Secondary battery and electronic device

Abstract

The present application relates to a secondary battery and an electronic device. The secondary battery comprises a housing, an electrolyte and an electrode assembly accommodated in the housing, and a first conductive member extending out of the housing. The electrode assembly comprises a first electrode sheet and a plurality of first tabs connected to the first electrode sheet. The plurality of first tabs are stacked and connected to the first conductive member. The first tabs comprise a first outer tab located at the outermost layer of the stack and first inner tabs located at inner layers of the stack. The first outer tab comprises a first connecting portion, a first bending portion, and a first welding portion that are connected in sequence in the extending direction of the first outer tab. The first connecting portion is connected to the first electrode sheet, the maximum curvature point of the first outer tab lies at the edge of the junction between the first bending portion and the first connecting portion, and the first welding portion is connected to the first conductive member. A surface of the first connecting portion is provided with a first insulating coating. In the extending direction of the first outer tab, the first insulating coating extends beyond the first connecting portion. The secondary battery and the electronic device of the present application can mitigate tab breakage and failure.

Description

Secondary batteries and electronic devices Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] Secondary batteries, as the power source for electronic devices, are crucial for ensuring their normal operation. A secondary battery consists of a casing and electrode assemblies located within it. During a drop, the electrode assemblies are prone to shifting within the casing, and the tabs connecting them to the electrode plates are easily broken and fail. Summary of the Invention

[0003] The inventors of this application have discovered that secondary batteries typically include a casing and an electrode assembly located within the casing. The portion where the tabs connect to the electrode plates is usually coated with an insulating layer to reduce the possibility of electrical connection between the tabs and the casing, other tabs, and other electrode plates. During a drop, the electrode assembly is prone to shifting within the casing. Due to the high hardness of the insulating coating, there is a significant hardness difference between the insulating coating and the tabs. This hardness difference leads to stress concentration. The hardness difference is greatest at the interface between the insulating coating and the non-insulating coating on the tabs. Therefore, the stress concentration is most pronounced at this interface, where the maximum stress concentration point of the tab is located. The tab is prone to breakage and failure at this interface.

[0004] The purpose of this application is to provide a secondary battery and electronic device that aims to improve the problem of tab breakage failure.

[0005] According to a first aspect of this application, a secondary battery is provided, including a casing, an electrolyte, an electrode assembly, and a first conductive element. The electrolyte and the electrode assembly are housed within the casing. The electrode assembly includes a first electrode plate and a plurality of first tabs connected to the first electrode plate. Along the thickness direction of the electrode assembly, the plurality of first tabs are stacked and connected to the first conductive element, which extends beyond the casing. Each first tab includes a first outer tab and a first inner tab. The first tab located on the outermost layer of the stack is the first outer tab, and the first tab located on the innermost layer of the stack is the first inner tab. All other first tabs besides the first outer tab are first inner tabs. Along the extending direction of the first outer tab, the first outer tab includes a first connecting portion, a first bending portion, and a first welding portion connected in sequence. The first connecting portion is connected to the first electrode plate, and the first welding portion is connected to the first conductive element. A first insulating coating is provided on the surface of the first connecting portion along its thickness direction, and the first insulating coating extends beyond the first connecting portion along the extending direction of the first outer tab.

[0006] In the above technical solution, the electrode assembly includes a first electrode plate and multiple first tabs connected to the first electrode plate. The multiple first tabs are connected to a first conductive element, which extends out of the housing and can transfer energy from the first electrode plate to the outside of the housing. Stacking multiple first tabs can reduce the space occupied by the first tabs. Along the extension direction of the first outer tab, the first outer tab includes a first connecting portion, a first bending portion, and a first welding portion connected in sequence. The first connecting portion is connected to the first electrode plate. By providing a first insulating coating on the surface of the first connecting portion in the thickness direction, the possibility of electrical connection between the first outer tab and the housing, other tabs, and other electrode plates can be reduced. The maximum curvature point of the first outer tab is located at the junction edge of the first bending portion and the first connecting portion, and stress concentration is prone to occur at the maximum curvature point of the first outer tab. The surface of the first connection part in the thickness direction is provided with a first insulating coating. During the drop, the first outer electrode of the outermost layer of the secondary battery is prone to stress concentration at the junction where the first insulating coating is provided and where the first insulating coating is not provided. Moreover, the stress concentration at this junction is more obvious than the stress concentration at the point of maximum curvature. The point of maximum stress on the first outer electrode is located at this junction. The first outer electrode is prone to bending and squeezing the first electrode of the inner layer of the stack at this junction, and the first outer electrode is prone to breakage. Along the extension direction of the first outer tab, by providing a first insulating coating that extends beyond the first connecting portion, stress concentration in the first outer tab is only likely to occur at the point of maximum curvature, i.e., stress concentration is likely to occur at the boundary edge between the first bend and the first connecting portion. The point of maximum stress on the first outer tab is transferred to the boundary edge between the first bend and the first connecting portion. Since the boundary edge between the first bend and the first connecting portion is covered by the first insulating coating, the first insulating coating can share the stress at this boundary edge, thus reducing the stress at the point of maximum stress. Compared to when the first insulating coating does not extend beyond the first connecting portion, the first outer tab is less prone to breakage, which can improve the problem of breakage failure of the first outer tab. Although adhesive paper can also insulate the first outer tab by bonding it to the surface in the thickness direction, the adhesiveness of the adhesive paper will decrease when it is wetted by the electrolyte. The adhesive paper may slide relative to the tab or even fall off, and the supporting effect of the adhesive paper is poor.

[0007] In some preferred embodiments, a first insulating coating is provided on the surface of the first outer tab facing the first inner tab. During a drop, the stress concentration on the surface of the first outer tab facing the first inner tab is more pronounced than on the surface of the first outer tab facing away from the first inner tab. By providing a first insulating coating on the surface of the first outer tab facing the first inner tab, the problem of breakage failure of the first outer tab can be improved.

[0008] In some preferred embodiments, a first insulating coating is provided on both opposite surfaces of the first outer electrode in the thickness direction, which can further improve the problem of breakage failure of the first outer electrode.

[0009] In some preferred embodiments, the first weld portion is welded to the first conductive element to form a first solder mark, which can improve the stability of the connection between the first weld portion and the first conductive element. Along the extension direction of the first outer tab, the distance between the first insulating coating and the first solder mark is T1, where T1 ≥ 0.5 mm, which can reduce the possibility that the first insulating coating will affect the welding effect between the first weld portion and the first conductive element.

[0010] In some preferred embodiments, the first insulating coating includes ceramic insulating particles and an adhesive. The ceramic insulating particles have high strength, which can improve the support effect of the first insulating coating.

[0011] In some preferred embodiments, the ceramic insulating particles include boehmite and / or alumina, which can improve the strength of the ceramic insulating particles.

[0012] In some preferred embodiments, the first insulating coating includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide, which can improve the insulating effect of the first insulating coating.

[0013] In some preferred embodiments, the thickness of the first insulating coating is between 10 μm and 45 μm. If the thickness of the first insulating coating is less than 10 μm, its insulating effect is not significant. Because of the large difference in hardness between the first insulating coating and the first outer tab, if the thickness of the first insulating coating is greater than 45 μm, stress concentration is likely to occur at the interface between the first outer tab where the first insulating coating is applied and where it is not applied. Furthermore, this can easily lead to a significant loss of energy density in the secondary battery.

[0014] In some preferred embodiments, the first electrode is a cathode electrode, and the first tab is a cathode tab. Since the cathode electrode is usually shorter than the anode electrode, the cathode tab can easily come into contact with the anode electrode. By providing an insulating coating on the surface of the cathode tab in the thickness direction, the possibility of electrical connection between the cathode tab and the anode electrode can be reduced.

[0015] In some preferred embodiments, along the extending direction of the first inner electrode tab, the first inner electrode tab includes a second connecting portion, a second bending portion, and a second welding portion connected in sequence. The second connecting portion is connected to the first electrode plate, and the second welding portion is connected to the first conductive element, which can transfer energy from the first electrode plate to the first conductive element. A second insulating coating is provided on the surface of the second connecting portion in the thickness direction. Along the extending direction of the first inner electrode tab, the second insulating coating extends beyond the second connecting portion, which can reduce the possibility of stress concentration at the interface between the first inner electrode tab with and without the second insulating coating, and can improve the problem of fracture failure of the first inner electrode tab.

[0016] In some preferred embodiments, the second weld portion is welded to the first conductive element and forms a second weld mark; along the extension direction of the first inner electrode tab, the distance between the second insulating coating and the second weld portion is T2, where T2 ≥ 0.5 mm, which can reduce the possibility that the second insulating coating will affect the welding effect between the second weld portion and the first conductive element.

[0017] In some preferred embodiments, the second insulating coating comprises ceramic insulating particles and an adhesive. The ceramic insulating particles have greater strength, which can improve the support effect of the second insulating coating.

[0018] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0019] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0020] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the dimensions in the drawings do not constitute a limitation on scale.

[0021] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0022] Figure 2 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0023] Figure 3 is a schematic diagram of the structure of an electrode assembly according to some embodiments of this application;

[0024] Figure 4 is a schematic diagram of the structure of an electrode assembly according to some embodiments of this application;

[0025] Figure 5 is a schematic diagram of the structure of the first electrode, the first electrode tab, and the first conductive element in some embodiments of this application;

[0026] Figure 6 is a schematic diagram of the structure of the first electrode, the first electrode tab, and the first conductive element in some embodiments of this application;

[0027] Figure 7 is a schematic diagram of the structure of the first electrode, the first electrode tab, and the first conductive element in some embodiments of this application;

[0028] Figure 8 is a schematic diagram of the structure of the first electrode, the first electrode tab, and the first conductive element in some embodiments of this application;

[0029] Figure 9 is a schematic diagram of the structure of the first electrode, the first electrode tab, and the first conductive element in some embodiments of this application;

[0030] Figure 10 is a schematic diagram of the structure of the first electrode, the first tab, and the first conductive element in some embodiments of this application.

[0031] Explanation of reference numerals in the attached drawings: 100, secondary battery; 10, casing; 20, electrode assembly; 21, first electrode; 211, first current collector; 212, first active layer; 22, second electrode; 221, second current collector; 222, second active layer; 23, separator; 24, first tab; 241, first outer tab; 2411, first connecting part; 2412, first bending part; 2413, first weld; 2414, first solder mark; 242, first inner tab; 2421, second connecting part; 2422, second bending part; 2423, second weld; 2424, second solder mark; 25, second tab; 26, first insulating coating; 27, second insulating coating; 30, first conductive element; 40, second conductive element. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0033] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0034] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0035] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0036] The term "perpendicular" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately perpendicular. For example, in numerical terms, perpendicularity can refer to the angle between two straight lines within the range of 90 ± 10°, the dihedral angle between two planes within the range of 90 ± 10°, or the angle between a straight line and a plane within the range of 90 ± 10°. The two components described as "perpendicular" do not have to be absolutely straight lines or planes; they can be approximately straight lines or planes. From a macroscopic perspective, if the overall direction of extension is straight or plane, the component can be considered a "straight line" or "plane".

[0037] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0038] In a first aspect, embodiments of this application provide a secondary battery 100. Referring to Figure 1, the secondary battery 100 includes a housing 10, an electrode assembly 20, a first conductive element 30, and a second conductive element 40. The housing 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure), with the electrolyte permeating the electrode assembly 20 within the housing 10. The first conductive element 30 and the second conductive element 40 are respectively connected to the electrode assembly 20, and both the first conductive element 30 and the second conductive element 40 extend out of the housing 10 to assist the electrode assembly 20 in energy transfer with external electronic devices.

[0039] Referring to Figure 2, which illustrates the stacked structure of the electrode assembly 20, the electrode assembly 20 includes a first electrode 21, a diaphragm 23, and a second electrode 22. The first electrode 21 and the second electrode 22 have opposite polarities. A diaphragm 23 is disposed between adjacent second electrode 22 and first electrode 21. The first electrode 21, diaphragm 23, and second electrode 22 are stacked. In the embodiments of this application, the electrode assembly 20 is described as a stacked structure. In other embodiments, the electrode assembly 20 may also be a wound structure. For example, the first electrode 21, diaphragm 23, and second electrode 22 are sequentially stacked and wound to form a wound electrode assembly 20.

[0040] In some embodiments, please refer to FIG3, the first electrode 21 includes a first current collector 211 and a first active layer 212, and the surface of the first current collector 211 is provided with the first active layer 212.

[0041] In some embodiments, the first current collector 211 may be an aluminum foil or a copper foil.

[0042] In some embodiments, the first active layer 212 is immersed in the electrolyte within the housing 10 to undergo an electrochemical reaction. The first active layer 212 includes a cathode active material, a conductive agent, an adhesive, etc., and the above materials are mixed and stirred evenly and coated onto the surface of the first current collector 211 to obtain the first active layer 212. The cathode active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0043] In some embodiments, referring to Figures 2, 3, and 4, the first current collector 211 is connected to a plurality of first tabs 24. In the thickness direction of the electrode assembly 20, the plurality of first tabs 24 are stacked and connected to the first conductive element 30, enabling the transfer of energy from the first electrode 21 to the first conductive element 30. The stacking of the plurality of first tabs 24 reduces the space occupied by the first tabs 24. In some embodiments, the first current collector 211 and the first tabs 24 are integrally formed.

[0044] In some embodiments, the second electrode 22 includes a second current collector 221 and a second active layer 222, with the second active layer 222 disposed on the surface of the second current collector 221. The second current collector 221 is connected to a plurality of second tabs 25. In the thickness direction of the electrode assembly 20, the plurality of second tabs 25 are stacked and connected to the second conductive element 40, enabling the transfer of energy from the second electrode 22 to the second conductive element 40. The stacking of the plurality of second tabs 25 reduces the space occupied by the second tabs 25. In some embodiments, the second current collector 221 can be an aluminum foil or a copper foil. In some embodiments, the second current collector 221 and the second tabs 25 are integrally formed.

[0045] In some embodiments, the second active layer 222 is immersed in the electrolyte within the housing 10 to undergo an electrochemical reaction. The second active layer 222 includes an anodic active material, a conductive agent, an adhesive, etc., which are mixed and stirred evenly and then coated onto the surface of the second current collector 221 to obtain the second active layer 222. The anodic active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0046] In some embodiments, please refer to Figures 2 and 5. The first electrode tab 24 includes a first outer electrode tab 241 and a first inner electrode tab 242. The first electrode tab 24 located on the outermost layer of the stack is the first outer electrode tab 241, and the first electrode tab 24 located on the inner layer of the stack is the first inner electrode tab 242. All other first electrode tabs 24 except the first outer electrode tab 241 are the first inner electrode tabs 242. Along the extending direction of the first outer tab 241, the first outer tab 241 includes a first connecting portion 2411, a first bending portion 2412, and a first welding portion 2413 connected in sequence. The first connecting portion 2411 is connected to the first electrode 21. The maximum curvature point of the first outer tab 241 is located at the boundary edge between the first bending portion 2412 and the first connecting portion 2411. The first welding portion 2413 is connected to the first conductive element 30. A first insulating coating 26 is provided on the surface of the first connecting portion 2411 in the thickness direction, which can reduce the possibility of electrical connection between the first outer tab 241 and the housing 10, other tabs, and other electrodes. However, during the drop of the secondary battery 100, the electrode assembly 20 is prone to shifting within the housing 10, and stress concentration is likely to occur at the maximum curvature point of the first outer tab 241, that is, stress concentration is likely to occur at the boundary edge between the first bending portion 2412 and the first connecting portion 2411. Furthermore, due to the high hardness of the first insulating coating 26, there is a significant hardness difference between the first insulating coating 26 and the first outer tab 241. This hardness difference leads to stress concentration. The hardness difference of the first outer tab 241 located on the outermost layer of the stack is greatest at the junction where the first insulating coating 26 is provided and where the first insulating coating 26 is not provided. Therefore, stress concentration will also occur at the junction where the first insulating coating 26 is provided and where the first insulating coating 26 is not provided. Moreover, the stress concentration at this junction is more obvious than the stress concentration at the point of maximum curvature. The point of maximum stress on the first outer tab 241 is located at this junction. The first outer tab 241 is prone to bending and squeezing the first inner tab 242 of the stacked inner layer at this junction, and the first outer tab 241 is prone to breakage.

[0047] To improve the above problems, please refer to Figure 6. In the embodiment of this application, along the extending direction of the first outer tab 241, the first insulating coating 26 extends beyond the first connecting portion 2411. The first outer tab 241 is prone to stress concentration only at the point of maximum curvature, that is, stress concentration is prone to occur at the junction edge of the first bending portion 2412 and the first connecting portion 2411. The point of maximum stress on the first outer tab 241 is transferred to the junction edge of the first bending portion 2412 and the first connecting portion 2411. Since the junction edge of the first bending portion 2412 and the first connecting portion 2411 is covered by the first insulating coating 26, the first insulating coating 26 can share the stress at the junction edge. Therefore, the stress at the point of maximum stress will be reduced. Compared with the first insulating coating 26 not extending beyond the first connecting portion 2411, the first outer tab 241 is less likely to break, which can improve the problem of the first outer tab 241 breaking and failing. Although adhesive paper can also insulate the first outer tab 241 by bonding it to the surface in the thickness direction of the first outer tab 241, the adhesiveness of the adhesive paper will decrease when it is wetted by the electrolyte. The adhesive paper may slide or even fall off relative to the tab, and the supporting effect of the adhesive paper is poor.

[0048] In some embodiments, referring to Figure 7, a first insulating coating 26 is provided on the surface of the first outer tab 241 facing the first inner tab 242. During a drop, the stress concentration on the surface of the first outer tab 241 facing the first inner tab 242 is more pronounced than on the surface of the first outer tab 241 facing away from the first inner tab 242. By providing the first insulating coating 26 on the surface of the first outer tab 241 facing the first inner tab 242, the problem of breakage failure of the first outer tab 241 can be improved.

[0049] In some embodiments, referring to Figure 8, a first insulating coating 26 is provided on both opposite surfaces of the first outer tab 241 in the thickness direction, which can further improve the problem of breakage failure of the first outer tab 241. In some embodiments, the lengths of the first insulating coating 26 on the opposite surfaces of the first outer tab 241 can be the same along the extending direction of the first outer tab 241. It should be noted that, due to dimensional errors, the same length of the first insulating coating 26 on the opposite surfaces of the first outer tab 241 means that the length difference of the first insulating coating 26 on the opposite surfaces of the first outer tab 241 is ≤0.2mm.

[0050] In some embodiments, the first weld portion 2413 is welded to the first conductive element 30 to form a first solder mark 2414, which can improve the stability of the connection between the first weld portion 2413 and the first conductive element 30. Along the extending direction of the first outer tab 241, the distance between the first insulating coating 26 and the first solder mark 2414 is T1, where T1 ≥ 0.5 mm, which can reduce the possibility that the first insulating coating 26 will affect the welding effect between the first weld portion 2413 and the first conductive element 30.

[0051] In some embodiments, the first insulating coating 26 includes ceramic insulating particles and an adhesive. The ceramic insulating particles have high strength, which can improve the support effect of the first insulating coating 26.

[0052] In some embodiments, the ceramic insulating particles include boehmite and / or alumina, which can enhance the strength of the ceramic insulating particles.

[0053] In some embodiments, the first insulating coating 26 includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide, which can improve the insulating effect of the first insulating coating 26.

[0054] In some embodiments, the thickness of the first insulating coating 26 is between 10 μm and 45 μm. If the thickness of the first insulating coating 26 is less than 10 μm, its insulating effect is not significant. Because the hardness difference between the first insulating coating 26 and the first outer tab 241 is large, if the thickness of the first insulating coating 26 is greater than 45 μm, stress concentration is likely to occur at the interface between the first outer tab 241 where the first insulating coating 26 is provided and where it is not provided. Furthermore, this can easily lead to a significant loss of energy density in the secondary battery 100.

[0055] In some embodiments, the first electrode 21 is a cathode electrode, and the first tab 24 is a cathode tab. Since the cathode electrode is usually shorter than the anode electrode, the cathode tab can easily come into contact with the anode electrode. By providing an insulating coating on the surface of the cathode tab in the thickness direction, the possibility of electrical connection between the cathode tab and the anode electrode can be reduced.

[0056] In some embodiments, the surface of the first inner tab 242 is provided with a second insulating coating 27, which can reduce the possibility of the first inner tab 242 being electrically connected to the housing 10, other tabs and other electrode plates.

[0057] In some embodiments, referring to Figure 9, a second insulating coating 27 is provided on both opposite surfaces of the first inner electrode 242, which can further reduce the possibility of electrical connection between the first inner electrode 242 and the housing 10, other electrodes, and other electrode plates. In some embodiments, the lengths of the second insulating coatings 27 on both opposite surfaces of the first inner electrode 242 may be the same along the extending direction of the first inner electrode 242. It should be noted that, due to dimensional errors, the same length of the second insulating coatings 27 on both opposite surfaces of the first inner electrode 242 means that the length difference of the second insulating coatings 27 on both opposite surfaces of the first inner electrode 242 is ≤0.2mm.

[0058] In some embodiments, the length of the second insulating coating 27 along the extending direction of the first inner tab 242 is L1, where L1 ≥ 0.5 mm, to improve the insulation effect of the second insulating coating 27 on the first inner tab 242.

[0059] In some embodiments, referring to FIG10, along the extending direction of the first inner electrode tab 242, the first inner electrode tab 242 includes a second connecting portion 2421, a second bending portion 2422, and a second welding portion 2423 connected in sequence. The second connecting portion 2421 is connected to the first electrode 21. The maximum curvature point of the first inner electrode tab 242 is located at the boundary edge between the second bending portion 2422 and the second connecting portion 2421. The second welding portion 2423 is welded to the first conductive element 30, which can transfer the energy of the first electrode 21 to the first conductive element 30. A second insulating coating 27 is provided on the surface of the second connecting portion 2421 in the thickness direction. Along the extending direction of the first inner electrode tab 242, the second insulating coating 27 extends beyond the second connecting portion 2421, which can reduce the possibility of stress concentration at the boundary between the first inner electrode tab 242 where the second insulating coating 27 is provided and where the second insulating coating 27 is not provided, and can improve the problem of fracture failure of the first inner electrode tab 242.

[0060] In some embodiments, the second weld portion 2423 is welded to the first conductive element 30, forming a second solder mark 2424. Along the extending direction of the first inner tab 242, the distance between the second insulating coating 27 and the second solder mark 2424 is T2, where T2 ≥ 0.5 mm, which can reduce the possibility that the second insulating coating 27 will affect the welding effect between the second weld portion 2423 and the first conductive element 30.

[0061] In some embodiments, the second insulating coating 27 includes ceramic insulating particles and an adhesive. The ceramic insulating particles have greater strength, which can improve the support effect of the second insulating coating 27.

[0062] In some embodiments, all first insulating coatings 26 have the same width and the same thickness, which can improve the uniformity of force on the first outer electrode tab 241. In other embodiments, the width and thickness of each first insulating coating 26 may be different.

[0063] In some embodiments, all second insulating coatings 27 have the same width and the same thickness, which can improve the uniformity of force on the first inner tab 242. In other embodiments, the width and thickness of each second insulating coating 27 may be different.

[0064] In some embodiments, the width of the first insulating coating 26 and the width of the second insulating coating 27 are the same, and the thickness of the first insulating coating 26 and the thickness of the second insulating coating 27 are the same, which can improve the uniformity of force on the first electrode tab 24. In other embodiments, the width of the first insulating coating 26 and the width of the second insulating coating 27 may be different, and the thickness of the first insulating coating 26 and the thickness of the second insulating coating 27 may be different.

[0065] A second aspect of this application also provides an electronic device including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art. For example, electronic devices include, but are not limited to, Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0066] Test section:

[0067] 1. Drop test of secondary batteries:

[0068] In a test environment of 20±5℃, on a stainless steel or marble floor, the sample is dropped from a height of 1.8m along the head and tail sides once, and then dropped from the four corners once, for a total of 7 rounds of testing. The drop order is (head -> tail -> head right corner -> tail right corner -> head left corner -> tail left corner (angle: 45±15 degrees, 6 times per round)). Judgment criteria: no fire, no explosion, no smoke, no leakage.

[0069] Example 1

[0070] <Preparation of the positive electrode>:

[0071] Lithium cobalt oxide (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly.

[0072] Aluminum foil is selected as the positive electrode current collector. The above-mentioned slurry is coated on one surface of the positive electrode current collector, leaving a blank positive electrode foil section. The slurry is dried to obtain a single-sided positive electrode sheet with a positive electrode active material layer coated on one side. The above steps are repeated on the other surface of the positive electrode current collector to obtain a double-sided positive electrode sheet with a positive electrode active material layer coated on both sides. The blank positive electrode foil section is die-cut to form a positive electrode tab.

[0073] <Preparation of negative electrode sheet>:

[0074] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) were mixed in a weight ratio of 96:2:2, and deionized water was added as a solvent to prepare a slurry with a solid content of 70 wt%, which was then stirred evenly.

[0075] Copper foil is selected as the negative electrode current collector. The above-mentioned slurry is coated on one surface of the negative electrode current collector, leaving a blank negative electrode foil section. The slurry is dried to obtain a single-sided negative electrode sheet with a negative electrode active material layer coated on one side. The above steps are repeated on the other surface of the negative electrode current collector to obtain a double-sided negative electrode sheet with a negative electrode active material layer coated on both sides. The blank negative electrode foil section is die-cut to form a negative electrode tab.

[0076] <Preparation of the diaphragm>:

[0077] A porous polyethylene membrane is used as the substrate layer, and a ceramic layer containing alumina ceramic and PVDF binder is coated on one side of the substrate layer as a separator (CCS), wherein the mass percentage of alumina ceramic in the ceramic layer is 95%.

[0078] <Electrolyte Preparation>:

[0079] In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent, dissolved, and mixed evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0080] <Preparation of Secondary Batteries>:

[0081] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. The stacked electrodes form the electrode assembly.

[0082] Aluminum foil is selected as the first conductive element. First tabs are stacked and connected to the first conductive element. The first tabs include a first outer tab and a first inner tab. The first tab located on the outermost layer of the stack is the first outer tab, and the first tab located on the innermost layer is the first inner tab. All other first tabs besides the first outer tab are first inner tabs. Along the extending direction of the first outer tab, the first outer tab includes a first connecting portion, a first bending portion, and a first welding portion connected in sequence. The first connecting portion is connected to the first electrode sheet. The maximum curvature point of the first outer tab is located at the boundary edge between the first bending portion and the first connecting portion. The first welding portion is welded to the first conductive element, forming a first solder mark. The first connecting portion includes an inner surface facing the first inner tab and an outer surface facing away from the first inner tab. Both the inner and outer surfaces of the first connecting portion are coated with alumina particles and adhesive slurry to form a first insulating coating. Along the extending direction of the first outer tab, the first insulating coating extends beyond the first connecting portion. The length of the first insulating coating is 3 mm, and the distance T1 between the first insulating coating and the first solder mark is 2 mm.

[0083] Along the extending direction of the first inner electrode tab, the first inner electrode tab includes a second connecting portion, a second bending portion, and a second welding portion connected in sequence. The second connecting portion is connected to the first electrode plate. The point of maximum curvature of the first inner electrode tab is located at the boundary edge between the second bending portion and the second connecting portion. The second welding portion is welded to the first conductive element. Both opposing surfaces of the second connecting portion are coated with alumina particles and adhesive slurry to form a second insulating coating. Along the extending direction of the first inner electrode tab, the second insulating coating does not extend beyond the second connecting portion, and the length of the second insulating coating is 2 mm.

[0084] The electrode assembly is hot-pressed, placed into the aluminum-plastic film of the housing, injected with electrolyte, and encapsulated to obtain a secondary battery. The first conductive element extends out of the housing, the length of the secondary battery is 60 mm, and the width of the secondary battery is 50 mm.

[0085] The relevant parameters in Comparative Examples 1 to 3 and Examples 1 to 9 are shown in Table 1 below.

[0086] In Comparative Example 1 and Examples 1 to 5, both the first and second insulating coatings are two layers. The only difference between Comparative Example 1 and Examples 1 to 4 is the length of the first insulating coating. In Comparative Example 1, the first insulating coating does not extend beyond the first connecting portion, while in Examples 1 to 4, the first insulating coating extends beyond the first connecting portion. In Example 5, the first insulating coating extends beyond the first connecting portion, and the second insulating coating extends beyond the second connecting portion.

[0087] In Comparative Examples 2 to 3 and Examples 6 to 9, both the first and second insulating coatings are single layers. In Comparative Examples 2, 6, and 8, the first insulating coating is located on the surface (inner surface) of the first outer electrode facing the first inner electrode. In Comparative Examples 3, 7, and 9, the first insulating coating is located on the surface (outer surface) of the first outer electrode away from the first inner electrode. In Comparative Examples 2 and 3, the first insulating coating does not extend beyond the first connecting portion; in Examples 6 and 7, the first insulating coating extends beyond the first connecting portion. In Examples 8 and 9, the first insulating coating extends beyond the first connecting portion, and the second insulating coating extends beyond the second connecting portion.

[0088] Table 1

[0089] As can be seen from Comparative Examples 1 to 3 and Examples 1 to 9 in Table 1 above, by setting the first insulating coating on the surface of the first outer tab to extend beyond the first connection portion, the problem of the first outer tab breaking and failing can be improved, the number of drop test passes of the secondary battery will increase, and the safety performance of the secondary battery can be improved.

[0090] As can be seen from Comparative Example 1 and Examples 1 to 4, when the first insulating coating has two layers, the number of drop test passes for the secondary battery increases as the first insulating coating extends beyond the first connection portion. Furthermore, the number of drop test passes also increases as the length of the first insulating coating extending beyond the first connection portion increases. However, the length of the first insulating coating cannot be too large, as this would affect the welding effect between the first welding portion and the first conductive component.

[0091] Based on Comparative Examples 2 to 3 and Examples 6 to 9, it can be seen that when the first insulating coating is one layer, the first insulating coating extends beyond the first connection portion, increasing the number of drop test passes for the secondary battery. Moreover, compared to the surface (outer surface) of the first outer electrode tab facing away from the first inner electrode tab, the surface (inner surface) of the first outer electrode tab facing the first inner electrode tab is closer to the stacked inner layers, resulting in more significant stress concentration. By setting the first insulating coating on the surface of the first outer electrode tab facing the first inner electrode tab, compared to setting the first insulating coating on the surface of the first outer electrode tab facing away from the first inner electrode tab, the number of drop test passes is higher, which can better improve the problem of first outer electrode tab breakage failure.

[0092] As can be seen from Embodiments 1, 6, and 7, when the first insulating coating extends beyond the first connecting portion, a higher number of drop test passes are achieved when the first insulating coating is applied to only one surface of the first outer electrode compared to applying it to both opposite surfaces. This is because the first insulating coating contains materials with high hardness, such as aluminum titanate or aluminum oxide, resulting in a higher hardness than the first electrode. The significant hardness difference between the first insulating coating and the first electrode leads to more pronounced surface stress concentration on both opposite surfaces compared to applying it to only one surface, making breakage more likely. However, considering short-circuit safety, applying the first insulating coating to both opposite surfaces of the first outer electrode better reduces the risk of short circuits. Therefore, if the breakage problem is not significantly worse when the first insulating coating is applied to both opposite surfaces, further considering short-circuit safety, applying the first insulating coating to both opposite surfaces is better than applying it to only one surface.

[0093] As can be seen from Examples 4 and 5, Examples 6 and 8, and Examples 7 and 9, the improvement in the drop test pass rate of the secondary battery is not significant after the second insulating coating extends beyond the second connection portion. This is because the stress on the first outer tab of the outermost layer is more severe than the stress on the first inner tab of the inner layer. The stress at the boundary edge between the first inner tab with and without the second insulating coating is relatively low. Therefore, although the second insulating coating extending beyond the second connection portion can reduce the possibility of stress concentration on the first inner tab, it is difficult to reflect the effect of the first insulating coating extending beyond the first connection portion on improving the stress concentration on the first outer tab through the drop test pass rate of the secondary battery.

[0094] The relevant parameters for Examples 1 and 10 to 14 are shown in Table 2 below. The only difference between Examples 1 and 10 to 14 is the thickness of the first insulating coating.

[0095] Table 2

[0096] Based on Examples 1 and 10 to 14 in Table 2 above, it can be seen that when the thickness of the first insulating coating is 5 μm to 45 μm, the drop safety is good. Furthermore, when the thickness of the first insulating coating is 10 μm to 45 μm, the secondary battery exhibits a good drop test pass rate (number of passes / number of tests). Due to the significant difference in hardness between the first insulating coating and the first outer tab, stress concentration occurs at the interface between the first and non-first insulating coating areas on the first outer tab. The smaller the thickness of the first insulating coating, the smaller the impact of the hardness difference on the first outer tab, and the smaller the stress concentration at the interface between the first and non-first insulating coating areas on the first outer tab. This improves the effectiveness of preventing breakage of the first outer tab and results in a better drop test pass rate for the secondary battery. However, when the thickness of the first insulating coating is less than 10 μm, the insulation effect of the first insulating coating decreases. When the thickness of the first insulating coating is greater than 45 μm, stress concentration will be more pronounced at the interface between the first outer tab and the area without the first insulating coating, leading to a lower drop test pass rate for the secondary battery. Furthermore, it can easily result in a significant loss of energy density in the secondary battery. Conversely, when the thickness of the first insulating coating is between 10 μm and 30 μm, it offers better drop safety and insulation performance.

[0097] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A secondary battery, comprising a casing, an electrolyte, an electrode assembly, and a first conductive element, wherein the electrolyte and the electrode assembly are housed within the casing, the electrode assembly comprising a first electrode plate and a plurality of first tabs connected to the first electrode plate; in the thickness direction of the electrode assembly, the plurality of first tabs are stacked and connected to the first conductive element, the first conductive element extending out of the casing; Its features are, The first electrode tab includes a first outer electrode tab and a first inner electrode tab. The first electrode tab located on the outermost layer of the stack is the first outer electrode tab, and the first electrode tab located on the inner layer of the stack is the first inner electrode tab. Along the extending direction of the first outer electrode tab, the first outer electrode tab includes a first connecting portion, a first bending portion, and a first welding portion connected in sequence. The first connecting portion is connected to the first electrode sheet, and the first welding portion is connected to the first conductive element. A first insulating coating is provided on the surface of the first connecting portion in the thickness direction. Along the extending direction of the first outer electrode tab, the first insulating coating extends beyond the first connecting portion.

2. The secondary battery according to claim 1, characterized in that, The first insulating coating is provided on the surface of the first outer electrode facing the first inner electrode.

3. The secondary battery according to any one of claims 1 or 2, characterized in that, The first insulating coating is provided on both opposite surfaces of the first outer tab in the thickness direction.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The first welding part is welded to the first conductive element and forms a first solder mark; along the extension direction of the first outer electrode, the distance between the first insulating coating and the first solder mark is T1, where T1 ≥ 0.5 mm.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The first insulating coating comprises ceramic insulating particles and an adhesive.

6. The secondary battery according to claim 5, characterized in that, The ceramic insulating particles include boehmite and / or alumina.

7. The secondary battery according to any one of claims 1 to 4, characterized in that, The first insulating coating comprises at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The thickness of the first insulating coating is 5 μm to 45 μm.

9. The secondary battery according to claim 8, characterized in that, The thickness of the first insulating coating is 10 μm to 45 μm.

10. The secondary battery according to claim 9, characterized in that, The thickness of the first insulating coating is 10 μm to 30 μm.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The first electrode is a cathode electrode, and the first electrode tab is a cathode tab.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, Along the extending direction of the first inner electrode tab, the first inner electrode tab includes a second connecting portion, a second bending portion, and a second welding portion connected in sequence. The second connecting portion is connected to the first electrode plate, and the second welding portion is connected to the first conductive element. A second insulating coating is provided on the surface of the second connecting portion in the thickness direction. Along the extending direction of the first inner electrode tab, the second insulating coating extends beyond the second connecting portion.

13. The secondary battery according to claim 12, characterized in that, The second welding part is welded to the first conductive element and forms a second solder mark; along the extension direction of the first inner electrode, the distance between the second insulating coating and the second solder mark is T2, where T2 ≥ 0.5 mm.

14. The secondary battery according to any one of claims 12 or 13, characterized in that, The second insulating coating comprises ceramic insulating particles and an adhesive.

15. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 14.

Images