Secondary battery and electrical device

Abstract

A secondary battery (72) and an electrical device. The secondary battery (72) comprises a casing (1), an electrode assembly (17) provided in the casing (1), and a first tab (23). The electrode assembly (17) comprises a first electrode sheet (20), and the first tab (23) is connected to the first electrode sheet (20). The secondary battery (72) further comprises a first current guide member (42) and a first insulating protection layer (60). At least part of the first current guide member (42) is provided in the casing (1). The first current guide member (42) comprises a first connecting region (50), at least one second connecting region (51), and a third connecting region (52), and the second connecting region (51) is connected between the first connecting region (50) and the third connecting region (52). The first connecting region (50) is connected to the first tab (23). The third connecting region (52) is connected to the casing (1). The minimum cross-sectional area of the second connecting region (51) in the thickness direction of the second connecting region (51) is S1, the cross-sectional area of the third connecting region (52) in the thickness direction of the third connecting region (52) is S2, and the at least one second connecting region (51) satisfies: 0.1S2≤S1≤0.5S2. The first insulating protection layer (60) at least covers the surface of the second connecting region (51). The first insulating protection layer (60) comprises a first polymer, and the melting point of the first polymer is 100°C to 170°C.

Description

Secondary batteries and electrical appliances Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and an electrical device having the secondary battery. Background Technology

[0002] With the widespread use of secondary batteries (such as lithium-ion batteries) in electronic mobile devices, power tools, and electric vehicles, people have increasingly stringent requirements for secondary batteries (such as lithium-ion secondary batteries).

[0003] However, secondary batteries may short-circuit during operation, causing the internal temperature to rise continuously and leading to safety issues. Furthermore, if a large current discharge, micro-short circuit, or high ambient temperature occurs inside the secondary battery, even if the internal temperature may not reach the high temperature required for a short circuit, safety hazards still exist, and continued use will result in safety problems.

[0004] Summary of the Invention

[0005] In view of this, it is necessary to provide a secondary battery that can improve safety and reliability, and an electrical device having the above-mentioned secondary battery.

[0006] This application provides a secondary battery, including a housing, an electrode assembly disposed within the housing, and a first tab. The electrode assembly includes a first electrode plate, and the first tab is connected to the first electrode plate. The secondary battery also includes a first current-conducting element and a first insulating protective layer. At least a portion of the first current-conducting element is disposed within the housing. The first current-conducting element includes a first connecting region, at least one second connecting region, and a third connecting region, with the second connecting region connected between the first connecting region and the third connecting region. The first connecting region is connected to the first tab. The third connecting region is connected to the housing. The minimum cross-sectional area of ​​the second connecting region along its thickness direction is S1, and the cross-sectional area of ​​the third connecting region along its thickness direction is S2, wherein at least one second connecting region satisfies: 0.1S2≤S1≤0.5S2. The first insulating protective layer at least covers the surface of the second connecting region. The first insulating protective layer includes a first polymer, the first polymer having a melting point of 100 degrees Celsius to 170 degrees Celsius.

[0007] In this application, when the secondary battery is operating normally, the first insulating protective layer can cover the second connection area, which has a smaller minimum cross-sectional area. This protects the second connection area from mechanical abuse, reducing the risk of breakage. By setting the relationship between S1 and S2, when a short circuit occurs in the secondary battery, the second connection area can preferentially melt under the influence of the short-circuit current, disconnecting the first tab from external components and reducing safety issues caused by continued temperature increases. It also reduces the impact of the second connection area melting during normal operation on the battery's lifespan. On the other hand, when the internal temperature of the secondary battery reaches the melting point of the first polymer (e.g., when the ambient temperature is high and there is a safety hazard), the first polymer melts promptly, weakening or even eliminating the protective effect of the first insulating protective layer on the second connection area. This makes the second connection area more susceptible to breakage during mechanical abuse, preventing the secondary battery with potential safety hazards from continuing to operate. Therefore, the combined effect of the second connection area and the first insulating protective layer improves the safety and reliability of the secondary battery.

[0008] Based on the first aspect, in some possible implementations, the electrode assembly further includes a separator, wherein the melting point of the first polymer is less than or equal to the melting point of the separator. This allows the first polymer to melt before or simultaneously with the separator when a short circuit occurs in the secondary battery, reducing the risk of the short circuit being exacerbated by the preferential melting of the separator.

[0009] Based on the first aspect, in some possible implementations, the material of the first polymer is selected from at least one of polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene modified material, or polyethylene modified material.

[0010] Based on the first aspect, in some possible implementations, the first insulating protective layer also covers a portion of the surface of the first connection region and a portion of the surface of the third connection region. Thus, during normal operation of the secondary battery, the first insulating protective layer can adequately protect the second connection region, reducing the risk of breakage of the second connection region in the event of mechanical abuse.

[0011] Based on the first aspect, in some possible implementations, at least one second connection region satisfies: 0.2S² ≤ S₁ ≤ 0.4S². Thus, the second connection region is more sensitive under short-circuit current and high temperature, not only able to melt promptly when a short circuit occurs in the secondary battery, but also more easily broken during mechanical abuse after the first polymer melts due to safety hazards in the secondary battery, thereby further improving the safety of the secondary battery. Furthermore, during normal operation of the secondary battery, the impact of the melting of the second connection region on the battery's lifespan can be further reduced.

[0012] Based on the first aspect, in some possible implementations, viewed along the thickness direction of the second connection region, the second connection region includes a first side and a second side disposed opposite to each other. Both the first and second sides connect the first connection region and the third connection region. The first side is curved. The first side includes a first endpoint connected to the first connection region, a second endpoint connected to the third connection region, and a top located between the first and second endpoints. The top is recessed towards the interior of the second connection region relative to both the first and second endpoints. This ensures that when a short circuit occurs in the secondary battery, the second connection region preferentially melts at the location corresponding to the top.

[0013] Based on the first aspect, in some possible implementations, the first side is at least partially polygonal. Thus, when the protective effect of the first insulating layer on the second connection region weakens or even disappears, the second connection region is more prone to breakage during mechanical abuse, preventing the potentially hazardous secondary battery from continuing to operate.

[0014] Based on the first aspect, in some possible implementations, the thickness of the second connection region is less than the thickness of either the first or third connection region. This results in a smaller minimum cross-sectional area for each second connection region.

[0015] Based on the first aspect, in some possible implementations, the first connection region, the second connection region, and the third connection region are integrated into a single structure. This reduces the risk of the second connection region breaking under mechanical abuse during normal operation of the secondary battery.

[0016] Based on the first aspect, in some possible implementations, the housing is a packaging bag comprising a connected receiving portion and a sealing edge, the electrode assembly being received within the receiving portion, at least a portion of the second connection area being located within the sealing edge, within the receiving portion, or outside the housing, and at least a portion of the third connection area extending out of the housing. The first insulating protective layer comprises a first layer and a second layer stacked together. The first layer comprises the aforementioned first polymer. The second layer comprises a second polymer, and the melting point of the second polymer is 160 to 170 degrees Celsius. The second layer is connected to the sealing edge and the first layer, respectively. This allows the third connection area to connect to external components, and the second layer of the first insulating protective layer has high sealing performance, reducing the risk of leakage during use and the risk of separation between the first flow guide and the sealing edge, while also maintaining electrical insulation between the first flow guide and the housing.

[0017] Based on the first aspect, in some possible implementations, the first connection region, the second connection region, and the third connection region are coplanar.

[0018] Based on the first aspect, in some possible implementations, the first connection region includes a first partition connected to the second connection region and a second partition connected to the first partition. The second connection region, the third connection region, and the first partition are coplanar. The second partition is bent relative to the first partition. The second partition is connected to the first tab. Since the bend of the first guide member is located in the first connection region rather than the second connection region, the risk of the second connection region, with its smaller minimum cross-sectional area, easily breaking under mechanical abuse is reduced when the secondary battery is operating normally.

[0019] Based on the first aspect, in some possible implementations, the housing is a metal housing, comprising a first end wall and a second end wall disposed opposite each other, a side wall connecting the first end wall and the second end wall, and a first electrode post disposed on the first end wall. The first electrode post is electrically isolated from the first end wall. A third connection region is connected to the first electrode post. In this way, the first electrode post can have the same polarity as the first electrode plate.

[0020] Based on the first aspect, in some possible implementations, the electrode assembly is a wound structure. The first electrode includes a first current collector. The first current collector includes a first end edge facing a first end wall, and a first tab extends from the first end edge. The first tab includes a first tab region connecting to the first end edge and a second tab region connecting to the first tab region. The second tab region is bent relative to the first tab region to form a first end face, and a first connection region is connected to the first end face. This full-tab structure prevents the current distribution of the first electrode from becoming too concentrated, reducing the internal resistance of the first electrode and thus improving the charge / discharge rate of the first electrode. The second tab region forming the first end face facilitates the connection between the second tab region and the first connection region.

[0021] Based on the first aspect, in some possible implementations, the third connection region includes a third partition connected to the second connection region and a fourth partition connected to the third partition. The first connection region, the second connection region, and the third partition are coplanar, and the fourth partition is bent relative to the third partition. Viewed along the thickness direction of the first connection region, the first connection region and the fourth partition overlap. Since the bend of the first guide element is located in the third connection region rather than the second connection region, the risk of the second connection region, with its smaller minimum cross-sectional area, easily breaking under mechanical abuse is reduced when the secondary battery is operating normally.

[0022] Based on the first aspect, in some possible implementations, the first current guide further includes a bending region and a transition region. The transition region includes a third side and a fourth side arranged adjacent to each other. A second connecting region is connected to the third side. The bending region is connected between the fourth side and the third connecting region. The bending region is bent relative to both the transition region and the third connecting region. Viewed from the thickness direction of the third connecting region, the transition region and the third connecting region overlap. The transition region and the third connecting region can jointly fill the gap between the housing and the electrode assembly, reducing the shaking of the electrode assembly within the housing when the secondary battery is mechanically abused. Even if the electrode assembly shakes within the housing and pulls the first tab, the transition region connected to the bending region can provide a larger buffer space, reducing the risk that the first tab will detach from the first current guide and cause the secondary battery to malfunction.

[0023] A second aspect of this application also provides an electrical device, including a battery compartment and the aforementioned secondary battery. The secondary battery is housed within the battery compartment. The electrical device is powered by the aforementioned secondary battery, and the safety and reliability of the secondary battery are improved. Attached Figure Description

[0024] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0025] Figure 1 is a schematic diagram of the structure of a secondary battery provided in one embodiment of this application.

[0026] Figure 2 is a cross-sectional view of the secondary battery shown in Figure 1 along section line II-II in some embodiments.

[0027] Figure 3 is a cross-sectional view of the secondary battery shown in Figure 1 along section line II-II in some other embodiments.

[0028] Figure 4A is a cross-sectional view of the secondary battery shown in Figure 1 along section line IV-IV in some embodiments.

[0029] Figure 4B is a magnified view of the secondary battery shown in Figure 4A at point IVA.

[0030] Figure 5A is an unfolded view of the first current guide of the secondary battery shown in Figure 4 in some embodiments.

[0031] Figure 5B is an unfolded view of the first current-conducting element of the secondary battery shown in Figure 4 in some other embodiments.

[0032] Figure 5C is an unfolded view of the first current-conducting element of the secondary battery shown in Figure 4 in some other embodiments.

[0033] Figure 5D is an unfolded view of the first current-conducting element of the secondary battery shown in Figure 4 in some other embodiments.

[0034] Figure 6 is a bottom view of the first current guide of the secondary battery shown in Figure 5A.

[0035] Figure 7 is a partially enlarged cross-sectional view along section line IV-IV of the secondary battery shown in Figure 1 in some other embodiments.

[0036] Figure 8 is a partially enlarged cross-sectional view along section line IV-IV of the secondary battery shown in Figure 1 in some other embodiments.

[0037] Figure 9 is a cross-sectional view of the secondary battery shown in Figure 1 along section line IV-IV in some other embodiments.

[0038] Figure 10 is a schematic diagram of the structure of a secondary battery provided in another embodiment of this application.

[0039] Figure 11 is a cross-sectional view of the secondary battery shown in Figure 10 along the cutting line XII-XII.

[0040] Figure 12 is an unfolded view of the first current-conducting component of the secondary battery shown in Figure 11.

[0041] Figure 13 is a schematic diagram of the structure of a secondary battery provided in another embodiment of this application.

[0042] Figure 14 is a cross-sectional view of the secondary battery shown in Figure 13 along the cutting line XV-XV.

[0043] Figure 15 is a cross-sectional view of the secondary battery shown in Figure 13 along the cutting line XVI-XVI.

[0044] Figure 16 is an unfolded view of the first current-conducting component of the secondary battery shown in Figure 14 or Figure 15.

[0045] Figure 17 is a schematic diagram of the structure of an electrical device provided in one embodiment of this application.

[0046] Key Component Symbols Explanation: Electrical Device 1; Housing 10; First End Wall 11; Second End Wall 12; Side Wall 13; First Terminal 14; Second Terminal 15; Receiving Part 16; Sealing Edge 17; Electrode Assembly 20; First Electrode 21; First End Edge 21a; Second Electrode 22; Second End Edge 22a; Separator 23; First Tab 30; First Section 30a; Second Section 30b; First Tab Area 31; Second Tab Area 32; Second Tab 40; Third Tab Area 41; Fourth Tab Area 42; First Current Guide 50; First Connection Area 51; Second Connection Area 52; Third Connection Area 53; Bending Area 54; Adapter Area 55; Second Current Guide 60; First Insulating Protective Layer 70; First Layer 71; Second Layer 72; Secondary Battery 100, 200; Battery Compartment 101; First Current Collector 210; First Active Material Layer 211; Second Current Collector 220; Second Active Material Layer 221; First End Face 320; Second End Face 420; First Section 511; Second Section 512 First side 521 Second side 522 Third section 531 Fourth section 532 Third side 551 Fourth side552 Top 5210 First Endpoint 5211 Second Endpoint 5212 First Direction X Second Direction Y Third Direction Z Cross-sectional Area S1, S2 Width W1, W2, W3 Thickness H1, H2, H3

[0047] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0048] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0049] The embodiments of this application will be described in detail below. However, this application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided to thereby convey this application thoroughly and in detail to those skilled in the art.

[0050] Additionally, for brevity and clarity, the dimensions or thicknesses of various components and layers may be enlarged in the accompanying drawings. Throughout the text, the same numerical values ​​refer to the same elements. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more of the associated enumerated items. Furthermore, it should be understood that when element A is referred to as "connecting" element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0051] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".

[0052] The technical terms used herein are for the purpose of describing particular embodiments and are not intended to limit this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. It should be further understood that the term "comprising," as used in this specification, means the presence of the described features, values, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof.

[0053] Spatial terms, such as "above," may be used herein for convenience in describing the relationship between one element or feature and another element (or feature) or feature (or feature) illustrated in the figures. It should be understood that, in addition to the directions depicted in the figures, spatial terms are intended to include different orientations of the device or apparatus during use or operation. For example, if the device in the figure is flipped, an element described as "above" or "on" other elements or features would be oriented "below" or "under" other elements or features. Therefore, the exemplary term "above" can include both above and below orientations. It should be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Therefore, a first element, component, region, layer, or portion discussed below may be referred to as a second element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.

[0054] As used in this article, "parallel" and "perpendicular" are used to describe the ideal state between two components. In actual production or use, two components may exist in a state that is approximately parallel or perpendicular. For example, combined with numerical descriptions, parallel can refer to the angle between two straight lines within ±10°, parallel can also refer to the dihedral angle between two planes within ±10°, and parallel can also refer to the angle between a straight line and a plane within ±10°. Perpendicular can refer to the angle between two straight lines within 90±10°, perpendicular can also refer to the dihedral angle between two planes within 90±10°, and perpendicular can also refer to the angle between a straight line and a plane within 90±10°. The two components described as "parallel" or "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 a straight line or plane, the component can be considered a "straight line" or "plane".

[0055] In this application, the design relationships of greater than, less than, or not equal to parameter values ​​need to exclude reasonable errors of the measuring equipment.

[0056] Referring to Figures 1 to 4A, one embodiment of this application provides a secondary battery 100, including a housing 10, at least one electrode assembly 20 disposed within the housing 10, an electrolyte (not shown), a first tab 30, and a second tab 40. In some embodiments, the housing 10 may be a packaging bag, and correspondingly, the secondary battery 100 may be a pouch battery. The housing 10 includes a receiving portion 16 and a sealing edge 17 connected together. The electrode assembly 20 is received within the receiving portion 16.

[0057] Taking the electrode assembly 20 as an example, as shown in Figure 2, the electrode assembly 20 can be a wound structure, which includes a first electrode 21, a second electrode 22, and a separator 23. The separator 23 is disposed between the first electrode 21 and the second electrode 22, and the separator 23 is used to prevent the first electrode 21 and the second electrode 22 from directly contacting each other, thereby reducing the possibility of short circuit between the first electrode 21 and the second electrode 22. The number of first tabs 30 can be one or more, which are electrically connected to the first electrode 21 and extend beyond the first electrode 21. The number of second tabs 40 can be one or more, which are electrically connected to the second electrode 22 and extend beyond the second electrode 22. As shown in Figure 3, in some embodiments, the electrode assembly 20 can also be a stacked structure, which includes multiple first electrodes 21, multiple second electrodes 22, and multiple separators 23. In the stacked structure, the first electrodes 21 and the second electrodes 22 are stacked alternately in sequence, with one second electrode 22 in every two adjacent first electrodes 21 and one first electrode 21 in every two adjacent second electrodes 22. The separator 23 is disposed between adjacent first electrode 21 and second electrode 22.

[0058] A three-dimensional coordinate system is established based on three mutually perpendicular directions: a first direction X, a second direction Y, and a third direction Z. In the description of the embodiments of this application, the first direction X is the direction in which the first electrode tab 30 extends from the first electrode plate 21, the second direction Y is the thickness direction of the electrode assembly 20, and the third direction Z is the direction from the first electrode tab 30 to the second electrode tab 40.

[0059] As shown in Figures 2 to 4A, the first electrode 21 includes a stacked first current collector 210 and a first active material layer 211. The first electrode 21 can be a positive electrode. Correspondingly, the first current collector 210 can be a positive current collector, and the first active material layer 211 can be a positive active material layer. The second electrode 22 includes a stacked second current collector 220 and a second active material layer 221. The second electrode 22 can be a negative electrode. Correspondingly, the second current collector 220 can be a negative current collector, and the second active material layer 221 can be a negative active material layer. When the electrode assembly 20 has a wound structure, the first tab 30 can be connected to the surface of the first current collector 210 by welding or other means, and the second tab 40 can be connected to the surface of the second current collector 220 by welding or other means. When the electrode assembly 20 has a stacked structure, the first tab 30 can be integrally formed with the first current collector 210, and the second tab 40 can be integrally formed with the second current collector 220.

[0060] The positive electrode current collector can be aluminum foil or nickel foil, and the negative electrode current collector can be at least one of copper foil, nickel foil, or carbon-based current collector. The positive electrode active material layer contains a positive electrode active material, which includes a compound that reversibly inserts and extracts lithium ions (lithiation intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material is selected from lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0061] The negative electrode active material layer comprises a negative electrode active material, which is a known negative electrode active material capable of reversible intercalation and deintercalation of active ions, and this application is not limited thereto. For example, it may be one or more combinations of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Among them, graphite may be selected from one or more combinations of artificial graphite, natural graphite, and modified graphite; silicon-based materials may be selected from one or more combinations of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials may be selected from one or more combinations of elemental tin, tin oxide compounds, and tin alloys.

[0062] The separator 23 comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene, in particular, have good effects on improving short-circuit performance.

[0063] Referring to Figures 4A to 5A, the secondary battery 100 further includes a first current guide 50 and a first insulating protective layer 70, wherein Figure 5A is a structural schematic diagram of the first current guide 50 in the deployed state as shown in Figures 4A and 4B. At least a portion of the first current guide 50 is disposed within the housing 10. The first current guide 50 is connected to the first tab 30 and extends out of the housing 10, and the first current guide 50 can connect to external components (not shown). The first current guide 50 includes a first connecting region 51, at least one second connecting region 52, and a third connecting region 53. Each second connecting region 52 is connected between the first connecting region 51 and the third connecting region 53. The first connecting region 51 is connected to the first tab 30; for example, the first connecting region 51 can be welded and fixed to the first tab 30, thereby improving the connection strength between the first connecting region 51 and the first tab 30. As shown in Figures 4A and 4B, at least a portion of the second connecting region 52 can be located within the sealing edge 17. The third connection area 53 is connected to the housing 10. For example, the third connection area 53 can be connected to the sealing edge 17 and extend out of the housing 10 from the sealing edge 17. The first flow guide 50 can be a one-piece structure, i.e., the first connection area 51, the second connection area 52, and the third connection area 53 are integrally connected. Therefore, when the secondary battery 100 is operating normally, the risk of the second connection area 52 breaking under mechanical abuse is reduced. In other embodiments, the first connection area 51, the second connection area 52, and the third connection area 53 can also be connected together by welding or other methods. The material of the first flow guide 50 can be one of aluminum, nickel, copper, steel, or nickel-plated copper.

[0064] As shown in Figures 4A and 4B, in some embodiments, the first tab 30 is bent. The first tab 30 includes a first segment 30a connecting the first electrode 21 and a second segment 30b connecting the first segment 30a, the second segment 30b being bent relative to the first segment 30a. The first connection region 51 is connected to the second segment 30b of the first tab 30. By bending the first tab 30, it is beneficial to reduce the space occupied by the first tab 30 on one side of the electrode assembly 20 in the first direction X, thereby increasing the energy density of the secondary battery 200.

[0065] In some embodiments, the first guide member 50 is bendable. The first connecting region 51 includes a first partition 511 connected to the second connecting region 52 and a second partition 512 connected to the first partition 511. The second connecting region 52, the third connecting region 53, and the first partition 511 are coplanar, and the second partition 512 is bent relative to the first partition 511. That is, the bend of the first guide member 50 is located in the first connecting region 51. The second partition 512 is connected to the first tab 30. At this time, the first partition 511, the second connecting region 52, and the third connecting region 53 are arranged along the first direction X, and the plane containing the second connecting region 52, the third connecting region 53, and the first partition 511 is perpendicular to the second direction Y.

[0066] As shown in Figure 6, which is a bottom view of the first current guide 50 of the secondary battery 100 shown in Figure 5A, the minimum cross-sectional area of ​​each second connection region 52 along its thickness direction is S1, and the cross-sectional area of ​​the third connection region 53 along its thickness direction is S2. At least one second connection region 52 satisfies: 0.1S2≤S1≤0.5S2. Since the minimum cross-sectional area S1 of each second connection region 52 is small, when the secondary battery 100 is short-circuited, the second connection region 52 can preferentially melt under the action of the short-circuit current. At the same time, it can also reduce the impact of the melting of the second connection region 52 during normal operation of the secondary battery 100 on the service life of the secondary battery 100. It can be understood that, as shown in Figures 4A and 4B, when the first current guide 50 is bent, the thickness direction of the second connection region 52 and the thickness direction of the third connection region 53 are both the second direction Y. Since the bend of the first guide member 50 is located in the first connection area 51 rather than the second connection area 52, the risk that the second connection area 52, with its smaller minimum cross-sectional area, is prone to breakage when the secondary battery 100 is subjected to mechanical abuse (such as vibration or drop), thus preventing the secondary battery 100 from functioning properly, is reduced. In some embodiments, the number of second connection areas 52 is two or more. Providing multiple second connection areas 52 can reduce the risk that all second connection areas 52 will break when the secondary battery 100 is subjected to mechanical abuse, thus preventing the secondary battery 100 from functioning properly. Furthermore, the minimum cross-sectional area S1 of each second connection area 52 is smaller, so that each second connection area 52 can preferentially melt under the action of short-circuit current when the secondary battery 100 is short-circuited.

[0067] In some embodiments, each second connection region 52 satisfies: 0.2S2≤S1≤0.4S2. By further limiting the upper limit of S1, the second connection region 52 becomes more sensitive under short-circuit current and high temperature, enabling it to melt promptly not only when a short circuit occurs in the secondary battery 100, but also to more easily break under mechanical abuse after the first polymer melts due to safety hazards in the secondary battery 100, thereby further improving the safety of the secondary battery 100. By further limiting the lower limit of S1, the impact of the melting of the second connection region 52 on the service life of the secondary battery 100 can be further reduced when the secondary battery 100 is operating normally.

[0068] As shown in Figure 6, in some embodiments, the thickness H2 of each second connecting region 52 is less than the thickness H1 of the first connecting region 51 and also less than the thickness H3 of the third connecting region 53, thereby making the minimum cross-sectional area S1 of each second connecting region 52 smaller. The thicknesses of the first connecting region 51 and the third connecting region 53 can be the same or different. In other embodiments, the thickness H2 of each second connecting region 52 can also be equal to the thickness H1 of the first connecting region 51 or equal to the thickness H3 of the third connecting region 53. At the same time, in the second direction Y (the arrangement direction of the two second connecting regions 52 in Figure 6 is the second direction Y), the width W2 of each second connecting region 52 is less than the width W1 of the first connecting region 51 or less than the width W3 of the third connecting region 53, which also makes the minimum cross-sectional area S1 of each second connecting region 52 smaller.

[0069] As shown in Figure 5A, in some embodiments, viewed along the thickness direction of the second connecting region 52, the second connecting region 52 includes a first side 521 and a second side 522 disposed opposite to each other. Both the first side 521 and the second side 522 connect the first connecting region 51 and the third connecting region 53. Viewed along the thickness direction of the second connecting region 52, both the first side 521 and the second side 522 can be straight lines. In this case, the minimum cross-sectional area S1 of each second connecting region 52 is the area of ​​the cross-section passing through any point of the first side 521 along the thickness direction of the second connecting region 52.

[0070] As shown in Figures 4A to 5A, the first insulating protective layer 70 at least covers the surface of the second connection region 52. Since the first insulating protective layer 70 can cover the second connection region 52, which has a relatively small cross-sectional area, it protects the second connection region 52 from mechanical abuse, reducing the risk of the second connection region 52 breaking (e.g., during a drop, the electrode assembly 20 shakes within the housing 10, pulling on the first tab 30 and the first current guide 50, causing the second connection region 52 to break), thus preventing the secondary battery 100 from functioning properly. In some embodiments, the first insulating protective layer 70 may cover multiple surfaces of the second connection region 52 to enclose it, thereby sufficiently protecting the second connection region 52 when the secondary battery 100 is functioning normally, reducing the risk of the second connection region 52 breaking during mechanical abuse. The first insulating protective layer 70 may also cover part of the surface of the first connection region 51 and part of the surface of the third connection region 53, thereby sufficiently protecting the second connection region 52 when the secondary battery 100 is functioning normally.

[0071] Furthermore, the first insulating protective layer 70 includes a first polymer with a melting point of 100 to 170 degrees Celsius. This allows the first polymer to melt promptly when the internal temperature of the secondary battery 100 reaches this melting point (e.g., when a large current discharge or micro-short circuit occurs inside the secondary battery 100, or when the ambient temperature is high, even though the internal temperature of the secondary battery 100 has not reached the high temperature of a short circuit, there is still a safety hazard). This weakens or even eliminates the protective effect of the first insulating protective layer 70 on the second connection area 52, making the second connection area 52 prone to breakage during mechanical abuse and preventing the secondary battery 100, which poses a safety hazard, from continuing to operate. In some embodiments, the material of the first polymer is selected from at least one of polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene modified materials, or polyethylene modified materials. For example, the polyethylene can be selected from at least one of low-density polyethylene (LDPE) with a melting point of 108-126 degrees Celsius, high-density polyethylene (HDPE) with a melting point of 126-140 degrees Celsius, or linear low-density polyethylene (LLDPE) with a melting point of 110-125 degrees Celsius. Therefore, the melting point of the first polymer can be adjusted by selecting different types of polyethylene. Additionally, polyethylene-modified materials obtained by adding other materials to polyethylene can also have different melting points. Similarly, when the first polymer includes other components such as polypropylene, the melting point of the first polymer can be adjusted using a similar method. Optionally, the melting point of the first polymer is between 100 and 130 degrees Celsius, thereby improving the sensitivity of the first polymer when there is a safety hazard with the secondary battery 100.

[0072] In this application, when the secondary battery 100 is operating normally, the first insulating protective layer 70 can cover the second connection area 52, which has a smaller minimum cross-sectional area. This protects the second connection area 52 from mechanical abuse, reducing the risk of breakage. When the secondary battery 100 experiences a short circuit, the second connection area 52, with its smaller minimum cross-sectional area, can preferentially melt under the short-circuit current, disconnecting the first electrode 30 from external components, thus placing the secondary battery 100 in an open-circuit state and reducing safety issues caused by continued internal temperature increases. On the other hand, when the internal temperature of the secondary battery 100 reaches the melting point of the first polymer, the first polymer in the first insulating protective layer 70 melts promptly, weakening or even eliminating the protective effect of the first insulating protective layer 70 on the second connection area 52. This makes the second connection area 52 more susceptible to breakage during mechanical abuse, preventing the secondary battery 100, which poses a safety hazard, from continuing to operate. Therefore, the combined effect of the second connection area 52 and the first insulating protective layer 70 improves the safety and reliability of the secondary battery 100.

[0073] The secondary battery 100 may further include a second current guide 60 and a second insulating protective layer (not shown), with the second current guide 60 connected to the second tab 40. To further improve the safety and reliability of the secondary battery 100 in the event of a short circuit, the second current guide 60 may have a structure similar to the first current guide 50, and the second insulating protective layer may have a structure similar to the first insulating protective layer 70.

[0074] Referring to Figures 5B to 5D, in some embodiments, viewed along the thickness direction of the second connection region 52, the first side 521 may also be curved, i.e., non-linear. The first side 521 includes a first endpoint 5211 connected to the first connection region 51, a second endpoint 5212 connected to the third connection region 53, and a top 5210 disposed between the first endpoint 5211 and the second endpoint 5212. The top 5210 is recessed towards the interior of the second connection region 52 relative to both the first endpoint 5211 and the second endpoint 5212. Because the first side 521 is curved and its top 5210 is recessed towards the interior of the second connection region 52, the minimum cross-sectional area of ​​the second connection region 52 is the area of ​​the cross-section passing through the top 5210 along the thickness direction of the second connection region 52, such that when the secondary battery 100 experiences a short circuit, the second connection region 52 preferentially melts at the location corresponding to the top 5210. Further, in some specific embodiments, the first side 521 may at least partially be a polygonal shape. As shown in Figure 5B, the first side 521 is a partial outline of a trapezoid, and the top 5210 of the first side 521 is the upper base of the trapezoid. As shown in Figure 5C, the first side 521 is V-shaped, and the top 5210 of the first side 521 can be a pointed apex. As shown in Figure 5D, the first side 521 is serrated, and the top 5210 of the first side 521 is the peak of the serration. By setting the first side 521 to at least part of a zigzag shape, when the protective effect of the first insulating protective layer 70 on the second connection area 52 weakens or even disappears, the second connection area 52 is more likely to break during mechanical abuse, preventing the secondary battery 100, which poses a safety hazard, from continuing to operate. The shape of the second side 522 can be the same as the shape of the first side 521. The width W2 of each second connection area 52 is the distance between the top 5210 of the first side 521 and the top (not shown) of the second side 522 in that second connection area 52.

[0075] In some embodiments, the melting point of the first polymer is less than or equal to the melting point of the separator 23. This allows the first polymer to melt before or simultaneously with the separator 23 when a short circuit occurs in the secondary battery 100, reducing the risk of the separator 23 melting preferentially and exacerbating the short circuit. For example, polyethylene or polypropylene with a melting point of 130-170 degrees Celsius can be used as the separator 23, while polyethylene or polypropylene with a melting point of 100-130 degrees Celsius can be used as the first polymer, ensuring that the first polymer melts before the separator 23 when a short circuit occurs in the secondary battery 100, thereby further reducing the risk of the separator 23 melting preferentially and exacerbating the short circuit.

[0076] As shown in Figures 4A and 4B, when the casing 10 is a packaging bag, the first insulating protective layer 70 is sandwiched within the sealing edge 17. The first insulating protective layer 70 also seals the connection between the first flow guide 50 and the sealing edge 17. Specifically, the first insulating protective layer 70 can fill any gaps that may exist between the second connecting area 52 or the third connecting area 53 and the sealing edge 17, thereby sealing the connection between the first flow guide 50 and the sealing edge 17, reducing the risk of leakage during use and the risk of separation between the first flow guide 50 and the sealing edge 17, and also maintaining electrical insulation between the first flow guide 50 and the casing 10. The first insulating protective layer 70 can be a double-layer structure, comprising a first layer 71 and a second layer 72 stacked together. The first layer 71 includes the aforementioned first polymer, so that the first layer 71 can melt in time when the melting point of the first polymer is reached inside the secondary battery 100. The second layer 72 includes a second polymer, and the melting point of the second polymer is 160 to 170 degrees Celsius. For example, the second polymer can be polypropylene with a melting point of 160 to 170 degrees Celsius. The second layer 72 is connected to the sealing edge 17 and the first layer 71 respectively. The second layer 71 has high sealing performance, which can further reduce the risk of leakage during use and the risk of separation between the first guide element 50 and the sealing edge 17. In some embodiments, the first insulating protective layer 70 can also be a single-layer structure. In addition to the first polymer, the first insulating protective layer 70 may also include a second polymer. The melting point of the second polymer may be higher than that of the first polymer. In this case, when the interior of the secondary battery 100 reaches the melting point, the first polymer melts in time, while the second polymer does not melt. This can also weaken the protective effect of the first insulating protective layer 70 on the second connection area 52. In this case, the mass percentage of the first polymer in the first insulating protective layer 70 can be set to be greater than or equal to 50%, thereby weakening the protective effect of the first insulating protective layer 70 on the second connection area 52 when the interior of the secondary battery 100 reaches the melting point.

[0077] As shown in Figures 4A and 4B, in some embodiments, at least a portion of the second connection area 52 is located within the sealing edge 17. As shown in Figure 7, in other embodiments, at least a portion of the second connection area 52 may also be located outside the housing 10. When the protective effect of the first layer 71 on the second connection area 52 weakens or even disappears, the second connection area 52 located outside the housing 10 is more prone to breakage during mechanical abuse. As shown in Figure 8, in other embodiments, at least a portion of the second connection area 52 may also be located within the receiving portion 16.

[0078] As shown in Figure 9, in some embodiments, the first connecting region 51, the second connecting region 52, and the third connecting region 53 may also be coplanar. That is, the first guide member 50 is not bent as a whole. In this case, the arrangement direction of the first connecting region 51, the second connecting region 52, and the third connecting region 53 is the first direction X, and the plane where the first guide member 50 is located is perpendicular to the second direction Y. When the first electrode 30 is connected to the first guide member 50, the first connecting region 51 of the first guide member 50 extends out of the shell 10 from the sealing edge 17 along the first direction X.

[0079] Referring to Figures 10 and 11, another embodiment of this application also provides a secondary battery 200. The difference from the secondary battery 100 described above includes that the casing 10 can also be made of metal. Correspondingly, the secondary battery 200 can be a cylindrical battery, a prismatic battery, or a button battery. Figures 10 and 11 show that the secondary battery 200 is a cylindrical battery, and the electrode assembly 20 has a wound structure. A coordinate system is established based on a first direction X and a second direction Y that are perpendicular to each other. In the description of the embodiments of this application, the first direction X is the direction in which the first tab 30 extends from the first electrode plate 21. Any direction in a two-dimensional plane perpendicular to the first direction X can be considered as the second direction Y of this application. In some embodiments, the casing 10 includes a first end wall 11 and a second end wall 12 disposed opposite each other in the first direction X, a side wall 13 connecting the first end wall 11 and the second end wall 12, and a first electrode post 14 disposed on the first end wall 11. The side wall 13 and the second end wall 12 enclose a receiving space for accommodating the electrode assembly 20 and the electrolyte, and the first end wall 11 covers this receiving space. The first terminal post 14 is electrically isolated from the first end wall 11. At this time, the third connection region 53 is connected to the first terminal post 14.

[0080] When the housing 10 is made of metal, the first insulating protective layer 70 is a single-layer structure. The first insulating protective layer 70 may include a first polymer and a second polymer, and the first polymer accounts for more than or equal to 50% of the mass of the first insulating protective layer 70. The first insulating protective layer 70 may also include only the first polymer, that is, the first polymer accounts for 100% of the mass of the first insulating protective layer 70.

[0081] As shown in Figure 11, the first current collector 210 of the first electrode 21 includes a first end edge 21a facing the first end wall 11, and a first tab 30 extends from the first end edge 21a. Along the extension direction of the first end edge 21a in the electrode assembly 20, the width of the first tab 30 can be equal to the width of the first current collector 210. This prevents the current distribution of the first electrode 21 from becoming too concentrated, reducing the internal resistance of the first electrode 21 and thus improving the charge / discharge rate of the first electrode 21. The first tab 30 includes a first tab region 31 connecting the first end edge 21a and a second tab region 32 connecting the first tab region 31. The second tab region 32 is bent relative to the first tab region 31 to form a first end face 320. A first connection region 51 is connected to the first end face 320, thereby connecting the first tab 30 to the first electrode post 14 via a first current guide 50. Thus, the first electrode post 14 can exhibit the same polarity as the first electrode 21. During manufacturing, a portion of the first electrode tab 30 is flattened using a flattening device to form a flat surface, which is the first end face 320 formed by the second electrode tab region 32.

[0082] The second current collector 220 of the second electrode 22 includes a second end edge 22a facing the second end wall 12, and a second tab 40 extends from the second end edge 22a. Along the extension direction of the second end edge 22a in the electrode assembly 20, the width of the second tab 40 may be equal to the width of the second current collector 220. The second tab 40 includes a third tab region 41 connecting the second end edge 22a and a fourth tab region 42 connecting the third tab region 41. The fourth tab region 42 is bent relative to the third tab region 41 to form a second end face 420. During manufacturing, a portion of the second tab 40 is flattened using a flattening device to form a flat surface, which is the second end face 420 formed by the fourth tab region 42. The second end face 420 may be directly connected to the second end wall 12 or connected to the second end wall 12 via the second guide member 60. Thus, the second end wall 12 may exhibit the same polarity as the second electrode 22.

[0083] As shown in Figure 11, in some embodiments, the first flow guide 50 is bendable, such that when viewed along the thickness direction of the first connecting region 51, the first connecting region 51 and the third connecting region 53 overlap. Specifically, please refer to Figure 12, which is a schematic diagram of the unfolded structure of the first flow guide 50 shown in Figure 11. In some embodiments, the third connecting region 53 includes a third partition 531 connected to the second connecting region 52 and a fourth partition 532 connected to the third partition 531. The first connecting region 51, the second connecting region 52, and the third partition 531 are coplanar, and the fourth partition 532 is bent relative to the third partition 531. That is, the bend of the first flow guide 50 is located in the third connecting region 53, which reduces the risk of the second connecting region 52, which has a smaller minimum cross-sectional area, easily breaking under mechanical abuse when the secondary battery 100 is working normally. When viewed along the thickness direction of the first connecting region 51, the first connecting region 51 and the fourth partition 532 overlap. The first connection area 51 is connected to the first end face 320, for example, the first connection area 51 can be welded and fixed to the first end face 320. The fourth section 532 of the third connection area 53 is connected to the first pole post 14, for example, the fourth section 532 can be welded and fixed to the first pole post 14.

[0084] Figures 13 to 15 show that the secondary battery 200 is a prismatic battery, in which case the electrode assembly 20 can be a wound structure or a stacked structure. In some embodiments, the housing 10 includes a first end wall 11 and a second end wall 12 disposed opposite each other in a first direction X, a side wall 13 connecting the first end wall 11 and the second end wall 12, and a first electrode post 14 and a second electrode post 15 respectively disposed on the first end wall 11. The first electrode post 14 and the second electrode post 15 are both electrically isolated from the first end wall 11. The first end wall 11 and the second end wall 12 can be arranged in parallel. The side wall 13 and the second end wall 12 enclose a receiving space for accommodating the electrode assembly 20 and the electrolyte, and the first end wall 11 covers the receiving space.

[0085] Please refer to Figure 16, which is a schematic diagram of the unfolded structure of the first flow guide 50 shown in Figure 14 or Figure 15. In addition to the first connecting area 51, the second connecting area 52, and the third connecting area 53, the first flow guide 50 may also include a bending area 54 and a transition area 55. The transition area 55 includes a third side 551 and a fourth side 552 arranged adjacent to each other. The second connecting area 52 is connected to the third side 551. The bending area 54 is connected between the fourth side 552 and the third connecting area 53. The bending area 54 is bent relative to both the transition area 55 and the third connecting area 53. Viewed from the thickness direction of the third connecting area 53, the transition area 55 and the third connecting area 53 overlap. The transition area 55 and the third connection area 53 together fill the gap between the housing 10 and the electrode assembly 20, reducing the shaking of the electrode assembly 20 within the housing 10 when the secondary battery 200 is subjected to mechanical abuse. Even if the electrode assembly 20 shakes within the housing 10 and pulls the first tab 30, the transition area 55 connected to the bending area 54 provides a large buffer space, reducing the risk that the first tab 30 will detach from the first current guide 50 and cause the secondary battery 200 to malfunction. Although Figure 14 shows that the second segment 30b of the first tab 30 is connected to the transition area 55, it can be understood that the first connection area 51 in Figure 14 is actually located behind the transition area 55. Therefore, the second segment 30b of the first tab 30 is actually connected to the first connection area 51 located behind the transition area 55.

[0086] The secondary battery 100 or secondary battery 200 of this application can be a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries and lithium-ion polymer secondary batteries.

[0087] Referring to Figure 17, one embodiment of this application also provides an electrical device 1, including a battery compartment 101 and a secondary battery 100 (or secondary battery 200) housed within the battery compartment 101. The electrical device 1 is powered by the aforementioned secondary battery 100, and the safety and reliability of the secondary battery 100 are improved. In some embodiments, the electrical device 1 of this application may be, but is not limited to, a laptop computer, a pen input computer, a mobile computer, an e-book player, a portable telephone, a portable fax machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini CD, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, an electric bicycle, a bicycle, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0088] The performance of the secondary battery provided in this application is described below through specific embodiments and comparative examples. Specifically, a lithium-ion pouch battery, a first electrode as a positive electrode, and a second electrode as a negative electrode are used as examples to illustrate this application, along with specific preparation processes and testing methods. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0089] Example 1

[0090] (1) Preparation of the first electrode: Lithium cobalt oxide (LiCoO2), conductive 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. Foaming adhesive was first applied to a predetermined area of ​​a current collector aluminum foil with a thickness of 12 μm. The slurry was then uniformly coated on one surface of the aluminum foil. Heating was used to remove the foaming adhesive and expose the predetermined area of ​​the aluminum foil. The foil was then dried at 90 °C to obtain a positive electrode active material layer with a coating thickness of 100 μm. The above coating steps were repeated on the other surface of the aluminum foil to obtain a double-sided coated first electrode. Next, a first electrode tab was welded to the predetermined area of ​​the aluminum foil. The material of the first electrode tab was aluminum.

[0091] (2) Preparation of the second electrode: Artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:1.5:2.5, with deionized water added as a solvent to prepare a slurry with a weight percentage of 70 wt%, and stirred evenly. Foaming adhesive was pre-applied to a predetermined area of ​​a 10 μm current collector copper foil. The slurry was then uniformly coated onto one surface of the copper foil. Heating was applied to remove the foaming adhesive, exposing the predetermined area of ​​the copper foil. The foil was then dried at 110°C to obtain a negative electrode active material layer with a coating thickness of 130 μm. The above steps were repeated on the other surface of the copper foil to obtain a double-sided coated second electrode. Next, a second electrode tab, made of copper, was soldered onto the predetermined area of ​​the copper foil.

[0092] (3) Preparation of electrolyte: In a dry argon atmosphere, the organic solvents 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. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0093] (4) Preparation of the isolation membrane: A polyethylene (PE) membrane with a thickness of 15 μm was selected.

[0094] (5) Assembly of the secondary battery: The first electrode, the separator, and the second electrode are sequentially stacked and wound to obtain a wound electrode assembly, which is then placed inside the housing. Next, the first tab is stacked and welded to the first current guide, which is made of aluminum foil, and a first insulating protective layer is applied to the second connection area of ​​the first current guide. The second tab is stacked and welded to the second current guide, which is made of copper foil. The first insulating protective layer has a double-layer structure; the second layer is made of PP with a melting point of 160-170 degrees Celsius. The relevant parameters of the first current guide and the first layer of the first insulating protective layer are recorded in Table 1. The first current guide and the second insulating protective layer have structures similar to those of the first current guide and the first insulating protective layer. Then, liquid injection, formation, and encapsulation are performed. The first insulating protective layer is sealed to the edge and the first current guide to obtain the secondary battery shown in Figures 1 to 4B.

[0095] Examples 2-13 and Comparative Examples 1-6

[0096] The difference from Embodiment 1 above lies in the relevant parameters of the first flow guide and the first insulating protective layer.

[0097] Comparative Example 7

[0098] The difference from Embodiment 1 above is that the first insulating protective layer is omitted.

[0099] One hundred secondary batteries from each embodiment and comparative example were taken and subjected to external short-circuit test, room temperature drop test, high temperature drop test and DC resistance growth rate test. The corresponding test results are recorded in Table 1.

[0100] The melting point test steps for the first polymer include: 1) Discharging the secondary battery to 3V and then disassembling it, removing the first insulating protective layer covering the surface of the first electrode tab, cleaning it, and drying it at 80℃ to obtain the sample; 2) Placing the sample in an aluminum crucible, with a sample weight of 1mg, and using a differential scanning calorimeter (instrument model: DSC214, manufacturer: Netzsch, Germany) to test the DSC curve of the sample. The test temperature range is 60℃ to 200℃, and the heating rate is 10℃ / min. The melting point is obtained by analyzing the DSC curve.

[0101] The external short-circuit test procedure for secondary batteries includes: 1) Charging the secondary battery to 100% SOC (State of Charge) under an ambient temperature of 25±5℃; 2) Placing the secondary battery in a test environment of 25±5℃, and short-circuiting the first and second current-conducting components of the secondary battery with a load resistor of 10±2mΩ respectively. If the secondary battery does not catch fire or explode, continue the test until the voltage drops below 0.2V. Monitor the temperature change of the secondary battery during the test. The test is terminated when the battery temperature drops to ±5℃ of the ambient temperature or when the short-circuit time reaches 24 hours; 3) Disassembling the secondary battery and observing whether the second connection area of ​​the first current-conducting component is broken. Then, calculate the breakage rate of the first current-conducting component in each sample (i.e., the proportion of samples that have broken in all samples).

[0102] The room temperature drop test procedure for secondary batteries includes: 1) Charging the secondary battery to 100% SOC under an environment of 25±5℃; 2) Placing the secondary battery in the fixture chamber and using an automatic drop device to drop the bottom, side, and top surfaces of the secondary battery sequentially from a position of 1.8m onto the steel plate, for a total of 6 drops, or 18 drops; 3) After the drops are completed, disassembling the secondary battery and observing whether the second connection area of ​​the first guide component is broken, and then calculating the breakage rate of the first guide component in each sample.

[0103] The high-temperature drop test procedure for secondary batteries includes: 1) Inspecting the appearance of the secondary batteries and taking photos before and after the test; 2) Attaching the temperature sensing wire to the center of the secondary battery surface, then placing the secondary battery vertically in the hot chamber, heating it to 130±2℃ at a heating rate of 5±2℃ and maintaining it for 10 minutes; 3) Charging the secondary battery to 100% SOC under an ambient temperature of 25±5℃; 4) Placing the battery in the clamping chamber, and using an automatic drop device to drop the bottom, side, and top of the battery sequentially from a position of 1.8m onto a steel plate, for a total of 6 rounds, or 18 drops; 5) After the drop test, disassembling the secondary battery, observing whether the second connection area of ​​the first current guide is broken, and then calculating the breakage rate of the first current guide in each sample.

[0104] The test steps for the DC resistance (DCR) growth rate of a secondary battery include: 1) Under ambient conditions of 25±5℃, charge the secondary battery at a constant current of 0.7C to 4.48V, then charge it at a constant voltage to a current of 0.05C, and then discharge it at a constant current of 0.1C for 10s. Measure the voltage V0 before discharge, and then discharge it at a constant current of 1C for 1s. Measure the voltage V1 after discharge. The initial DCR of the battery is then calculated as (V1-V0) / 1C; 2) Perform 30 charge-discharge cycles using the same charging and discharging steps as described above, and then test the DCR after each cycle; 3) Calculate the DCR growth rate after each cycle as (DCR after each cycle - initial DCR) / initial DCR × 100%.

[0105] Table 1

[0106] As shown in Table 1, compared to Comparative Example 1, Examples 4 and 9-14 satisfy 0.1S2≤S1, which reduces the risk of the second connection area melting during normal operation and breakage under room temperature drop. Therefore, the second connection area did not break during normal cycling, the DCR growth rate of the secondary battery was low, and the secondary battery could work normally. Compared to Comparative Example 2, Examples 4 and 9-14 satisfy S1≤0.5S2, the second connection area can melt in time when the secondary battery is short-circuited. Therefore, the breakage rate of the first current guide after short circuit is increased, and the safety of the secondary battery is improved. Compared to Comparative Example 3, the melting point of the first polymer in Examples 1-8 is not less than 100 degrees Celsius. Therefore, the first polymer will not melt and will continue to provide protection for the second connection area when there is no safety risk to the secondary battery. Therefore, the first current guide did not break under the room temperature drop test, and the secondary battery can continue to work. Compared to Comparative Example 4, the melting point of the first polymer in Examples 1-8 does not exceed 170 degrees Celsius. Therefore, the first polymer melts when there is a safety hazard in the secondary battery, thus increasing the fracture rate of the first current-conducting component under high-temperature drop testing, preventing the secondary battery with safety hazards from continuing to operate, and improving the safety of the secondary battery. In Comparative Examples 5-6, S1 and the melting point of the first polymer do not meet the requirements, and Comparative Example 7 omits the first insulating protective layer, resulting in poor performance test results for multiple secondary batteries.

[0107] Comparing Examples 1-8, it can be seen that when the melting point of the first polymer gradually decreases within a predetermined range, the sensitivity of the first polymer to the internal temperature of the secondary battery increases, and the fracture rate of the first current guide gradually increases after the high-temperature drop test.

[0108] Comparing Examples 4 and 9-14, it can be seen that when the minimum cross-sectional area S1 of the second connection region gradually increases within a predetermined range, the sensitivity of the second connection region under short-circuit current and high temperature decreases accordingly, and the safety of the secondary battery decreases accordingly. However, at the same time, the DCR growth rate of the secondary battery also decreases, which is beneficial to the normal cycling of the secondary battery. Therefore, when Examples 4 and 10-11 satisfy 0.2S2≤S1≤0.4S2, the sensitivity of the second connection region under short-circuit current and high temperature is high, while the secondary battery has a low DCR growth rate, allowing the secondary battery to balance high safety and cycling capability.

[0109] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with this application are still within the scope of this application.

Claims

1. A secondary battery, comprising a casing, an electrode assembly disposed within the casing, and a first tab, wherein the electrode assembly includes a first electrode plate, and the first tab is connected to the first electrode plate, wherein... The secondary battery also includes: A first flow guide, at least a portion of which is disposed within the housing, includes a first connecting region, at least one second connecting region, and a third connecting region. The second connecting region is connected between the first connecting region and the third connecting region. The first connecting region is connected to the first tab, and the third connecting region is connected to the housing. The minimum cross-sectional area of ​​the second connecting region along its thickness direction is S1, and the cross-sectional area of ​​the third connecting region along its thickness direction is S2. At least one second connecting region satisfies: 0.1S2≤S1≤0.5S2. A first insulating protective layer covers at least the surface of the second connection area, the first insulating protective layer comprising a first polymer having a melting point of 100 to 170 degrees Celsius.

2. The secondary battery as described in claim 1, wherein, The electrode assembly further includes a separator, wherein the melting point of the first polymer is less than or equal to the melting point of the separator.

3. The secondary battery as described in claim 1 or 2, wherein, The material of the first polymer is selected from at least one of polypropylene, polyethylene, polyethylene terephthalate, polyethylene naphthalate, modified polypropylene material, or modified polyethylene material.

4. The secondary battery as described in any one of claims 1 to 3, wherein, The first insulating protective layer also covers a portion of the surface of the first connection area and a portion of the surface of the third connection area.

5. The secondary battery as described in any one of claims 1 to 4, wherein, At least one of the second connection regions satisfies: 0.2S2≤S1≤0.4S2.

6. The secondary battery according to any one of claims 1 to 5, wherein, Viewed along the thickness direction of the second connecting region, the second connecting region includes a first side and a second side disposed opposite to each other. The first side and the second side are both connected between the first connecting region and the third connecting region. The first side is curved and includes a first end point connected to the first connecting region, a second end point connected to the third connecting region, and a top point disposed between the first end point and the second end point. The top point is recessed toward the interior of the second connecting region relative to the first end point and the second end point.

7. The secondary battery as described in claim 6, wherein, The first side is at least partially polygonal.

8. The secondary battery according to any one of claims 1 to 7, wherein, The thickness of the second connection region is less than the thickness of either the first connection region or the third connection region.

9. The secondary battery according to any one of claims 1 to 8, wherein, The first connection area, the second connection area, and the third connection area are an integral structure.

10. The secondary battery according to any one of claims 1 to 9, wherein, The housing is a packaging bag, which includes a connected receiving portion and a sealing edge. The electrode assembly is received within the receiving portion. At least a portion of the second connection area is located within the sealing edge, within the receiving portion, or outside the housing. At least a portion of the third connection area extends out of the housing. The first insulating protective layer includes a first layer and a second layer stacked together. The first layer includes the first polymer, and the second layer includes a second polymer. The melting point of the second polymer is 160 to 170 degrees Celsius. The second layer is connected to the sealing edge and the first layer, respectively.

11. The secondary battery as claimed in claim 10, wherein, The first connection region, the second connection region, and the third connection region are coplanar.

12. The secondary battery as described in claim 10, wherein, The first connection area includes a first partition connected to the second connection area and a second partition connected to the first partition. The second connection area, the third connection area, and the first partition are coplanar. The second partition is bent relative to the first partition and is connected to the first tab.

13. The secondary battery according to any one of claims 1 to 9, wherein, The housing is a metal housing, which includes a first end wall and a second end wall disposed opposite to each other, a side wall connected between the first end wall and the second end wall, and a first pole post disposed on the first end wall. The first pole post is electrically isolated from the first end wall, and the third connection area is connected to the first pole post.

14. The secondary battery as claimed in claim 13, wherein, The electrode assembly is a wound structure. The first electrode includes a first current collector, the first current collector includes a first end edge facing the first end wall, the first tab extends from the first end edge, the first tab includes a first tab region connected to the first end edge and a second tab region connected to the first tab region, the second tab region is bent relative to the first tab region to form a first end face, and the first connecting region is connected to the first end face; when viewed along the thickness direction of the first connecting region, the first connecting region and the third connecting region overlap.

15. The secondary battery as described in claim 14, wherein, The third connection area includes a third partition connected to the second connection area and a fourth partition connected to the third partition. The first connection area, the second connection area, and the third partition are coplanar. The fourth partition is bent relative to the third partition. When viewed along the thickness direction of the first connection area, the first connection area and the fourth partition overlap.

16. The secondary battery as claimed in claim 11, wherein, The first guide member further includes a bending area and a transition area. The transition area includes a third side and a fourth side arranged adjacent to each other. The second connecting area is connected to the third side. The bending area is connected between the fourth side and the third connecting area. The bending area is bent relative to both the transition area and the third connecting area. When viewed from the thickness direction of the third connecting area, the transition area and the third connecting area overlap.

17. An electrical device, comprising a battery compartment, wherein, The electrical device further includes a secondary battery as described in any one of claims 1 to 16, the secondary battery being housed in the battery compartment.

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