Battery

Abstract

The invention provides a battery, the battery comprises a positive plate, a negative plate, a first tab, a second tab and a protective layer, the positive plate and the negative plate are stacked in sequence and then are wound to form a roll core body, the roll core body is provided with a straight area and an arc area, the positive plate comprises a first positive straight section, a second positive straight section and a first positive bent section, and the second positive straight section comprises a second positive bent section. The negative plate comprises a first negative straight section, the first negative straight section is located between the first positive straight section and the second positive straight section in the second direction, at least part of the protective layer is correspondingly connected with the first positive bent section, and at least part of the protective layer extends to at least one of the first positive straight section and the second positive straight section; one of the first tab and the second tab is connected with the positive plate, the other one of the first tab and the second tab is connected with the negative plate, and the first tab and the second tab are arranged at an interval along a first direction; and in the second direction, the projection of the first tab and the projection of the second tab are staggered from the projection of the protective layer. The battery disclosed by the invention is relatively good in cycle performance and safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery. BACKGROUND

[0002] In the existing battery, the plug-in winding structure is widely used to improve the volume energy density of the lithium ion battery. The structure improves the space utilization rate in the battery by alternately winding the positive and negative electrode sheets and correspondingly arranging the first positive circular arc area formed when the first end of the negative electrode sheet is wound with the positive electrode sheet, thereby improving the energy density of the battery.

[0003] During the winding process, the first folding circular arc area of the positive electrode sheet is subjected to a large bending stress, and because the first end of the negative electrode sheet is opposite to the first positive circular arc area formed when the positive electrode sheet is wound, the volume of the negative electrode sheet changes greatly during the cycle process. The winding starting end of the negative electrode sheet can cause extrusion to the first circular arc area of the positive electrode sheet. These factors combined together can cause the first circular arc area of the positive electrode sheet to easily fall off the positive active layer, produce cracks, and cause the electrode sheet to crack, break, lithium precipitation, short circuit, and other problems, thereby reducing the cycle performance and safety performance of the battery. SUMMARY

[0004] Therefore, the present application provides a battery to solve the problems in the prior art.

[0005] The present application provides a battery, which comprises a positive electrode sheet, a negative electrode sheet, a first tab, a second tab, and a protective layer. The positive electrode sheet and the negative electrode sheet are sequentially stacked and wound to form a winding core body. The winding core body has a flat area and a circular arc area. The circular arc area is located on both sides of the flat area along a first direction. The first end of the positive electrode sheet and the first end of the negative electrode sheet are located on both sides of the flat area along the first direction and extend in opposite directions.

[0006] The positive electrode sheet comprises a first positive flat section and a second positive flat section located in the flat area, and a first positive bending section located in the circular arc area. The first positive flat section, the first positive bending section, and the second positive flat section are sequentially adjacent along the length direction of the positive electrode sheet. One end of the first positive flat section, which is away from the first positive bending section, constitutes the first end of the positive electrode sheet.

[0007] The negative electrode sheet comprises a first negative flat section located in the flat area. Along the second direction, the first negative flat section is located between the first positive flat section and the second positive flat section. One end of the first negative flat section, which is close to the first positive bending section, constitutes the first end of the negative electrode sheet.

[0008] At least part of the protective layer is connected to the first positive bending section in correspondence. The at least part of the protective layer extends to at least one of the first positive flat section and the second positive flat section.

[0009] One of the first and second tabs is connected with the positive tab, and the other is connected with the negative tab, both of which are located in the flat area and are arranged at intervals along the first direction;

[0010] Along the second direction, the projection of the first tab and the projection of the second tab are staggered with the projection of the protective layer.

[0011] In a possible implementation, along the first direction, the first tab is arranged close to the first positive tab bending segment relative to the second tab;

[0012] In the first direction, the minimum distance from the protective layer to the first tab is greater than or equal to 0.5mm, and / or, in the first direction, the minimum distance from the protective layer to the first tab is less than or equal to 15mm.

[0013] In a possible implementation, the protective layer includes a first protective layer and a second protective layer, and the first protective layer is located on the inner side surface of the first positive tab bending segment;

[0014] And / or, the protective layer includes a second protective layer, and the second protective layer is located on the inner side surface of the first positive tab bending segment;

[0015] And / or, the protective layer includes a third protective layer, and the third protective layer is located on the outer side surface of the first positive tab bending segment, and the third protective layer includes an ion-permeable layer.

[0016] In a possible implementation, the positive tab includes a positive current collector and a positive active layer, and the positive active layer is arranged on at least one side surface in the thickness direction of the positive current collector;

[0017] The side surface of the positive current collector of the first positive tab bending segment close to the winding center is provided with a first protective layer, and a second protective layer is arranged on the surface of the first protective layer away from the positive current collector;

[0018] Along the length direction of the positive tab, the width of the first protective layer is greater than the width of the second protective layer.

[0019] In a possible implementation, at least part of the first protective layer extends to the first positive tab flat segment, and the positive active layer located on the side of the first positive tab flat segment close to the winding center at least partially overlaps with the first protective layer;

[0020] At least part of the first protective layer extends to the second positive tab flat segment, and the positive active layer located on the side of the second positive tab flat segment close to the winding center at least partially overlaps with the first protective layer.

[0021] And / or, at least part of the second protective layer extends to the first positive tab flat segment, and the second protective layer is arranged away from the positive active layer on the side of the first positive tab flat segment close to the winding center;

[0022] At least part of the second protective layer extends to the second positive electrode flat section, and the second protective layer is arranged away from the positive electrode active layer on the side of the second positive electrode flat section close to the winding center.

[0023] In a possible implementation, along the width direction of the positive electrode sheet, the opposite two side edges of the first protective layer are flush with the opposite two side edges of the first positive electrode bending section;

[0024] And / or, along the width direction of the positive electrode sheet, the opposite two side edges of the second protective layer all exceed the opposite two side edges of the first positive electrode bending section;

[0025] And / or, along the width direction of the positive electrode sheet, the size by which any one side edge of the second protective layer exceeds the corresponding edge of the first positive electrode bending section is greater than or equal to 0.3 mm and less than or equal to 5 mm.

[0026] In a possible implementation, along the length direction of the positive electrode sheet, the overlapping size of the first protective layer and the positive electrode active layer on the side of the first positive electrode flat section close to the winding center is greater than or equal to 0.5 mm and less than or equal to 10 mm;

[0027] And / or, along the length direction of the positive electrode sheet, the overlapping size of the first protective layer and the positive electrode active layer on the side of the second positive electrode flat section close to the winding center is greater than or equal to 0.5 mm and less than or equal to 10 mm.

[0028] In a possible implementation, the surface of the first protective layer away from the positive electrode current collector and the surface of the second protective layer facing the positive electrode current collector are further provided with the positive electrode active layer, and the thickness of the positive electrode active layer between the first protective layer and the second protective layer is less than or equal to 15 μm;

[0029] The first protective layer comprises at least one of inorganic particles and a binder, the inorganic particles comprise at least one of alumina, silica, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, boron nitride, aluminum nitride, magnesium nitride, tin dioxide, magnesium hydroxide, barium sulfate, barium carbonate, barium titanate and boehmite, and the binder comprises at least one of polypropylene, polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, polyurethane, polyacrylonitrile and polyimide;

[0030] And / or, the first protective layer further comprises conductive particles, and the conductive particles comprise at least one of silver powder, copper powder, carbon nanotubes, graphene, conductive carbon black, ketjen black, acetylene black, conductive graphite and vapor grown carbon fiber.

[0031] In a possible implementation, the thickness of the positive electrode active layer on any one side surface of the positive electrode current collector in the flat area and away from the first protective layer is greater than the thickness of the first protective layer;

[0032] And / or, the thickness of the first protective layer is greater than or equal to 5 μm and less than or equal to 20 μm.

[0033] And / or, the thickness of the positive active layer on any one side surface of the positive current collector in the flat area and offset from the first protective layer is greater than or equal to 25 μm and less than or equal to 100 μm.

[0034] In a possible implementation, the battery further includes a separator, the separator is arranged between the positive sheet and the negative sheet, the separator has a backfolding part beyond the first end of the negative sheet, and a projection of the backfolding part is located in a projection of the first protective layer in the second direction.

[0035] The battery of the present application sets the protective layer on the first positive bending segment, the protective layer can isolate the first positive bending segment and the first negative flat segment, thereby preventing the lithium precipitation problem between the positive sheet and the negative sheet at the above-mentioned positions and the short circuit caused by contact, and the projections of the first tab and the second tab in the second direction of the battery are offset from the projection of the protective layer in the second direction of the battery, so that the first tab and the second tab are offset from the protective layer in the width direction of the roll core body, thereby preventing the protective layer from overlapping the first tab and the second tab in the second direction, and further preventing the area provided with the protective layer and the area close to the protective layer from being subjected to a large pressure during hot pressing, thereby reducing the risk of cracks and breakage in the area provided with the protective layer, the first positive bending segment and the area close thereto during the cycle process, thereby improving the cycle performance and safety performance of the battery.

[0036] In addition to the technical problems solved by the embodiments of the present application described above, the technical features constituting the technical solutions and the beneficial effects brought by these technical features, the other technical problems solved by the battery provided by the present application, the other technical features included in the technical solutions and the beneficial effects brought by these technical features will be further described in detail in the specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.

[0038] Figure 1 The structural schematic diagram of the battery provided by the embodiments of the present application is shown in the figure.

[0039] Figure 2 The structural schematic diagram of the positive sheet, the negative sheet, the separator and the protective layer in the battery provided by the embodiments of the present application is shown in the figure.

[0040] Figure 3Another structural schematic view of the positive plate, the negative plate, the separator and the protective layer in the battery provided by the embodiment of the present application;

[0041] Figure 4 Another structural schematic view of the positive plate, the negative plate, the separator and the protective layer in the battery provided by the embodiment of the present application;

[0042] Figure 5 A structural schematic view of the positive plate and the protective layer in the battery provided by the embodiment of the present application when being flattened; Figure 2

[0043] Another structural schematic view of the positive plate and the protective layer in the battery provided by the embodiment of the present application when being flattened; Figure 6

[0044] Another structural schematic view of the positive plate and the protective layer in the battery provided by the embodiment of the present application when being flattened; Figure 7

[0045] Another structural schematic view of the positive plate and the protective layer in the battery provided by the embodiment of the present application when being flattened. Figure 8 Explanation of reference signs:

[0046] 10 - core body; 10a - flat area; 10b - circular arc area;

[0047] 100 - positive plate; 110 - first positive flat section; 120 - second positive flat section; 130 - first positive bending section; 100a - positive current collector; 100b - positive active layer;

[0048] 200 - negative plate; 210 - first negative flat section;

[0049] 300 - first tab;

[0050] 400 - second tab;

[0051] 500 - protective layer; 510 - first protective layer; 520 - second protective layer; 530 - third protective layer;

[0052] 600 - separator; 610 - backfolding part.

[0053] DETAILED DESCRIPTION

[0054] ​In order to make the objects, technical solutions and advantages of the present application clearer, the following will be combined with the drawings of the preferred embodiments of the present application to make the technical solutions in the embodiments of the present application more clearly described. In the drawings, the same or similar notations represent the same or similar components or components with the same or similar functions throughout. The described embodiments are part of the embodiments of the present application, rather than all the embodiments. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application. The embodiments of the present application will be described in detail below with reference to the drawings.

[0055] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, it can be fixed connection, or indirect connection through an intermediate medium, or internal communication of two elements or interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0056] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0057] The terms "first", "second", "third" (if any) in the specification and claims of the present application and the above drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0058] In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or display including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or displays.

[0059] The following will be described in detail the specific embodiments of the battery provided by the embodiments of the present application in combination with the drawings.

[0060] With reference to Figure 1 As shown in the drawings, the battery provided by the embodiments of the present application comprises a positive electrode sheet 100 and a negative electrode sheet 200, the positive electrode sheet 100 and the negative electrode sheet 200 are sequentially stacked and then wound to form a winding core body 10, the winding core body 10 has a flat area 10a and a circular arc area 10b, the circular arc area 10b is located on both sides of the flat area 10a along a first direction, the first end of the positive electrode sheet 100 and the first end of the negative electrode sheet 200 are located on both sides of the flat area 10a along the first direction and extend in opposite directions, and the design of the negative single-sided sheet or the positive single-sided sheet in the inner circle of the traditional winding core can be cancelled. In this way, the internal space structure of the winding core body 10 can be made more compact, the space occupied by the negative single-sided sheet or the positive single-sided sheet in the inner circle of the winding core body 10 can be reduced, and the energy density of the battery can be improved.

[0061] With reference to Figures 2 to 4 As shown in the drawings, the positive electrode sheet 100 comprises a first positive electrode flat section 110 and a second positive electrode flat section 120 located in the flat area 10a, and a first positive electrode bending section 130 located in the circular arc area 10b, the first positive electrode flat section 110, the first positive electrode bending section 130 and the second positive electrode flat section 120 are sequentially adjacent along the length direction of the positive electrode sheet 100, and the end of the first positive electrode flat section 110 away from the first positive electrode bending section 130 constitutes the first end of the positive electrode sheet 100.

[0062] The negative electrode sheet 200 comprises a first negative electrode flat section 210 located in the flat area 10a, and the first negative electrode flat section 210 is located between the first positive electrode flat section 110 and the second positive electrode flat section 120 along a second direction, and the end of the first negative electrode flat section 210 close to the first positive electrode bending section 130 constitutes the first end of the negative electrode sheet 200.

[0063] With reference to Figure 1 As shown in the drawings, the battery further comprises a first tab 300 and a second tab 400, one of the first tab 300 and the second tab 400 is a positive electrode tab, and the other is a negative electrode tab, the positive electrode tab is connected with the positive electrode sheet 100, the negative electrode tab is connected with the negative electrode sheet 200, and the positive electrode tab and the negative electrode tab are both located in the flat area 10a and are arranged in a spaced manner along the first direction.

[0064] With reference to 1 to Figure 4 As shown in the drawings, the battery further comprises a protective layer 500, at least part of the protective layer 500 corresponds to the position of the first positive electrode bending section 130, and at least part of the protective layer 500 is connected with the first positive electrode bending section 130, that is, at least part of the protective layer 500 overlaps with the first positive electrode bending section 130 along the thickness direction of the positive electrode sheet 100, and at least part of the protective layer 500 extends to at least one of the first positive electrode flat section 110 and the second positive electrode flat section 120. Along the second direction, the projection of the positive electrode tab and the projection of the negative electrode tab are both staggered with the projection of the protective layer 500.

[0065] In the embodiment, the first direction is the width direction of the battery, and the second direction is the thickness direction of the battery. Specifically, the first direction can refer to the X direction in the drawings, and the second direction can refer to the Y direction in the drawings.

[0066] The length of the positive electrode sheet 100 and the negative electrode sheet 200 is greater than the width, and the width is greater than the thickness. The positive electrode sheet 100 and the negative electrode sheet 200 are both in a rectangular sheet structure, and are wound along the length direction. The side of the positive electrode sheet 100 facing the winding center is the inner side, and the side of the positive electrode sheet 100 facing away from the winding center is the outer side.

[0067] It should be noted that after the positive electrode sheet 100 is wound, the first positive electrode bending section 130 is prone to cracks, and then cracks and fragments occur. This is because the innermost circle of the winding core body 10 is an area with the smallest radius of curvature and the largest stress. When the positive electrode sheet 100 is bent, the radius of curvature of the first positive electrode bending section 130 located in the innermost circle of the winding core body 10 is small, and the winding stress it receives during winding is large. The bending degree is also large, and there is a high risk of microscopic cracks and fragments. The first negative electrode flat section 210 is clamped between the first positive electrode flat section 110 and the second positive electrode flat section 120, and the end of the first negative electrode flat section 210 corresponds to the first positive electrode bending section 130. During the battery cycle, the negative electrode active coating is provided on the first negative electrode flat section 210, and the negative electrode active coating will expand. Especially when the negative electrode active layer uses silicon-based materials such as silicon-carbon composite materials, silicon-oxygen materials, and silicon-based alloy materials to improve its energy density, the negative electrode active coating will significantly expand in volume, thereby causing extrusion to the first positive electrode bending section 130, the first positive electrode flat section 110, and the second positive electrode flat section 120, thereby increasing the risk of cracks and fragments in the first positive electrode bending section 130 of the positive electrode sheet 100.

[0068] The inventor finds that the protection layer 500 is arranged on the positive plate 100 and arranged corresponding to the first positive bending segment 130 of the positive plate 100, the first positive bending segment 130 can be protected by the protection layer 500, and the risk of lithium precipitation of the battery can be reduced to a certain extent. However, after the protection layer 500 is arranged on the positive plate 100, the thickness of the positive plate 100 as a whole is uneven, and during the rolling process of the positive plate 100, stress mutation occurs when the area of the positive plate 100 corresponding to the protection layer 500 is rolled, so that the positive plate 100 in the above area is easily damaged during rolling, and micro-cracks easily occur in the positive plate 100 in the damaged area. After the positive plate 100, the negative plate 200 and the separator 600 are wound to form a battery, the positive tab will partially overlap and connect with the positive plate 100, the negative tab will partially overlap and connect with the negative plate 200, the positive tab will protrude from the positive plate 100, and the negative tab will protrude from the negative plate 200. After the battery is formed, the positions of the positive tab and the negative tab become the two places with the maximum thickness of the battery, so that the areas where the positive tab and the negative tab are located bear a larger pressure during the heat pressing formation of the battery. If the protection layer 500 overlaps with the positive tab or the negative tab in the thickness direction of the battery, the above tab positions bear a larger pressure during the heat pressing formation of the battery, thereby increasing the pressure borne by the first positive bending segment 130 and the area near the first positive bending segment 130, accelerating the cracking and breaking of the first positive bending segment 130 and the area near the first positive bending segment 130, and reducing the cycle performance and safety performance of the battery.

[0069] Therefore, in the embodiment, the protection layer 500 is arranged on the inner side or the outer side of the positive plate 100, and after the positive plate 100 is wound, the protection layer 500 is arranged corresponding to the first positive bending segment 130. On the one hand, by arranging the protection layer 500, the CB value between the negative plate 200 corresponding to the first positive bending segment 130 can be reduced, the problem of lithium precipitation can be improved, and the risk of cracking and powdering of the positive active layer 100b on the inner side and / or the outer side of the first positive bending segment 130 can be reduced, thereby reducing the risk of internal short circuit of the battery. On the other hand, the protection layer 500 can also protect the first positive bending segment 130, increase the radius of curvature of the first positive bending segment 130, and enhance the bending resistance of the first positive bending segment 130 to prevent the first positive bending segment 130 from being cracked and broken due to the expansion stress of the negative plate 200 and the bending stress of the first positive bending segment 130 itself. The protection layer 500 on the inner side of the first positive bending segment 130 can also isolate the first positive bending segment 130 and the first negative straight segment 210, thereby preventing the first negative straight segment 210 from contacting the first positive bending segment 130 to cause short circuit.

[0070] To prevent the area where the protective layer 500 is located from being subjected to greater pressure after the protective layer 500 overlaps with the positive electrode tab, the protective layer 500 and the positive electrode tab are arranged to be staggered in the first direction, or the projection of the protective layer 500 in the second direction is staggered with the projection of the positive electrode tab in the second direction. In this way, one end or both ends of the protective layer 500 can be prevented from extending to the position where the positive electrode tab is located, and the area where the protective layer 500 is located and the nearby area close to the protective layer 500 can be prevented from being subjected to greater pressure when hot pressing, thereby effectively preventing the positive electrode tab 100 near the first positive electrode bending section 130 from being broken.

[0071] To prevent the area where the protective layer 500 is located from being subjected to greater pressure after the protective layer 500 overlaps with the positive electrode tab, the protective layer 500 and the positive electrode tab are arranged to be staggered in the first direction, or the projection of the protective layer 500 in the second direction is staggered with the projection of the positive electrode tab in the second direction. In this way, one end or both ends of the protective layer 500 can be prevented from extending to the position where the positive electrode tab is located, and the area where the protective layer 500 is located and the nearby area close to the protective layer 500 can be prevented from being subjected to greater pressure when hot pressing, thereby effectively preventing the positive electrode tab 100 near the first positive electrode bending section 130 from being broken.

[0072] The battery of the present application can prevent the lithium precipitation problem and the short circuit caused by contact between the positive electrode tab 100 and the negative electrode tab 200 at the above-mentioned positions by arranging the protective layer 500 at the first positive electrode bending section 130, which can isolate the first positive electrode bending section 130 and the first negative electrode straight section 210. By staggering the projection of the first tab 300 and the second tab 400 in the second direction with the projection of the protective layer 500 in the second direction, the protective layer 500 can be prevented from overlapping with the first tab 300 and the second tab 400 in the second direction, and the area where the protective layer 500 is located and the area close to the protective layer 500 can be prevented from being subjected to greater pressure when hot pressing. In this way, the risk of the first positive electrode bending section 130 provided with the protective layer 500 and the positive electrode tab 100 near the first positive electrode bending section 130 being cracked or broken during the cycle process can be reduced, thereby improving the cycle performance and safety performance of the battery.

[0073] Referring to Figure 1 In a possible implementation, the first tab 300 is arranged close to the first positive electrode bending section 130 relative to the second tab 400. In the first direction, the minimum distance L1 between the protective layer 500 and the first tab 300 is greater than or equal to 0.5 mm, and in the first direction, the minimum distance L1 between the protective layer 500 and the first tab 300 is less than or equal to 15 mm.

[0074] It should be noted that the first positive bending section 130 is located at one side of the flat area 10a along the first direction, and the first tab 300 can be a positive tab or a negative tab.

[0075] When the positive tab is arranged closer to the first positive bending section 130 than the negative tab, the first tab 300 is a positive tab, the tab slot is provided on the positive plate 100 to expose part of the positive current collector 100a, the positive tab is connected with the positive current collector 100a in the tab slot, and the protective adhesive paper is arranged on the side of the positive tab away from the positive current collector 100a. In the length direction of the positive plate 100, the two ends of the protective adhesive paper exceed the tab slot. In order to avoid the overlap between the protective layer 500 and the positive tab, and the overlap between the protective layer 500 and the protective adhesive paper, the minimum distance between the protective layer 500 and the positive tab needs to be greater than or equal to 0.5 mm. In this way, the projection of the protective layer 500 along the second direction can be effectively prevented from overlapping with the projection of the positive tab along the second direction, and the projection of the protective layer 500 along the second direction can be effectively prevented from overlapping with the projection of the protective adhesive paper along the second direction. The minimum distance between the protective layer 500 and the positive tab needs to be less than or equal to 15 mm, so as to prevent the positive tab from being too far away from the protective layer 500, thereby preventing the positive tab from being too close to the negative tab, increasing the risk of contact between the positive tab and the negative tab, and reducing the risk of short circuit of the battery.

[0076] For example, the minimum distance between the protective layer 500 and the positive tab can be any one of 0.5 mm, 1.2 mm, 2 mm, 3 mm, 4.5 mm, 6 mm, 8 mm, 10 mm, 15 mm, or within any two numerical ranges.

[0077] Similarly, when the negative tab is arranged closer to the first positive bending section 130 than the positive tab, the first tab 300 is a negative tab, and the minimum distance between the protective layer 500 and the negative tab is between 0.5 mm and 15 mm. In this way, the projection of the protective layer 500 along the second direction can be effectively prevented from overlapping with the projection of the negative tab along the second direction, and the negative tab can be prevented from being too far away from the protective layer 500, thereby preventing the positive tab from being too close to the negative tab and increasing the risk of short circuit.

[0078] For example, the minimum distance between the protective layer 500 and the negative tab can be any one of 0.5 mm, 1.5 mm, 2.5 mm, 4 mm, 5.5 mm, 7 mm, 9 mm, 12 mm, 15 mm, or within any two numerical ranges.

[0079] Referring to FIG. 1, Figures 2 to 5 In some embodiments, the protective layer 500 includes a first protective layer 510 or a second protective layer 520, the first protective layer 510 is arranged on the surface of the first positive bending section 130 on the side facing the winding center, and the second protective layer 520 is arranged on the surface of the first positive bending section 130 on the side facing the winding center.

[0080] In some embodiments, the protective layer 500 includes a first protective layer 510 and a second protective layer 520, the first protective layer 510 is located on the inner side surface of the first positive electrode bending segment 130, and the first protective layer 510 is located between the first positive electrode bending segment 130 and the second protective layer 520.

[0081] Referring to Figures 2 to 5 In some embodiments, the protective layer 500 further includes a third protective layer 530, and the third protective layer 530 is located on the outer side surface of the first positive electrode bending segment 130.

[0082] It should be understood that one of the first protective layer 510 and the second protective layer 520 can be arranged on the inner side of the first positive electrode bending segment 130, and the inner side of the first positive electrode bending segment 130 is protected by the first protective layer 510 or the second protective layer 520.

[0083] The first protective layer 510 and the second protective layer 520 can be arranged on the inner side of the first positive electrode bending segment 130, and the inner side of the first positive electrode bending segment 130 is protected by the first protective layer 510 and the second protective layer 520, or the third protective layer 530 is arranged on the outer side of the first positive electrode bending segment 130, and the outer side of the first positive electrode bending segment 130 is protected by the third protective layer 530.

[0084] The first protective layer 510 and the second protective layer 520 can be arranged on the inner side of the first positive electrode bending segment 130, and the inner side of the first positive electrode bending segment 130 is protected by the first protective layer 510 and the second protective layer 520, or the third protective layer 530 is arranged on the outer side of the first positive electrode bending segment 130, and the outer side of the first positive electrode bending segment 130 is protected by the third protective layer 530.

[0085] Since the third protective layer 530 is arranged on the outer side of the first positive electrode bending segment 130, the third protective layer 530 can include an ion-permeable layer, and the ion-permeable layer includes an ion-permeable adhesive paper or other coating layer that allows lithium ions to pass freely.

[0086] For example, the coating layer can include at least one of inorganic particles including at least one of alumina, boehmite, LLZO, LLTO, LATP, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zirconium oxide, zinc oxide, calcium oxide, magnesium hydroxide, aluminum hydroxide, barium hydroxide, barium sulfate, calcium silicate, and titanium dioxide, and a binder including at least one of polyisobutylene, styrene-isoprene copolymer, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, carboxymethyl cellulose Na, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber. This allows lithium ions to move freely between the first positive electrode bending section 130 and the negative electrode sheet 200 outside the first positive electrode bending section 130 without being hindered by the third protective layer 530, thereby preventing the positive electrode active layer 100b outside the first positive electrode bending section 130 from being cracked or peeled off, which can result in a failure to fully utilize the capacity of the battery or an internal short circuit of the battery.

[0087] Referring to Figures 2 to 5 In one possible implementation, the positive electrode sheet 100 includes a positive electrode current collector 100a and a positive electrode active layer 100b provided on at least one side surface of the positive electrode current collector 100a in the thickness direction.

[0088] The first protective layer 510 is provided on the side surface of the positive electrode current collector 100a of the first positive electrode bending section 130 close to the winding center, and the second protective layer 520 is provided on the surface of the first protective layer 510 away from the positive electrode current collector 100a.

[0089] It should be noted that the first protective layer 510 can be arranged on the inner side surface of the positive current collector 100a, and then the positive current collector 100a and the first protective layer 510 are taken as a whole, and the positive active layer 100b is arranged on the inner side of the positive current collector 100a and the first protective layer 510. After drying and rolling, the positive active layer 100b on the first protective layer 510 is removed, and the second protective layer 520 is arranged on the first protective layer 510. Further, the first protective layer 510 and the second protective layer 520 can be formed on the inner side of the positive plate 100, and the third protective layer 530 is arranged on the outer side of the positive plate 100. The first protective layer 510, the second protective layer 520 and the third protective layer 530 are arranged on opposite sides of the positive plate 100 correspondingly, and the positive plate 100, the first protective layer 510, the second protective layer 520 and the third protective layer 530 are taken as a whole, and then the positive plate 100, the first protective layer 510, the second protective layer 520 and the third protective layer 530 are stacked with the separator 600 and the negative plate 200 to form the roll core body 10, and the first protective layer 510, the second protective layer 520 and the third protective layer 530 are arranged correspondingly to the first positive bending section 130. In this way, the first protective layer 510, the second protective layer 520 and the third protective layer 530 can protect the first positive bending section 130, and effectively prevent the first positive bending section 130 from cracking, breaking or rupturing.

[0090] In the first protective layer 510, the hardness of the first protective layer 510 can be less than the hardness of the positive current collector 100a, so as to prevent the first positive bending section 130 from being broken due to the hardness of the first protective layer 510 being too high during winding. For example, the first protective layer 510 can be a ceramic layer, and the positive current collector 100a can be an aluminum foil.

[0091] In some embodiments, along the length direction of the positive plate 100, the width of the first protective layer 510 is greater than the width of the second protective layer 520. The second protective layer 520 can be an insulating adhesive paper, which can include a base material and an adhesive layer. The base material can include at least one of polyethylene terephthalate, polypropylene, and polyethylene. The adhesive layer can include at least one of styrene-isoprene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, polyurethane, butyl acrylate-co-hexyl octyl-ethyl copolymer, methyl methacrylate copolymer, acrylic acid copolymer, hydroxyethyl acrylate copolymer, epoxy resin, and ethylene-vinyl acetate copolymer.

[0092] That is, the width direction of the first protective layer 510 and the width direction of the second protective layer 520 are consistent with the length direction of the positive electrode, if the positive electrode sheet 100 covered by the first protective layer 510 is shorter, and the positive electrode sheet 100 covered by the second protective layer 520 is longer, the second protective layer 520 will extend to the positive active layer 100b inside the first positive electrode flat section 110 and the positive active layer 100b inside the second flat section, in addition to covering the first protective layer 510, which will cause the second protective layer 520 to cover too much of the positive active layer 100b inside the first positive electrode flat section 110 or the second positive electrode flat section 120, which is not conducive to improving the flatness of the battery and is not conducive to the capacity of the positive active layer 100b of the battery.

[0093] In the present embodiment, the first protective layer 510 covers a longer positive electrode sheet 100, and the second protective layer 520 covers a shorter positive electrode sheet 100, so that the second protective layer 520 can be arranged on the first protective layer 510, and after the second protective layer 520 overlaps the first protective layer 510, the second protective layer 520 will not protrude too much from the positive active layer 100b inside the first positive electrode flat section 110, and the second protective layer 520 will not protrude too much from the positive active layer 100b inside the second positive electrode flat section 120, which can prevent the thickness of the overlapping position of the first protective layer 510, the second protective layer 520 and the positive electrode sheet 100 from being too large, which is conducive to improving the thickness uniformity of the whole composed of the first protective layer 510, the second protective layer 520 and the positive electrode sheet 100, and preventing the above-mentioned protective layer 500 from being arranged on the positive electrode sheet 100, which will cause the area of the first positive electrode bending section 130 subjected to stress mutation to be larger when rolling, thereby increasing the risk of cracks or fractures of the first positive electrode bending section 130, and thus improving the overall flatness of the battery and ensuring the electrochemical performance of the battery.

[0094] Referring to FIG. 1, the second protective layer 520 does not extend to the positive active layer 100b inside the first positive electrode flat section 110, nor does it extend to the positive active layer 100b inside the second positive electrode flat section 120. Figures 5 to 7 Referring to FIG. 1, the second protective layer 520 does not extend to the positive active layer 100b inside the first positive electrode flat section 110, nor does it extend to the positive active layer 100b inside the second positive electrode flat section 120. Figure 8 Referring to FIG. 1, the second protective layer 520 does not extend to the positive active layer 100b inside the first positive electrode flat section 110, nor does it extend to the positive active layer 100b inside the second positive electrode flat section 120.

[0095] Referring to FIG. 1, the second protective layer 520 does not extend to the positive active layer 100b inside the first positive electrode flat section 110, nor does it extend to the positive active layer 100b inside the second positive electrode flat section 120. Figures 2 to 5As shown, in one possible implementation, at least a portion of the first protective layer 510 extends to the first positive electrode straight section 110, and the positive electrode active layer 100b located on the side of the first positive electrode straight section 110 near the winding center at least partially overlaps with the first protective layer 510. At least a portion of the first protective layer 510 extends to the second positive electrode straight section 120, and the positive electrode active layer 100b located on the side of the second positive electrode straight section 120 near the winding center at least partially overlaps with the first protective layer 510.

[0096] This configuration ensures that the first protective layer 510 completely covers the first positive electrode bending section 130, thereby effectively isolating the positive current collector 100a of the first positive electrode bending section 130 from the first negative electrode straight section 210, and thus effectively preventing the positive electrode 100 and negative electrode 200 from contacting and causing a short circuit. Furthermore, it also prevents the positive current collector 100a from being exposed on the inner side of the first positive electrode straight section 110 or the inner side of the second positive electrode straight section 120, thereby preventing the positive electrode 100 and negative electrode 200 from contacting and causing a short circuit.

[0097] The first protective layer 510 has two ends along the length of the positive electrode 100, namely the first end and the second end, as shown below. Figure 2 As shown, the projections of the first end and the second end in the second direction can overlap, as... Figure 3 and Figure 4 As shown, the projections of the first end and the second end in the second direction may not overlap.

[0098] It should be noted that the overlapping projections of the first end and the second end in the second direction are beneficial to ensuring the uniformity of stress in the region of the positive electrode 100 with the first protective layer 510, which can further reduce the risk of cracks or breakage of the positive electrode 100. However, to ensure that the projections of the first end and the second end in the second direction overlap, the processing precision of the battery is required to be high, which will reduce the battery manufacturing yield. Therefore, in order to ensure the battery manufacturing yield, the projections of the first end and the second end of the first protective layer 510 in the second direction can also be set to not overlap.

[0099] Reference Figures 2 to 5 As shown, in one possible implementation, at least a portion of the second protective layer 520 extends into the first positive electrode straight section 110, and the second protective layer 520 is offset from the positive electrode active layer 100b on the side of the first positive electrode straight section 110 near the winding center. This prevents the second protective layer 520 from extending onto the positive electrode active layer 100b inside the first positive electrode straight section 110, thereby preventing the second protective layer 520 from overlapping with the positive electrode active layer 100b inside the first positive electrode straight section 110 and causing a local increase in the thickness of the positive electrode sheet 100. This prevents the second protective layer 520 from affecting the overall flatness of the battery and reducing the battery's energy density.

[0100] At least part of the second protective layer 520 extends to the second positive flat section 120, and the second protective layer 520 is arranged away from the positive active layer 100b on the side of the second positive flat section 120 close to the winding center. In this way, the second protective layer 520 can be prevented from extending to the positive active layer 100b on the inner side of the second positive flat section 120, and the second protective layer 520 can be prevented from being superimposed on the positive active layer 100b on the inner side of the second positive flat section 120, thereby preventing the second protective layer 520 from increasing the local thickness of the positive plate 100 and reducing the energy density of the battery.

[0101] In the length direction of the positive plate 100, the two ends of the second protective layer 520 are respectively a third end and a fourth end, and the projections of the third end and the fourth end in the second direction can overlap or not overlap.

[0102] It should be noted that the overlapping of the projections of the third end and the fourth end in the second direction is beneficial to ensure the uniformity of the stress of the region of the positive plate 100 provided with the second protective layer 520, and can further reduce the risk of cracks or fractures of the positive plate 100. However, if the projections of the third end and the fourth end in the second direction are required to overlap, the processing precision of the battery is required to be higher, which reduces the preparation yield of the battery. Therefore, in order to ensure the preparation yield of the battery, the projections of the third end and the fourth end of the second protective layer 520 in the second direction can also not overlap.

[0103] In some embodiments, the third protective layer 530 can also extend to at least one of the first positive flat section 110 and the second positive flat section 120, and the two ends of the third protective layer 530 in the length direction of the positive plate 100 are respectively a fifth end and a sixth end, and the projections of the fifth end and the sixth end in the second direction can overlap or not overlap.

[0104] It should be noted that the overlapping of the projections of the fifth end and the sixth end in the second direction is beneficial to ensure the uniformity of the stress of the region of the positive plate 100 provided with the third protective layer 530, and can further reduce the risk of cracks or fractures of the positive plate 100. However, if the projections of the fifth end and the sixth end in the second direction are required to overlap, the processing precision of the battery is required to be higher, which reduces the preparation yield of the battery. Therefore, in order to ensure the preparation yield of the battery, the projections of the fifth end and the sixth end of the third protective layer 530 in the second direction can also not overlap.

[0105] In a possible implementation, in the width direction of the positive plate 100, the opposite two side edges of the first protective layer 510 are flush with the opposite two side edges of the first positive bending section 130.

[0106] In this way, the first protective layer 510 can completely cover the positive electrode current collector 100a of the first positive electrode bending section 130 in the width direction of the positive electrode sheet 100, and the first protective layer 510 can effectively isolate the positive electrode current collector 100a of the first positive electrode bending section 130 and the first negative electrode flat section 210.

[0107] It should be noted that, in the process of arranging the first protective layer 510 on the positive electrode current collector 100a of the first positive electrode bending section 130, within the range of tolerance or error allowed, if there is a certain deviation between the opposite two side edges of the first protective layer 510 and the opposite two side edges of the first positive electrode bending section 130, it should also be considered that the opposite two side edges of the first protective layer 510 are flush with the opposite two side edges of the first positive electrode bending section 130. For example, the error range can be 0-0.2mm.

[0108] In some embodiments, the first protective layer 510 can be sprayed by using a slurry made of inorganic particles and a binder, and when the slurry of the first protective layer 510 is cast or sprayed on the cross section of the edge of the first positive electrode bending section 130, it can be considered that the opposite two side edges of the first protective layer 510 are flush with the opposite two side edges of the first positive electrode bending section 130. In some embodiments, along the width direction of the positive electrode sheet 100, the opposite two side edges of the second protective layer 520 all exceed the opposite two side edges of the first positive electrode bending section 130.

[0109] In this way, the second protective layer 520 can continue to fully cover the first positive electrode bending section 130 in the width direction on the basis of the first protective layer 510, and the first protective layer 510 and the second protective layer 520 can effectively isolate the positive electrode current collector 100a of the first positive electrode bending section 130 and the first negative electrode flat section 210 together.

[0110] In some embodiments, along the width direction of the positive electrode sheet 100, the size by which any one side edge of the second protective layer 520 exceeds the corresponding edge of the first positive electrode bending section 130 is greater than or equal to 0.3mm and less than or equal to 5mm.

[0111] In this way, it can be ensured that along the width direction of the positive electrode sheet 100, any one side edge of the second protective layer 520 exceeds the corresponding edge of the first positive electrode bending section 130, and the second protective layer 520 can effectively cover the first positive electrode bending section 130, thereby improving the edge protection effect of the second protective layer 520 on the first positive electrode bending section 130, preventing the edge of the first positive electrode bending section 130 from being deformed or damaged due to external impact, and increasing the risk of fracture of the first positive electrode bending section 130.

[0112] For example, in the width direction of the positive electrode 100, the dimension by which one side edge of the second protective layer 520 extends beyond the corresponding edge of the first positive electrode bending section 130 can be any one of 0.3 mm, 0.5 mm, 1 mm, 1.2 mm, 3 mm, or 5 mm, or fall within any two of these values. This is to prevent the dimension by which one side edge of the second protective layer 520 extends beyond the corresponding edge of the first positive electrode bending section 130 from being too large, which could cause the edge of the second protective layer 520 to fold over and insert into the cell, thereby hindering lithium-ion transport during battery cycling, resulting in reduced battery cycle performance or localized lithium plating problems in the battery.

[0113] Reference Figure 2 As shown, in some embodiments, along the length direction of the positive electrode sheet 100, the overlap dimension L2 between the first protective layer 510 and the positive active layer 100b of the first positive electrode straight section 110 near the winding center is greater than or equal to 0.5 mm and less than or equal to 10 mm. The overlap dimension L3 between the first protective layer 510 and the positive active layer 100b of the second positive electrode straight section 120 near the winding center is greater than or equal to 0.5 mm and less than or equal to 10 mm.

[0114] Thus, on the one hand, the overlap dimension L2 between the first protective layer 510 and the positive active layer 100b inside the first positive straight section 110 is greater than or equal to 0.5 mm, and the overlap dimension L3 between the first protective layer 510 and the positive active layer 100b inside the second positive straight section 120 is greater than or equal to 0.5 mm. After the positive electrode sheet 100 is wound, the first protective layer 510 can extend to the first positive straight section 110 and the second positive straight section 120, thereby ensuring that the first protective layer 510 is correspondingly set with the first positive bending section. Thus, the first protective layer 510 protects the first positive bending section 130, thereby preventing the first negative straight section 210 and the first positive bending section 130 from contacting each other, and preventing the first positive bending section 130 from cracking or breaking due to stress.

[0115] On the other hand, the overlap size L2 between the first protective layer 510 and the positive active layer 100b inside the first positive electrode straight section 110 is less than or equal to 10 mm, and the overlap size L3 between the first protective layer 510 and the positive active layer 100b inside the second positive electrode straight section 120 is less than or equal to 10 mm. This can prevent the first protective layer 510 from extending too far into the first positive electrode straight section 110 and the second positive electrode straight section 120, thereby preventing the projection of the first protective layer 510 from coinciding with the projection of the first tab 300. This reduces the risk of microcracks or cracks appearing in the first positive electrode bending section 130 due to excessive pressure during battery hot pressing formation, which could lead to macroscopic fracture of the first positive electrode bending section 130 during subsequent use and reduce the electrochemical performance of the battery.

[0116] For example, the overlap size of the first protective layer 510 and the positive active layer 100b inside the first positive flat section 110 can be any one of 0.5㎜, 1㎜, 1.5㎜, 3㎜, 7㎜, 8㎜, 10㎜ or within any two ranges. The overlap size of the first protective layer 510 and the positive active layer 100b inside the second positive flat section 120 can be any one of 0.5㎜, 1.2㎜, 2㎜, 4.5㎜, 6㎜, 9㎜, 10㎜ or within any two ranges.

[0117] Referring to Figure 6 In one possible implementation, the positive active layer 100b is further provided between the surface of the positive current collector 100a away from the first protective layer 510 and the surface of the positive current collector 100a facing the second protective layer 520, and the thickness of the positive active layer 100b between the first protective layer 510 and the second protective layer 520 is less than or equal to 35μm.

[0118] It should be noted that the first protective layer 510 is provided on the inner surface of the positive current collector 100a, and the positive active layer 100b is provided on the positive current collector 100a and the first protective layer 510. The laser cleaning or scraping method can be used to remove all the positive active layer 100b on the first protective layer 510, or to remove part of the positive active layer 100b on the first protective layer 510 and retain the positive active layer 100b within 35μm, so as to prevent the positive active layer 100b on the first protective layer 510 from being too thick. It should be noted that the positive active layer 100b on the first protective layer 510 is thinner than the positive active layer 100b on the region of the positive sheet 100 where the first protective layer 510 is not provided, i.e., as Figure 6 As shown, the inner surface of the first positive bending section 130 is recessed in the region where the first protective layer 510 and the positive active layer 100b overlap, compared to other regions. This is beneficial to improve the risk of fracture of the first positive bending section 130.

[0119] When the positive active layer 100b on the first protective layer 510 is too thick, on the one hand, it cannot reduce the winding stress of the first positive bending section 130 during winding, thereby failing to improve the risk of micro-cracks and fracture of the first positive bending section 130. On the other hand, when the positive active layer 100b on the first protective layer 510 is too thick, if the second protective layer 520 is continuously provided at this position, it will cause the local thickness of the positive sheet 100 to be too large, which will cause the second protective layer 520 to easily fall off when bending at this position, i.e., the second protective layer 520 cannot be reliably provided on the side of the first protective layer 510 away from the positive current collector 100a, thereby reducing the benefits brought by the second protective layer 520.

[0120] It should be noted that the second protective layer 520 is arranged on the positive electrode active layer 100b, and the positive electrode active layer 100b is arranged between the first protective layer 510 and the second protective layer 520. At this time, for the inner side of the first positive electrode bending section 130, the positive electrode current collector 100a, the first protective layer 510, the positive electrode active layer 100b, and the second protective layer 520 are sequentially stacked.

[0121] The first protective layer 510 and the second protective layer 520 are arranged on the inner side of the first positive electrode bending section 130. The positive electrode active layer 100b with a thickness less than or equal to 35 μm is arranged on the first protective layer 510 and between the second protective layer 520. The thickness sum of the first protective layer 510, the second protective layer 520, and the positive electrode active layer 100b between the first protective layer 510 and the second protective layer 520 is less than the thickness of the positive electrode active layer 100b on the inner side of the first positive electrode flat section 110, so as to prevent the first protective layer 510, the second protective layer 520, and the positive electrode active layer 100b between the first protective layer 510 and the second protective layer 520 from protruding from the first positive electrode flat section 110 after being stacked, thereby preventing the formation of a local thickening point and increasing the risk of fracture of the first positive electrode bending section 130.

[0122] It should be noted that in an embodiment, the positive electrode active layer 100b can also not be arranged on the first protective layer 510 of the first positive electrode bending section 130, that is, as shown in FIG. 5, the first protective layer 510 and the second protective layer 520 directly contact. Figure 5

[0123] The first protective layer 510 includes at least one of inorganic particles and a binder. The inorganic particles include at least one of alumina, silica, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, boron nitride, aluminum nitride, magnesium nitride, tin dioxide, magnesium hydroxide, barium sulfate, barium carbonate, barium titanate, and boehmite. The binder includes at least one of polypropylene, polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, polyurethane, polyacrylonitrile, and polyimide. The above materials can be formed on the positive electrode current collector 100a of the first positive electrode bending section 130 by coating, thereby forming a stable first protective layer 510 that is not easy to fall off.

[0124] In some embodiments, the first protective layer 510 can also include conductive particles, and the conductive particles include at least one of silver powder, copper powder, aluminum powder, nickel powder, carbon nanotubes, graphene, conductive carbon black, Ketjen black, acetylene black, conductive graphite, and vapor grown carbon fiber.

[0125] ​Thus, when the positive active layer 100b is provided between the first protective layer 510 and the second protective layer 520, the first protective layer 510 can serve as a conductive medium to connect the positive current collector 100a and the positive active layer 100b on both sides of the first protective layer 510, so that the positive active layer 100b in this part can play a capacity.

[0126] In some embodiments, the thickness of the positive active layer 100b on any one side surface of the positive current collector 100a in the flat area 10a and offset from the first protective layer 510 is greater than the thickness of the first protective layer 510. The thickness of the positive active layer 100b on any one side surface of the positive current collector 100a in the flat area 10a and offset from the first protective layer 510 is greater than the thickness of the second protective layer 520. The thickness of the positive active layer 100b on any one side surface of the positive current collector 100a in the flat area 10a and offset from the first protective layer 510 is greater than the thickness of the third protective layer 530.

[0127] That is, the thickness of the first protective layer 510, the second protective layer 520 and the third protective layer 530 is less than the thickness of the positive active layer 100b on one side of the positive plate 100 that does not overlap the first protective layer 510, so that the thickness of any one of the first protective layer 510, the second protective layer 520 and the third protective layer 530 can be prevented from being too large, and the first protective layer 510, the second protective layer 520 and the third protective layer 530 can be prevented from causing the first positive bending section 130 to have a too large thickness difference with the positive plate 100 at other positions after the first protective layer 510, the second protective layer 520 and the third protective layer 530 are arranged on the first positive bending section 130, thereby facilitating to improve the flatness of the battery while reducing the risk of breaking of the first positive bending section 130.

[0128] In some embodiments, the thickness of the first protective layer 510 is greater than or equal to 5 μm and less than or equal to 20 μm, so that the first protective layer 510 is sufficient to effectively protect the positive current collector 100a of the first positive bending section 130 and prevent the first protective layer 510 from protruding from the positive active layer 100b of the first positive flat section 110.

[0129] For example, the thickness of the first protective layer 510 can be any one of 5 μm, 10 μm, 12 μm, 16 μm, 20 μm or any range between any two of them.

[0130] In some embodiments, the thickness of the positive active layer 100b on any one side surface of the positive current collector 100a in the flat area 10a and offset from the first protective layer 510 is greater than or equal to 25 μm and less than or equal to 100 μm. For example, the thickness can be any one of 25 μm, 30 μm, 50 μm, 65 μm, 80 μm, 100 μm or any range between any two of the values.

[0131] Referring to Figures 1 to 4 In a possible implementation, the battery further includes a separator 600 disposed between the positive electrode sheet 100 and the negative electrode sheet 200, the separator 600 has a folded portion 610 extending beyond the first end of the negative electrode sheet 200, and the projection of the folded portion 610 in the second direction is located within the projection of the first protective layer 510.

[0132] The end of the folded portion 610 can be disposed between the first negative flat section 210 and the first positive flat section 110, or between the first negative flat section 210 and the second positive flat section 120.

[0133] Taking the case where the end of the folded portion 610 is disposed between the first negative flat section 210 and the first positive flat section 110, the folded portion 610 is two layers of the separator 600, and there is one layer of the separator 600 between the first negative flat section 210 and the first positive flat section 110. If the end of the folded portion 610 extends beyond the first protective layer 510, the length of the extended portion inside the first negative flat section 210 and the first positive flat section 110 will be too long, which will hinder the transmission of lithium ions and increase the risk of lithium precipitation in the first negative flat section 210. Therefore, in the present embodiment, the projection of the folded portion 610 is located within the projection of the first protective layer 510 to prevent the length of the extended portion inside the flat area 10a from being too long, thereby preventing lithium precipitation in the negative electrode sheet 200.

[0134] Referring to Figure 5 In some embodiments, the surface of the second protective layer 520 facing the positive current collector 100a is entirely bonded to the first protective layer 510.

[0135] Alternatively, referring to Figure 6 In some embodiments, the surface of the second protective layer 520 facing the positive current collector 100a is entirely bonded to the positive active layer 100b.

[0136] Alternatively, referring to Figure 7As shown, in some embodiments, the second protective layer 520 includes a non-adhesion portion and two adhesion portions connected to each other, and the two adhesion portions are located on opposite sides of the non-adhesion portion along the length direction of the positive electrode sheet 100, one of the two adhesion portions is connected to the first positive electrode flat section 110, and the other adhesion portion is connected to the second positive electrode flat section 120. The non-adhesion portion is partially or entirely arranged corresponding to the first positive electrode bending section 130. In this way, the non-adhesion portion is not connected to the first protective layer 510, and after the non-adhesion portion, the first protective layer 510, and the first positive electrode bending section 130 are arranged correspondingly, the sum of the elastic modulus of the three can be reduced, thereby reducing the risk of fracture of the first positive electrode bending section 130.

[0137] In some embodiments, the compaction density of the positive electrode active layer 100b outside the first positive electrode bending section 130 is smaller than that of the positive electrode active layer 100b on any side of the first positive electrode flat section 110, and the porosity and thickness of the former are greater than those of the latter.

[0138] In this way, the risk of lithium precipitation caused by the difficulty of the positive electrode active layer 100b outside the first positive electrode bending section 130 in being infiltrated by the electrolyte can be reduced. The compaction density of the positive electrode active layer 100b outside the first positive electrode bending section 130 being smaller than that of the positive electrode active layer 100b on any side of the first positive electrode flat section 110 can be achieved by controlling the structure of the mechanical roller and the pressure exerted by the mechanical roller on the positive electrode sheet 100.

[0139] Before the positive electrode sheet 100 is rolled, part of the positive electrode active layer 100b on the first protective layer 510 needs to be removed, so that the thickness of the positive electrode sheet 100 at the position of the first protective layer 510 is smaller than that of the positive electrode sheet 100 at other positions, thereby selecting mechanical rollers with different thicknesses to exert force on the positive electrode sheet 100 at the position of the first protective layer 510 and the positive electrode sheet 100 at other positions.

[0140] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A battery, characterized in that, include: The assembly comprises a positive electrode sheet, a negative electrode sheet, a first electrode tab, a second electrode tab, and a protective layer. The positive electrode sheet and the negative electrode sheet are stacked in sequence and then wound to form a core body. The core body has a flat area and an arc area. The arc area is located on both sides of the flat area along a first direction. The beginning ends of the positive electrode sheet and the beginning ends of the negative electrode sheet are located on both sides of the flat area along the first direction and extend in opposite directions. The positive electrode sheet includes a first positive electrode straight section and a second positive electrode straight section located in the straight region, and a first positive electrode bent section located in the arc region. The first positive electrode straight section, the first positive electrode bent section and the second positive electrode straight section are sequentially adjacent to each other along the length direction of the positive electrode sheet. The end of the first positive electrode straight section away from the first positive electrode bent section constitutes the beginning end of the positive electrode sheet. The negative electrode sheet includes a first negative electrode straight section located in the straight region. Along the second direction, the first negative electrode straight section is located between the first positive electrode straight section and the second positive electrode straight section. The end of the first negative electrode straight section near the first positive electrode bending section constitutes the first end of the negative electrode sheet. At least a portion of the protective layer is connected to the first positive electrode bending section, and at least a portion of the protective layer extends to at least one of the first positive electrode straight section and the second positive electrode straight section; One of the first electrode tab and the second electrode tab is connected to the positive electrode plate, and the other is connected to the negative electrode plate. Both the first electrode tab and the second electrode tab are located in the flat region and are spaced apart along the first direction. Along the second direction, the projections of the first tab and the second tab are both offset from the projection of the protective layer.

2. The battery according to claim 1, characterized in that, Along the first direction, the first electrode tab is positioned relative to the second electrode tab near the first positive electrode bend section; In the first direction, the minimum distance between the protective layer and the first electrode tab is greater than or equal to 0.5 mm, and / or, in the first direction, the minimum distance between the protective layer and the first electrode tab is less than or equal to 15 mm.

3. The battery according to claim 1 or 2, characterized in that, The protective layer includes a first protective layer, which is located on the inner surface of the first positive electrode bending section; And / or, the protective layer includes a second protective layer located on the inner surface of the first positive electrode bending section; And / or, the protective layer includes a third protective layer located on the outer surface of the first positive electrode bending section, the third protective layer including an ion-permeable layer.

4. The battery according to claim 3, characterized in that, The positive electrode sheet includes a positive current collector and a positive active layer, wherein the positive active layer is disposed on at least one surface of the positive current collector in the thickness direction; The first protective layer is provided on the surface of the positive current collector of the first positive electrode bending section near the winding center, and the second protective layer is provided on the surface of the first protective layer opposite to the positive current collector; Along the length of the positive electrode sheet, the width of the first protective layer is greater than the width of the second protective layer.

5. The battery according to claim 4, characterized in that, At least a portion of the first protective layer extends to the first positive electrode straight section, and the positive electrode active layer located on the side of the first positive electrode straight section near the winding center at least partially overlaps with the first protective layer; At least a portion of the first protective layer extends into the second positive electrode straight section, and the positive electrode active layer located on the side of the second positive electrode straight section near the winding center at least partially overlaps with the first protective layer; And / or, at least a portion of the second protective layer extends to the first positive electrode straight section, and the second protective layer is offset from the positive electrode active layer on the side of the first positive electrode straight section near the winding center; At least a portion of the second protective layer extends into the second positive electrode straight section, and the second protective layer is offset from the positive electrode active layer on the side of the second positive electrode straight section near the winding center.

6. The battery according to claim 4, characterized in that, Along the width direction of the positive electrode sheet, the opposite two side edges of the first protective layer are flush with the opposite two side edges of the first positive electrode bending section; And / or, along the width direction of the positive electrode sheet, the opposite two side edges of the second protective layer extend beyond the opposite two side edges of the first positive electrode bending section; And / or, along the width direction of the positive electrode sheet, the dimension by which any edge of the second protective layer extends beyond the corresponding edge of the first positive electrode bending segment is greater than or equal to 0.3 mm and less than or equal to 5 mm.

7. The battery according to claim 6, characterized in that, Along the length of the positive electrode sheet, the overlap dimension between the first protective layer and the positive electrode active layer on the side of the first positive electrode straight section near the winding center is greater than or equal to 0.5 mm and less than or equal to 10 mm. And / or, along the length direction of the positive electrode sheet, the overlap dimension between the first protective layer and the positive electrode active layer on the side of the straight section of the second positive electrode near the winding center is greater than or equal to 0.5 mm and less than or equal to 10 mm.

8. The battery according to claim 5, characterized in that, A positive electrode active layer is further provided between the surface of the first protective layer away from the positive electrode current collector and the surface of the second protective layer facing the positive electrode current collector, and the thickness of the positive electrode active layer located between the first protective layer and the second protective layer is less than or equal to 35 μm; The first protective layer comprises at least one of inorganic particles and a binder. The inorganic particles include at least one of alumina, silicon dioxide, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, boron nitride, aluminum nitride, magnesium nitride, tin dioxide, magnesium hydroxide, barium sulfate, barium carbonate, barium titanate, and boehmite. The binder includes at least one of polypropylene, polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, polyurethane, polyacrylonitrile, and polyimide. And / or, the first protective layer further includes conductive particles, the conductive particles including at least one of silver powder, gold powder, copper powder, aluminum powder, nickel powder, carbon nanotubes, graphene, conductive carbon black, Ketjen black, acetylene black, conductive graphite, and vapor-grown carbon fiber.

9. The battery according to claim 5, characterized in that, The thickness of the positive electrode active layer located on either side of the positive electrode current collector in the flat region and offset from the first protective layer is greater than the thickness of the first protective layer; And / or, the thickness of the first protective layer is greater than or equal to 5 μm and less than or equal to 20 μm; And / or, the thickness of the positive electrode active layer located on either side of the positive electrode current collector in the flat region and offset from the first protective layer is greater than or equal to 25 μm and less than or equal to 100 μm.

10. The battery according to claim 3, characterized in that, It also includes a separator disposed between the positive electrode and the negative electrode, the separator having a folded portion extending beyond the first end of the negative electrode, and the projection of the folded portion along the second direction being located within the projection of the first protective layer.

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