Secondary battery and electronic device

Abstract

The application provides a secondary battery and an electronic device. The secondary battery comprises a shell, an electrode assembly, a first positive electrode lug and a first protective piece. The electrode assembly is flat and located in the shell. A positive electrode tab of the electrode assembly comprises a first positive electrode segment, and a negative electrode tab of the electrode assembly comprises a first negative electrode segment. The first negative electrode segment and the first positive electrode segment are arranged in a stack and adjacent to each other along a second direction perpendicular to a first direction. The first positive electrode segment comprises a first positive electrode active material layer. The first positive electrode active material layer is provided with a first groove accommodating the first positive electrode lug. Along the first direction, the first positive electrode segment comprises a first end. The first negative electrode segment has a second end and a first segment beyond the first end. The second end and the first end are located on the same side of the electrode assembly in the first direction. The first protective piece comprises a first part and a second part. The first part is located between the first positive electrode lug and the first negative electrode segment and covers the first segment. The second part covers the second end, which is conducive to improving the safety performance of the secondary battery.

Description

Technical Field

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

[0002] Rechargeable batteries are widely used in portable electronic devices, electric vehicles, power tools, drones, energy storage devices, and other fields. As application environments and conditions become increasingly complex, higher requirements are being placed on the safety performance of rechargeable batteries. Summary of the Invention

[0003] This application provides a secondary battery and an electronic device to improve the safety performance of the secondary battery.

[0004] In a first aspect, embodiments of this application provide a secondary battery, the secondary battery including a casing, an electrode assembly, a first positive electrode tab, and a first protective element; the electrode assembly is flat and located within the casing, the electrode assembly including a positive electrode sheet, a negative electrode sheet, and a separator membrane located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet, the separator membrane, and the negative electrode sheet being stacked and wound together, the winding center axis direction of the electrode assembly being a first direction; the positive electrode sheet including a first positive electrode segment, the negative electrode sheet including a first negative electrode segment, the first negative electrode segment and the first positive electrode segment being stacked and adjacent to each other along a second direction perpendicular to the first direction; the first positive electrode segment including a first positive electrode active material layer, the first positive electrode active material layer being disposed The electrode assembly has a first groove along the first direction. The first positive electrode segment includes a first end, and the first negative electrode segment has a second end and a first segment extending beyond the first end in the first direction. The second end and the first end are located on the same side of the electrode assembly in the first direction. The first positive electrode tab is partially accommodated in the first groove. The first positive electrode tab is connected to the first positive electrode segment and protrudes beyond the first end along the first direction. The first positive electrode tab is bent toward the first protective member. The first protective member includes a connected first part and a second part. The first part is disposed between the first positive electrode tab and the first negative electrode segment. Along the first direction, the first part covers the first segment, and the second part covers the second end.

[0005] In the above technical solution, a first protective component is provided on the electrode assembly. The first protective component includes a first part and a second part connected together. The first part of the first protective component is located between the first negative electrode segment and the first positive electrode tab, and the first part covers the first segment of the first negative electrode segment that extends beyond the first positive electrode segment. Therefore, the first part can effectively prevent short circuits between the first positive electrode tab and the first segment of the first negative electrode segment that extends beyond the positive electrode segment, reducing the risk of a short circuit in the secondary battery caused by contact between the first positive electrode tab and the first segment. This reduces the risk of fire and explosion in the secondary battery, improving its safety performance. In the event of a short circuit in the secondary battery, the temperature of the first positive electrode tab is high, and the separator between the first positive electrode segment and the first negative electrode segment may melt due to the high temperature of the first positive electrode tab. Because the first part of the first protective component is located between the first negative electrode segment and the first positive electrode tab, and covers the first segment of the first negative electrode segment that extends beyond the first positive electrode segment, even if the separator between the first positive electrode segment and the first negative electrode segment melts, the first part can still reduce the risk of contact between the first positive electrode tab and the first segment, thereby reducing the risk of a secondary short circuit in the secondary battery, further reducing the risk of fire and explosion in the secondary battery, and improving its safety performance. After a secondary battery short circuits, a large amount of gas is generated inside the secondary battery, which may cause the electrode assembly to deform and pull on the first positive electrode tab. This could cause the first positive electrode tab to come into contact with the end of the first negative electrode segment on the same side as the first end, resulting in a secondary short circuit. The first protective component includes a second part connected to the first part. The second part covers the second end of the first negative electrode segment on the same side as the first end, reducing the risk of the first positive electrode tab coming into contact with the second end due to deformation caused by pulling, thereby further reducing the risk of a secondary short circuit in the secondary battery.

[0006] In some embodiments of the first aspect of this application, the first portion is adhered to the surface of the first negative electrode segment facing the first positive electrode segment.

[0007] In the above technical solution, the first part is bonded to the surface of the first negative electrode section facing the first positive electrode section. This not only allows the first part to act as an insulating separator between the first negative electrode section and the first positive electrode tab, reducing the risk of short circuit caused by contact between the first positive electrode tab and the first negative electrode section, but also helps the first part to be stably positioned between the first negative electrode section and the first positive electrode tab, reducing the risk of movement of the first part. This allows the first part to better separate the first negative electrode section and the first positive electrode tab, reducing the risk of short circuit in the secondary battery and improving the safety performance of the secondary battery. Fixing the first part to the surface of the first negative electrode section facing the first positive electrode section by bonding is convenient and provides good stability.

[0008] In some embodiments of the first aspect of this application, the separator includes a first dividing segment along the second direction, the first dividing segment being located between the first positive electrode segment and the first negative electrode segment, and the first portion being adhered to the first dividing segment.

[0009] In the above technical solution, the first part is bonded to the first separator section. This not only allows the first part to act as an insulating separator between the first negative electrode section and the first positive electrode tab, reducing the risk of short circuit caused by contact between the first positive electrode tab and the first negative electrode section, but also helps the first part to be stably positioned between the first negative electrode section and the first positive electrode tab, reducing the risk of movement of the first part. This allows the first part to better separate the first negative electrode section and the first positive electrode tab, reducing the risk of short circuit in the secondary battery and improving the safety performance of the secondary battery. Bonding the first part to the first separator section also helps to reduce the risk of shrinkage and deformation of the first separator section. Fixing the first part to the first separator section by bonding is convenient and has good stability.

[0010] In some embodiments of the first aspect of this application, the first portion is adhered to the surface of the first separator facing the first positive electrode segment.

[0011] In the above technical solution, the first part is bonded to the surface of the first separator facing the first positive electrode section, which can reduce the risk of the first separator being melted by the high temperature of the first positive electrode tab, and also reduce the risk of the first separator shrinking and deforming due to the high temperature at the first positive electrode tab, thereby reducing the risk of secondary short circuit of the secondary battery and improving the safety performance of the secondary battery.

[0012] In some embodiments of the first aspect of this application, along a third direction perpendicular to the first and second directions, the width of the first groove is T mm, the width of the first portion is L1 mm, and 1.2≤L1 / T≤3.

[0013] In the above technical solution, 1.2≤L1 / T≤3 not only makes the first part have a large coverage area along the third direction, reducing the risk of short circuit in the secondary battery and improving safety performance, but also makes as many areas of the first part as possible correspond to the first groove. After the electrode assembly is subjected to pressure in the second direction, the first groove can alleviate the problem of the electrode assembly size increasing in the second direction caused by the setting of the first part, thereby helping the secondary battery to have a higher energy density.

[0014] In some embodiments of the first aspect of this application, along the first direction, the length of the first portion is N1 mm, the length of the first groove is M mm, and 1 ≤ N1 / M ≤ 1.5.

[0015] In the above technical solution, 1≤N1 / M≤1.5 makes the first part have a large coverage area along the first direction, which can effectively play a separating role between the first positive electrode tab and the first negative electrode segment, and can also reduce the effective area of ​​active material loss, thereby making the secondary battery have a high energy density.

[0016] In some embodiments of the first aspect of this application, the first protective member further includes a third portion, wherein the first portion, the second portion and the third portion are connected in sequence, and the third portion is bonded to the first outer surface of the electrode assembly, wherein the first outer surface and the first portion are located on the same side of the first positive electrode segment in the second direction.

[0017] In the above technical solution, the first part, the second part, and the third part of the first protective component are connected in sequence. The first part is located between the first negative electrode segment and the first positive electrode tab. The second part covers the second end of the first negative electrode segment. The third part is bonded to the first outer surface of the electrode assembly. The first outer surface and the first part are located on the same side of the first positive electrode segment in the second direction. Thus, the first protective component spans all the portions of the negative electrode sheets that extend beyond the first end on one side of the first positive electrode segment, thereby effectively preventing further contact and short circuit between the first positive electrode tab and the portions of the negative electrode sheets that extend beyond the positive electrode sheet. This reduces the risk of contact between the first positive electrode tab and the portions of the negative electrode sheets that extend beyond the first end on the side of the first positive electrode tab facing the first negative electrode segment, thereby reducing the risk of secondary battery fire and explosion and improving the safety performance of the secondary battery.

[0018] In some embodiments of the first aspect of this application, along a third direction perpendicular to the first and second directions, the width of the first groove is T mm, and the width of the third portion is L2 mm, where 0.5 ≤ L2 / T ≤ 1.

[0019] In the above technical solution, 0.5≤L2 / T≤1 not only makes the third part have a large coverage area along the third direction, reducing the risk of short circuit in the secondary battery and improving safety performance, but also allows as many areas of the third part as possible to correspond to the first groove. After the electrode assembly is subjected to pressure in the second direction, the first groove can alleviate the problem of the electrode assembly size increasing in the second direction due to the setting of the third part, thereby helping the secondary battery to have a higher energy density.

[0020] In some embodiments of the first aspect of this application, along the first direction, the length of the first groove is M mm, and the length of the third portion is N2 mm, where N2 ≤ M.

[0021] In the above technical solution, N2≤M. When viewed along the second direction, the projection of the third part can be completely located within the first groove in the first direction. After the electrode assembly is subjected to pressure in the second direction, the first groove can alleviate the problem of the electrode assembly size increasing in the second direction due to the setting of the third part, thereby helping the secondary battery to have a higher energy density.

[0022] In some embodiments of the first aspect of this application, the first protective element includes a substrate layer, the substrate layer being made of one or more of polyethylene terephthalate, polyimide, and polypropylene.

[0023] In the above technical solution, the substrate of the first protective component is made of one or more of polyethylene terephthalate, polyimide, or polypropylene, which gives the substrate good mechanical properties and heat resistance, reducing the risk of the first protective component being melted by high temperature.

[0024] In some embodiments of the first aspect of this application, the first protective member further includes an adhesive layer disposed on the surface of the substrate layer, the adhesive layer being made of one or more of polybutadiene, polypropylene, polypentadiene, styrene, butadiene copolymers, and petroleum resin.

[0025] In the above technical solution, the adhesive layer formed by the aforementioned material has high adhesive performance, which can improve connection stability. The adhesive layer formed by the aforementioned material also has a high melting point, reducing the risk that the first protective component may detach from the electrode assembly due to the adhesive layer melting caused by the increased internal temperature of the secondary battery.

[0026] In some embodiments of the first aspect of this application, the first protective member further includes a hot melt layer, wherein the hot melt layer and the adhesive layer are respectively disposed on two opposite surfaces of the substrate layer, and the material of the hot melt layer includes one or more of styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, polyurethane elastomer, polyurethane acrylate, polyisobutylene, or polybutadiene.

[0027] In the above technical solution, the hot-melt layer formed by the above materials has good adhesion after hot melting, which can improve the stability of the connection between the first protective component and other structures.

[0028] In some embodiments of the first aspect of this application, the electrode assembly further includes a second negative electrode segment. Along the second direction, the second negative electrode segment is stacked and adjacent to the first positive electrode segment. The second negative electrode segment and the first negative electrode segment are respectively located on opposite sides of the first positive electrode segment in the second direction. The second negative electrode segment has a second segment extending beyond the first end in the first direction. The second negative electrode segment includes a third end. The first end and the third end are located on the same side of the electrode assembly in the first direction. The secondary battery further includes a second protective member. The second protective member includes a fourth part, a fifth part, and a sixth part connected in sequence. The fourth part is disposed between the first positive electrode segment and the second negative electrode segment. Along the first direction, the fourth part covers the first segment. The fifth part connects the fourth part and the sixth part. The fifth part covers the third end. The sixth part is adhered to the second outer surface of the electrode assembly. The second outer surface and the fourth part are located on the same side of the first positive electrode segment in the second direction.

[0029] In the above technical solution, the first positive electrode segment is located between the first negative electrode segment and the second negative electrode segment. The first positive electrode tab is set in the middle ring of the electrode assembly. After a short circuit, the temperature rise is higher. The setting of the first protective component and the second protective component can effectively prevent the first positive electrode tab from making further contact and short circuit with the part of the negative electrode sheet that extends beyond the positive electrode sheet. This greatly reduces the risk of secondary battery fire and explosion and improves the safety performance of secondary battery. The fourth, fifth, and sixth parts of the second protective component are connected in sequence. The fourth part is located between the second negative electrode section and the first positive electrode section. The fifth part covers the third end of the second negative electrode section. The sixth part is bonded to the second outer surface of the electrode assembly, and the second outer surface and the fourth part are located on the same side of the first positive electrode section. Thus, the second protective component spans all the portions of the negative electrode sheets that extend beyond the first end on one side of the first positive electrode section, thereby effectively preventing further contact and short circuits between the first positive electrode tab and the portions of the negative electrode sheets that extend beyond the positive electrode sheet. This reduces the risk of contact between the first positive electrode tab and the portions of the negative electrode sheets that extend beyond the first end on the side of the first positive electrode tab facing the second negative electrode section, thereby reducing the risk of secondary battery fire and explosion and improving the safety performance of the secondary battery.

[0030] In some embodiments of the first aspect of this application, the secondary battery further includes an electrolyte, the composition of which includes one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, fluoroethylene carbonate, and 1,2-difluoroethylene carbonate.

[0031] In the above technical solution, the electrolyte contains one or more of the above-mentioned components, which makes the electrolyte have a high conductivity.

[0032] In some embodiments of the first aspect of this application, the housing is an aluminum-plastic film or a steel-plastic film.

[0033] In the above technical solution, the shell is made of aluminum-plastic film or steel-plastic film. The shell is more prone to deformation. After gas is generated inside the secondary battery due to high temperature, the shell can alleviate the problem of internal expansion of the secondary battery through its own deformation, thereby reducing the risk of secondary battery explosion.

[0034] Secondly, embodiments of this application provide an electronic device, which includes the secondary battery provided in any of the above embodiments.

[0035] In the above technical solutions, the secondary batteries provided in any of the above embodiments have high safety performance and can improve the power safety and power stability of electronic devices powered by the secondary batteries. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings.

[0037] Figure 1 Cross-sectional views of a secondary battery provided in some embodiments of this application;

[0038] Figure 2 Cross-sectional view of a secondary battery provided for other embodiments of this application;

[0039] Figure 3 This is a schematic diagram of the structure of a wound electrode assembly provided in some embodiments of this application;

[0040] Figure 4 This is a schematic diagram of the structure of a wound electrode assembly provided in other embodiments of this application;

[0041] Figure 5 This is a schematic diagram of the structure of a wound electrode assembly provided in some embodiments of this application;

[0042] Figure 6 A partial cross-sectional view of a secondary battery provided in some embodiments of this application;

[0043] Figure 7 A partial cross-sectional view of a secondary battery provided for other embodiments of this application;

[0044] Figure 8 A partial cross-sectional view of a secondary battery provided for some embodiments of this application;

[0045] Figure 9 A partial cross-sectional view of a secondary battery provided for further embodiments of this application;

[0046] Figure 10 A schematic diagram showing the first groove in the first positive electrode section;

[0047] Figure 11 This is a schematic diagram showing the relative relationship between the first positive electrode tab after it is installed in the first groove and the first part;

[0048] Figure 12 A schematic diagram from another perspective showing the first positive electrode tab installed in the first groove;

[0049] Figure 13 A schematic diagram of the structure of the first protective member provided in some embodiments of this application (unfolded state);

[0050] Figure 14A schematic diagram of the structure of the first protective member (unfolded state) provided for other embodiments of this application;

[0051] Figure 15 A partial cross-sectional view of a secondary battery provided for some other embodiments of this application;

[0052] Figure 16 This is a partial cross-sectional view of a secondary battery provided in some embodiments of this application.

[0053] Icons: 100 - Secondary battery; 10 - Casing; 20 - Electrode assembly; 21 - Positive electrode; 211 - First positive electrode segment; 211a - First positive electrode active material layer; 2111 - First end; 22 - Negative electrode; 22a - Negative electrode tab; 221 - First negative electrode segment; 2211 - First segment; 2212 - Second end; 2213 - First surface; 2214 - First groove; 222 - Second negative electrode segment; 2221 - Second segment; 2222 - Third end; 23 - Separator; 231 - First separator segment; 232 - Second separator segment; 233 - Third separator Segment; 234-Fourth dividing segment; 30-Positive electrode tab; 30a-First positive electrode tab; 40-First protective element; 41-First part; 42-Substrate layer; 43-Adhesive layer; 44-Hot melt layer; 45-Second part; 46-Third part; 50-Positive electrode lead; 60-Second protective element; 61-Fourth part; 62-Fifth part; 63-Sixth part; 70-Third protective element; 80-Fourth protective element; X-First direction; Y-Second direction; Z-Third direction; A-Straight area; B-Bending area; Q1-First outer surface; Q2-Second outer surface. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0055] Therefore, the following detailed description of embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the present application.

[0056] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0057] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0058] In the description of the embodiments of this application, it should be noted that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing this application and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation on this application. Furthermore, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0059] Currently, the application of rechargeable batteries is becoming increasingly widespread in the market. They are widely used in electric bicycles, electric motorcycles, electric cars, and other electric vehicles, as well as in power tools, drones, energy storage devices, and many other fields. As the application areas of rechargeable batteries continue to expand, the market demand is also constantly increasing.

[0060] A secondary battery consists of a casing, electrode assembly, positive tab, and negative tab. The electrode assembly is housed within the casing. The positive tab is electrically connected to the positive electrode plate of the electrode assembly, and the negative tab is electrically connected to the negative electrode plate. When a secondary battery short-circuits, the temperature at the tabs rises, especially at the positive tab. The significant heat causes the tab adhesive to melt, exposing part of the tab. The tab adhesive is a gel that seals and insulates the part of the tab that extends beyond the casing. Simultaneously, a large amount of gas is generated inside the secondary battery after the short circuit. The electrode assembly deforms, stretching the flexible tab, causing it to compress the separator, melt and rupture the separator, and contact the portion of the negative electrode plate that extends beyond the positive electrode plate, resulting in a secondary short circuit. This can lead to a fire or explosion of the secondary battery. For secondary batteries with low-viscosity electrolytes, the gas generation inside the battery is more severe after a short circuit, and the deformation of the electrode assembly and the stretching of the flexible tab are more pronounced. This increases the risk of a secondary short circuit caused by the tab contacting the portion of the negative electrode plate that extends beyond the positive electrode plate, thus increasing the risk of fire and explosion.

[0061] Based on the above considerations, in order to alleviate the problems of secondary battery explosion and fire caused by secondary short circuits, this application provides a secondary battery, which includes a casing, an electrode assembly, a first positive electrode tab, and a first protective element; the electrode assembly is flat and located inside the casing, and includes a positive electrode plate, a negative electrode plate, and a separator between the positive and negative electrode plates, wherein the positive electrode plate, the separator, and the negative electrode plate are stacked and wound together, and the winding center axis of the electrode assembly is in a first direction; the positive electrode plate includes a first positive electrode segment, and the negative electrode plate includes a first negative electrode segment, wherein the first negative electrode segment and the first positive electrode segment are stacked and adjacent to each other along a second direction perpendicular to the first direction; the first positive electrode tab... The electrode segment includes a first positive electrode active material layer, the first positive electrode active material layer is provided with a first groove, along a first direction, the first positive electrode segment includes a first end, the first negative electrode segment has a first segment extending beyond the first end in the first direction, and a second end is located on the same side of the electrode assembly in the first direction as the first end; a first positive electrode tab is partially accommodated in the first groove, the first positive electrode tab is connected to the first positive electrode segment and protrudes from the first end in the first direction; the first positive electrode tab is bent toward the direction of the first protective member, the first protective member includes a connected first part and a second part, the first part is disposed between the first positive electrode tab and the first negative electrode segment, along the first direction, the first part covers the first segment, and the second part covers the second end.

[0062] A first protective element is provided on the electrode assembly. The first protective element includes a first part and a second part connected together. The first part of the first protective element is located between the first negative electrode segment and the first positive electrode tab, and the first part covers the first segment of the first negative electrode segment that extends beyond the first positive electrode segment. Therefore, the first part can effectively prevent short circuits between the first positive electrode tab and the first segment of the first negative electrode segment that extends beyond the positive electrode segment, reducing the risk of a short circuit in the secondary battery caused by contact between the first positive electrode tab and the first segment. This reduces the risk of fire and explosion in the secondary battery, improving its safety performance. In the event of a short circuit in the secondary battery, the temperature of the first positive electrode tab is high, and the separator between the first positive electrode segment and the first negative electrode segment may melt due to the high temperature of the first positive electrode tab. Because the first part of the first protective element is located between the first negative electrode segment and the first positive electrode tab, and covers the first segment of the first negative electrode segment that extends beyond the first positive electrode segment, even if the separator between the first positive electrode segment and the first negative electrode segment melts, the first part can still reduce the risk of contact between the first positive electrode tab and the first segment, thereby reducing the risk of a secondary short circuit in the secondary battery, further reducing the risk of fire and explosion in the secondary battery, and improving its safety performance.

[0063] After a secondary battery short circuits, a large amount of gas is generated inside the secondary battery, which may cause the electrode assembly to deform and pull on the first positive electrode tab. This could cause the first positive electrode tab to come into contact with the end of the first negative electrode segment on the same side as the first end, resulting in a secondary short circuit. The first protective component includes a second part connected to the first part. The second part covers the second end of the first negative electrode segment on the same side as the first end, reducing the risk of the second positive electrode tab coming into contact with the second end due to deformation caused by pulling, thereby further reducing the risk of a secondary short circuit in the secondary battery.

[0064] The secondary batteries disclosed in the embodiments of this application can be used, but are not limited to, in electronic devices such as electric two-wheelers, power tools, drones, and energy storage devices. Secondary batteries meeting the operating conditions of this application can also be used as the power system for electronic devices, which helps improve the safety performance of the secondary batteries.

[0065] This application provides an electronic device that uses a secondary battery as a power source. The electronic device can be, but is not limited to, electronic devices, power tools, electric vehicles, drones, and energy storage devices. Specifically, electronic devices can include mobile phones, tablets, laptops, etc.; power tools can include electric drills, chainsaws, etc.; and electric vehicles can include electric cars, electric motorcycles, electric bicycles, etc.

[0066] like Figure 1 , Figure 2As shown, this application embodiment provides a secondary battery 100, which includes a housing 10, an electrode assembly 20, a first positive electrode tab 30a, and a first protective member 40. The electrode assembly 20 is flat and located inside the housing 10. The electrode assembly 20 includes a positive electrode 21, a negative electrode 22, and a separator 23 located between the positive electrode 21 and the negative electrode 22. The positive electrode 21, the separator 23, and the negative electrode 22 are stacked and wound together, and the winding center axis of the electrode assembly 20 is in the first direction X. The positive electrode 21 includes a first positive electrode segment 211, and the negative electrode 22 includes a first negative electrode segment 221. The first negative electrode segment 221 and the first positive electrode segment 211 are stacked and adjacent to each other along a second direction Y perpendicular to the first direction X. The first positive electrode segment 211 includes a first positive electrode segment 221. The first positive electrode active material layer 211a has a first groove 2214. Along the first direction X, the first positive electrode segment 211 includes a first end 2111, and the first negative electrode segment 221 has a second end 2212 and a first segment 2211 that extends beyond the first end 2111 in the first direction X. The first positive electrode tab 30a is connected to the first positive electrode segment 211 and protrudes from the first end 2111 along the first direction X. The first positive electrode tab 30a is bent toward the first protective member 40. The first protective member 40 includes a connected first part 41 and a second part 45. The first part 41 is disposed between the first positive electrode tab 30a and the first negative electrode segment 221. Along the first direction X, the first part 41 covers the first segment 2211, and the second part 45 covers the second end 2212.

[0067] A first protective element 40 is provided on the electrode assembly 20. The first protective element 40 includes a first part 41 and a second part 45 connected together. The first part 41 of the first protective element 40 is located between the first negative electrode section 221 and the first positive electrode tab 30a, and the first part 41 covers the first section 2211 of the first negative electrode section 221 that extends beyond the first positive electrode section 211. Thus, the first part 41 can effectively prevent the first positive electrode tab 30a from contacting the first section 2211 of the first negative electrode 221 that extends beyond the positive electrode 21, thereby reducing the risk of short circuit of the secondary battery 100 caused by the first positive electrode tab 30a contacting the first section 2211, thereby reducing the risk of fire and explosion of the secondary battery 100 and improving the safety performance of the secondary battery 100.

[0068] In the event of a short circuit in the secondary battery 100, the temperature of the first positive tab 30a is high, and the separator 23 between the first positive electrode segment 211 and the first negative electrode segment 221 may be melted by the high temperature of the first positive tab 30a. Since the first part 41 of the first protective member 40 is located between the first negative electrode segment 221 and the first positive tab 30a, and the first part 41 covers the first segment 2211 of the first negative electrode segment 221 that extends beyond the first positive electrode segment 211, even if the separator 23 between the first positive electrode segment 211 and the first negative electrode segment 221 is melted, the first part 41 can still reduce the risk of contact between the first positive tab 30a and the first segment 2211, thereby reducing the risk of a secondary short circuit in the secondary battery 100, further reducing the risk of fire and explosion in the secondary battery 100, and improving the safety performance of the secondary battery 100.

[0069] After the secondary battery 100 is short-circuited, a large amount of gas is generated inside the secondary battery 100, which may cause the electrode assembly 20 to deform and pull the first positive electrode tab 30a. This may cause the first positive electrode tab 30a to come into contact with the end of the first negative electrode segment 221 on the same side as the first end 2111, resulting in a secondary short circuit. The first protective member 40 includes a second part 45 connected to the first part 41. The second part 45 covers the second end 2212 on the same side as the first negative electrode segment 221 and the first end 2111, reducing the risk that the first positive electrode tab 30a may come into contact with the second end 2212 due to deformation caused by pulling, thereby further reducing the risk of secondary short circuit of the secondary battery 100.

[0070] The casing 10 can be a rigid casing, such as a steel casing or an aluminum casing, forming a steel casing secondary battery or an aluminum casing secondary battery.

[0071] The casing 10 can also be made of a softer material, such as an aluminum-plastic film or a steel-plastic film, forming a soft-pack battery cell. Since the casing 10 is made of aluminum-plastic film or steel-plastic film, it is more prone to deformation. When gas is generated inside the secondary battery 100 due to high temperatures, the casing 10 can mitigate the internal expansion problem of the secondary battery 100 through its own deformation, reducing the risk of explosion.

[0072] like Figure 3 , Figure 4 , Figure 5 As shown, a positive electrode 21, a negative electrode 22, and a separator 23 are stacked and wound around a central axis to form a wound electrode assembly. The separator 23 is disposed between the positive electrode 21 and the negative electrode 22, and serves to insulate and separate the positive electrode 21 and the negative electrode 22. The secondary battery 100 is charged and discharged by the movement of metal ions from the positive electrode 21 between the positive electrode 21 and the negative electrode 22.

[0073] The positive electrode 21 includes a positive current collector and a positive active material layer, the positive active material layer being coated on the surface of the positive current collector. Taking a lithium-ion battery as an example, the material of the positive current collector can include aluminum, and the positive active material can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. The negative electrode 22 includes a negative current collector and a negative active material layer, the negative active material layer being coated on the surface of the negative current collector. The material of the negative current collector can include copper, and the negative active material can be carbon or silicon, etc. The separator 23 can be made of PP (polypropylene) or PE (polyethylene), etc.

[0074] like Figures 3-5 As shown, the wound electrode assembly 20 may include two straight regions A and two bent regions B. The two bent regions B are respectively connected to both ends of each straight region A along the third direction Z. The two straight regions A are respectively located on both sides of the winding axis of the electrode assembly 20 in the second direction Y. The first direction X, the second direction Y, and the third direction Z are mutually perpendicular. The two straight regions A and the two bent regions B together form a flat wound electrode assembly.

[0075] In some embodiments, the first positive electrode segment 211 and the first negative electrode segment 221 are both located in the flat region A, and the first positive electrode tab 30a is located in the flat region A. The first positive electrode tab 30a is connected to the first positive electrode segment 211 to achieve electrical connection between the first positive electrode tab 30a and the positive electrode plate 21.

[0076] In some embodiments, the positive electrode 21 and the first positive electrode tab 30a are separately disposed. The surface of the positive current collector of the positive electrode 21 is fully coated with a positive active material layer in the first direction X, that is, the ends of the positive current collector and the positive active material layer are flush along the first direction X. The end of the positive active material layer and the positive current collector that is flush in the first direction X forms the first end 2111 of the first positive electrode segment 211. The first positive electrode tab 30a and the first positive electrode segment 211 are connected by means of conductive adhesive connection, welding connection, riveting connection, etc., thereby realizing the electrical connection between the first positive electrode tab 30a and the positive electrode 21.

[0077] like Figures 6-12As shown, the positive electrode active material layer includes a first positive electrode active material layer 211a located in the first positive electrode segment 211. A first groove 2214 is provided on the first surface 2213 of the first positive electrode active material layer 211a in the second direction Y. The first groove 2214 is formed by recessing from the first surface 2213 of the first positive electrode active material layer 211a away from the positive current collector and towards the positive current collector. Along the first direction X, the first groove 2214 extends to the first end 2111, and the first groove 2214 forms a slot at the first end 2111. The first positive electrode tab 30a can extend from the slot of the first groove 2214 at the first end 2111, thereby causing the first positive electrode tab 30a to protrude from the first end 2111 along the first direction X.

[0078] Along the second direction Y, the two opposite surfaces of the positive current collector of the first positive electrode segment 211 are provided with a first positive electrode active material layer 211a, and each first positive electrode active material layer 211a is provided with a first groove 2214. The first positive electrode tab 30a can be accommodated in any one of the first grooves 2214 of the first positive electrode segment 211.

[0079] The depth of the first groove 2214 is consistent with the thickness of the first positive electrode active material layer 211a, so as to expose the positive electrode current collector in the first groove 2214. The first positive electrode tab 30a contacts the positive electrode current collector in the first groove 2214. The first positive electrode tab 30a is welded to the positive electrode current collector in the first groove 2214, or connected by conductive adhesive, etc., thereby realizing the electrical connection between the first positive electrode tab 30a and the first positive electrode segment 211.

[0080] In the second direction Y, the depth of the first groove 2214 can be greater than or equal to the thickness of the first positive electrode tab 30a, so that the first positive electrode tab 30a can be completely embedded in the first groove 2214, avoiding the first positive electrode tab 30a increasing the size of the electrode assembly 20 in the first direction X. In this embodiment, in the first direction X, the depth of the first groove 2214 is greater than the thickness of the first positive electrode tab 30a, so that the first groove 2214 can reserve space to compensate for the thickness of the first part 41 in the first direction X, alleviating the problem that the size of the electrode assembly 20 in the first direction X is increased due to the first part 41 being placed between the first positive electrode tab 30a and the first negative electrode segment 221.

[0081] Of course, in some other embodiments, along the second direction Y, the first positive electrode tab 30a may be partially located within the first groove 2214, and the other part may protrude along the second direction Y from the groove of the first surface 2213. In this case, it is understood that the depth of the first groove 2214 along the second direction Y is less than the thickness of the first positive electrode tab 30a along the second direction Y.

[0082] The positive electrode plate 21 can be electrically connected to one positive electrode tab 30, which is the first positive electrode tab 30a. The positive electrode plate 21 can also be electrically connected to multiple positive electrode tabs 30, with the multiple positive electrode tabs 30 connected to different layers of the positive electrode plate 21, and one of the multiple positive electrode tabs 30 being the first positive electrode tab 30a. All positive electrode tabs 30 can be located in the flat region A. Exemplarily, the positive electrode plate 21 is electrically connected to two or three positive electrode tabs 30. It should be noted that, in the embodiments of this application, "multiple" refers to two or more. Figure 3 The diagram shows a case where the positive electrode 21 is electrically connected to two positive tabs 30. One positive tab 30 is connected to the uncoated foil area of ​​the starting section of the positive electrode 21 when it is wound. The other positive tab 30 is located in the middle layer of the positive electrode 21. Both tabs are electrically connected to the positive current collector of the positive electrode 21 by forming a tab groove (first groove 2214) on the positive electrode 21 in the middle layer. Figure 4 The diagram shows a case where the positive electrode plate 21 is electrically connected to two positive electrodes 30. Both positive electrodes 30 are electrically connected to the positive current collector of the positive electrode plate 21 by forming electrode slots on the positive electrode plate 21. Figure 5 The diagram shows a case where a positive electrode 21 is electrically connected to a positive electrode tab 30, which is electrically connected to the positive current collector of the positive electrode 21 within a tab groove formed on the positive electrode 21. Figures 3-5 The dashed line extending along the second direction Y is the boundary line between the straight area A and the curved area B.

[0083] The first positive electrode tab 30a can be completely located within the housing 10. The first positive electrode tab 30a can be electrically connected to the positive electrode lead 50. Part of the positive electrode lead 50 is located inside the housing 10 and connected to the first positive electrode tab 30a. The other part of the positive electrode lead 50 extends out of the housing 10 to form the positive terminal of the secondary battery 100. Figure 1 (as shown in the image).

[0084] Of course, the first positive electrode tab 30a can also be partially located inside the housing 10, with the other part extending out of the housing 10 to form the positive terminal of the secondary battery 100. Figure 2 (as shown in the image).

[0085] The first positive electrode tab 30a can be bent toward the first protective member 40, which not only facilitates the lead-out of the positive electrode, but also reduces the risk of short circuit due to the protection of the first protective member 40 in the bending direction. Observed along the first direction X, the first positive electrode tab 30a, after being bent toward the first protective member 40, can overlap with the second part 45.

[0086] In some embodiments, the secondary battery 100 further includes a negative electrode tab 22a, which is electrically connected to the negative electrode plate 22. The negative electrode tab 22a may also be located in the flat region A. The structure, location, number of negative electrode tabs 22a, and connection method between the negative electrode tab 22a and the negative electrode plate 22 are not limited in this application.

[0087] The negative electrode plate 22 and the negative electrode tab are separately arranged. The negative electrode current collector of the negative electrode plate 22 is fully coated with a negative electrode active material layer in the first direction X, that is, along the first direction X, the ends of the negative electrode current collector and the negative electrode active material layer are flush. The negative electrode tab and the negative electrode plate 22 are connected by conductive adhesive, welding, riveting or other methods to achieve electrical connection between the negative electrode tab and the negative electrode plate 22.

[0088] In other embodiments, the negative current collector and the negative tab of the negative electrode sheet 22 can be integrally formed. The negative current collector of the negative electrode sheet 22 is coated with a negative active material layer in a partial area in the first direction X, and the negative active material layer is not coated in a partial area. The part of the negative current collector that is not coated with a negative active material layer can be formed into a negative tab by die cutting or other methods.

[0089] The negative electrode 22 can be electrically connected to one negative electrode tab, or it can be electrically connected to multiple negative electrode tabs, with the multiple negative electrode tabs connected to different layers of the negative electrode 22. For example, the negative electrode 22 can be electrically connected to two or three negative electrode tabs.

[0090] The negative electrode tab can be completely located in the housing 10. The negative electrode tab can be electrically connected to the negative electrode lead. Part of the negative electrode lead is located inside the housing 10 and connected to the negative electrode tab. The other part of the negative electrode lead extends out of the housing 10 to form the negative terminal of the secondary battery 100.

[0091] Of course, the negative electrode tab can also be partially located inside the housing 10, and the other part can extend out of the housing 10 to form the negative terminal of the secondary battery 100 (not shown in the figure).

[0092] The first protective element 40 includes a first portion 41, which is located between the first positive electrode segment 211 and the first negative electrode segment 221, and also between the first positive electrode tab 30a and the first negative electrode segment 221. When viewed along the second direction Y, the projection of the first positive electrode tab 30a is located within the first portion 41, so that the first portion 41 can serve to insulate and separate the first positive electrode tab 30a and the first segment 2211.

[0093] Along the first direction X, the first part 41 covers the entire first segment 2211. One end of the first part 41 may be flush with the second end 2212 of the first segment 2211, or the first part 41 may extend beyond the second end 2212 of the first segment 2211. Here, the second end 2212 of the first segment 2211 refers to the end of the first segment 2211 located on the same side of the electrode assembly 20 as the first end 2111.

[0094] The first protective element 40 is made of insulating material. The first part 41 can be the entirety of the first protective element 40 or a portion of the first protective element 40.

[0095] In some embodiments, the first protective member 40 includes a substrate layer 42. The substrate layer 42 is the main structure in the first protective member 40 that serves as an insulating separator.

[0096] The melting point of the substrate layer 42 is higher than that of the separator 23. In this way, after the separator 23 melts and breaks due to the high temperature at the first positive electrode tab 30a, the first protective element 40 can separate the first positive electrode tab 30a and the first negative electrode segment 221, thereby reducing the risk of short circuit in the secondary battery 100.

[0097] The substrate layer 42 is made of one or more of polyethylene terephthalate, polyimide, and polypropylene.

[0098] The substrate layer 42 may be made of polyethylene terephthalate, polyimide or polypropylene, or it may be a composite structure formed of at least two of polyethylene terephthalate, polyimide or polypropylene.

[0099] The substrate of the first protective component 40 is made of one or more of polyethylene terephthalate, polyimide, or polypropylene, which gives the substrate good mechanical properties and heat resistance, reducing the risk of the first protective component 40 being melted by high temperature.

[0100] In some embodiments, the first part 41 can be sandwiched between the first positive electrode section 211 and the first negative electrode section 221, and is held between the first positive electrode section 211 and the first negative electrode section 221 by the friction between the first part 41 and the first positive electrode section 211 or the separator 23 or the first negative electrode section 221, which can reduce the assembly difficulty of the secondary battery 100.

[0101] The substrate layer 42 may be part or all of the first protective element 40. That is, the first protective element 40 may include only the substrate layer 42, or the first protective element 40 may include other structures besides the substrate layer 42.

[0102] like Figure 6 , Figure 7As shown, in some embodiments, the first part 41 may also be fixed to the first negative electrode section 221 so that the first part 41 is stably located between the first positive electrode section 211 and the first negative electrode section 221.

[0103] In some embodiments, the first protective member 40 further includes an adhesive layer 43 disposed on the surface of the substrate layer 42.

[0104] The first part 41 is bonded to the surface of the first negative electrode section 221 facing the first positive electrode section 211. This not only allows the first part 41 to act as an insulating separator between the first negative electrode section 221 and the first positive electrode tab 30a, reducing the risk of short circuit due to contact between the first positive electrode tab 30a and the first negative electrode section 221, but also helps the first part 41 to be stably positioned between the first negative electrode section 221 and the first positive electrode tab 30a, reducing the risk of movement of the first part 41. This allows the first part 41 to better separate the first negative electrode section 221 and the first positive electrode tab 30a, reducing the risk of short circuit in the secondary battery 100 and improving the safety performance of the secondary battery 100. Fixing the first part 41 to the surface of the first negative electrode section 221 facing the first positive electrode section 211 by bonding is convenient and provides good stability.

[0105] The first part 41 can be bonded to the surface of the first negative electrode section 221 facing the first positive electrode section 211 by the adhesive layer 43 of the first protective member 40. The melting point of the adhesive layer 43 can be higher than that of the separator 23. Therefore, when the internal temperature of the secondary battery 100 is high, the risk of the adhesive layer 43 melting and causing the first part 41 to detach from the first negative electrode section 221 is small, which is beneficial to improving the bonding stability of the first part 41.

[0106] The adhesive layer 43 is made of one or more of the following materials: polybutadiene, polypropylene, polypentadiene and styrene, butadiene copolymer, and petroleum resin. The adhesive layer 43 formed from these materials has high adhesive performance, which improves connection stability. The adhesive layer 43 also has a high melting point, reducing the risk that the first protective element 40 may detach from the electrode assembly 20 due to the adhesive layer 43 melting caused by increased internal temperature of the secondary battery 100.

[0107] The adhesive layer 43 may be made of polybutadiene, polypropylene, polypentadiene and styrene-butadiene copolymer or petroleum resin. The adhesive layer 43 may also be a composite structure formed of at least two of polybutadiene, polypropylene, polypentadiene and styrene-butadiene copolymer or petroleum resin.

[0108] In some embodiments, the first protective member 40 further includes a hot melt layer 44, the hot melt layer 44 and the adhesive layer 43 are respectively disposed on two opposite surfaces of the substrate layer 42, and the material of the hot melt layer 44 includes one or more of styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, polyurethane elastomer, polyurethane acrylate, polyisobutylene and polybutadiene.

[0109] The hot-melt layer 44 may be made of styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, polyurethane elastomer, polyurethane acrylate, polyisobutylene, or polybutadiene. The hot-melt layer 44 may be a composite structure made of at least two of styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, polyurethane elastomer, polyurethane acrylate, polyisobutylene, and polybutadiene.

[0110] The first protective component 40 can be connected to other structures of the secondary battery 100 through the hot-melt layer 44. For example, the first protective component 40 can be connected to the inner surface of the housing 10 through the hot-melt layer 44 to improve the stability of the connection of the first protective component 40 and alleviate the problem of the electrode assembly 20 moving around in the housing 10, thereby improving the drop performance of the secondary battery.

[0111] The hot-melt layer 44 formed by the above materials has good adhesion after hot melting, which can improve the stability of the connection between the first protective component 40 and other structures.

[0112] In the embodiment where the first part 41 is bonded to the surface of the first negative electrode section 221 facing the first positive electrode section 211, the first positive electrode tab 30a can be connected to the side of the positive current collector of the first positive electrode section 211 away from the first negative electrode section 221. Figure 6 As shown in the diagram, the first positive electrode tab 30a can be connected to the side of the positive current collector of the first positive electrode section 211 facing the first negative electrode section 221. Figure 7 (as shown in the image).

[0113] like Figure 8 , Figure 9 As shown, the first portion 41 can also be fixed to the separator 23. In some embodiments, the separator 23 includes a first partition segment 231 along the second direction Y, the first partition segment 231 being located between the first positive electrode segment 211 and the first negative electrode segment 221, and the first portion 41 being adhered to the first partition segment 231.

[0114] The first separating segment 231 is the portion of the separator 23 located between the first positive electrode segment 211 and the first negative electrode segment 221, which serves to insulate and separate the first positive electrode segment 211 and the first negative electrode segment 221.

[0115] The first part 41 can be bonded to the first partition 231 through the adhesive layer 43 of the first protective member 40.

[0116] The first part 41 is bonded to the first separator section 231, which not only allows the first part 41 to act as an insulating separator between the first negative electrode section 221 and the first positive electrode tab 30a, reducing the risk of short circuit caused by contact between the first positive electrode tab 30a and the first negative electrode section 221, but also helps the first part 41 to be stably positioned between the first negative electrode section 221 and the first positive electrode tab 30a, reducing the risk of the first part 41 moving. This allows the first part 41 to better separate the first negative electrode section 221 and the first positive electrode tab 30a, reducing the risk of short circuit in the secondary battery 100 and improving the safety performance of the secondary battery 100. Bonding the first part 41 to the first separator section also helps reduce the risk of shrinkage and deformation of the first separator section. Fixing the first part 41 to the first separator section 231 by bonding is convenient and provides good stability.

[0117] In embodiments where the first portion 41 is adhered to the first dividing segment 231 of the separator 23, the first portion 41 may be adhered to any surface of the first dividing segment 231 in the second direction Y. In some embodiments, the first portion 41 may be adhered to the surface of the first dividing portion in the second direction Y that is opposite to the first positive electrode segment 211.

[0118] In some embodiments, the first part 41 may also be bonded to the surface of the first separator 231 facing the first positive electrode section 211, which can reduce the risk of the first separator 231 being melted by the high temperature of the first positive electrode tab 30a, and also reduce the risk of the first separator 231 shrinking and deforming due to the high temperature at the first positive electrode tab 30a, reduce the risk of secondary short circuit of the secondary battery 100, and improve the safety performance of the secondary battery 100.

[0119] In the embodiment where the first part 41 is bonded to the surface of the first dividing section 231 facing the first positive electrode section 211, the first positive electrode tab 30a can be connected to the side of the positive current collector of the first positive electrode section 211 away from the first negative electrode section 221. Figure 8 As shown in the diagram, the first positive electrode tab 30a can be connected to the side of the positive current collector of the first positive electrode section 211 facing the first negative electrode section 221. Figure 9 (as shown in the image).

[0120] like Figures 6-12As shown, along a third direction Z perpendicular to the first direction X and the second direction Y, the width of the first groove 2214 is T mm, and the width of the first part 41 is L1 mm. Along the first direction X, the length of the first part 41 is N1 mm, and the length of the first groove 2214 is M mm. It should be noted that: the width T of the first groove 2214 is its dimension along the third direction Z; the width L1 of the first part 41 is its dimension along the third direction Z; the length N1 of the first part 41 is its dimension along the first direction X; and the length M of the first groove 2214 is its dimension along the first direction X. A third direction Z perpendicular to the first direction X and the second direction Y means that both the first direction X and the second direction Y are perpendicular to the third direction, thus the first direction X, the second direction Y, and the third direction Z are mutually perpendicular.

[0121] In some embodiments, 1.2 ≤ L1 / T ≤ 3.

[0122] For example, L1 / T can be 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, etc.

[0123] The value of 1.2≤L1 / T≤3 not only ensures that the first part 41 has a large coverage area along the third direction Z, reducing the risk of short circuit in the secondary battery 100 and improving safety performance, but also allows as many areas of the first part 41 as possible to correspond to the first groove 2214. When the electrode assembly 20 is subjected to pressure in the second direction Y, the first groove 2214 can alleviate the problem of the electrode assembly 20 increasing in size in the second direction Y due to the setting of the first part 41, thereby helping the secondary battery 100 to have a higher energy density.

[0124] In some embodiments, 1 ≤ N1 / M ≤ 1.5.

[0125] For example, N1 / M can be 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc.

[0126] The condition 1≤N1 / M≤1.5 ensures that the first part 41 has a large coverage area along the first direction X, which can effectively separate the first positive electrode tab 30a and the first negative electrode section 221, and also reduce the effective area for loss of active material, thereby giving the secondary battery 100 a high energy density.

[0127] Figure 11 and Figure 12 The dashed lines in the text represent the parts that are obscured.

[0128] like Figures 6-9As shown, in some embodiments, the first negative electrode segment 221 includes a second end 2212, the first end 2111 and the second end 2212 are located on the same side of the electrode assembly 20 in the first direction X; the first protective member 40 also includes a second part 45 connected to the first part 41, the second part 45 covering the second end 2212.

[0129] The second part 45 and the first part 41 can be molded as a single piece.

[0130] Part 41 and Part 45 can also be separate components that are then connected together. Part 41 and Part 45 can be connected by methods such as adhesive bonding or welding.

[0131] Depending on the length of the second portion 45 along the second direction Y, the area that the second portion 45 can cover also varies. The second portion 45 may only cover the second end 2212 of the first negative electrode, or the second portion 45 may cover other areas of the electrode assembly 20 on the same side as the first negative electrode segment 221.

[0132] The second part 45 may have the same structure as the first part 41 or it may be different. For example, the first part 41 may include a substrate layer 42 and an adhesive layer 43, while the second part 45 may only include the substrate layer 42, so that the structures of the first part 41 and the second part 45 are different; or the first part 41 may include a substrate layer 42 and an adhesive layer 43, while the second part 45 may also include a substrate layer 42 and an adhesive layer 43, so that the structures of the first part 41 and the second part 45 are the same.

[0133] After the secondary battery 100 is short-circuited, a large amount of gas is generated inside the secondary battery 100, which may cause the electrode assembly 20 to deform and pull the first positive electrode tab 30a. This may cause the first positive electrode tab 30a to come into contact with a section on the same side as the first negative electrode segment 221 and the first end 2111, resulting in a secondary short circuit. The first protective member 40 includes a second part 45 connected to the first part 41. The second part 45 covers the second end 2212 on the same side as the first negative electrode segment 221 and the first end 2111, reducing the risk that the second positive electrode tab 30 may come into contact with the second end 2212 due to deformation caused by pulling, thereby reducing the risk of secondary short circuit of the secondary battery 100.

[0134] like Figures 6-9 As shown, in some embodiments, the separator 23 includes a second partition segment 232 located on the side of the first negative electrode segment 221 opposite to the first positive electrode segment 211, and the second portion 45 is fixed to the second partition segment 232.

[0135] The second part 45 can be bonded to the second partition segment 232 through the adhesive layer 43 of the first protective member 40, so as to fix the second part 45 to the second partition segment 232. Specifically, the second part 45 can be bonded to the end of the second partition segment 232 on the same side as the first end 2111.

[0136] The second part 45 is fixed to the second partition section 232, which helps the first protective member 40 to stably block the first positive electrode tab 30a from further contact and short circuit with the negative electrode plate 22 beyond the positive electrode plate 21, greatly reducing the risk of fire and explosion of the secondary battery 100, improving the safety performance of the secondary battery 100, and also reducing the risk of shrinkage and deformation of the separator 23 and the risk of the separator 23 moving along the first direction X.

[0137] In some embodiments, the first protective member 40 further includes a third portion 46, wherein the first portion 41, the second portion 45 and the third portion 46 are connected in sequence, and the third portion 46 is bonded to the first outer surface Q1 of the electrode assembly 20. The first outer surface Q1 and the first portion 41 are located on the same side of the first positive electrode segment 211 in the second direction Y.

[0138] When viewed along the second direction Y, the projection of the first positive electrode 30a is located within the third part 46, and the projections of the first part 41 and the third part 46 at least partially overlap.

[0139] Part 41, Part 45, and Part 46 can be molded as a single piece.

[0140] Part 1 (41), Part 2 (45), and Part 3 (46) can also be separate components that are then joined together. Part 1 (41), Part 2 (45), and Part 3 (46) can be connected sequentially through methods such as adhesive bonding or fusion welding. Part 3 (46) and Part 1 (41) are connected through Part 2 (45).

[0141] The first outer surface Q1 of the electrode assembly 20 can be determined based on the structure of the outermost ring of the electrode assembly 20. If the outermost ring of the electrode assembly 20 is a separator 23, the first outer surface Q1 is formed by one surface of the separator 23. If the outermost ring of the electrode assembly 20 is a negative electrode 22, the first outer surface Q1 is formed by one surface of the negative electrode 22. If the outermost ring of the electrode assembly 20 is a positive electrode 21, the first outer surface Q1 is formed by one surface of the positive electrode 21.

[0142] The first part 41, the second part 45, and the third part 46 of the first protective member 40 are connected in sequence. The first part 41 is located between the first negative electrode section 221 and the first positive electrode tab 30a. The second part 45 covers the second end 2212 of the first negative electrode section 221. The third part 46 is bonded to the first outer surface Q1 of the electrode assembly 20. The first outer surface Q1 and the first part 41 are located on the same side of the first positive electrode section 211. The first protective member 40 spans all the portions of the negative electrode plates 22 that extend beyond the first end 2111 on one side of the first positive electrode section 211. This effectively prevents further contact and short circuit between the first positive electrode tab 30a and the portions of the negative electrode plates 22 that extend beyond the positive electrode plate 21. This reduces the risk of the second battery 100 coming into contact with the portions of the negative electrode plates 22 that extend beyond the first end 2111 on the side of the first positive electrode tab 30a facing the first negative electrode section 221. This reduces the risk of the second battery 100 catching fire and exploding, and improves the safety performance of the second battery 100.

[0143] Along the third direction Z, the width of the third part 46 is L2mm; along the first direction X, the length of the third part 46 is N2. It should be noted that the width L2 of the third part 46 is the dimension of the third part 46 along the third direction Z, and the length N2 of the third part 46 is the dimension of the third part 46 along the first direction X.

[0144] In an embodiment where a first groove 2214 is provided on the first surface 2213 of the first positive electrode section 211 and the first groove 2214 accommodates a portion of the first positive electrode tab 30a in the second direction, 0.5≤L2 / T≤1.

[0145] For example, L2 / T can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc.

[0146] The value of 0.5≤L2 / T≤1 not only allows the third part 46 to have a larger coverage area along the third direction Z, reducing the risk of short circuit in the secondary battery 100 and improving safety performance, but also allows as much area of ​​the third part 46 as possible to correspond to the first groove 2214. After the electrode assembly 20 is subjected to pressure in the second direction Y, the first groove 2214 can alleviate the problem of the electrode assembly 20 increasing in size in the second direction Y due to the setting of the third part 46, thereby helping the secondary battery 100 to have a higher energy density.

[0147] In some embodiments, N2≤M.

[0148] When N2 ≤ M, and viewed along the second direction Y, the projection of the third part 46 onto the first direction X can be completely located within the first groove 2214. After the electrode assembly 20 is subjected to pressure in the second direction Y, the first groove 2214 can alleviate the problem of the electrode assembly 20 increasing in size in the second direction Y due to the setting of the third part 46, thereby helping the secondary battery 100 to have a higher energy density.

[0149] In some embodiments, 0.5T≤L2≤L1 not only allows the third part 46 to have a larger coverage area along the third direction Z, reducing the risk of secondary short circuits and improving safety performance, but also allows as many areas of the third part 46 as possible to correspond to the first groove 2214. After the electrode assembly 20 is subjected to pressure in the second direction Y, the third part 46 can be accommodated in the first groove 2214, thereby reducing the size of the electrode assembly 20 along the second direction Y and increasing the volumetric energy density of the secondary battery 100.

[0150] The width L1 of the first part 41, the width L2 of the third part 46, and the width L3 of the second part 45 can be the same to form a first protective member 40 with a relatively regular shape. Figure 13 (As shown), it is easy to manufacture and shape. Figure 13 The dashed lines in the diagram represent the boundary between the first part 41 and the second part 45, as well as the boundary between the second part 45 and the third part 46. The first part 41, after being folded around the dashed boundary line between the first part 41 and the second part 45, can be located between the first positive electrode segment 211 and the first negative electrode segment 221. The third part 46, after being folded around the dashed boundary line between the third part 46 and the second part 45, can be located on the side where the first outer surface Q1 is located.

[0151] The width L1 of the first part 41, the width L2 of the third part 46, and the width L3 of the second part 45 may also be at least partially different to form an irregularly shaped first protective member 40. Figure 14 (As shown). For example, the width L1 of the first part 41 is greater than the width L2 of the third part 46, and the width L2 of the third part 46 is less than the width L3 of the second part 45. Or, for another example, the width L1 of the first part 41 is the same as the width L3 of the second part 45, and both the width L1 of the first part 41 and the width L3 of the second part 45 are greater than the width L2 of the third part 46. Figure 14 (as shown in the image). Figure 14 The dashed lines in the diagram are the dividing lines between the first part 41 and the second part 45, as well as the dividing lines between the second part 45 and the third part 46.

[0152] It should be noted that after the first protective element 40 is installed on the electrode assembly 20, the transition between the first part 41 and the second part 45 is not necessarily through a right-angle bend, but may be through an arc transition. This makes the boundary line between the first part 41 and the second part 45 indistinct. In this case, it can be considered that when viewed in the second direction Y, the part of the first protective element 40 located between the first positive electrode segment 211 and the first negative electrode segment 221 that overlaps with the first negative electrode segment 221 is the first part 41.

[0153] After the first protective member 40 is installed on the electrode assembly 20, the transition between the second part 45 and the third part 46 is not necessarily through a right-angle bend, but may be through an arc transition. This makes the boundary line between the second part 45 and the third part 46 indistinct. In this case, it can be determined that when viewed in the second direction Y, the part of the first protective member 40 located between the first outer surface Q1 and the housing 10 that overlaps with the first outer surface Q1 is the third part 46.

[0154] like Figure 15 , Figure 16 As shown, in some embodiments, the electrode assembly 20 further includes a second negative electrode segment 222. Along the second direction Y, the second negative electrode segment 222 is stacked and adjacent to the first positive electrode segment 211. The second negative electrode segment 222 and the first negative electrode segment 221 are respectively located on opposite sides of the first positive electrode segment 211 in the second direction Y. The second negative electrode segment 222 has a second segment 2221 extending beyond the first end 2111 in the first direction X. The second negative electrode segment 222 includes a third end 2222. The first end 2111 and the third end 2222 are located on the same side of the electrode assembly 20 in the first direction X. Secondary battery 1 00 also includes a second protective member 60, which includes a fourth part 61, a fifth part 62 and a sixth part 63 connected in sequence. The fourth part 61 is disposed between the first positive electrode segment 211 and the second negative electrode segment 222 along the first direction X. The fourth part 61 covers the first segment 2211. The fifth part 62 connects the fourth part 61 and the sixth part 63 and covers the third end 2222. The sixth part 63 is bonded to the second outer surface Q2 of the electrode assembly 20. The second outer surface Q2 and the fourth part 61 are located on the same side of the first positive electrode segment 211 in the second direction Y.

[0155] The first positive electrode segment 211 is located between the first negative electrode segment 221 and the second negative electrode segment 222. The first positive electrode tab 30a is located in the middle layer of the electrode assembly 20. After a short circuit, the temperature rise is higher. The first protective element 40 and the second protective element 60 can effectively prevent the first positive electrode tab 30a from making further contact with the part of the negative electrode 22 that extends beyond the positive electrode 21, greatly reducing the risk of fire and explosion of the secondary battery 100 and improving the safety performance of the secondary battery 100.

[0156] The fourth part 61, the fifth part 62, and the sixth part 63 of the second protective member 60 are connected in sequence. The fourth part 61 is located between the second negative electrode section 222 and the first positive electrode section 211. The fifth part 62 covers the third end 2222 of the second negative electrode section 222. The sixth part 63 is bonded to the second outer surface Q2 of the electrode assembly 20. The second outer surface Q2 and the fourth part 61 are located on the same side of the first positive electrode section 211. The second protective member 60 spans all the portions of the negative electrode plates 22 that extend beyond the first end 2111 on one side of the first positive electrode section 211. This effectively prevents further contact and short circuit between the first positive electrode tab 30a and the portion of the negative electrode plate 22 that extends beyond the positive electrode plate 2111. This reduces the risk of the secondary battery 100 coming into contact with the portion of the negative electrode plate 22 that extends beyond the first end 2111 on the side of the first positive electrode tab 30a facing the second negative electrode section 222. This reduces the risk of the secondary battery 100 catching fire and exploding, and improves the safety performance of the secondary battery 100.

[0157] The structure of the second protective element 60 can be the same as that of the first protective element 40, or the structure of the second protective element 60 can be different from that of the first protective element 40.

[0158] like Figure 15 As shown, in some embodiments, the fourth part 61 can be bonded to the surface of the second negative electrode segment 222 facing the first positive electrode segment 211. This not only allows the fourth part 61 to act as an insulating separator between the second negative electrode segment 222 and the first positive electrode segment 211, reducing the risk of a short circuit caused by contact between the first positive electrode tab 30a and the second negative electrode segment 222, but also helps the fourth part 61 to be stably positioned between the second negative electrode segment 222 and the first positive electrode segment 211, reducing the risk of movement of the fourth part 61. This allows the fourth part 61 to better separate the second negative electrode segment 222 and the first positive electrode tab 30a, reducing the risk of a short circuit in the secondary battery 100 and improving the safety performance of the secondary battery 100. Fixing the fourth part 61 to the surface of the second negative electrode segment 222 facing the first positive electrode segment 211 by bonding is convenient and provides good stability.

[0159] like Figure 16As shown, in some embodiments, the separator 23 includes a third separating segment 233 along the second direction Y. The third separating segment 233 is located between the second negative electrode segment 222 and the first negative electrode segment 221. The fourth part 61 is bonded to the third separating segment 233. This not only allows the fourth part 61 to act as an insulating separator between the second negative electrode segment 222 and the first positive electrode segment 211, reducing the risk of a short circuit caused by contact between the first positive electrode tab 30a and the second negative electrode segment 222, but also helps the fourth part 61 to be stably positioned between the second negative electrode segment 222 and the first positive electrode tab 30a, reducing the risk of movement of the fourth part 61. This allows the fourth part 61 to better separate the second negative electrode segment 222 and the first positive electrode tab 30a, reducing the risk of a short circuit in the secondary battery 100 and improving the safety performance of the secondary battery 100. Bonding the fourth part 61 to the third separating segment also helps to reduce the risk of shrinkage and deformation of the third separating segment. Fixing the fourth part 61 to the third separating segment 233 by bonding is convenient and provides good stability.

[0160] Of course, the fourth part 61 can be sandwiched between the first positive electrode section 211 and the second negative electrode section 222, and is held between the first positive electrode section 211 and the second negative electrode section 222 by the friction between the fourth part 61 and the first positive electrode section 211 or the third separator section 233 or the second negative electrode section 222. This can reduce the assembly difficulty of the secondary battery 100.

[0161] In some embodiments, the separator 23 includes a fourth partition segment 234 located on the side of the second negative electrode segment 222 opposite to the first positive electrode segment 211, and a fifth portion 62 is fixed to the fourth partition segment 234.

[0162] The fifth part 62 can be bonded to the fourth partition segment 234 through the adhesive layer 43 of the first protective member 40, so as to fix the fifth part 62 to the fourth partition segment 234. Specifically, the fifth part 62 can be bonded to the end of the fourth partition segment 234 on the same side as the first end 2111.

[0163] The fifth part 62 is fixed to the fourth dividing section 234, which helps the first protective member 40 to stably block the first positive electrode tab 30a from further contact and short circuit with the negative electrode 22 beyond the positive electrode 21, greatly reducing the risk of fire and explosion of the secondary battery 100, improving the safety performance of the secondary battery 100, and also reducing the risk of shrinkage and deformation of the separator 23 and the risk of the separator 23 moving along the first direction X.

[0164] The second outer surface Q2 of the electrode assembly 20 can be determined based on the structure of the outermost ring of the electrode assembly 20. If the outermost ring of the electrode assembly 20 is a separator 23, the second outer surface Q2 is formed from one surface of the separator 23. If the outermost ring of the electrode assembly 20 is a negative electrode 22, the second outer surface Q2 is formed from one surface of the negative electrode 22. If the outermost ring of the electrode assembly 20 is a positive electrode 21, the second outer surface Q2 is formed from one surface of the positive electrode 21.

[0165] In some embodiments, the secondary battery 100 further includes a third protective member 70 and a fourth protective member 80, which are respectively bonded to both sides of the welding position of the first positive electrode tab 30a and the first positive electrode segment 211 along the first direction X, so as to reduce the risk of burrs piercing the separator 23 in the welding area of ​​the positive current collector of the first positive electrode tab 30a and the first positive electrode segment 211.

[0166] In some embodiments, the positive electrode 21 includes a positive active material layer, the positive active material layer includes a positive active material, and the Dv50 of the positive active material is ≤15μm; the negative electrode 22 includes a negative active material layer, the negative active material layer includes a negative active material, and the Dv50 of the negative active material is ≤12μm.

[0167] The Dv50 ≤ 15 μm for positive electrode active materials means that the total volume of positive electrode active materials with a particle size of less than or equal to 15 μm accounts for 50% of the total volume of the positive electrode active material layer. The Dv50 ≤ 12 μm for negative electrode active materials means that the total volume of negative electrode active materials with a particle size of less than or equal to 12 μm accounts for 50% of the total volume of the negative electrode active material layer.

[0168] The particle size detection methods for the positive electrode active material and the negative electrode active material are as follows: the secondary cell is discharged to 2.5V, disassembled, rinsed with DMC, and air-dried; the positive electrode is calcined at 550℃ for 2 hours and powder is collected; the negative electrode is calcined at 450℃ for 2 hours and powder is collected; the particle size is detected by a laser particle size analyzer.

[0169] In the positive electrode active material layer, the total volume of positive electrode active material with a particle size of less than 15 μm accounts for 50% of the total volume of the positive electrode active material layer, and in the negative electrode active material layer, the total volume of negative electrode active material with a particle size of less than 15 μm accounts for 50% of the total volume of the negative electrode active material layer. This is beneficial to increasing the active area of ​​the positive electrode 21 and the negative electrode 22, thereby improving the electrical performance of the secondary battery 100.

[0170] In some embodiments, the secondary battery 100 further includes an electrolyte, the components of which include one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, fluoroethylene carbonate, and 1,2-difluoroethylene carbonate.

[0171] The electrolyte is used to wet the electrode assembly 20. The electrolyte contains one or more of the components mentioned above, resulting in a high conductivity of the electrolyte.

[0172] In some embodiments of this application, the electrolyte comprises a lithium salt and a non-aqueous solvent. The lithium salt is selected from one or more of LiPF6, LiBF4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. Exemplarily, the lithium salt is selected from LiPF6. Therefore, it can provide high ionic conductivity and improve cycling characteristics.

[0173] The non-aqueous solvent may be a carbonate compound, an ether compound, other organic solvents, or a combination thereof. The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof. Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), or combinations thereof. Examples of the fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0174] Examples of ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof. Examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters, or combinations thereof.

[0175] This application also provides an electronic device, which includes the secondary battery 100 provided in any of the above embodiments.

[0176] The secondary battery 100 provided in any of the above embodiments has high safety performance and can improve the power safety and power stability of electronic devices powered by the secondary battery 100.

[0177] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes: case; An electrode assembly, which is flat and located within a housing, includes a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. The positive electrode, the separator, and the negative electrode are stacked and wound together, with the winding center axis of the electrode assembly pointing in a first direction. The positive electrode includes a first positive segment, and the negative electrode includes a first negative segment. The first negative segment and the first positive segment are stacked and adjacent to each other along a second direction perpendicular to the first direction. The first positive segment includes a first positive active material layer with a first groove. Along the first direction, the first positive segment includes a first end, and the first negative segment has a second end and a first segment extending beyond the first end in the first direction. The second end and the first end are located on the same side of the electrode assembly in the first direction. The first positive electrode tab is partially accommodated in the first groove, and the first positive electrode tab is connected to the first positive electrode segment and protrudes from the first end along the first direction; The first protective element has a first positive electrode tab that bends toward the first protective element. The first protective element includes a first part and a second part connected together. The first part is disposed between the first positive electrode tab and the first negative electrode segment. Along the first direction, the first part covers the first segment, and the second part covers the second end.

2. The secondary battery according to claim 1, characterized in that, The first part is bonded to the surface of the first negative electrode segment facing the first positive electrode segment.

3. The secondary battery according to claim 1, characterized in that, The separator includes a first dividing segment along the second direction, the first dividing segment being located between the first positive electrode segment and the first negative electrode segment, and the first portion being adhered to the first dividing segment.

4. The secondary battery according to claim 3, characterized in that, The first part is adhered to the surface of the first separator section facing the first positive electrode section.

5. The secondary battery according to claim 1, characterized in that, Along a third direction perpendicular to the first and second directions, the width of the first groove is T mm, the width of the first portion is L1 mm, and 1.2≤L1 / T≤3.

6. The secondary battery according to claim 1, characterized in that, Along the first direction, the length of the first portion is N1 mm, the length of the first groove is M mm, and 1≤N1 / M≤1.

5.

7. The secondary battery according to claim 1, characterized in that, The first protective component further includes a third part, the first part, the second part and the third part are connected in sequence, the third part is bonded to the first outer surface of the electrode assembly, and the first outer surface and the first part are located on the same side of the first positive electrode segment in the second direction.

8. The secondary battery according to claim 7, characterized in that, Along a third direction perpendicular to the first and second directions, the width of the first groove is T mm, the width of the third part is L2 mm, and 0.5 ≤ L2 / T ≤ 1.

9. The secondary battery according to claim 7, characterized in that, Along the first direction, the length of the first groove is M mm, and the length of the third part is N2 mm, where N2 ≤ M.

10. The secondary battery according to claim 1, characterized in that, The first protective element includes a substrate layer, the material of which includes one or more of polyethylene terephthalate, polyimide, and polypropylene.

11. The secondary battery according to claim 10, characterized in that, The first protective component further includes an adhesive layer disposed on the surface of the substrate layer. The adhesive layer is made of one or more of polybutadiene, polypropylene, polypentadiene, styrene, butadiene copolymers, and petroleum resin.

12. The secondary battery according to claim 11, characterized in that, The first protective component further includes a hot-melt layer, wherein the hot-melt layer and the adhesive layer are respectively disposed on two opposite surfaces of the substrate layer, and the material of the hot-melt layer includes one or more of styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, polyurethane elastomer, polyurethane acrylate, polyisobutylene, or polybutadiene.

13. The secondary battery according to claim 1, characterized in that, The electrode assembly further includes a second negative electrode segment. Along the second direction, the second negative electrode segment is stacked and adjacent to the first positive electrode segment. The second negative electrode segment and the first negative electrode segment are respectively located on opposite sides of the first positive electrode segment in the second direction. The second negative electrode segment has a second segment that extends beyond the first end in the first direction. The second negative electrode segment includes a third end. The first end and the third end are located on the same side of the electrode assembly in the first direction. The secondary battery further includes a second protective component, which includes a fourth part, a fifth part, and a sixth part connected in sequence. The fourth part is disposed between the first positive electrode segment and the second negative electrode segment. Along the first direction, the fourth part covers the second segment. The fifth part connects the fourth part and the sixth part and covers the third end. The sixth part is bonded to the second outer surface of the electrode assembly. The second outer surface and the fourth part are located on the same side of the first positive electrode segment in the second direction.

14. The secondary battery according to claim 1, characterized in that, The secondary battery also includes an electrolyte, the components of which include one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, fluoroethylene carbonate, and 1,2-difluoroethylene carbonate.

15. The secondary battery according to claim 1, characterized in that, The casing is made of aluminum-plastic film or steel-plastic film.

16. An electronic device, characterized in that, Includes the secondary battery according to any one of claims 1-15.

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