, the extension 1332 and the pressing part 1333 may not necessarily form the starting point of the separator 13. It is possible that the extension 1332 and the pressing part 1333 are still some distance away from the starting point of the winding of the separator 13.

[0034] The following explanation uses the case of being divided into two parts as an example. It can be understood that dividing into multiple parts can also have the effect of strengthening the cylindrical structure.

[0035] Currently, the electrode assembly (including the first electrode 11, the second electrode 12, and the separator 13) needs to be wound with a winding needle. As a result, after winding, a through hole will inevitably be formed in the middle of the cylindrical structure. When the hollow cylindrical structure comes into contact with the electrode tab, it is easy to collapse if the force is too great.

[0036] In this embodiment, the third winding starting section 133, in addition to the winding portion 1331 for forming a cylindrical structure, also includes an extension portion 1332 and a pressing portion 1333 arranged sequentially along the length direction of the battery cell. The extension portion 1332 extends from one side of the inner wall of the through hole to the other side (as shown in FIG1, from the right side to the left side) to form a generally S-shaped support structure. This extension portion 1332 is used to support the cylindrical structure in the radial direction to compensate for the structural strength of the cylindrical structure. Furthermore, since the extension portion 1332 also penetrates the through hole in the axial direction, it can also disperse the force on the cylindrical structure in the axial direction when supporting the electrode tabs, which helps to prevent the cylindrical structure from collapsing due to excessive force. The pressing part 1333 abuts against the inner wall of the through hole. For this purpose, the friction between the pressing part 1333 and the inner wall of the through hole can restrict the extension part 1332 from approaching the inner wall of the through hole on one side (the upper or lower side as shown in Figure 1), so that the extension part 1332 is kept in a position approximately in the middle of the cylindrical structure.

[0037] Wherein, the length direction of cell 1 is the direction in which it spirals along the winding direction (i.e., direction D as shown in Figure 1) with the winding center (i.e., point O as shown in Figure 1) as the endpoint; the thickness direction is the direction tangent to a certain position of the length direction of cell 1; and the height direction is the direction orthogonal to both the length direction and the thickness direction. Unless otherwise specified, the following descriptions of the length direction, thickness direction, and height direction of the cell refer to this section.

[0038] In some illustrative embodiments, as shown in FIG1, when viewed along the axial direction of the through hole, the extension 1332 and the pressing portion 1333 form a generally S-shaped structure. The S-shaped extension 1332 can be directly formed during manufacturing using a needle coil without requiring additional processes.

[0039] The extension 1332 divides the through-hole into a first part and a second part. Based on the winding process of the battery cell, two clamp-like parts formed by the main branch of the winding needle are located in either the first or second part. The approximate S-shaped structure formed by the extension 1332 and the pressing part 1333 can be understood as follows: during the winding process, the opposing surfaces of the extension 1332 abut against one of the clamp-like parts of the winding needle in a misaligned manner, and deform along the pressure direction under the pressure provided by the winding needle. Furthermore, observing along the axial direction of the through-hole, it can be seen that the two sides of the extension 1332 form misaligned recessed portions. These two recessed portions form a continuous and smooth transition. Since the pressing part 1333 is integral with the extension 1332, it also bends along the extension direction of the inner wall of the through-hole. It should be noted that the two recessed portions are not necessarily symmetrical about the center of the through-hole; there may be cases where one recessed portion has a different degree of concavity than the other.

[0040] According to embodiments of this disclosure, the extension 1332 and the pressing portion 1333 are each formed of at least one layer of separator film. Depending on the arrangement of the separator film 13 before winding, the extension 1332 and the pressing portion 1333 can be formed of a single layer of separator film 13, or they can be formed of separator films 13 stacked on both sides and above. The more layers of separator film 13 forming the extension 1332 and the pressing portion 1333, the greater the radial support force that the extension 1332 can provide to the cylindrical structure.

[0041] In some illustrative embodiments, as shown in FIG1, the extension 1332 and the pressing portion 1333 have two layers of insulating membrane. It should be understood that the embodiments of this disclosure are not limited thereto.

[0042] For example, the extension 1332 and the pressing part 1333 may have one, two, three, four or other arbitrary layers of separator film, specifically configured according to the number of layers of separator film 13 provided on the battery cell and whether the third winding start section 133 of separator film 13 is aligned.

[0043] In some illustrative embodiments, as shown in FIG1, a first electrode 11, a separator 13, and a second electrode 12 are sequentially stacked and wound to form a wound electrode assembly. Specifically, the electrode assembly has a winding center perpendicular to the paper surface (i.e., point O as shown in FIG1). Further, the initial winding sections of the first electrode 11, the separator 13, and the second electrode 12 are wound around the winding center along the winding direction (direction D as shown in FIG1, i.e., counterclockwise) from the inside out to form a generally cylindrical electrode assembly. The generally cylindrical shape is characterized by a continuous curved surface formed on the outer periphery of the wound electrode assembly when viewed from a radial cross-section (or from a top view). Although the thickness of the first electrode, the second electrode, and the separator may cause slight differences in the distance from the center at different parts of the outer periphery during actual manufacturing, these differences are negligible compared to the approximately constant diameter. It should be understood that the embodiments of this disclosure are not limited thereto.

[0044] For example, the electrode assembly can also be configured to be wound in a clockwise winding direction.

[0045] In some illustrative embodiments, as shown in FIG1, the third winding starting segment 133 includes a pressing portion 1333, an extension portion 1332, and a winding portion 1331 arranged sequentially along the length direction of the battery cell. Specifically, when winding the third winding starting segment 133, an external winding needle can be engaged with the extension portion 1332 to wind along the winding direction. During winding, the pressing portion 1333 and the extension portion 1332 form a complete winding cycle, while the winding portion 1331 winds layer by layer around the winding center in a winding cycle, so that the portion of the separator 13 located in the battery cell 1 forms a cylindrical structure.

[0046] According to embodiments of this disclosure, as shown in FIG1, the diameter of the through-hole (i.e., D shown in FIG1) is configured to be greater than or equal to 0.6 mm and less than or equal to 2.3 mm. That is, 2.3 mm ≥ D ≥ 0.6 mm. This makes the diameter of the through-hole (i.e., D) smaller, thus avoiding occupying excessive central space, thereby achieving the design requirement of increasing the energy density of the battery cell.

[0047] According to an embodiment of this disclosure, as shown in FIG1, the diameter of the through-hole is less than 2.0 mm. That is, 2.0 mm ≥ D. In related art, the battery cell is welded using ejector pins. Currently, the ejector pins used are mostly 2 mm in diameter, and space is reserved for the insertion of the ejector pins. Therefore, the spacing between the through-holes formed in the middle of the existing battery cell needs to be greater than 2 mm, and it is difficult to design them to be smaller, thus limiting the energy density of the battery cell. Based on the above embodiment, since ejector pins are not required, the diameter of the through-hole can be configured to be less than or equal to 2 mm, thereby improving the design requirements for the energy density of the battery cell.

[0048] In this implementation, the through-hole is formed based on the characteristics of the winding process (i.e., winding the battery cell using pins). Based on the aforementioned diameter parameters, the diameter of the through-hole can be relatively small, thus avoiding occupying excessive space in the middle of the battery cell and achieving the design requirement of increasing the battery cell's energy density. In the prior art, the battery cell is welded using ejector pins. Currently, the ejector pins used are mostly 2 mm in diameter, and space is reserved for their insertion. Therefore, the spacing between the through-holes formed in the middle of the existing battery cell must be greater than 2 mm, and it is difficult to design them smaller, thus limiting the battery cell's energy density. It should be understood that the embodiments of this disclosure are not limited to this.

[0049] For example, the diameter of the aforementioned through hole can be configured as 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, or 2.3 mm.

[0050] Alternatively, the diameter of the aforementioned through hole can also be configured to be less than 0.6 mm, such as 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, or 0.5 mm;

[0051] Alternatively, the diameter of the aforementioned through hole can be configured to be 3 mm or more, such as 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm, and any other arbitrary diameter, specifically set as small as possible while meeting the size requirements of the measuring tape.

[0052] In this embodiment, the third winding starting section 133 of the separator 13 is wound to form a multi-layered cylindrical structure with high structural strength. When welding the tabs of the battery cell 1 to the outer casing and / or cover, the cylindrical structure can directly abut the tabs to support the welding process. Since it is not necessary to insert a push pin (also known as a pressure bar or punch) into the through hole during welding, the inner diameter of the through hole formed by the winding of the separator 13 does not need to consider the size of the push pin. Consequently, the outer diameter of the cylindrical structure formed by the winding of the separator 13 (D as shown in Figure 1) can be designed to be smaller, thereby increasing the energy density of the battery cell 1.

[0053] Taking the welding method using a pin to support the electrode tab in the existing technology as an example, due to the size of the pin (mainly the radial size), a sufficient inner diameter needs to be reserved so that the through hole formed by the winding of the separator 13 can accommodate the pin. Therefore, the outer diameter of the cylindrical structure formed by the winding of the separator 13 is also limited. However, the cylindrical structure in the embodiment shown in Figure 1 is not limited by the size of the pin, so its outer diameter can be reduced accordingly.

[0054] Assuming that the first outer diameter of the cylindrical structure formed in the middle of the battery cell 1 using the prior art is configured to be 2.3 mm, i.e., D1 = 2.3 mm; while the second outer diameter of the cylindrical structure using the above embodiment is reduced to 1.2 mm, i.e., D2 = 1.2 mm, then the difference N between the two occupancy rates for the central space of the battery cell 1 (i.e., the space formed by the outer diameter of the cylindrical structure formed by the winding of the separator 13) can be calculated using the following formula 1.

[0055] In Formula 1, N represents the difference in the occupancy rate of the center space of the battery cell in this application and the battery cell in the prior art, D1 represents the first outer diameter (the outer diameter of the cylindrical structure in the prior art), D2 represents the second outer diameter (the outer diameter of the cylindrical structure in this application), and H represents the battery cell height.

[0056] Calculations using Equation 1 show that the above-described implementation method improves the utilization rate of the cell's central space by 72.78% compared to existing technologies. Therefore, the cylindrical structure using the above-described implementation method occupies a smaller volume in the cell's central space. The total volume of the cell is limited by the internal space of the individual battery cell's casing and can be considered constant. Because the cylindrical structure occupies a smaller volume, more active material can be incorporated into the cell, thereby increasing its energy density.

[0057] According to embodiments of this disclosure, the innermost ring of the battery cell has N layers of separator films 13, where 8 ≥ N ≥ 5. That is, the cylindrical structure with three separator films can be formed by winding the third winding starting segment 133 of a single-layer separator film 13 around the winding center (O as shown in Figure 1) three times. The cylindrical structure formed by winding the separator films 13 is welded with support tabs. The more layers the cylindrical structure has, the higher its strength, but it will also occupy a larger space in the middle of the battery cell. Based on this range of the number of layers (i.e., 8 ≥ N ≥ 5), the cylindrical structure has both high strength and does not occupy too much space, thereby achieving the design requirement of improving the energy density of the battery cell.

[0058] In some illustrative embodiments, the cylindrical structure includes, but is not limited to, having at least five layers of insulating membrane (i.e., N=5). It should be understood that the embodiments of this disclosure are not limited thereto.

[0059] For example, the cylindrical structure may include 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 layers and other arbitrary layers of separator membrane.

[0060] In some illustrative embodiments, as shown in FIG1, a first separator 131 and a second separator 132 are included. A first electrode 11, the first separator 131, the second electrode 12, and the second separator 132 are sequentially stacked in the thickness direction of the battery cell. Specifically, the end of the first electrode 11 near the winding center serves as a first winding start segment 111, the end of the second electrode 12 near the winding center serves as a second winding start segment 121, and the ends of the first separator 131 and the second separator 132 near the winding center serve as a third winding start segment 133. The third winding start segment 133 of the first separator 131 and the second separator 132 is located upstream of the first winding start segment 111 of the first electrode 11 and the second winding start segment 121 of the second electrode 12, meaning that the end of the third winding start segment 133 is closer to the winding center than the first winding start segment 111 and the second winding start segment 121.

[0061] In some illustrative embodiments, the third winding start segment 133 of the first separator 131 and the third winding start segment 133 of the second separator 132 can be configured to be staggered along the length direction of the cell 1. Furthermore, the cylindrical structure is formed only by winding the longer first separator 131. The number of layers of the separator 131 used to form the cylindrical structure can be either an even number or an odd number.

[0062] In other illustrative embodiments, the third winding start segment 133 of the first separator 131 and the third winding start segment 133 of the second separator 132 can be configured to be substantially aligned along the length direction of the cell 1. Further, the cylindrical structure is formed by winding the stacked first separator 131 and second separator 132 together. The separators forming the cylindrical structure by winding the stacked first separator 131 and second separator 132 together have an even number of layers.

[0063] In other illustrative embodiments, the third winding start segment 133 of the first separator 131 and the third winding start segment 133 of the second separator 132 can be configured to be staggered along the length direction of the cell 1, with the stagger distance being approximately one winding cycle. The first separator 131 is wound before the second separator 132. After the overlapping portions of the first separator 131 and the second separator 132 are wound, they are jointly wound to form a cylindrical structure, such that the separator in the cylindrical structure has an odd number of layers. It should be understood that the embodiments of this disclosure are not limited thereto.

[0064] For example, the first separator 131 and the second separator 132 mentioned above can be two parts of the same separator. In detail, the separator 13 includes a first part and a second part arranged sequentially in the length direction of the cell 1. The first part and the second part are folded in half along the thickness direction of the cell 1 to form a double-layer separator, that is, the winding end of the first part and the winding end of the second part are connected.

[0065] In this implementation, the number of layers of the separator membrane in the cylindrical structure can be configured according to the structural strength required to effectively support the tabs. Too many layers of separator membrane can lead to a large outer diameter of the cylindrical structure, while too few layers can make it difficult to maintain the structural strength. Therefore, the number of separator membrane layers should be minimized while still meeting the requirements for supporting the tabs.

[0066] According to an embodiment of this disclosure, as shown in FIG1, the thickness of the cylindrical structure (i.e., X as shown in FIG1) is configured to be greater than or equal to 0.06 mm and less than or equal to 0.5 mm. That is, 0.5 mm ≥ X ≥ 0.06 mm. If the thickness of the cylindrical structure is set too thin, it may cause the cylindrical structure to deform along the axial direction when supporting the electrode lug, failing to provide effective support for the lug. If the thickness is set too thick, the outer diameter of the cylindrical structure may be too large, thus increasing the space occupied by the cylindrical structure. Therefore, the cylindrical structure configured with the above-mentioned thickness achieves a better balance between support effect and space occupation.

[0067] According to an embodiment of this disclosure, as shown in FIG1, the thickness of the cylindrical structure is further configured to be greater than or equal to 0.1 mm and less than or equal to 0.2 mm. That is, 0.2 mm ≥ x ≥ 0.1 mm. Similar to the principle described in the above embodiments, a cylindrical structure based on this thickness range can achieve a better balance between support effect and space occupation.

[0068] In some illustrative embodiments, the thickness of the cylindrical structure is, but is not limited to, configured to be 0.1 mm to 0.2 mm. That is, 0.2 mm ≥ x ≥ 0.1 mm. It should be understood that the embodiments of this disclosure are not limited thereto.

[0069] For example, the thickness of the cylindrical structure can be configured to any value of 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, 0.1 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, 0.16 mm, 0.17 mm, 0.18 mm, 0.19 mm, 0.2 mm, 0.21 mm, 0.22 mm, 0.23 mm, 0.24 mm, 0.25 mm, and other thicknesses.

[0070] In this embodiment, the cylindrical structure formed by winding the separator 13 is used to abut the axial end of the cylindrical structure against the electrode tab when welding the housing and / or cover to the electrode tab. For this purpose, the electrode tab can be replaced by a pin support so that the electrode tab is pressed tightly against the housing or cover for welding.

[0071] According to embodiments of this disclosure, the thickness of the separator 13 is less than or equal to 11 micrometers. At least three layers of separator 13 and their respective thicknesses can broadly meet the structural strength requirements of various separators when wound into a cylindrical structure. It should be understood that the number of separator layers and their thickness should be designed holistically; for example, a thicker separator can have fewer layers, and a thinner separator can have more layers.

[0072] In some illustrative embodiments, the thickness of the separator 13 is, but is not limited to, configured to be greater than or equal to 5 micrometers and less than or equal to 11 micrometers. That is, 11 μm ≥ δ ≥ 5 μm. It should be understood that the embodiments of this disclosure are not limited thereto.

[0073] For example, the thickness of the separator 13 may include, but is not limited to, being configured as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm and other arbitrary thickness values.

[0074] The thickness of the separator 13 is limited to 11μm ≥ δ ≥ 5μm to balance safety performance and lithium-ion transport performance. On the other hand, if the thickness of the separator 13 is too large, it will be difficult to control the thickness of the cylindrical structure.

[0075] According to embodiments of this disclosure, the separator 13 includes a substrate. Alternatively, the separator 13 includes a substrate and a coating adhered to at least one surface of the substrate.

[0076] According to embodiments of this disclosure, the separator 13 comprises one of a polyethylene separator, a polypropylene separator, and a polyvinylidene fluoride separator. Based on the supporting function of the cylindrical structure formed by the separator, it should have high structural strength to prevent deformation when abutting the tabs. Therefore, a high structural strength can be provided based on the substrate, or based on the substrate and a coating attached to the substrate, which helps prevent deformation of the cylindrical structure under pressure.

[0077] According to embodiments of this disclosure, the coating includes at least one of a ceramic coating, a nano-coating, and an organosilicon coating.

[0078] In one illustrative embodiment, the separator 13 includes a substrate. Specifically, the substrate includes, but is not limited to, polyethylene (PE), polypropylene (PP), composite materials (such as a PE / PP / PE three-layer composite separator), and any other membrane material used as a separator between the first and second electrodes.

[0079] In other illustrative embodiments, the separator 13, in addition to including a substrate, may also have a coating applied to at least one surface of the substrate (i.e., one or both surfaces). Specifically, the coating includes, but is not limited to, at least one of ceramic coatings, nano-coatings, and silicone coatings. That is, the coating may be a composite coating formed from any two of the aforementioned coatings. It should be understood that the embodiments of this disclosure are not limited thereto.

[0080] The above coating can further increase the mechanical strength of the separator 13, thereby making the cylindrical structure stronger.

[0081] For example, the coating can also be a conductive coating, a flame-retardant coating, a functional coating (such as an ion transport promoter, an electrolyte adsorbent, etc.) or any other coating used to improve the mechanical properties, thermal stability and ionic conductivity of the separator 13.

[0082] In this implementation, assuming the material used for the separator 13 remains constant, it can be considered that the thicker the separator 13, or the more layers of the separator formed by winding, the stronger the structural strength of the resulting cylindrical structure. However, a thicker separator 13, or more layers of the separator formed by winding, also results in a larger outer diameter of the formed cylindrical structure. Therefore, the thickness of the separator 13 and the number of layers of the separator formed by winding should be designed holistically. If a thicker separator 13 is used, the number of separator layers can be reduced; if a thinner separator 13 is used, the number of separator layers can be increased. Specifically, it is advisable to meet the thickness requirements and structural strength requirements of the cylindrical structure.

[0083] Figure 2 is a schematic diagram of a cylindrical structure according to an illustrative embodiment of the present disclosure.

[0084] According to embodiments of this disclosure, as shown in FIG2, in the projection of the cell in the height direction (facing the paper as shown in FIG2), the projection of the cylindrical structure is configured as a circular ring (as shown in FIG2a), an elliptical ring (as shown in FIG2b), or a polygonal ring (a triangular ring as shown in FIG2c). The cylindrical structure configured as a circular, elliptical, or through-hole ring is advantageous for creating a smaller space in the middle of the cell; the cylindrical structure configured as a polygonal ring is also advantageous for preventing deformation of the separator under pressure.

[0085] In this embodiment, as shown in FIG2, the winding portion 1331 of the separator 13 can be formed into at least one of a circular cylindrical structure, an elliptical cylindrical structure, or a polygonal cylindrical structure during the forming process by a needle winding device or by a shaping device (such as an extrusion forming device). The cylindrical structure configured as a circular ring, an elliptical ring, or a through-ring has the advantage of creating a smaller space in the middle of the battery cell; the cylindrical structure configured as a polygonal ring also helps to prevent deformation of the separator under pressure. It should be understood that the embodiments of this disclosure are not limited thereto. For example, in the projection of the cylindrical structure in the height direction of the battery cell, the projection can also be a racetrack-shaped ring, a quadrilateral ring, a pentagonal ring, a horseshoe-shaped ring, or other irregular annular structures.

[0086] Figure 3 is an exploded view of the battery cell shown in Figure 1.

[0087] According to embodiments of this disclosure, the first electrode 11 has a first current collector and a first active material layer disposed on the surface of the first current collector. The second electrode 12 has a second current collector and a first active material layer disposed on the surface of the second current collector. As shown in FIG3, the battery cell further includes at least one first tab 14 and at least one second tab 15. The first tab 14 is electrically connected to the first current collector, and the second tab 15 is electrically connected to the second current collector. In the height direction of the battery cell 1, the first tab 14 abuts against one end of the cylindrical structure (the upper end as shown in FIG3); and / or, the second tab 15 abuts against the other end of the cylindrical structure (the lower end as shown in FIG3). For this purpose, the cylindrical structure can support the tab in the axial direction without the need for a pin, and the tab can also be effectively welded to the housing and / or the cover. In this process, one of the first electrode 11 and the second electrode 12 is a positive electrode and the other is a negative electrode. The first active material or the second active material can be coated on both sides of the current collector, which helps to reduce the number of times the coating method is changed during the electrode manufacturing process and improves production efficiency.

[0088] In some illustrative embodiments, the first electrode 11 can be a negative electrode, and the second electrode 12 can be a positive electrode. Along the length of the cell, the second winding start segment 121 of the second electrode 12 (i.e., the negative electrode) can be positioned downstream of the first winding start segment 111 of the first electrode 11 (i.e., the positive electrode). Specifically, the spacing between the second winding start segment 121 and the first winding start segment 111 includes, but is not limited to, being configured to be greater than or equal to half a winding cycle and less than or equal to one winding cycle. This helps to avoid lithium plating and also helps to avoid wasting negative electrode material due to an excessively long negative electrode.

[0089] In one illustrative embodiment, the first current collector of the first electrode 11 (i.e., the positive electrode) includes, but is not limited to, aluminum foil, and the first active material layer disposed on the first current collector includes, but is not limited to, lithium transition metal oxides, such as lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium iron phosphorus oxide, and lithium nickel cobalt aluminum oxide. Furthermore, the second current collector of the second electrode 12 (i.e., the negative electrode) includes, but is not limited to, copper foil, and the second active material layer disposed on the second current collector includes, but is not limited to, graphite; of course, silicon-based materials and lithium metal can also be used.

[0090] In one illustrative embodiment, as shown in FIG3, in the height direction of the cell (the up-down direction as shown in FIG3), the first tab 14 abuts against one end of the cylindrical structure (the upper end as shown in FIG3); and / or, the second tab 15 abuts against the other end of the cylindrical structure (the lower end as shown in FIG3).

[0091] In some illustrative embodiments, as shown in FIG3, one end of the first tab 14 (the lower end shown in FIG3) is configured to extend into the electrode assembly and be welded to the first current collector. The first tab 14 may include, but is not limited to, the portion of the first current collector welded to the upstream portion of the first active material layer, or the portion of the first current collector exposed in the first active material layer (e.g., a groove structure is provided in the first active material layer, exposing the first current collector to the bottom of the groove). Similarly, one end of the second tab 15 (the upper end shown in FIG3) is configured to extend into the electrode assembly and be welded to the second current collector. Of course, the first electrode 11 can also be used as a positive electrode, and correspondingly, the second electrode 12 can also be used as a negative electrode. It should be understood that the embodiments of this disclosure are not limited thereto.

[0092] For example, the battery cell can be configured with multiple first tabs 14 and / or multiple second tabs 15, which helps to improve the current collection effect.

[0093] In some illustrative embodiments, the height of the cylindrical structure protruding from the contact portion of the first electrode 11 and the second electrode 12 is, but is not limited to, configured to be less than or equal to 0.6 mm and greater than 0.3 mm. Other portions of the separator 13 outside the cylindrical structure are, but are not limited to, configured to protrude from the first electrode 11 and the second electrode 12 at a height less than or equal to 0.3 mm. That is, the cylindrical structure is higher than other portions of the separator 13, and this height difference can be formed by heat treatment using a device such as a heat-sealing machine.

[0094] In this implementation, the cylindrical structure is configured to be slightly higher than the other parts so that it can fit tightly against the tab during welding, thereby limiting the welding position of the tab. During welding, due to the reaction force applied by the tab, the cylindrical structure may be compressed and deformed towards the cell 1, thereby reducing the height difference between the cylindrical structure and the other parts of the separator 13, or even making them roughly flush.

[0095] Based on this, this disclosure presents a comparative experiment on a cylindrical structure with a contact portion, and provides a comparative experimental table of cylindrical structure parameters based on the comparative experiment, as detailed in Table 1 below:

[0096] Note: The cylindrical structure with through holes formed by winding the separator film, wherein the pressing part that presses against the inner wall of the through hole and the connected extension part are called the support structure.

[0097] Referring to Table 1 above, a comparison of Comparative Example 1-1 with Examples 1-4, and a comparison of Comparative Example 1-2 with Examples 1-3, it can be seen that setting the above-mentioned support structure can reduce the welding defect rate.

[0098] As can be seen from Examples 1-1 to 1-8, when the thickness of the cylindrical structure is constant, the larger the aperture of the cylindrical structure, the larger the space occupied, and the lower the energy density of the battery. However, the smaller the cylindrical structure, the higher the breakage rate of the coiled needle.

[0099] As can be seen from Examples 2-1 to 2-6, the thickness of the cylindrical structure also affects the welding defect rate. Within the scope of the claims, the energy density and welding defect rate of the battery cell are reasonably controlled.

[0100] Figure 4 is an exploded view of a battery cell according to an illustrative embodiment of the present disclosure.

[0101] This disclosure also provides a battery cell, as shown in FIG4, including a cell 1, a housing 3, and a cover 2. The housing 3 has an opening that defines a receiving cavity, in which the cell 1 is disposed. The cover 2 is disposed at the opening to close the receiving cavity. One of the housing 3 and the cover 2 is welded to a first tab of the cell, forming an electrical connection, and the other of the housing 3 and the cover 2 is welded to a second tab of the cell, forming an electrical connection. The housing 3 has a through-hole for adding electrolyte, such as lithium salts like lithium hexafluorophosphate, into the housing; a plug 31 is provided in the filling port to close the filling port after electrolyte addition. Since the battery cell includes the cell 1, when welding the housing 3 and / or the cover 2 to the tabs, it is not necessary to insert pins for support within the through-holes formed by winding the separator 13, thus enabling the formation of a battery cell with higher energy density.

[0102] In some illustrative embodiments, as shown in Figures 3 and 4, the ends of the first tab 14 and / or the second tab 15 extending from the electrode assembly are configured to bend toward the electrode assembly. Specifically, the ends of the first tab 14 and the second tab 15 extending from the electrode assembly abut tightly against one and the other end of the cylindrical structure along its axial direction, and cover the cylindrical structure.

[0103] In this embodiment, when welding the tabs (i.e., the first tab 14 or the second tab 15) to the housing 3 or the cover 2, the cylindrical structure acts as a support and pressure point for the tabs, thus replacing the ejector pins used in the prior art. This ensures that the tabs are tightly bonded to the housing 3 or the cover 2 during welding. The through-hole formed by the separator 13 in the middle of the cell is no longer limited by the size of the ejector pin, reducing the space occupied by the cylindrical structure in the middle of the cell. Therefore, more active material can be placed inside the cell to form a battery cell with higher energy density.

[0104] Other technical features of the battery cell have been described in detail in the above-described embodiments concerning the battery cell, and the battery cell has similar technical effects to the battery cell. Therefore, they will not be repeated here.

[0105] Figure 5 is a flowchart of a method for preparing a battery cell according to an illustrative embodiment of the present disclosure.

[0106] This disclosure also provides a method for preparing a battery cell, for preparing a battery cell as described in the above embodiments, comprising:

[0107] Step S110: The first electrode 11 and the separator 13 are held by a winding needle. In the length direction of the electrode, the third winding starting section of the separator 13 extends from the first winding starting section of the first electrode 11.

[0108] Step S120: Feed the second electrode 12;

[0109] Step S130: Wind the first electrode 11 and the separator 13, so that the third winding starting section is wound to form a cylindrical structure with a through hole. The extension 1332 of the separator 13 located in the through hole extends from one side of the inner wall of the through hole to the other side facing each other. The pressing part 1333 of the separator 13 presses against the inner wall of the through hole and bends to one side along the inner wall of the through hole. Along the winding direction, the second winding starting section of the second electrode 12 extends beyond the first winding starting section to form an electrode assembly.

[0110] Step S140: Weld the electrode assembly to the first tab 14 and the second tab 15 to form the battery cell 1.

[0111] In this embodiment, the battery cell prepared by this method does not require inserting and removing ejector pins during the process of welding the tabs (i.e., the first tab 14 and / or the second tab 15) to the housing and / or the housing cover, thus simplifying the battery cell preparation process.

[0112] According to embodiments of this disclosure, the method for preparing a battery cell further includes:

[0113] In step S160, the wound separator protrudes from the first electrode in the width direction of the first electrode, and the portion of the separator protruding from the first electrode outside the cylindrical structure is heat-treated.

[0114] According to an embodiment of the present disclosure, in step S130, the third winding starting segment is wound to form a multi-layered cylindrical structure, including: winding the third winding starting segment to form a cylindrical structure having a three- to eight-layered separator membrane 13 structure.

[0115] According to an embodiment of this disclosure, in step S130, winding the third winding starting segment to form a multi-layered cylindrical structure includes: winding the third winding starting segment to form a cylindrical structure with a thickness of at least 0.06 mm and less than or equal to 0.5 mm.

[0116] According to embodiments of this disclosure, the method for preparing a battery cell further includes:

[0117] Step S150: Remove the coiling needle and hot-press the electrode assembly so that the cross-section of the electrode assembly along the first plane is approximately circular, the first plane being perpendicular to the winding axis of the electrode assembly.

[0118] The fact that the cross-section of the electrode assembly along the first plane is roughly circular can be understood as follows: visually, the cross-section of the electrode assembly presents a roughly continuous and relatively uniform curve without obvious corners or protrusions, making the observer perceive it as essentially a circle.

[0119] In this embodiment, during step S150, when the winding needle winds the third winding starting segment, the outer winding needle can cooperate with the extension 1332 and wind along the winding direction. During winding, the pressing part 1333 and the extension 1332 form a complete winding cycle, while the winding part 1331 winds around the winding center layer by layer in a winding cycle to form a cylindrical structure with a multi-layered separator 13 structure.

[0120] According to an embodiment of this disclosure, step S140, welding the electrode assembly to the first tab 14 and the second tab 15, includes:

[0121] Step S141: Weld one end of the first tab 14 to the first current collector of the first electrode plate 11 to form an electrical connection; and

[0122] Step S142: Weld one end of the second tab 15 to the second current collector of the second electrode plate 12 to form an electrical connection.

[0123] Figure 6 is a flowchart of a method for preparing a battery cell according to an illustrative embodiment of the present disclosure.

[0124] This disclosure also provides a method for preparing a battery cell, used to prepare a battery cell as described in the above embodiments, comprising:

[0125] Step S210: Place the battery cell into the receiving cavity formed by the housing;

[0126] Step S220: The cylindrical structure formed by the battery cell abuts against the end face of the second tab of the battery cell away from the housing, and the second tab is welded to the housing;

[0127] Step S230: Assemble the cover into the opening of the housing to close the receiving cavity;

[0128] Step S240: Weld the first tab of the battery cell to the casing.

[0129] In this implementation, the separator of the battery cell is wound into a cylindrical structure. When welding the battery cell to the casing and / or casing cover, the cylindrical structure can be used to abut the tabs instead of the ejector pins, which simplifies the welding process. Furthermore, since ejector pins are not required during welding, the outer diameter of the corresponding cylindrical structure can be wound to be smaller, thereby reducing the space occupied by the cylindrical structure in the middle of the battery cell and improving the energy density of the battery cell.

[0130] It should also be noted that the directional terms mentioned in the embodiments, such as "up," "down," "front," "back," "left," and "right," are only for reference in the accompanying drawings and are not intended to limit the scope of protection of this disclosure. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or constructions will be omitted where they may cause confusion in understanding this disclosure.

[0131] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A battery cell, wherein, include: First electrode and second electrode; A separating membrane is disposed between the first electrode and the second electrode to isolate the first electrode and the second electrode, and forms a wound structure with the first electrode and the second electrode; Along the winding direction of the battery cell, the innermost ring of the battery cell is provided with N layers of insulating film, where N≥2. The N layers of insulating film are wound to form a cylindrical structure with through holes inside. The end of the insulating film located in the through holes has a connected extension and a pressing part. Wherein, when viewed along the axial direction of the through hole, the extension divides the through hole into at least two parts; the pressing part presses against the inner wall of the through hole.

2. The battery cell according to claim 1, wherein, The extension and the pressing portion are each formed by at least one layer of insulating membrane.

3. The battery cell according to claim 1, wherein, Viewed along the axial direction of the through hole, the extension is S-shaped.

4. The battery cell according to claim 1, wherein, The diameter of the through hole is configured to be greater than or equal to 0.6 mm and less than or equal to 2.3 mm.

5. The battery cell according to claim 4, wherein, The diameter of the through hole is less than 2.0 mm.

6. The battery cell according to claim 1, wherein, 8≥N≥5。 7. The battery cell according to claim 1, wherein, The thickness of the cylindrical structure is configured to be greater than or equal to 0.06 mm and less than or equal to 0.5 mm.

8. The battery cell according to claim 7, wherein, The thickness of the cylindrical structure is configured to be greater than or equal to 0.1 mm and less than or equal to 0.2 mm.

9. The battery cell according to claim 1, wherein, The thickness of the isolation membrane is configured to be less than or equal to 11 micrometers.

10. The battery cell according to claim 1, wherein, The isolation membrane includes a substrate and a coating attached to at least one surface of the substrate; The substrate includes one of polyethylene, polypropylene and polyvinylidene fluoride; The coating includes at least one of ceramic coating, nano coating and organosilicon coating.

11. The battery cell according to claim 1, wherein, The first electrode has a first current collector and a first active material layer disposed on the surface of the first current collector; The second electrode has a second current collector and a first active material layer disposed on the surface of the second current collector; The battery cell further includes at least one first tab and at least one second tab, the first tab being electrically connected to the first current collector and the second tab being electrically connected to the second current collector, and the first tab abutting against one end of the cylindrical structure in the height direction of the battery cell; And / or, the second electrode abuts against the other end of the cylindrical structure.

12. The battery cell according to claim 1, wherein, Using the bottom surface of the battery cell as the projection surface, the projection of the cylindrical structure along the height direction of the battery cell is configured as one of a circular ring, an elliptical ring, and a polygonal ring.

13. A single battery cell, wherein, include: The battery cell as described in any one of claims 1 to 12; A housing having an opening defining a receiving cavity, the battery cell being disposed within the receiving cavity; A cover is disposed at the opening to close the receiving cavity; One of the housing and the cover is welded to the first tab of the battery cell to form an electrical connection, and the other of the housing and the cover is welded to the second tab of the battery cell to form an electrical connection.

14. A method for manufacturing a battery cell, wherein, include: The first electrode and the separator are held by a winding needle, and the third winding start section of the separator extends from the first winding start section of the first electrode in the length direction of the first electrode. Feed the second electrode sheet; The first electrode and the separator are wound together to form a cylindrical structure with an internal through hole in the third winding starting section. The extension of the separator located in the through hole extends from one side of the inner wall of the through hole to the opposite side. The pressing part of the separator presses against the inner wall of the through hole and bends to one side along the inner wall of the through hole. Along the winding direction, the second winding starting section of the second electrode extends beyond the first winding starting section to form an electrode assembly. The electrode assembly is welded to the first tab and the second tab to form a battery cell.

15. The method according to claim 14, wherein, Also includes: The wound separator protrudes from the first electrode in the width direction of the first electrode; The portion of the separator membrane protruding from the first electrode sheet outside the cylindrical structure is heat-treated.

16. The method of claim 14, wherein, The step of winding the third winding starting segment into a cylindrical structure with a through hole includes: The third winding starting segment is wound to form a cylindrical structure with at least two layers of insulating membrane.

17. The method according to claim 16, wherein, The step of winding the third winding starting segment into a multi-layered cylindrical structure includes: The third winding starting segment is wound to form a cylindrical structure with a thickness of at least 0.06 mm and less than or equal to 0.5 mm.

18. The method according to any one of claims 15 to 17, wherein, Also includes: Remove the winding needle and heat-press the electrode assembly so that the cross-section of the electrode assembly along a first plane is approximately circular, the first plane being perpendicular to the winding axis of the electrode assembly.

19. The method according to claim 18, wherein, The step of welding the electrode assembly to the first electrode tab and the second electrode tab includes: One end of the first tab is welded to the first current collector of the first electrode plate to form an electrical connection; one end of the second tab is welded to the second current collector of the second electrode plate to form an electrical connection.

20. A method for preparing a battery cell as described in claim 13, wherein, include: The battery cell is placed inside the cavity formed by the casing; The cylindrical structure formed by the battery cell abuts against the end face of the second tab of the battery cell away from the housing, and the second tab is welded to the housing; The cover is fitted into the opening of the housing to close the receiving cavity; The first tab of the battery cell is welded to the casing.

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