Secondary battery and electronic device

Abstract

The present application relates to a secondary battery and an electronic device. The secondary battery comprises a casing, an electrolyte, an electrode assembly, and a first conductive member, wherein the electrolyte and the electrode assembly are accommodated in the casing; 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 bent in the thickness direction of the electrode assembly and are connected to the first conductive member; and the first conductive member extends out of the casing. The first tabs include a first outer tab, the first tab located at the outermost layer of the stack is the first outer tab, a first insulating coating layer is provided on one surface of the first outer tab in the thickness direction, and a second insulating coating layer is provided on the surface of the first outer tab facing away from the first insulating coating layer. In the direction of extension of the first outer tab, the length of the first insulating coating layer is L1, and the length of the second insulating coating layer is L2, wherein L1>L2. The secondary battery and the electronic device of the present application can ameliorate the problem of tab fracture 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. The plurality of first tabs are stacked and bent in the thickness direction of the electrode assembly and connected to the first conductive element, which extends out of the casing. Each first tab includes a first outer tab, with the outermost first tab being the first outer tab. 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 sequentially. 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 disposed on one surface of the first connecting portion in the thickness direction, and a second insulating coating is disposed on the surface of the first connecting portion opposite to the first insulating coating. Along the extending direction of the first outer tab, the length of the first insulating coating is L1, and the length of the second insulating coating is L2, where L1 > L2.

[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 the energy of the first electrode plate to the outside of the housing. Stacking multiple first tabs can reduce the space occupied by the first tabs. By providing a first insulating coating on one surface of the first outer tab in the thickness direction, and providing a second insulating coating on the surface of the first outer tab away from the first insulating coating, the possibility of electrical connection between the first outer tab and the housing, other tabs, and other electrodes can be reduced. Stress concentration will occur at the junction of the first outer tab where the insulating coating is provided and where the insulating coating is not provided. When the length L1 of the first insulating coating and the length L2 of the second insulating coating are the same, the junction where the first insulating coating is provided and where the first insulating coating is not provided coincides with the junction where the second insulating coating is provided and where the second insulating coating is not provided in the thickness direction of the first outer tab. Therefore, there will be a large stress concentration at this junction, and the maximum stress concentration point is located at this junction, making the first outer tab prone to breakage and failure at this junction. By setting the length L1 of the first insulating coating to be greater than the length L2 of the second insulating coating, the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction will not coincide in the thickness direction of the first outer electrode. Stress concentration will occur at each of the two junctions, and the stress at the stress concentration point will be reduced, which can improve the problem of first outer electrode fracture failure. Although adhesive paper can also insulate the first outer electrode by bonding it to the surface in the thickness direction of the first outer electrode, the adhesion of the adhesive paper will decrease when it is wetted by the electrolyte. The adhesive paper may slide relative to the electrode or even fall off, and the supporting effect of the adhesive paper is poor. Furthermore, when the first insulating coating or the second insulating coating extends beyond the first connecting portion, setting the length L1 of the first insulating coating to be greater than the length L2 of the second insulating coating does not significantly improve the problem of the first outer tab breaking. Also, the first bending portion will bend during the insertion of the first tab into the housing. If the first insulating coating or the second insulating coating extends beyond the first connecting portion, part of the first insulating coating or part of the second insulating coating will be located on the surface of the first bending portion. Since the first insulating coating and the second insulating coating are relatively hard, the first insulating coating or the second insulating coating is prone to breakage during the bending process of the first bending portion. The breakage of the first insulating coating or the second insulating coating can easily lead to the breakage of the first tab. Therefore, it is preferable that the first insulating coating is located on one surface of the first connecting portion in the thickness direction, and the second insulating coating is provided on the surface of the first connecting portion away from the first insulating coating, that is, the first insulating coating and the second insulating coating do not extend beyond the first connecting portion.

[0007] In some preferred embodiments, the first weld portion is welded to the first conductive element, forming a first solder mark. 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. This reduces the likelihood of the first insulating coating approaching the first solder mark, thereby reducing the possibility that the first insulating coating will affect the welding effect between the first weld portion and the first conductive element.

[0008] In some preferred embodiments, the distance between the second insulating coating and the first solder mark along the extension direction of the first outer tab is T2, where T2 ≥ 0.5 mm. This reduces the possibility that the second insulating coating may approach the first solder mark, thereby reducing the possibility that the second insulating coating may affect the welding effect between the first weld and the first conductive component.

[0009] In some preferred embodiments, L2 ≥ 0.5 mm, which is beneficial to improving the insulation effect of the second insulating coating on the first outer electrode.

[0010] In some preferred embodiments, L2≤0.9L1 can reduce the possibility that the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the second ... second

[0011] In some preferred embodiments, L1-L2≥0.5mm can further reduce the possibility that the junction where the first insulating coating is provided and the junction where the second insulating coating is provided and the junction where the second insulating coating is provided coincide in the thickness direction of the first outer electrode.

[0012] In some preferred embodiments, L1-L2 ≤ 2 mm. A larger difference in length between the first insulating coating and the second insulating coating results in a longer first insulating coating and a shorter second insulating coating. This makes it easier for the first insulating coating to extend beyond the first connecting portion and for the second insulating coating to be shorter than 0.5 mm. Consequently, the insulation performance of both the first and second insulating coatings to the first outer tab decreases. By setting L1-L2 ≤ 2 mm, the likelihood of the first insulating coating extending beyond the first connecting portion and the likelihood of the second insulating coating being shorter than 0.5 mm can be reduced, thus improving the insulation performance of both the first and second insulating coatings to the first outer tab. In some preferred embodiments, L1 ≤ 4 mm. A longer first insulating coating results in a shorter area on the surface of the first outer tab without an insulating coating. This reduces the deformable space of the first outer tab, leading to a poorer stress buffering effect and a higher probability of breakage. L1 ≤ 4 mm increases the deformable space of the first outer tab, thereby reducing the probability of breakage.

[0013] In some preferred embodiments, L1≤3mm, which helps to further increase the deformable space of the first outer electrode, thereby further reducing the possibility of the first outer electrode breaking.

[0014] In some preferred embodiments, a first insulating coating is provided on the surface of the first outer tab facing the inner layer of the stack. Since the first outer tab is located on the outermost layer of the stack, if the first insulating coating is provided on the surface of the first outer tab away from the inner layer of the stack, the first insulating coating is likely to form a fulcrum, and the first outer tab is likely to bend relative to the fulcrum and break. Therefore, by providing a first insulating coating on the surface of the first outer tab facing the inner layer of the stack, it is beneficial to reduce the possibility of the first outer tab bending and breaking.

[0015] In some preferred embodiments, a first insulating coating is provided on the surface of the first outer tab away from the inner layer of the laminate. If the first insulating coating is provided on the surface of the first outer tab facing the inner layer of the laminate, the insulation performance of the surface of the first outer tab away from the inner layer of the laminate is reduced. By providing a first insulating coating on the surface of the first outer tab away from the inner layer of the laminate, it is beneficial to improve the insulation performance of the surface of the first outer tab away from the inner layer of the laminate.

[0016] 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.

[0017] In some preferred embodiments, the first insulating coating and the second insulating coating each independently comprise ceramic insulating particles and a binder. The ceramic insulating particles have high strength, which can improve the support effect of the first insulating coating and the second insulating coating.

[0018] In some preferred embodiments, the ceramic insulating particles include boehmite and / or alumina, which can improve the strength of the ceramic insulating particles.

[0019] In some preferred embodiments, the thickness of the first insulating coating is between 5 μm and 45 μm. A thickness ≥ 5 μm of the first insulating coating is beneficial for improving the insulation effect of the first insulating coating on the first outer electrode. A thickness ≤ 45 μm of the first insulating coating is beneficial for reducing the possibility of the first insulating coating losing energy density of the secondary battery.

[0020] In some preferred embodiments, the thickness of the second insulating coating is from 5 μm to 45 μm. A thickness of ≥5 μm in the second insulating coating is beneficial for improving the insulation effect of the second insulating coating on the first outer electrode. A thickness of ≤45 μm in the second insulating coating is beneficial for reducing the possibility of the second insulating coating losing energy density of the secondary battery.

[0021] In some preferred embodiments, the first electrode is a positive electrode, and the first tab is a positive tab. Since the positive electrode is usually shorter than the negative electrode, the positive tab can easily come into contact with the negative electrode. By providing an insulating coating on the surface of the positive tab in the thickness direction, the possibility of electrical connection between the positive tab and the negative electrode can be reduced.

[0022] In some preferred embodiments, the first electrode tab further includes a first inner electrode tab. The first electrode tab located in the inner layer of the stack is the first inner electrode tab. The surface of the first inner electrode tab is provided with a third insulating coating, which can reduce the possibility of the first inner electrode tab becoming electrically connected to the shell, other electrode tabs, and other electrode plates. Among them, all first electrode tabs other than the first outer electrode tab are first inner electrode tabs.

[0023] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0024] 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

[0025] 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.

[0026] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0027] Figure 2 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0028] Figure 3 is a schematic diagram of the structure of an electrode assembly according to some embodiments of this application;

[0029] Figure 4 is a schematic diagram of the structure of an electrode assembly according to some embodiments of this application;

[0030] 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;

[0031] 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;

[0032] Figure 7 is a schematic diagram of the unfolded structure of the first tab and the first conductive element according to some embodiments of this application.

[0033] 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 part; 2414, first solder mark; 242, first inner tab; 25, second tab; 26, first insulating coating; 27, second insulating coating; 28, third insulating coating; 30, first conductive element; 40, second conductive element. Detailed Implementation

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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".

[0039] 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.

[0040] 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 electrolyte (not shown in the figure), 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 the electrolyte, with the electrolyte wetting 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.

[0041] 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.

[0042] 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.

[0043] In some embodiments, the first current collector 211 may be an aluminum foil or a copper foil.

[0044] 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 positive electrode active material, a conductive agent, a binder, 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 positive electrode 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.

[0045] In some embodiments, referring to Figures 2, 3, and 4, the first current collector 211 is connected to a plurality of first tabs 24. The plurality of first tabs 24 are stacked and bent in the thickness direction of the electrode assembly 20 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.

[0046] 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. The plurality of second tabs 25 are stacked in the thickness direction of the electrode assembly 20 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.

[0047] 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 a negative electrode active material, a conductive agent, a binder, etc., and the above materials are mixed and stirred evenly and coated onto the surface of the second current collector 221 to obtain the second active layer 222. The negative electrode active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0048] In some embodiments, referring to Figures 2 and 5, the first electrode tab 24 includes a first outer electrode tab 241. The first electrode tab 24 located on the outermost layer of the stack is the first outer electrode tab 241. A first insulating coating 26 is provided on one surface of the first outer electrode tab 241 in the thickness direction, and a second insulating coating 27 is provided on the surface of the first outer electrode tab 241 facing away from the first insulating coating 26. This can reduce the possibility of the first outer electrode tab 241 being electrically connected to the housing 10, other electrode tabs, and other electrode sheets. During a drop, the electrode assembly 20 of the secondary battery 100 is prone to shifting within the housing 10. Due to the high hardness of the insulating coating, there is a large hardness difference between the insulating coating and the electrode tab. This hardness difference can lead to stress concentration. The hardness difference of the electrode tab is greatest at the interface between the insulating coating and the non-insulating coating. Stress concentration will occur at the interface between the insulating coating and the non-insulating coating of the first outer electrode tab 241. When the length L1 of the first insulating coating 26 and the length L2 of the second insulating coating 27 are the same, the junction where the first insulating coating 26 is provided and where the first insulating coating 26 is not provided coincides with the junction where the second insulating coating 27 is provided and where the second insulating coating 27 is not provided in the thickness direction of the first outer electrode 241. Therefore, there will be a large stress concentration at this junction, and the maximum stress concentration point is located at this junction. The first outer electrode 241 is prone to breakage and failure at this junction.

[0049] To improve the above problems, please refer to Figure 6. In the embodiment of this application, by setting the length L1 of the first insulating coating 26 to be greater than the length L2 of the second insulating coating 27, the junction between the first insulating coating 26 and the junction between the second insulating coating 27 and the junction between the first insulating coating 26 and the junction between the second insulating coating 27 and the junction between the first insulating coating 27 and the junction between the first insulating coating 27 and the junction between the first insulating coating 27 and the junction between the first insulating coating 27 and the junction between the first insulating coating 27 and the junction between the first insulating coating 26 ...

[0050] In some embodiments, along the extending direction of the first outer electrode 241, the first outer electrode 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 electrode 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 member 30, and a first insulating coating 26 is provided on one surface of the first connecting portion 2411 in the thickness direction. Stress concentration is likely to occur at the junction edge of the first connecting portion 2411 and the first bending portion 2412. When the first insulating coating 26 extends beyond the first connecting portion 2411, the first insulating coating 26 can cover the junction edge of the first connecting portion 2411 and the first bending portion 2412. The first insulating coating 26 can share the stress at the junction edge, thus improving the problem of the first outer tab 241 breaking. At this time, by setting the length L1 of the first insulating coating 26 to be greater than the length L2 of the second insulating coating 27, the improvement on the problem of the first outer tab 241 breaking is not obvious. Therefore, it is preferable that the first insulating coating 26 is located on the surface of the first connecting portion 2411, that is, the first insulating coating 26 does not extend beyond the first connecting portion 2411. Furthermore, during the insertion of the first tab 24 into the housing 10, the first bending portion 2412 will bend, and the first insulating coating 26 will extend beyond the first connecting portion 2411. Part of the first insulating coating 26 will be located on the surface of the first bending portion 2412. Since the first insulating coating 26 is relatively hard, it is easy for the first insulating coating 26 to break during the bending process of the first bending portion 2412. The breakage of the first insulating coating 26 can easily lead to the breakage of the first tab 24. By setting the first insulating coating 26 to be located on one surface of the first connecting portion 2411 in the thickness direction, that is, the first insulating coating 26 does not extend beyond the first connecting portion 2411, the possibility of the first insulating coating 26 breaking can be reduced, thereby reducing the possibility of the first tab 24 breaking.

[0051] In some embodiments, a second insulating coating 27 is provided on the surface of the first connecting portion 2411 facing away from the first insulating coating 26. If the second insulating coating 27 extends beyond the first connecting portion 2411, the second insulating coating 27 can cover the boundary edge between the first connecting portion 2411 and the first bending portion 2412. The second insulating coating 27 can share the stress at the boundary edge, thus improving the problem of the first outer tab 241 breaking. In this case, by setting the length L1 of the first insulating coating 26 to be greater than the length L2 of the second insulating coating 27, the improvement on the problem of the first outer tab 241 breaking is less significant. Therefore, it is preferable that the second insulating coating 27 is located on the surface of the first connecting portion 2411, that is, the second insulating coating 27 does not extend beyond the first connecting portion 2411. Furthermore, during the insertion of the first tab 24 into the housing 10, the first bending portion 2412 will bend, and the second insulating coating 27 will extend beyond the first connecting portion 2411. Part of the second insulating coating 27 will be located on the surface of the first bending portion 2412. Since the second insulating coating 27 is relatively hard, it is easy for the second insulating coating 27 to break during the bending process of the first bending portion 2412. The breakage of the second insulating coating 27 can easily lead to the breakage of the first tab 24. By setting the second insulating coating 27 on the surface of the first connecting portion 2411 away from the surface of the first insulating coating 26, that is, the second insulating coating 27 does not extend beyond the first connecting portion 2411, the possibility of the second insulating coating 27 breaking can be reduced, thereby reducing the possibility of the first tab 24 breaking.

[0052] In some embodiments, referring to Figures 6 and 7, the first weld portion 2413 is welded to the first conductive element 30, forming a first solder mark 2414. 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. This reduces the likelihood of the first insulating coating 26 approaching the first solder mark 2414, thereby reducing 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.

[0053] In some embodiments, along the extending direction of the first outer tab 241, the distance between the second insulating coating 27 and the first solder mark 2414 is T2, where T2 ≥ 0.5 mm. This can reduce the possibility that the second insulating coating 27 is close to the first solder mark 2414, thereby reducing the possibility that the second insulating coating 27 will affect the welding effect between the first weld portion 2413 and the first conductive element 30.

[0054] In some embodiments, L2≥0.5mm is beneficial to improving the insulation effect of the second insulating coating 27 on the first outer tab 241.

[0055] In some embodiments, L2≤0.9L1 can reduce the likelihood that the junction of the first insulating coating 26 and the junction of the second insulating coating 27 and the junction of the second insulating coating 27 coincides in the thickness direction of the first outer tab 241, which can further reduce the stress at the maximum stress concentration point of the first outer tab 241, thereby improving the problem of fracture failure of the first outer tab 241.

[0056] In some embodiments, L1-L2≥0.5mm can further reduce the possibility that the junction of the first insulating coating 26 and the junction of the second insulating coating 27 and the junction of the second insulating coating 27 coincides in the thickness direction of the first outer tab 241.

[0057] In some embodiments, L1-L2 ≤ 2 mm. The greater the length difference between the first insulating coating 26 and the second insulating coating 27, the longer the first insulating coating 26 will be, and the shorter the second insulating coating 27 will be. The first insulating coating 26 is more likely to extend beyond the first connecting portion 2411, and the length of the second insulating coating 27 is more likely to be less than 0.5 mm. The insulation performance of the first insulating coating 26 and the second insulating coating 27 to the first outer tab 241 will be reduced. By setting L1-L2 ≤ 2 mm, the possibility of the first insulating coating 26 extending beyond the first connecting portion 2411 can be reduced, and the possibility of the length of the second insulating coating 27 being less than 0.5 mm can be reduced, thereby improving the insulation performance of the first insulating coating 26 and the second insulating coating 27 to the first outer tab 241.

[0058] In some embodiments, L1 ≤ 4 mm. The longer the length of the first insulating coating 26, the shorter the length of the area on the surface of the first outer tab 241 without the insulating coating, the smaller the deformable space of the first outer tab 241, the worse the stress buffering effect of the first outer tab 241, and the greater the possibility of the first outer tab 241 breaking. L1 ≤ 4 mm can increase the deformable space of the first outer tab 241, thereby reducing the possibility of the first outer tab 241 breaking.

[0059] In some embodiments, L1≤3mm, which helps to further increase the deformable space of the first outer electrode 241, thereby further reducing the possibility of the first outer electrode 241 breaking.

[0060] In some embodiments, a first insulating coating 26 is provided on the surface of the first outer tab 241 facing the inner layer of the stack. Since the first outer tab 241 is located on the outermost layer of the stack, if the first insulating coating 26 is provided on the surface of the first outer tab 241 away from the inner layer of the stack, the first insulating coating 26 is likely to form a fulcrum, and the first outer tab 241 is likely to bend relative to the fulcrum and break. Therefore, by providing the first insulating coating 26 on the surface of the first outer tab 241 facing the inner layer of the stack, it is beneficial to reduce the possibility of the first outer tab 241 bending and breaking.

[0061] In some embodiments, a first insulating coating 26 is provided on the surface of the first outer tab 241 facing away from the inner layer of the stack. If the first insulating coating 26 is provided on the surface of the first outer tab 241 facing the inner layer of the stack, there is a problem of reduced insulation performance on the surface of the first outer tab 241 facing away from the inner layer of the stack. By providing the first insulating coating 26 on the surface of the first outer tab 241 facing away from the inner layer of the stack, it is beneficial to improve the insulation performance of the surface of the first outer tab 241 facing away from the inner layer of the stack.

[0062] 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.

[0063] In some embodiments, the first insulating coating 26 and the second insulating coating 27 each independently include 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 and the second insulating coating 27.

[0064] In some embodiments, the ceramic insulating particles include boehmite and / or alumina, which can enhance the strength of the ceramic insulating particles.

[0065] In some embodiments, the second insulating coating 27 comprises at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide, which can improve the insulating effect of the second insulating coating 27.

[0066] In some embodiments, the thickness H1 of the first insulating coating 26 is 5 μm to 45 μm. A thickness ≥ 5 μm of the first insulating coating 26 is beneficial for improving the insulation effect of the first insulating coating 26 on the first outer tab 241. A thickness ≤ 45 μm of the first insulating coating 26 is beneficial for reducing the possibility of the first insulating coating 26 losing energy density of the secondary battery 100.

[0067] In some embodiments, the thickness H2 of the second insulating coating 27 is 5 μm to 45 μm. A thickness ≥ 5 μm of the second insulating coating 27 is beneficial for improving the insulation effect of the second insulating coating 27 on the first outer tab 241. A thickness ≤ 45 μm of the second insulating coating 27 is beneficial for reducing the possibility of the second insulating coating 27 losing energy density of the secondary battery 100.

[0068] 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 outer electrode 241. 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.

[0069] In some embodiments, the first electrode 21 is a positive electrode, and the first tab 24 is a positive tab. Since the positive electrode is usually shorter than the negative electrode, the positive tab can easily come into contact with the negative electrode. By providing an insulating coating on the surface of the positive tab in the thickness direction, the possibility of electrical connection between the positive tab and the negative electrode can be reduced.

[0070] In some embodiments, the first electrode tab 24 further includes a first inner electrode tab 242. The first electrode tab 24 located in the inner layer of the stack is the first inner electrode tab 242. The surface of the first inner electrode tab 242 is provided with a third insulating coating 28, which can reduce the possibility of the first inner electrode tab 242 being electrically connected to the housing 10, other electrode tabs, and other electrode plates. Among them, all first electrode tabs 24 except for the first outer electrode tab 241 are first inner electrode tabs 242.

[0071] In some embodiments, all third insulating coatings 28 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 third insulating coating 28 may be different.

[0072] 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.

[0073] Test section:

[0074] 1. Drop test of secondary batteries:

[0075] 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)). The drop test pass standard is: after removing the battery cell from the casing, observe the surface of the tabs for cracks using SEM (scanning electron microscope). If there are cracks on the surface of the tabs, the drop test fails.

[0076] Example 1

[0077] <Preparation of the first electrode>:

[0078] The first electrode is the positive electrode. The positive electrode active materials lithium cobalt oxide (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt% and stirred evenly.

[0079] 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 the first electrode tab.

[0080] <Preparation of the Second Electrode>:

[0081] The second electrode is the negative electrode. The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:2:2, deionized water is added as a solvent, and a slurry with a solid content of 70wt% is prepared and stirred evenly.

[0082] 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 second electrode tab.

[0083] <Preparation of the diaphragm>:

[0084] 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%.

[0085] <Electrolyte Preparation>:

[0086] 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%.

[0087] <Preparation of Secondary Batteries>:

[0088] The first electrode, the diaphragm, and the second electrode are stacked in sequence, with the diaphragm positioned between the first electrode to act as a separator. The stacked electrodes form the electrode assembly.

[0089] 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 of the stack is the first inner tab. All other first tabs except the first outer tab are first inner 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 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 and forms 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. The outer surface of the first connecting portion is coated with alumina particles and adhesive slurry to form a 25μm thick first insulating coating. Along the extension direction of the first outer tab, the first insulating coating does not extend beyond the first connecting portion. The length L1 of the first insulating coating is 2.5 mm, and the distance T1 between the first insulating coating and the first welding portion is 2.5 mm. The inner surface of the first connecting portion is coated with alumina particles and adhesive slurry to form a 25 μm thick second insulating coating. Along the extension direction of the first outer tab, the second insulating coating does not extend beyond the first connecting portion. The length L2 of the second insulating coating is 2 mm, and the distance T2 between the second insulating coating and the first welding portion is 3 mm.

[0090] Both opposing surfaces of the first inner tab are coated with alumina particles and binder slurry to form a 25 μm thick third insulating coating. The length of the third insulating coating is 2 mm along the extension direction of the first inner tab.

[0091] 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.

[0092] The relevant parameters in Comparative Examples 1 and 3, as well as Examples 1 to 7, are shown in Table 1 below.

[0093] In Comparative Examples 1 and 2, the lengths L1 and L2 of the first insulating coating are the same. In Comparative Example 3 and Examples 1 to 7, the length L1 of the first insulating coating is greater than the length L2 of the second insulating coating. In Comparative Examples 2 and 3, the first insulating coating extends beyond the first connecting portion. In Example 2, the first insulating coating is located on the surface (inner surface) of the first outer electrode ear facing the first inner electrode ear.

[0094] Table 1

[0095] According to Table 1 above, and in conjunction with Comparative Example 1 and Examples 1 to 7, the first outer electrode has a first insulating coating and a second insulating coating on its two opposing surfaces. Stress concentration occurs at the interface between the insulating coating and the non-insulating coating on the first outer electrode. When the length L1 of the first insulating coating and the length L2 of the second insulating coating are the same, the interface between the first insulating coating and the non-insulating coating coincides with the interface between the second insulating coating and the non-insulating coating in the thickness direction of the first outer electrode. Therefore, there is significant stress concentration at this interface, and the maximum stress concentration point is located at this interface. The first outer electrode is prone to breakage and failure at this interface, resulting in a low drop test pass rate for the secondary battery and poor safety performance. By setting the length L1 of the first insulating coating to be greater than the length L2 of the second insulating coating, the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the second insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the first insulating coating and the junction between the second ...

[0096] As can be seen from Comparative Examples 1 and 2, as well as Comparative Examples 3 and Example 5, the drop test pass rate is higher when the first insulating coating extends beyond the first connecting portion. This is because stress concentration easily occurs at the boundary edge between the first connecting portion and the first bending portion. When the first insulating coating extends beyond the first connecting portion, it can cover the boundary edge, thus sharing the stress and improving the problem of first outer tab breakage. As can be seen from Comparative Examples 2 and 3, the secondary battery has a higher drop test pass rate when the first insulating coating extends beyond the first connecting portion. While setting the length L1 of the first insulating coating to be greater than the length L2 of the second insulating coating can also improve the problem of first outer tab breakage, this improvement is difficult to reflect in the drop test pass rate of the secondary battery.

[0097] When the length of the first insulating coating is less than 0.5 mm, the insulation effect of the first insulating coating on the first outer electrode tab will be poor. Therefore, it is preferable that the length of the first insulating coating L1 ≥ 0.5 mm. When the length of the first insulating coating is long, the first insulating coating is likely to be close to the first solder mark, which may affect the welding effect between the first welded part and the first conductive component. It is preferable that the distance T1 between the first insulating coating and the first solder mark is ≥ 0.5 mm, which can reduce the possibility that the first insulating coating will affect the welding effect between the first welded part and the first conductive component. Similarly, it is preferable that the length of the second insulating coating L2 ≥ 0.5 mm, and preferably that the distance T2 between the second insulating coating and the first solder mark is ≥ 0.5 mm.

[0098] As can be seen from Examples 3 to 6, the larger the difference between the length L1 of the first insulating coating and the length L2 of the second insulating coating, the less likely the junction between the first insulating coating and the junction between the second insulating coating and ... However, the greater the length difference between the first and second insulating coatings, the longer the first insulating coating will be, and the shorter the second insulating coating will be. This makes it easier for the first insulating coating to extend beyond the first connection portion, and for the length of the second insulating coating to be less than 0.5 mm. Consequently, the insulation performance of both the first and second insulating coatings to the first outer tab will decrease. Preferably, L1-L2 ≤ 2 mm, which can reduce the likelihood of a large length difference between the first and second insulating coatings and improve their insulation performance to the first outer tab.

[0099] Based on embodiments 1, 5, and 7, it can be seen that the larger the maximum length of the insulating coating on the surface of the first outer tab (the larger of L1 and L2), the shorter the length of the area on the surface of the first outer tab without an insulating coating, the smaller the deformable space of the first outer tab, the worse the stress buffering effect of the first outer tab, the greater the possibility of the first outer tab breaking, and the lower the drop test pass rate of the secondary battery. Preferably, L1 ≤ 4mm, which can increase the deformable space of the first outer tab, thereby reducing the possibility of the first outer tab breaking. More preferably, L1 ≤ 3mm, which is beneficial to further increase the deformable space of the first outer tab, thereby further reducing the possibility of the first outer tab breaking. In addition, when L1 is greater than 3mm, the first insulating coating will extend beyond the first connection part.

[0100] As can be seen from Examples 1 and 2, compared to having the first insulating coating disposed on the surface of the first outer tab away from the inner layer of the stack, the secondary battery has a better drop test pass rate by disposing of the first insulating coating on the surface of the first outer tab facing the inner layer of the stack. Therefore, it is preferable that the first insulating coating is located on the surface of the first outer tab facing the inner layer of the stack. However, if the first insulating coating is disposed on the surface of the first outer tab facing the inner layer of the stack, the insulation performance of the surface of the first outer tab away from the inner layer of the stack is reduced. Therefore, considering the insulation performance, it is preferable that the first insulating coating is disposed on the surface of the first outer tab away from the inner layer of the stack.

[0101] The relevant parameters for Examples 1 and 8 to 13 are shown in Table 2 below. The only difference between Examples 1 and 8 to 13 is the thickness of the first insulating coating.

[0102] Table 2

[0103] Based on Examples 1 and 9 to 14 in Table 2 above, it can be seen that when the thickness of the first insulating coating is between 5 μm and 45 μm, the drop safety is relatively good. 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 outer tab where the first insulating coating is applied and where it is not. 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, resulting in better improvement in preventing breakage of the first outer tab and a higher drop test pass rate for the secondary battery. However, when the thickness of the first insulating coating is less than 5 μm, the insulation effect of the first insulating coating decreases. When the thickness of the first insulating coating is greater than 45 μm, the stress concentration at the interface between the first and non-first insulating coatings on the first outer tab is more pronounced, reducing the drop test pass rate of the secondary battery and potentially leading to a significant loss of energy density. Since the second insulating coating has similar properties to the first insulating coating, the preferred thickness of the second insulating coating is the same as that of the first insulating coating.

[0104] 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, the plurality of first tabs being stacked and bent in the thickness direction of the electrode assembly 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 the first electrode tab located on the outermost layer of the stack is the first outer 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, the first welding portion is connected to the first conductive element, a first insulating coating is provided on one surface of the first connecting portion in the thickness direction, and a second insulating coating is provided on the surface of the first connecting portion opposite to the first insulating coating; along the extending direction of the first outer electrode tab, the length of the first insulating coating is L1, the length of the second insulating coating is L2, and L1>L2.

2. The secondary battery according to claim 1, 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.

3. The secondary battery according to claim 2, characterized in that, Along the extending direction of the first outer tab, the distance between the second insulating coating and the first solder mark is T2, where T2 ≥ 0.5 mm.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, L2≥0.5mm.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, L2≤0.9L1.

6. The secondary battery according to claim 5, characterized in that, L1-L2≥0.5mm.

7. The secondary battery according to claim 5 or 6, characterized in that, L1-L2≤2mm.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, L1≤4mm.

9. The secondary battery according to claim 8, characterized in that, L1≤3mm.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The first outer tab has the first insulating coating on its surface facing the inner layer of the stack.

11. The secondary battery according to any one of claims 1 to 9, characterized in that, The first insulating coating is provided on the surface of the first outer electrode ear away from the inner layer of the stack.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The first insulating coating comprises at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide.

13. The secondary battery according to any one of claims 1 to 11, characterized in that, The first insulating coating and the second insulating coating each independently comprise ceramic insulating particles and a binder.

14. The secondary battery according to claim 13, characterized in that, The ceramic insulating particles include boehmite and / or alumina.

15. The secondary battery according to any one of claims 1 to 14, characterized in that, The thickness of the first insulating coating is 5 μm to 45 μm; and / or, the thickness of the second insulating coating is 5 μm to 45 μm.

16. The secondary battery according to any one of claims 1 to 15, characterized in that, The first electrode is a positive electrode, and the first tab is a positive tab.

17. The secondary battery according to any one of claims 1 to 16, characterized in that, The first electrode also includes a first inner electrode, which is located in the inner layer of the stack. The surface of the first inner electrode is provided with a third insulating coating.

18. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 17.

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