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 devices Technical Field

[0001] The present 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 Art

[0002] As secondary batteries (eg, lithium-ion batteries) are widely used in electronic products such as electronic mobile devices, power tools, and electric vehicles, people have increasingly stringent requirements on secondary batteries (eg, lithium-ion secondary batteries).

[0003] However, secondary batteries can short-circuit during operation, causing the internal temperature to continue to rise, raising safety concerns. Furthermore, if a high-current discharge, micro-short circuit, or high-temperature environment occurs within the secondary battery, while the internal temperature may not reach the high temperature of a short-circuit, it still presents a safety hazard and can lead to safety issues if the battery is continued in use.

[0004] Summary of the Invention

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

[0006] In a first aspect, the present application provides a secondary battery comprising a housing, an electrode assembly disposed within the housing, and a first tab. The electrode assembly comprises a first electrode plate, the first tab being connected to the first electrode plate. The secondary battery further comprises a first flow guide and a first insulating protective layer. At least a portion of the first flow guide is disposed within the housing. The first flow guide comprises a first connection region, at least one second connection region, and a third connection region, the second connection region being connected between the first connection region and the third connection region. The first connection region is connected to the first tab. The third connection region is connected to the housing. The minimum cross-sectional area of ​​the second connection region along the thickness direction of the second connection region is S1, and the cross-sectional area of ​​the third connection region along the thickness direction of the third connection region is S2, and at least one second connection region satisfies the following conditions: 0.1S2≤S1≤0.5S2. The first insulating protective layer covers at least the surface of the second connection region. The first insulating protective layer comprises a first polymer, the melting point of the first polymer being between 100 degrees Celsius and 170 degrees Celsius.

[0007] In the present application, when the secondary battery is operating normally, the first insulating protective layer can cover the second connection area with a smaller minimum cross-sectional area, protect the second connection area when the secondary battery is mechanically abused, and reduce the risk of the second connection area breaking. By setting the relationship between S1 and S2, when the secondary battery is short-circuited, the second connection area can be preferentially melted under the action of the short-circuit current, disconnecting the first pole ear from the external component, reducing the safety problem caused by the continued rise in internal temperature, and also reducing the impact of the second connection area melting on the service life of the secondary battery when the secondary battery is operating normally. On the other hand, when the melting point of the first polymer is reached inside the secondary battery (such as the ambient temperature of the secondary battery is high and there is a safety hazard), the first polymer melts in time, so that the protective effect of the first insulating protective layer on the second connection area is weakened or even disappears, thereby making the second connection area easy to break during mechanical abuse, preventing the secondary battery with a safety hazard from continuing to work. Therefore, the second connection area and the first insulating protective layer work together to improve 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, and 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 in the event of a secondary battery short circuit, thereby reducing the risk of the separator melting preferentially and exacerbating the short circuit.

[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, when the secondary battery is operating normally, the first insulating protective layer can fully protect the second connection region, reducing the risk of the second connection region fracturing due to mechanical abuse.

[0011] Based on the first aspect, in some possible implementations, at least one second connection region satisfies the following condition: 0.2S2 ≤ S1 ≤ 0.4S2. This makes the second connection region more sensitive to short-circuit currents and high temperatures. Not only can it fuse promptly when a short circuit occurs in the secondary battery, but it can also more easily break under mechanical abuse if the first polymer melts due to a safety hazard in the secondary battery, thereby further improving the safety of the secondary battery. Furthermore, when the secondary battery is operating normally, the impact of a second connection region fusing on the secondary battery's service life can be further reduced.

[0012] Based on the first aspect, in some possible implementations, when observed along the thickness direction of the second connection area, the second connection area includes a first side and a second side that are arranged opposite to each other. The first side and the second side are both connected between the first connection area and the third connection area. The first side is a curved shape. The first side includes a first endpoint connected to the first connection area, a second endpoint connected to the third connection area, and a top located between the first endpoint and the second endpoint. The top is recessed toward the interior of the second connection area compared to the first endpoint and the second endpoint. In this way, when a short circuit occurs in the secondary battery, the second connection area is preferentially fused at the position corresponding to the top.

[0013] Based on the first aspect, in some possible implementations, the first side is at least partially in the shape of a broken line. In this way, when the protective effect of the first insulating protective layer on the second connection area is weakened or even disappears, the second connection area is more likely to break under mechanical abuse, preventing the secondary battery with safety hazards from continuing to operate.

[0014] Based on the first aspect, in some possible implementations, the thickness of the second connection region is smaller than the thickness of either the first connection region or the third connection region, so that the minimum cross-sectional area of ​​each second connection region is smaller.

[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 one structure. In this way, when the secondary battery is operating normally, the risk of the second connection region breaking under mechanical abuse is reduced.

[0016] Based on the first aspect, in some possible implementations, the shell is a packaging bag, which includes a connected receiving portion and an edge seal, the electrode assembly is accommodated in the receiving portion, at least part of the second connection area is located in the edge seal, in the receiving portion or outside the shell, and at least part of the third connection area extends out of the shell. The first insulating protective layer includes a first layer and a second layer that are stacked. The first layer includes the above-mentioned first polymer. The second layer includes a second polymer, and the melting point of the second polymer is 160 to 170 degrees. The second layer is connected to the edge seal and the first layer respectively. In this way, the third connection area can be connected to external elements, and the second layer of the first insulating protective layer has a higher sealing performance, which can reduce the risk of leakage during use and the risk of separation of the first flow guide from the edge seal, and can also maintain electrical insulation between the first flow guide and the shell.

[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 subregion connected to the second connection region and a second subregion connected to the first subregion. The second connection region, the third connection region, and the first subregion are coplanar. The second subregion is bent relative to the first subregion. The second subregion is connected to the first tab. Because the bend of the first flow guide is located in the first connection region rather than the second connection region, when the secondary battery is operating normally, the risk of the second connection region, which has a smaller minimum cross-sectional area, being susceptible to fracture under mechanical abuse is reduced.

[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 connected between the first end wall and the second end wall, and a first pole disposed on the first end wall. The first pole is electrically isolated from the first end wall. The third connection region is connected to the first pole. This allows the first pole to have the same electrical polarity as the first pole piece.

[0020] Based on the first aspect, in some possible implementations, the electrode assembly is a wound structure. The first pole piece includes a first current collector. The first current collector includes a first end edge facing the first end wall, and the first pole lug is formed by extending from the first end edge. The first pole lug includes a first pole lug region connected to the first end edge and a second pole lug region connected to the first pole lug region. The second pole lug region is bent compared to the first pole lug region and forms a first end face, and the first connection region is connected to the first end face. The full pole lug structure prevents the current distribution of the first pole piece from being too concentrated, reduces the internal resistance of the first pole piece, and thus improves the charge and discharge rate of the first pole piece. The second pole lug region forms a first end face, which facilitates the connection between the second pole lug region and the first connection region.

[0021] Based on the first aspect, in some possible implementations, the third connection area includes a third subarea connected to the second connection area and a fourth subarea connected to the third subarea. The first connection area, the second connection area, and the third subarea are coplanar, and the fourth subarea is bent relative to the third subarea. Observed along the thickness direction of the first connection area, the first connection area and the fourth subarea overlap. Because the bend of the first flow guide is located in the third connection area rather than the second connection area, when the secondary battery is operating normally, the risk of the second connection area, which has a smaller minimum cross-sectional area, being easily broken under mechanical abuse is reduced.

[0022] Based on the first aspect, in some possible implementations, the first flow guide further includes a bending area and a transition area. The transition area includes a third side and a fourth side that are adjacently arranged. The second connection area is connected to the third side. The bending area is connected between the fourth side and the third connection area. The bending area is bent relative to both the transition area and the third connection area. Observed from the thickness direction of the third connection area, the transition area and the third connection area overlap. The transition area and the third connection area can jointly fill the gap between the shell and the electrode assembly, reducing the shaking of the electrode assembly in the shell when the secondary battery is mechanically abused, and even if the electrode assembly shakes in the shell and pulls the first pole ear, the transition area connected to the bending area can provide a larger buffer space, reducing the risk of the first pole ear detaching from the first flow guide and causing the secondary battery to malfunction.

[0023] A second aspect of the present application further provides an electrical device comprising a battery compartment and a secondary battery as described above. The secondary battery is housed in the battery compartment. The electrical device is powered by the secondary battery, and the safety and reliability of the secondary battery are improved. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] FIG1 is a schematic structural diagram of a secondary battery provided in one embodiment of the present application.

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

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

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

[0029] FIG. 4B is a partial enlarged view of the secondary battery shown in FIG. 4A at position IVA.

[0030] FIG. 5A is an expanded view of the first flow guide of the secondary battery shown in FIG. 4 in some embodiments.

[0031] FIG. 5B is an expanded view of the first flow guide of the secondary battery shown in FIG. 4 in other embodiments.

[0032] FIG. 5C is an expanded view of the first flow guide of the secondary battery shown in FIG. 4 in other embodiments.

[0033] FIG. 5D is an expanded view of the first flow guide of the secondary battery shown in FIG. 4 in other embodiments.

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

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

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

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

[0038] FIG10 is a schematic structural diagram of a secondary battery provided in another embodiment of the present application.

[0039] FIG11 is a cross-sectional view of the secondary battery shown in FIG10 along the cutting line XII-XII.

[0040] FIG. 12 is an expanded view of the first flow guide of the secondary battery shown in FIG. 11 .

[0041] FIG13 is a schematic structural diagram of a secondary battery provided in another embodiment of the present application.

[0042] FIG14 is a cross-sectional view of the secondary battery shown in FIG13 taken along the cutting line XV-XV.

[0043] FIG15 is a cross-sectional view of the secondary battery shown in FIG13 taken along the cutting line XVI-XVI.

[0044] FIG. 16 is an expanded view of the first flow guide of the secondary battery shown in FIG. 14 or FIG. 15 .

[0045] FIG17 is a schematic structural diagram of an electrical device provided in one embodiment of the present application.

[0046] Description of Main Component Symbols Electric device 1 Housing 10 First end wall 11 Second end wall 12 Side wall 13 First pole 14 Second pole 15 Accommodation portion 16 Edge seal 17 Electrode assembly 20 First pole piece 21 First end edge 21a Second pole piece 22 Second end edge 22a Separator 23 First pole tab 30 First section 30a Second section 30b First pole tab region 31 Second pole tab region 32 Second pole tab 40 Third pole tab region 41 Fourth pole tab region 42 First current guide 50 First connection region 51 Second connection region 52 Third connection region 53 Bending region 54 Transition region 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 surface 320 Second end surface 420 First partition 511 Second partition 512 First side 521 Second side 522 Third partition 531 Fourth partition 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 specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application are described clearly and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0049] Below, embodiments of the present application will be described in detail. However, the present application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments illustrated herein. Rather, these exemplary embodiments are provided to make the present application thorough and detailed for those skilled in the art.

[0050] In addition, for the sake of brevity and clarity, the size or thickness of various components, layers may be exaggerated in the accompanying drawings. Throughout the text, the same numerical value refers to the same element. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more related enumerated items. In addition, 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] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0052] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit this application. As used herein, the singular is intended to include the plural, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to 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 related terms, such as "on" etc., can be used herein for convenient description, to describe the relationship between an element or feature and another element (multiple elements) or feature (multiple features) as illustrated in the figure. It should be understood that, in addition to the directions described in the figure, spatial related terms are intended to include different directions of equipment or devices in use or operation. For example, if the equipment in the figure is turned over, the elements described as "above" or "on" other elements or features will be oriented "below" or "below" other elements or features. Therefore, the exemplary term "on" can include the direction above and below. It should be understood that although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are used to distinguish an element, component, region, layer or part from another element, component, region, layer or part. Therefore, the first element, component, region, layer or part discussed below can be referred to as the second element, component, region, layer or part, without departing from the teachings of the exemplary embodiments.

[0054] As used herein, "parallel" and "perpendicular" are used to describe an ideal state between two components. In actual production or use, there may be a state between two components that is approximately parallel or perpendicular. For example, in combination with numerical descriptions, parallel can refer to the angle between two straight lines being between ±10°, parallel can also refer to the dihedral angle between two planes being between ±10°, and parallel can also refer to the angle between a straight line and a plane being between ±10°. Perpendicular can refer to the angle between two straight lines being between 90±10°, perpendicular can also refer to the dihedral angle between two planes being between 90±10°, and perpendicular can also refer to the angle between a straight line and a plane being between 90±10°. The two components described as "parallel" or "perpendicular" may not be absolute straight lines or planes, but may be roughly straight lines or planes. From a macroscopic perspective, a component can be considered a "straight line" or "plane" if its overall extension direction is a straight line or plane.

[0055] In this application, the relationship between parameter values ​​that is greater than, less than, or not equal to the design relationship needs to exclude the reasonable error of the measuring equipment.

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

[0057] As shown in FIG2 , the electrode assembly 20 may be a wound structure comprising a first electrode sheet 21, a second electrode sheet 22, and a separator 23. The separator 23 is disposed between the first electrode sheet 21 and the second electrode sheet 22 to prevent direct contact between the first electrode sheet 21 and the second electrode sheet 22, thereby reducing the possibility of a short circuit between the first electrode sheet 21 and the second electrode sheet 22. There may be one or more first electrode tabs 30, each electrically connected to and extending from the first electrode sheet 21. There may also be one or more second electrode tabs 40, each electrically connected to and extending from the second electrode sheet 22. As shown in FIG3 , in other embodiments, the electrode assembly 20 may be a stacked structure comprising multiple first electrode sheets 21, multiple second electrode sheets 22, and multiple separators 23. In this stacked structure, the first electrode sheets 21 and the second electrode sheets 22 are alternately stacked, with one second electrode sheet 22 positioned between every two adjacent first electrode sheets 21 and one first electrode sheet 21 positioned between every two adjacent second electrode sheets 22. The isolation film 23 is disposed between the adjacent first pole piece 21 and the adjacent second pole piece 22 .

[0058] A three-dimensional coordinate system is established based on mutually perpendicular first direction X, second direction Y, and third direction Z. In the description of the embodiment of the present application, the first direction X is the direction in which the first electrode tab 30 extends from the first electrode sheet 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 sheet 21 includes a stacked first current collector 210 and a first active material layer 211. The first electrode sheet 21 can be a positive electrode sheet. Accordingly, the first current collector 210 can be a positive electrode current collector, and the first active material layer 211 can be a positive electrode active material layer. The second electrode sheet 22 includes a stacked second current collector 220 and a second active material layer 221. The second electrode sheet 22 can be a negative electrode sheet. Accordingly, the second current collector 220 can be a negative electrode current collector, and the second active material layer 221 can be a negative electrode active material layer. When the electrode assembly 20 has a wound structure, the first electrode tab 30 can be connected to the surface of the first current collector 210 by welding or other means, and the second electrode 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 laminated structure, the first electrode tab 30 can be integrally formed with the first current collector 210, and the second electrode tab 40 can be integrally formed with the second current collector 220.

[0060] The positive electrode current collector may be made of aluminum foil or nickel foil, and the negative electrode current collector may be made of 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, and the positive electrode active material includes a compound that can reversibly embed and deintercalate lithium ions (lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The 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 cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or at least one of lithium iron phosphate (LiFePO4).

[0061] The negative electrode active material layer contains a negative electrode active material, which is a negative electrode active material known in the art that can reversibly deintercalate active ions, and is not limited in this application. For example, it can be a combination of one or more 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 can be selected from a combination of one or more of artificial graphite, natural graphite and modified graphite; silicon-based materials can be selected from a combination of one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials can be selected from a combination of one or more of elemental tin, tin oxide compounds, and tin alloys.

[0062] The isolation film 23 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene have a good effect on improving short circuits.

[0063] With reference to Figures 4A to 5A , the secondary battery 100 further includes a first flow guide 50 and a first insulating protective layer 70 . Figure 5A is a schematic structural diagram of the first flow guide 50 shown in Figures 4A and 4B in an expanded state. At least a portion of the first flow guide 50 is disposed within the housing 10 . The first flow guide 50 is connected to the first electrode tab 30 and extends beyond the housing 10 . The first flow guide 50 can be connected to external components (not shown). The first flow guide 50 includes a first connection region 51 , at least one second connection region 52 , and a third connection region 53 . Each second connection region 52 is connected between the first connection region 51 and the third connection region 53 . The first connection region 51 is connected to the first electrode tab 30 . For example, the first connection region 51 can be welded to the first electrode tab 30 to enhance the connection strength between the first connection region 51 and the first electrode tab 30 . As shown in Figures 4A and 4B , at least a portion of the second connection region 52 can be located within the edge seal 17 . The third connection area 53 is connected to the housing 10. For example, the third connection area 53 can be connected to the edge seal 17 and extend from the housing 10 from the edge seal 17. The first flow guide 50 can be an integrated structure, that is, the first connection area 51, the second connection area 52, and the third connection area 53 are connected as a whole. 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 copper-plated nickel.

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

[0065] In some embodiments, the first flow guide 50 can be bent. The first connection region 51 includes a first subarea 511 connected to the second connection region 52 and a second subarea 512 connected to the first subarea 511. The second connection region 52, the third connection region 53, and the first subarea 511 are coplanar, and the second subarea 512 is bent relative to the first subarea 511. That is, the bend of the first flow guide 50 is located in the first connection region 51. The second subarea 512 is connected to the first tab 30. In this case, the first subarea 511, the second connection region 52, and the third connection region 53 are arranged along the first direction X, and the plane containing the second connection region 52, the third connection region 53, and the first subarea 511 is perpendicular to the second direction Y.

[0066] As shown in Figure 6, which is a bottom view of the first flow guide 50 of the secondary battery 100 shown in Figure 5A, the minimum cross-sectional area of ​​each second connection region 52 along the thickness direction of the second connection region 52 is S1, and the cross-sectional area of ​​the third connection region 53 along the thickness direction of the third connection region 53 is S2. At least one second connection region 52 satisfies the following conditions: 0.1S2≤S1≤0.5S2. Because the minimum cross-sectional area S1 of each second connection region 52 is small, the second connection region 52 can be melted preferentially under the action of the short-circuit current when the secondary battery 100 short-circuits. This also reduces the impact of the melting of the second connection region 52 on the service life of the secondary battery 100 during normal operation. It can be understood that, as shown in Figures 4A and 4B, when the first flow guide 50 is bent, the thickness directions of the second connection region 52 and the thickness directions of the third connection region 53 are both in the second direction Y. Because the bend of the first flow guide 50 is located in the first connection area 51 rather than the second connection area 52, the risk of the second connection area 52, which has a smaller minimum cross-sectional area, fracturing easily when the secondary battery 100 is subjected to mechanical abuse (such as vibration or dropping), thereby reducing the risk of the secondary battery 100 malfunctioning due to the fracturing of all second connection areas 52 during mechanical abuse. Furthermore, the smaller minimum cross-sectional area S1 of each second connection area 52 allows each second connection area 52 to be preferentially fused under the short-circuit current when the secondary battery 100 short-circuits.

[0067] In some embodiments, each second connection region 52 satisfies the following: 0.2S2 ≤ S1 ≤ 0.4S2. By further limiting the upper limit of S1, the second connection region 52 becomes more sensitive to short-circuit currents and high temperatures. Not only can it be promptly fused when a short circuit occurs in the secondary battery 100, but it can also be more easily fused when the first polymer melts due to a safety hazard 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 fusion 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 FIG6 , in some embodiments, the thickness H2 of each second connection region 52 is less than the thickness H1 of the first connection region 51 and is also less than the thickness H3 of the third connection region 53, thereby making the minimum cross-sectional area S1 of each second connection region 52 smaller. The thicknesses of the first connection region 51 and the third connection region 53 may be the same or different. In other embodiments, the thickness H2 of each second connection region 52 may also be equal to the thickness H1 of the first connection region 51 or equal to the thickness H3 of the third connection region 53. At the same time, in the second direction Y (the arrangement direction of the two second connection regions 52 in FIG6 is the second direction Y), the width W2 of each second connection region 52 is less than the width W1 of the first connection region 51 or less than the width W3 of the third connection region 53, which can also make the minimum cross-sectional area S1 of each second connection region 52 smaller.

[0069] As shown in FIG5A , in some embodiments, when viewed along the thickness direction of the second connection region 52, the second connection region 52 includes a first side 521 and a second side 522 disposed opposite each other. The first side 521 and the second side 522 are both connected between the first connection region 51 and the third connection region 53. When viewed along the thickness direction of the second connection region 52, the first side 521 and the second side 522 can both be straight lines. In this case, the minimum cross-sectional area S1 of each second connection region 52 is the area of ​​the cross section taken along the thickness direction of the second connection region 52 through any point on the first side 521.

[0070] As shown in Figures 4A to 5A, the first insulating protective layer 70 covers at least the surface of the second connection area 52. Because the first insulating protective layer 70 can cover the second connection area 52 with a smaller minimum cross-sectional area, it protects the second connection area 52 when the secondary battery 100 is subjected to mechanical abuse, reducing the risk of the second connection area 52 breaking (for example, when dropped, the electrode assembly 20 shakes within the housing 10, thereby pulling on the first electrode tab 30 and the first flow guide 50, causing the second connection area 52 to break), which could cause the secondary battery 100 to malfunction. In some embodiments, the first insulating protective layer 70 can cover multiple surfaces of the second connection area 52 to enclose the second connection area 52. This allows the first insulating protective layer 70 to fully protect the second connection area 52 during normal operation of the secondary battery 100, reducing the risk of the second connection area 52 breaking during mechanical abuse. The first insulating protective layer 70 can also cover a portion of the surface of the first connection area 51 and a portion of the surface of the third connection area 53. This allows the first insulating protective layer 70 to fully protect the second connection area 52 during normal operation of the secondary battery 100.

[0071] Furthermore, the first insulating protective layer 70 includes a first polymer having a melting point of 100 to 170 degrees Celsius. This allows the first polymer to melt promptly when the interior of the secondary battery 100 reaches this melting point (e.g., when a high current discharge or micro-short circuit occurs within the secondary battery 100, or when the ambient temperature is high, although the internal temperature of the secondary battery 100 does not reach the short-circuit high temperature, a safety hazard still exists). This weakens or even eliminates the protective effect of the first insulating protective layer 70 on the second connection region 52, making the second connection region 52 more susceptible to rupture under mechanical abuse, thus preventing the secondary battery 100 from continuing to operate despite the safety hazard. In some embodiments, the first polymer is made of at least one of polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), a modified polypropylene material, or a modified polyethylene material. For example, 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. In addition, the polyethylene modified material obtained by adding other materials to polyethylene for modification 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 also be adjusted by a similar method. Optionally, the melting point of the first polymer is 100 degrees Celsius to 130 degrees Celsius, thereby improving the sensitivity of the first polymer when there are safety hazards in the secondary battery 100.

[0072] In the present application, when the secondary battery 100 is operating normally, the first insulating protective layer 70 can cover the second connection region 52, which has a smaller minimum cross-sectional area. This protects the second connection region 52 from mechanical abuse and reduces the risk of fracture. In the event of a short circuit in the secondary battery 100, the second connection region 52, which has a smaller minimum cross-sectional area, can preferentially fuse under the action of the short-circuit current, severing the connection between the first tab 30 and external components, effectively placing the secondary battery 100 in an open-circuit state and mitigating safety issues caused by continued internal temperature increases. Furthermore, when the melting point of the first polymer within the secondary battery 100 is reached, the first polymer of 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 region 52. This makes the second connection region 52 more susceptible to fracture during mechanical abuse, preventing the secondary battery 100 from continuing to operate despite potential safety hazards. Therefore, the second connection region 52 and the first insulating protective layer 70 work together to improve the safety and reliability of the secondary battery 100.

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

[0074] Referring to Figures 5B to 5D , in some other embodiments, the first side 521 may be curved, i.e., non-linear, when viewed along the thickness of the second connection region 52. 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 portion 5210 disposed between the first and second endpoints 5211, 5212. The top portion 5210 is recessed toward the interior of the second connection region 52 relative to the first and second endpoints 5211, 5212. Because the first side 521 is curved and the top portion 5210 of the first side 521 is recessed toward 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 taken along the thickness of the second connection region 52 through the top portion 5210. This allows the second connection region 52 to preferentially fuse at the location corresponding to the top portion 5210 when a short circuit occurs in the secondary battery 100. Furthermore, in some specific embodiments, at least a portion of the first side 521 may be in the shape of a broken line. As shown in FIG5B , 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 FIG5C , the first side 521 is V-shaped, and the top 5210 of the first side 521 can be a pointed top. As shown in FIG5D , the first side 521 is sawtooth-shaped, and the top 5210 of the first side 521 is the peak of the sawtooth. By setting the first side 521 to be at least partially zigzag-shaped, when the protective effect of the first insulating protective layer 70 on the second connection area 52 is weakened or even eliminated, the second connection area 52 is more likely to break during mechanical abuse, preventing the secondary battery 100 with safety hazards from continuing to operate. The shape of the second side 522 can be the same as that 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 of the second side 522 (not shown) in the 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 preferentially melting 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. This allows the first polymer to melt before the separator 23 when a short circuit occurs in the secondary battery 100, further reducing the risk of the separator 23 preferentially melting and exacerbating the short circuit.

[0076] As shown in Figures 4A and 4B, when the housing 10 is a packaging bag, the first insulating protective layer 70 is sandwiched within the edge seal 17. The first insulating protective layer 70 also seals the first flow guide 50 and the edge seal 17. Specifically, the first insulating protective layer 70 fills any gaps between the second connection area 52 or the third connection area 53 and the edge seal 17, thereby sealing the first flow guide 50 and the edge seal 17. This reduces the risk of leakage and separation of the first flow guide 50 from the edge seal 17 during use, and also maintains electrical insulation between the first flow guide 50 and the housing 10. The first insulating protective layer 70 can have a two-layer structure, comprising a first layer 71 and a second layer 72 stacked together. The first layer 71 comprises the aforementioned first polymer, so that it can melt promptly when the melting point of the first polymer is reached within the secondary battery 100. The second layer 72 comprises a second polymer with a melting point of 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 edge seal 17 and the first layer 71, respectively. The second layer 71 has a high sealing performance, which can further reduce the risk of leakage during use and the risk of separation of the first flow guide 50 from the edge seal 17. In other 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 can also include a second polymer. The melting point of the second polymer can be higher than the melting point of the first polymer. In this case, when the melting point is reached inside the secondary battery 100, the first polymer melts immediately, 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%, so that when the melting point is reached inside the secondary battery 100, the protective effect of the first insulating protective layer 70 on the second connection area 52 is weakened.

[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 edge seal 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 is weakened or even eliminated, the second connection area 52 located outside the housing 10 is more likely to break under 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 accommodating portion 16.

[0078] As shown in Figure 9 , in other embodiments, the first connection region 51, the second connection region 52, and the third connection region 53 may also be coplanar. That is, the first flow guide 50 is not bent as a whole. In this case, the first connection region 51, the second connection region 52, and the third connection region 53 are arranged in the first direction X, and the plane of the first flow guide 50 is perpendicular to the second direction Y. After the first tab 30 is connected to the first flow guide 50, the first connection region 51 of the first flow guide 50 extends from the edge seal 17 along the first direction X and out of the housing 10.

[0079] Referring to Figures 10 and 11 , another embodiment of the present application also provides a secondary battery 200. Differences from the aforementioned secondary battery 100 include that the housing 10 can also be made of metal. Accordingly, the secondary battery 200 can be a cylindrical battery, a prismatic battery, or a button battery. Figures 10 and 11 illustrate the secondary battery 200 as a cylindrical battery, with the electrode assembly 20 having a wound structure. A coordinate system is established based on mutually perpendicular first and second directions X and Y. In the description of the present embodiment, the first direction X is the direction in which the first electrode tab 30 extends from the first electrode sheet 21. Any direction within a two-dimensional plane perpendicular to the first direction X can be considered the second direction Y of the present application. In some embodiments, the housing 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 connected between 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 storage space for accommodating the electrode assembly 20 and electrolyte, and the first end wall 11 covers the storage space. The first pole 14 is electrically isolated from the first end wall 11 . At this time, the third connection region 53 is connected to the first pole 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, with the mass percentage of the first polymer in the first insulating protective layer 70 being greater than or equal to 50%. The first insulating protective layer 70 may also include only the first polymer, i.e., the mass percentage of the first polymer in the first insulating protective layer 70 is 100%.

[0081] As shown in Figure 11, the first current collector 210 of the first electrode sheet 21 includes a first edge 21a facing the first end wall 11, and the first electrode tab 30 is formed by extending from the first edge 21a. Along the direction in which the first edge 21a extends within the electrode assembly 20, the width of the first electrode tab 30 can be equal to the width of the first current collector 210. This prevents excessive current concentration in the first electrode sheet 21, reduces the internal resistance of the first electrode sheet 21, and thereby improves the charge and discharge rate of the first electrode sheet 21. The first electrode tab 30 includes a first electrode tab region 31 connected to the first edge 21a and a second electrode tab region 32 connected to the first electrode tab region 31. The second electrode tab region 32 is bent relative to the first electrode tab region 31 and forms a first end face 320. A first connection region 51 is connected to the first end face 320, thereby connecting the first electrode tab 30 to the first electrode post 14 via the first current guide 50. In this way, the first electrode post 14 can exhibit the same electrical polarity as the first electrode sheet 21. During the manufacturing process, a portion of the first tab 30 is flattened by a flattening device to form a flat surface, and the flat surface is the first end surface 320 formed by the second tab region 32 .

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

[0083] As shown in Figure 11, in some embodiments, the first flow guide 50 can be bent so that, when viewed along the thickness of the first connection region 51, the first connection region 51 and the third connection region 53 overlap. Specifically, please refer to Figure 12, which shows the structure of the first flow guide 50 shown in Figure 11 after unfolding. In some embodiments, the third connection region 53 includes a third subregion 531 connected to the second connection region 52 and a fourth subregion 532 connected to the third subregion 531. The first connection region 51, the second connection region 52, and the third subregion 531 are coplanar, and the fourth subregion 532 is bent relative to the third subregion 531. In other words, the bend of the first flow guide 50 is located in the third connection region 53. This reduces the risk of the second connection region 52, which has a smaller minimum cross-sectional area, fracturing under mechanical abuse when the secondary battery 100 is operating normally. When viewed along the thickness of the first connection region 51, the first connection region 51 and the fourth subregion 532 overlap. The first connection area 51 is connected to the first end surface 320 , for example, the first connection area 51 can be welded to the first end surface 320 . The fourth section 532 of the third connection area 53 is connected to the first pole 14 , for example, the fourth section 532 can be welded to the first pole 14 .

[0084] Figures 13 to 15 show that the secondary battery 200 is a square shell battery, in which case the electrode assembly 20 can be a wound structure or a laminated structure. In some embodiments, the housing 10 includes a first end wall 11 and a second end wall 12 arranged opposite to each other in a first direction X, a side wall 13 connected between the first end wall 11 and the second end wall 12, and a first pole 14 and a second pole 15 respectively provided on the first end wall 11. The first pole 14 and the second pole 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 storage space for accommodating the electrode assembly 20 and the electrolyte, and the first end wall 11 covers the storage space.

[0085] Please also refer to Figure 16, which is a schematic diagram of the structure of the first flow guide 50 shown in Figure 14 or Figure 15 after it is unfolded. In addition to the first connection area 51, the second connection area 52, and the third connection 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 connection area 52 is connected to the third side 551. The bending area 54 is connected between the fourth side 552 and the third connection area 53. The bending area 54 is bent relative to both the transition area 55 and the third connection area 53. Observed from the thickness direction of the third connection area 53, the transition area 55 and the third connection area 53 overlap. The transition region 55 and the third connection region 53 can jointly 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 region 55 connected to the bend region 54 can provide a larger buffer space, reducing the risk of the first tab 30 detaching from the first flow guide 50 and causing the secondary battery 200 to malfunction. Although FIG14 shows that the second segment 30b of the first tab 30 is connected to the transition region 55, it is understood that the first connection region 51 in FIG14 is actually located behind the transition region 55. Therefore, the second segment 30b of the first tab 30 is actually connected to the first connection region 51 located behind the transition region 55.

[0086] The secondary battery 100 or the secondary battery 200 of the present application may be a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

[0087] Referring to Figure 17, an embodiment of the present application further provides an electric device 1, comprising a battery compartment 101 and a secondary battery 100 (or secondary battery 200) housed in the battery compartment 101. The electric device 1 is powered by the above-mentioned secondary battery 100, and the safety and reliability of the secondary battery 100 are improved. In some embodiments, the electric device 1 of the present application can be, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electric notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0088] The performance of the secondary battery provided by this application is described below through specific examples and comparative examples. The present application is described using a lithium-ion soft-pack secondary battery, a positive electrode as the first electrode sheet, and a negative electrode as the second electrode sheet as an example, in conjunction 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: The positive electrode active material lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. Pre-apply foam glue to the predetermined area of ​​the current collector aluminum foil with a thickness of 12μm, and evenly apply the slurry on one surface of the aluminum foil. Heat the foam glue to remove the foam glue so that the predetermined area of ​​the aluminum foil is exposed, and then dry it at 90°C to obtain a positive electrode active material layer with a coating thickness of 100μm. Repeat the above coating steps on the other surface of the aluminum foil to obtain a double-sided coated first electrode. Next, weld the first pole ear on the predetermined area of ​​the aluminum foil. The material of the first pole ear is aluminum.

[0091] (2) Preparation of the second electrode sheet: Mix the negative electrode active materials artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) in a weight ratio of 96:1.5:2.5, add deionized water as a solvent, and prepare a slurry with a weight percentage of 70wt%, and stir evenly. Pre-apply foam glue on the predetermined area of ​​the 10μm current collector copper foil, evenly apply the slurry on one surface of the copper foil, heat it to make the foam glue fall off so that the predetermined area of ​​the copper foil is exposed, and dry it at 110℃ to obtain a negative electrode active material layer with a coating thickness of 130μm. Repeat the above steps on the other surface of the copper foil to obtain a double-sided coated second electrode sheet. Then, weld the second pole ear on the predetermined area of ​​the copper foil. The material of the second pole ear is copper.

[0092] (3) Preparation of electrolyte: In a dry argon atmosphere, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed at a mass ratio of EC:EMC:DEC = 30:50:20. Then, lithium salt lithium hexafluorophosphate (LiPF6) was 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 isolation film: A polyethylene (PE) film with a thickness of 15 μm was selected.

[0094] (5) Assembly of secondary battery: The first electrode sheet, the isolation membrane and the second electrode sheet are stacked and wound in sequence to obtain an electrode assembly with a wound structure, and the electrode assembly is placed in a shell. Then, the first tab is stacked and welded to the first flow guide, the material of the first flow guide is aluminum foil, and the first insulating protective layer is covered on the second connection area of ​​the first flow guide. The second tab is stacked and welded to the second flow guide, the material of the second flow guide is copper foil. The first insulating protective layer is a double-layer structure, and the second layer uses PP with a melting point of 160-170 degrees Celsius. The relevant parameters of the first flow guide and the first layer of the first insulating protective layer are recorded in Table 1. The first flow guide and the second insulating protective layer have structures similar to those of the first flow guide and the first insulating protective layer, respectively. Then, liquid injection, chemical formation and packaging are carried out, and the first insulating protective layer is sealed to connect the edge sealing and the first flow 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 the above-mentioned embodiment 1 lies in the relevant parameters of the first flow guide and the first insulating protective layer.

[0097] Comparative Example 7

[0098] The difference from the above-mentioned embodiment 1 is that the first insulating protection layer is omitted.

[0099] 100 secondary batteries of 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 respectively. The corresponding test results are recorded in Table 1.

[0100] The melting point test steps of 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 tab, cleaning it, and drying it at 80°C to obtain a sample; 2) placing the sample in an aluminum crucible, the sample weight is 1 mg, 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°C to 200°C, the heating rate is 10°C / min, and the DSC curve is analyzed to obtain the melting point.

[0101] The external short-circuit test steps for secondary batteries include: 1) charging the secondary battery to 100% SOC (State of Charge) under environmental conditions of 25±5°C; 2) placing the secondary battery in a test environment at 25±5°C, using a 10±2mΩ load resistor to short-circuit the first and second flow guide members of the secondary battery respectively. If the secondary battery does not catch fire or explode, test until the voltage is lower than 0.2V. Monitor the temperature changes of the secondary battery during the test. The test is terminated when the battery temperature drops to ±5°C of the ambient temperature or the short-circuit time reaches 24 hours; 3) disassembling the secondary battery to observe whether the second connection area of ​​the first flow guide is broken, and then calculate the fracture rate of the first flow guide in each sample (that is, the proportion of broken samples in all samples).

[0102] The room temperature drop test steps for secondary batteries include: 1) charging the secondary battery to 100% SOC under environmental conditions of 25±5℃; 2) placing the secondary battery in a fixture compartment and using an automatic dropping device to drop the bottom, side, and top surfaces of the secondary battery in sequence from a position of 1.8m to a steel plate, for a total of 6 drops, or 18 times; 3) disassembling the secondary battery after the drop, observing whether the second connection area of ​​the first guide member is broken, and then calculating the fracture rate of the first guide member in each sample.

[0103] The high-temperature drop test steps for secondary batteries include: 1) inspecting the appearance of the secondary battery before and after the test and taking photos; 2) attaching a temperature-sensing wire to the center of the surface of the secondary battery, and then placing the secondary battery vertically in a hot box, heating it to 130±2°C at a heating rate of 5±2°C and maintaining it for 10 minutes; 3) charging the secondary battery to 100% SOC under environmental conditions of 25±5°C; 4) placing the battery in a fixture compartment, and using an automatic drop device to drop the bottom, side, and top of the battery in a round from a position of 1.8m to a steel plate, for a total of 6 rounds, or 18 times; 5) disassembling the secondary battery after the drop is completed, observing whether the second connection area of ​​the first guide member is broken, and then calculating the fracture rate of the first guide member in each sample.

[0104] The test steps for the DC resistance (DCR) growth rate of a secondary battery include: 1) charging the secondary battery at a constant current of 0.7C to 4.48V under an environmental condition of 25±5°C, then charging at a constant voltage to a current of 0.05C, then discharging at a constant current of 0.1C for 10 seconds, and measuring the voltage V0 before discharge. Then, discharging at a constant current of 1C for 1 second, and measuring the voltage V1 after discharge. The initial DCR of the battery = (V1-V0) / 1C; 2) performing 30 charge and discharge cycles according to the same charge and discharge steps as above, and then measuring the DCR after the cycle; 3) calculating the DCR growth rate after the cycle = (DCR after the cycle - initial DCR) / initial DCR×100%.

[0105] Table 1

[0106] As shown in the test results in Table 1, compared to Comparative Example 1, Examples 4, 9-14 satisfy the requirement of 0.1S2≤S1, reducing the risk of the second connection region fusing during normal secondary battery operation and fracturing during a room-temperature drop. Consequently, the second connection region does not rupture during normal cycling, the DCR growth rate of the secondary battery is low, and the secondary battery can operate normally. Compared to Comparative Example 2, Examples 4, 9-14 satisfy the requirement of S1≤0.5S2, allowing the second connection region to fuse promptly when a short circuit occurs in the secondary battery. This increases the fracturing rate of the first flow guide after a short circuit, improving the safety of the secondary battery. Compared to Comparative Example 3, the melting point of the first polymer in Examples 1-8 is not less than 100 degrees Celsius. Therefore, when the secondary battery does not pose a safety risk, the first polymer will not melt and will continue to provide protection to the second connection region. Consequently, the first flow guide does not rupture during the room-temperature drop test, allowing the secondary battery to continue operating. Compared to Comparative Example 4, the melting point of the first polymer in Examples 1-8 does not exceed 170°C. Therefore, the first polymer melts in the event of a safety hazard in the secondary battery. Consequently, the fracture rate of the first flow guide is increased during the high-temperature drop test, preventing the secondary battery from continuing to operate despite the safety hazard, thereby improving the safety of the secondary battery. In Comparative Examples 5-6, both 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 results in multiple secondary battery performance tests.

[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 flow guide after the high-temperature drop test also gradually increases.

[0108] Comparing Example 4 with Examples 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 to short-circuit current and high temperature decreases accordingly, thereby reducing the safety of the secondary battery. However, 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 meet the condition of 0.2S2≤S1≤0.4S2, the sensitivity of the second connection region to short-circuit current and high temperature is high, while the secondary battery has a low DCR growth rate, allowing the secondary battery to achieve both high safety and cycling capacity.

[0109] The above disclosure is only a preferred embodiment of the present application, and certainly cannot be used to limit the present application. Therefore, equivalent changes made based on the present application are still within the scope covered by the present application.

Claims

1. A secondary battery comprising a housing, an electrode assembly disposed in the housing, and a first electrode tab, wherein the electrode assembly comprises a first electrode sheet, the first electrode tab is connected to the first electrode sheet, wherein: The secondary battery further includes: a first flow guide, at least a portion of which is disposed within the housing, the first flow guide comprising a first connection region, at least one second connection region, and a third connection region, the second connection region being connected between the first connection region and the third connection region, the first connection region being connected to the first tab, the third connection region being connected to the housing, the minimum cross-sectional area of ​​the second connection region along a thickness direction of the second connection region being S1, the cross-sectional area of ​​the third connection region along a thickness direction of the third connection region being S2, and at least one of the second connection regions satisfying the following conditions: 0.1S2≤S1≤0.5S2; The first insulating protective layer at least covers the surface of the second connection area. The first insulating protective layer includes a first polymer. The melting point of the first polymer is 100 degrees Celsius to 170 degrees Celsius.

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

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

4. The secondary battery according to any one of claims 1 to 3, wherein The first insulating protection layer also covers a portion of the surface of the first connection region and a portion of the surface of the third connection region.

5. The secondary battery according to 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 Observing along the thickness direction of the second connection area, the second connection area includes a first side and a second side arranged opposite to each other, the first side and the second side are both connected between the first connection area and the third connection area, the first side is a curved shape, and the first side includes a first endpoint connected to the first connection area, a second endpoint connected to the third connection area, and a top located between the first endpoint and the second endpoint, and the top is recessed toward the interior of the second connection area compared to the first endpoint and the second endpoint.

7. The secondary battery according to claim 6, wherein At least a portion of the first side is in the shape of a broken line.

8. The secondary battery according to any one of claims 1 to 7, wherein The thickness of the second connection region is smaller than the thickness of any one of the first connection region and 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 integrated structure.

10. The secondary battery according to any one of claims 1 to 9, wherein The shell is a packaging bag, which includes a connected accommodating portion and a sealed edge. The electrode assembly is accommodated in the accommodating portion, at least part of the second connection area is located in the sealed edge, in the accommodating portion or outside the shell, and at least part of the third connection area extends out of the shell. The first insulating protective layer includes a first layer and a second layer that are stacked, the first layer includes the first polymer, the second layer includes a second polymer, the melting point of the second polymer is 160 to 170 degrees, and the second layer is connected to the sealed edge and the first layer respectively.

11. The secondary battery according to claim 10, wherein The first connection region, the second connection region, and the third connection region are coplanar.

12. The secondary battery according to 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 compared to the first partition. The second partition is connected to the first tab.

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

14. The secondary battery according to claim 13, wherein The electrode assembly has a wound structure, the first pole sheet includes a first current collector, the first current collector includes a first end edge facing the first end wall, the first pole tab is formed by extending from the first end edge, the first pole tab includes a first pole tab area connected to the first end edge and a second pole tab area connected to the first pole tab area, the second pole tab area is bent compared to the first pole tab area and forms a first end face, the first connection area is connected to the first end face; when observed along the thickness direction of the first connection area, the first connection area and the third connection area overlap.

15. The secondary battery according to 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, and the fourth partition is bent compared to the third partition. When observed along the thickness direction of the first connection area, the first connection area and the fourth partition overlap.

16. The secondary battery according to claim 11, wherein The first flow guide also 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 connection area is connected to the third side, the bending area is connected between the fourth side and the third connection area, the bending area is bent relative to the transition area and the third connection area, and when observed from the thickness direction of the third connection area, the transition area and the third connection area overlap.

17. An electrical device comprising a battery compartment, wherein: The electrical device further comprises a secondary battery according to any one of claims 1 to 16, and the secondary battery is accommodated in the battery compartment.

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