Secondary battery and electronic device

Abstract

The present application discloses a secondary battery and an electronic device. In the extension direction of a first tab, a first active material layer comprises a first edge. The first active material layer is provided with a first recess and comprises a first region, and the part of the first active material layer located between the first recess and the first edge forms the first region. One part of the first tab is disposed in the first recess, and the first tab is welded to a first current collector to form a first welded portion. The first current collector has a first surface facing the first tab, the height of the first welded portion on the first surface is H1, and the thickness of the first tab is Ta, wherein 10 μm≤H1-Ta≤60 μm. The other part of the first tab is disposed on the surface of the first region facing away from the first current collector, and extends out of a first electrode sheet from the first region. Damage and tearing of the first tab can be reduced, and the drop resistance and impact resistance of the secondary battery can be improved.

Description

Secondary batteries and electronic devices

[0001] Cross-reference of related applications

[0002] This application claims priority to Chinese Patent Application No. 202411554265.6, filed on November 1, 2024, entitled "Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a secondary battery and electronic device. Background Technology

[0004] The tab, acting as a bridge connecting the battery to external circuitry, is typically made of metal. Part of the tab is welded to the current collector inside the battery, while the other part extends outside the casing, allowing the tab to conduct electricity with the internal electrode assembly, thus enabling current transfer. However, during drops, impacts, or other incidents, the tab or the area around it is prone to damage and tearing, potentially leading to battery failure. Summary of the Invention

[0005] This application aims to provide a secondary battery and electronic device that reduces the technical problem of battery failure caused by damage or tearing of the tab or surrounding area.

[0006] The embodiments of this application adopt the following technical solutions:

[0007] In one aspect, this application proposes a secondary battery, including a first tab, a housing, and an electrode assembly. The electrode assembly is disposed within the housing and includes a first electrode plate. One end of the first tab is connected to the first electrode plate, and the other end of the first tab extends outside the housing. The first electrode plate includes a first current collector and a first active material layer disposed on at least one surface of the first current collector. Along the extension direction of the first tab, the first active material layer includes a first edge. The first active material layer is provided with a first groove and includes a first region. The portion of the first active material layer located between the first groove and the first edge forms the first region. A portion of the first tab is disposed in the first groove, and the first tab is welded to the first current collector to form a first weld portion. The first current collector has a first surface facing the first tab. Along the thickness direction of the first electrode plate, the height of the first weld portion on the first surface is H1, and the thickness of the first tab is T. a 10μm≤H1-T a ≤60μm. Another part of the first electrode tab is disposed on the surface of the first region away from the first current collector and extends out of the first region from the first electrode plate.

[0008] In the above technical solution, a higher first welding part is set, and the thickness is limited to 10μm ≤ H1-T. a With a thickness ≤60μm, the welding between the first tab and the first current collector is more thorough, providing a stronger mechanical connection and enhancing the bonding force between them. This also increases the strength of the first tab and its surrounding area, reducing breakage and tearing around the first and second tabs, and minimizing weld breakage during drops or impacts. Furthermore, it reduces the contact resistance between the first tab and the first current collector, thereby improving their conductivity and contributing to a higher charge / discharge rate for the secondary battery. Simultaneously, H1-T a With a thickness of ≤60μm, the influence of the first weld on the thickness of the first electrode can be reduced, as can the burrs on the first weld pierce the separator, thereby reducing the occurrence of short circuits.

[0009] In addition, the portion of the first electrode located at the first edge is supported by the first region, which allows the first region to buffer the first electrode, disperse the stress and shear force on the first electrode, thereby effectively reducing the damage and tearing of the first electrode, reducing poor contact between the first electrode and the first current collector, and improving the drop resistance and impact resistance of the secondary battery.

[0010] Simultaneously, the first tab is in direct contact with the first region (first active material layer), allowing electrons to be directly transferred from the first active material layer to the first tab, reducing electron transport resistance in intermediate stages and improving electron transport efficiency. Combined with the aforementioned high-height first welded joint, the first tab possesses high tear resistance and high current carrying capacity, thereby improving the secondary battery's impact resistance and charge / discharge rate.

[0011] In some embodiments, the first electrode is a positive electrode, where 10μm ≤ H1-T a ≤40μm. This is beneficial for optimizing the internal space utilization of the secondary battery. Alternatively, the first electrode can be the negative electrode, with 35μm ≤H1-T. a ≤60μm, to accommodate the expansion of the negative electrode active material and reduce contact resistance.

[0012] In some embodiments, the first electrode is a positive electrode, and the first current collector and the first tab are made of aluminum with a diameter of 15μm ≤ H1-T. a ≤30μm. Aluminum has good ductility, limited to 15μm ≤H1-T. a ≤30μm can reduce the risk of damage and tearing of the first electrode tab and the first current collector.

[0013] In some embodiments, the thickness of the first electrode tab is T along the thickness direction of the first electrode sheet. a 70μm≤Ta The diameter is ≤110μm, which gives the first tab high strength and reduces the risk of breakage and tearing.

[0014] In some embodiments, when viewed along the thickness direction of the first electrode sheet, the area of ​​the first weld portion on the surface of the first electrode tab opposite to the first current collector is S1, 30 mm. 2 ≤S1≤70mm 2 This reduces the resistance between the first current collector and the first tab, alleviating heat concentration and improving the connection strength between them. Simultaneously, it simplifies the welding process, reduces burrs piercing the separator, and thus reduces the occurrence of short circuits.

[0015] In some embodiments, viewed along the thickness direction of the first electrode, on the surface of the first tab facing away from the first current collector: along the extension direction of the first tab, the maximum length of the first weld portion is L, 9mm ≤ L ≤ 15mm. Along the length direction of the first electrode, the maximum width of the first weld portion is W, 3mm ≤ W ≤ 5mm. This allows for a better welding area between the first tab and the first current collector, improving the connection strength between the first tab and the first current collector while reducing the contact resistance between them.

[0016] In some embodiments, when viewed along the thickness direction of the first electrode sheet, the width of the portion of the first electrode tab overlapping the first region along the extension direction of the first electrode tab is W1, where 2mm≤W1≤4mm. This allows the first region to have higher strength, effectively supporting the first electrode tab, fully dispersing stress and shear force, thereby reducing tearing of the first electrode tab, and reducing material costs.

[0017] In some embodiments, the first electrode further includes a third active material layer disposed on the surface of the first current collector facing away from the first active material layer. Along the extension direction of the first electrode tab, the third active material layer includes a third edge. The third active material layer is provided with a third groove, and the third active material layer includes a third region, the portion of the third active material layer located between the third groove and the third edge forming the third region. Along the thickness direction of the first electrode, the projection of the first region partially overlaps with the third groove. This allows the first electrode tab to smoothly transition to the first region, reducing the impact of excessive thickness abruptness on the welding of the first electrode tab and the first current collector.

[0018] In some embodiments, when viewed along the thickness direction of the first electrode sheet, the width of the portion overlapping the first electrode tab and the third region along the extension direction of the first electrode tab is W3, where 1mm≤W3≤2mm. This can improve the first electrode sheet's resistance to breakage and tearing while reducing the impact of the third region on the energy density of the secondary battery. It can also facilitate the welding of the first electrode tab and the first current collector, thereby improving welding accuracy.

[0019] In some embodiments, the first electrode is a positive electrode, and along the thickness direction of the first electrode, the thickness of the first active material layer is T1, and the thickness of the third active material layer is T3. 35μm≤T1≤55μm, and / or, 35μm≤T3≤55μm. This effectively supports the first electrode tab, fully disperses stress and shear force, and reduces the risk of weld breakage between the first electrode tab and the first current collector.

[0020] In some embodiments, the first electrode is a negative electrode, and along the thickness direction of the first electrode, the thickness of the first active material layer is T1, and the thickness of the third active material layer is T3. 40μm≤T1≤60μm, and / or, 40μm≤T3≤60μm. This effectively supports the first electrode tab, fully disperses stress and shear force, and reduces the risk of weld breakage between the first electrode tab and the first current collector.

[0021] In some embodiments, the secondary battery further includes a first adhesive layer disposed on the first active material layer, covering the first groove and a portion of the first tab along the thickness direction of the first electrode sheet. The first adhesive layer includes a first portion extending beyond the first edge along the extension direction of the first tab. The width of the first portion along the extension direction of the first tab is W5, 0.5mm ≤ W5 ≤ 2mm, which can reduce the impact of the first adhesive layer on the energy density of the secondary battery while reducing the risk of breakage and tearing of the first tab.

[0022] In some embodiments, the electrode assembly further includes a second electrode and a separator, with the separator disposed between the first electrode and the second electrode. The secondary battery also includes a second tab, one end of which is connected to the second electrode and the other end extending outside the casing. The second electrode includes a second current collector and a second active material layer disposed on at least one surface of the second current collector. Along the extension direction of the second tab, the second active material layer includes a second edge. The second active material layer has a second groove and includes a second region, the portion of the second active material layer located between the second groove and the second edge forming the second region. A portion of the second tab is disposed in the second groove, and the second tab is welded to the second current collector, such that the second tab and the second current collector together form a second weld portion. The second current collector has a second surface facing the second tab. Along the thickness direction of the second electrode, the height of the second weld portion on the second surface is H2, and the thickness of the second tab is T. b 10μm≤H2-T b ≤60μm. Another part of the second electrode tab is disposed on the surface of the second region away from the second current collector and extends out of the second region from the second electrode plate.

[0023] This allows for a more thorough weld between the second tab and the second current collector, providing a stronger mechanical connection, enhancing the bonding force between them, and increasing the strength of the second tab and its surrounding area. This reduces breakage and tearing of the second tab and its surrounding area, and minimizes the risk of weld breakage during drops, impacts, or other disturbances to the secondary battery. Simultaneously, it provides a larger contact area, thereby improving the conductivity between the second tab and the second current collector, reducing contact resistance, and ultimately increasing the charge / discharge rate of the secondary battery.

[0024] The portion of the second tab located at the second edge is supported by the second region, which allows the second region to buffer the second tab, disperse the stress and shear force on the second tab, thereby effectively reducing the damage and tearing of the second tab and improving the drop resistance and impact resistance of the secondary battery.

[0025] Simultaneously, the second tab is in direct contact with the second region (second active material layer), allowing electrons to be directly transferred from the second active material layer to the second tab. This reduces electron transport resistance in intermediate stages and improves electron transport efficiency. Combined with the aforementioned second welded portion, the second tab exhibits high tear resistance and high current carrying capacity, thereby enhancing the secondary battery's impact resistance and charge / discharge rate.

[0026] In some embodiments, when viewed along the thickness direction of the second electrode sheet, the area of ​​the second weld portion on the surface of the second electrode tab opposite to the second current collector is S2, 30 mm. 2 ≤S2≤70mm 2 This reduces the resistance between the second current collector and the second tab, alleviating heat concentration and improving the connection strength between them. Simultaneously, it simplifies the welding process, reduces burrs piercing the separator, and thus reduces the occurrence of short circuits.

[0027] In some embodiments, when viewed along the thickness direction of the second electrode sheet, the width of the portion overlapping the second electrode tab with the second region along the extension direction of the second electrode tab is W2, where 2mm≤W2≤4mm. This allows the second region to have higher strength, effectively supporting the second electrode tab, fully dispersing stress and shear force, thereby reducing tearing of the second electrode tab, and further reducing material costs.

[0028] In some embodiments, the second electrode further includes a fourth active material layer disposed on the surface of the second current collector facing away from the second active material layer. Along the extension direction of the second electrode tab, the fourth active material layer includes a fourth edge. The fourth active material layer is provided with a fourth groove and includes a fourth region, the portion of the fourth active material layer located between the fourth groove and the fourth edge forming the fourth region. Along the thickness direction of the second electrode, the projection of the second region partially overlaps with the fourth groove. This allows for a smooth transition from the second electrode tab to the second region, reducing the impact of excessive thickness abruptness on the welding of the second electrode tab and the second current collector.

[0029] In some embodiments, when viewed along the thickness direction of the second electrode sheet, the width of the portion overlapping the second electrode tab and the fourth region along the extension direction of the second electrode tab is W4, where 1mm ≤ W4 ≤ 2mm. This can improve the second electrode sheet's resistance to breakage and tearing while reducing the impact of the fourth region on the energy density of the secondary battery, and also facilitate the welding of the second electrode tab and the second current collector, improving welding accuracy.

[0030] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0031] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0032] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0033] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0034] Figure 2 is a schematic diagram of the stacked structure of the first electrode, the separator, and the second electrode in some embodiments of this application;

[0035] Figure 3 is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application;

[0036] Figure 4 shows the cross-sectional view of AA and BB in Figure 2 (excluding the first and second adhesive layers).

[0037] Figure 5 is a schematic diagram of the structure of the first electrode located in the first groove in some embodiments of this application;

[0038] Figure 6 shows the cross-sectional view of AA and BB in Figure 2 (including the first adhesive layer and the second adhesive layer).

[0039] Figure 7 is a schematic diagram of the structure of the first electrode located in the first groove in some embodiments of this application.

[0040] Explanation of reference numerals in the attached figures:

[0041] 100. Secondary batteries;

[0042] 10. Shell;

[0043] 20. Electrode assembly;

[0044] 21. First electrode; 211. First current collector; 2111. First surface; 212. First active material layer; 212a. First edge; 2121. First region; 2121a. First sub-region; 213. Third active material layer; 213a. Third edge; 2131. Third region; 214. First groove; 215. Third groove;

[0045] 22. Second electrode; 221. Second current collector; 2211. Second surface; 222. Second active material layer; 222a. Second edge; 2221. Second region; 223. Fourth active material layer; 223a. Fourth edge; 2231. Fourth region; 224. Second groove; 225. Fourth groove;

[0046] 23. Separating membrane;

[0047] 30. First pole ear; 40. Second pole ear;

[0048] 50. First welding section; 60. Second welding section;

[0049] 70. First adhesive layer; 80. Second adhesive layer;

[0050] X, first direction; Y, second direction; Z, third direction. Embodiments of the present invention

[0051] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0052] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0053] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0054] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0055] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0056] In one aspect, this application proposes a secondary battery 100. Referring to Figure 1, the secondary battery 100 includes a casing 10, an electrode assembly 20, a first tab 30, and a second tab 40. The casing 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte wets the electrode assembly 20 within the casing 10, thereby causing an electrochemical reaction. One end of the first tab 30 is connected to the electrode assembly 20 inside the casing 10, and the other end of the first tab 30 extends outside the casing 10. One end of the second tab 40 is connected to the electrode assembly 20 inside the casing 10, and the other end of the second tab 40 extends outside the casing 10. The first tab 30 and the second tab 40 have opposite polarities and are used to lead out the positive and negative electrodes of the secondary battery 100.

[0057] Referring to Figures 1 and 2, the electrode assembly 20 includes a first electrode 21, a second electrode 22, and a separator 23. The electrode assembly 20 can employ a stacked structure, for example, along the thickness direction (third direction Z) of the first electrode 21, several first electrode 21s and several second electrode 22s are alternately stacked, with a separator 23 disposed between adjacent first electrode 21s and second electrode 22s. In other embodiments, the electrode assembly 20 can also employ a wound structure, where the first electrode 21, separator 23, and second electrode 22 are stacked along the thickness direction (third direction Z) of the first electrode 21 and wound along the length direction (first direction X) of the first electrode 21, thereby forming a wound electrode assembly 20.

[0058] Referring to Figure 2, taking the first electrode 21 as the positive electrode as an example, the first electrode 21 includes a first current collector 211 and a first active material layer 212. The first current collector 211 serves as the conductive substrate of the first electrode 21 and can be an integrally flat aluminum foil. Aluminum foil has high conductivity and low resistance, which can improve the charge and discharge rate of the secondary battery 100. The first active material layer 212 can be disposed on at least one surface of the first current collector 211 in the thickness direction (third direction Z). The first active material layer 212 includes a positive electrode active material, a conductive agent, and a binder, etc. The above material components are mixed, stirred evenly, and coated on the surface of the first current collector 211 to obtain the first active material layer 212. Among them, the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium manganese iron phosphate.

[0059] Referring to Figure 2, taking the second electrode 22 as the negative electrode as an example, the second electrode 22 includes a second current collector 221 and a second active material layer 222. The second current collector 221 serves as the conductive substrate of the second electrode 22 and can be an integrally flat copper foil. Copper foil has high conductivity and low resistance, which can improve the charge and discharge rate of the secondary battery 100. The second active material layer 222 can be disposed on at least one surface of the second current collector 221 in the thickness direction (third direction Z). The second active material layer 222 includes a negative electrode active material, a conductive agent, and a binder, etc. These materials are mixed, stirred evenly, and coated on the surface of the second current collector 221 to obtain the second active material layer 222. Among them, the negative electrode active material includes one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxide, silicon alloy, etc.

[0060] The first tab 30 is a metal conductor that draws current from the first electrode 21. It can be made of aluminum, copper, or nickel. The first tab 30 is welded to the first current collector 211 so that the first tab 30 and the first electrode 21 are connected.

[0061] In the embodiments of this application, referring to Figures 3 and 4, the first active material layer 212 has a first edge 212a. For example, the first edge 212a is located on one side of the width direction (second direction Y) of the first electrode 21. To facilitate the electrical connection between the first tab 30 and the first current collector 211, the first active material layer 212 is provided with a first groove 214, which can be formed by laser cleaning or by foaming adhesive process. The first current collector 211 can be exposed from the first groove 214. By placing a part of the first tab 30 in the first groove 214, the first tab 30 and the first current collector 211 can be welded. The other part of the first tab 30 extends out of the first electrode 21 from the first edge 212a.

[0062] The second tab 40 is a metal conductor that draws current from the second electrode 22. It can be made of aluminum, copper, or nickel. The second tab 40 is welded to the second current collector 221 so that the second tab 40 and the second electrode 22 are connected.

[0063] In the embodiments of this application, referring to FIG4, the second active material layer 222 has a second edge 222a. For example, the second edge 222a is located on one side of the width direction of the second electrode 22. To facilitate the electrical connection between the second electrode tab 40 and the second current collector 221, the second active material layer 222 is provided with a second groove 224, which can be formed by laser cleaning or foaming process. The second current collector 221 can be exposed from the second groove 224. By placing a part of the second electrode tab 40 in the second groove 224, the second electrode tab 40 and the second current collector 221 can be welded. The other part of the second electrode tab 40 extends out of the housing 10 from the second edge 222a.

[0064] The inventors of this application have discovered that, in order to improve the sealing performance of the housing 10, the tabs are fixed to the housing 10. During the process of the secondary battery 100 being dropped or impacted, the electrode assembly 20 is prone to relative displacement with the housing 10, which causes the electrode assembly 20 to pull on the tabs, which can easily cause damage or tearing of the tabs or some current collectors around the tabs, and can easily cause the electrical connection between the tabs and the current collectors to be broken, resulting in the failure of the secondary battery.

[0065] To mitigate the aforementioned problems, in the embodiments of this application, taking the welding of the first electrode tab 30 and the first electrode plate 21 as an example, please refer to Figures 4 and 5. The first electrode tab 30 is welded to the first current collector 211 to form a first welding portion 50. The first current collector 211 has a first surface 2111 facing the first electrode tab 30. Along the thickness direction (third direction Z) of the first electrode plate 21, the height of the first welding portion 50 on the first surface 2111 is H1, and the thickness of the first electrode tab 30 is T. a 10μm≤H1-T a ≤60μm.

[0066] By employing a first weld portion 50 with a relatively large height, and limiting it to 10μm≤H1-T aThe weld width is ≤60μm, which allows for a more thorough weld between the first tab 30 and the first current collector 211, providing a stronger mechanical connection, enhancing the bonding force between the first tab 30 and the first current collector 211, and improving the strength of the first tab 30 and its surrounding area. This reduces the risk of breakage and tearing of the first tab 30 and the surrounding first current collector 211, as well as reducing the risk of weld breakage during drops, impacts, etc., of the secondary battery 100. Furthermore, it reduces the contact resistance between the first tab 30 and the first current collector 211, thereby improving their conductivity and contributing to a higher charge / discharge rate for the secondary battery 100.

[0067] Meanwhile, the inventors of this application discovered that excessive height of the first welding portion 50 affects the thickness of the first electrode 21, leading to uneven thickness in some areas of the first electrode 21. Furthermore, excessive height can also cause welding burrs on the first welding portion 50 to pierce the separator 23, potentially causing the first electrode 21 to contact the second electrode 22 and resulting in a short circuit. In this application, H1-T is defined as... a With a thickness of ≤60μm, the influence of the first weld portion 50 on the thickness of the first electrode 21 can be reduced, as can the burrs on the first weld portion 50 piercing the separator 23, thereby reducing the occurrence of short circuits.

[0068] The surface of the first welded part 50 may be uneven. It is necessary to ensure that the height of each part of the first welded part 50 is ≤ 10μm H1-T. a ≤60μm is acceptable. For measuring the height of the first welded part 50, a laser displacement sensor can be used to measure the three-dimensional morphology of the surface of the first welded part 50, and the height of the first welded part 50 can be obtained through the high-precision measurement function of the sensor.

[0069] Regarding the thickness of the first electrode tab 30, in some embodiments, the thickness of the first electrode tab 30 along the thickness direction (third direction Z) of the first electrode 21 is T. a 70μm≤T a A thickness of ≤110μm ensures that the first tab 30 has high strength, reducing the likelihood of breakage or tearing. The thickness of the first tab 30 refers to the thickness of the unwelded area of ​​the first tab 30.

[0070] In some embodiments, the welding method for the first tab 30 and the first current collector 211 is ultrasonic welding, and the ultrasonic welding device includes a welding head. Different welding heights of the first weld portion 50 can be achieved by setting different groove depths on the welding head. Different heights of the first weld portion 50 can also be achieved by controlling the energy of the welding head. Alternatively, the height of the first weld portion 50 can be adjusted by adjusting the ultrasonic frequency and thus the energy transfer during the welding process. The height of the first weld portion 50 can also be adjusted by adjusting the welding time, welding pressure, amplitude, etc.

[0071] In some embodiments, the welding method is laser welding, and the height of the first welding part 50 can be adjusted in the following ways: (1) Laser power: Laser power directly affects the temperature and melting depth of the welding area. Higher power increases the height of the first welding part 50; lower power results in a smaller height of the first welding part 50. (2) Laser pulse width: Laser pulse width affects the energy transfer during the welding process. A longer pulse width increases the height of the first welding part 50; a shorter pulse width results in a smaller height of the first welding part 50. (3) Laser spot size: Laser spot size affects the concentration of the welding area. A larger spot increases the height of the first welding part 50; a smaller spot results in a smaller height of the first welding part 50.

[0072] It is understood that in some other embodiments, resistance welding, electron beam welding, cold pressure welding, etc., may also be used.

[0073] The inventors of this application have also discovered that, due to the use of a first welded part 50 with a relatively large height, the gap between the first tab 30 and the first edge 212a is easily too large, and part of the first tab 30 may be in a suspended state. During the process of the secondary battery 100 being dropped or impacted, the first tab 30 will repeatedly impact the first edge 212a, which can easily cause stress and shear force concentration at the first edge 212a of the first tab 30, resulting in damage and tearing of the first tab 30.

[0074] To mitigate the aforementioned problems, in the embodiments of this application, referring to Figures 4 and 5, the first active material layer 212 includes a first region 2121, the portion of the first active material layer 212 located between the first groove 214 and the first edge 212a forming the first region 2121. Another portion of the first tab 30 is disposed on the surface of the first region 2121 facing away from the first current collector 211, and this other portion extends from the first region 2121 out of the first electrode sheet 21. The portion of the first tab 30 located at the first edge 212a is supported by the first region 2121, allowing the first region 2121 to buffer the first tab 30, dispersing the stress and shear force experienced by the first tab 30, thereby effectively reducing the risk of breakage and tearing of the first tab 30 and improving the drop and impact resistance of the secondary battery 100.

[0075] Simultaneously, the first tab 30 is in direct contact with the first region 2121 (first active material layer 212), allowing electrons to be directly transferred from the first active material layer 212 to the first tab 30. This reduces electron transport resistance in intermediate stages and improves electron transport efficiency. Combined with the aforementioned height of the first welded portion 50, the first tab 30 possesses high tear resistance and high current carrying capacity, thereby improving the impact resistance of the secondary battery 100 while also increasing its charge / discharge rate.

[0076] In the embodiments of this application, the first electrode 21 is a positive electrode, and along the thickness direction (third direction Z) of the first electrode 21, the height of the first welding part 50 satisfies 10μm≤H1-T a ≤40μm. Alternatively, the first electrode 21 can also be the negative electrode, 35μm≤H1-T a ≤60μm. During the charging and discharging process of a secondary battery 100, the expansion coefficient of the negative electrode active material is typically greater than that of the positive electrode active material. Furthermore, lithium ions embed into the negative electrode active material layer, causing its volume to expand. Using a higher weld joint in the negative electrode is more effective in adapting to the volume changes of the negative electrode active material layer, reducing the risk of weld joint breakage due to expansion. Moreover, compared to the positive electrode, the negative electrode generates more heat; a higher weld joint means a more thorough weld, reducing resistance and heat generation.

[0077] Positive electrode active materials typically have high potential and relatively stable structure, with small volume changes and relatively regular electron conduction; furthermore, the heat generated by the positive electrode is usually less than that of the negative electrode, and the use of a smaller welded part on the positive electrode is more conducive to optimizing the internal space utilization of the secondary battery 100.

[0078] When the first electrode 21 is a positive electrode, the first current collector 211 and the first tab 30 are made of aluminum, preferably with a diameter of 15μm ≤ H1-T. a ≤30μm. The aluminum first tab 30 and first current collector 211 have high strength and ductility, limited to 15μm ≤H1-T. a A diameter of ≤30μm can reduce the risk of breakage and tearing of the first tab 30 and the first current collector 211, thereby improving the drop resistance and impact resistance of the secondary battery 100.

[0079] Regarding the thickness of the active material layer, in some embodiments, referring to Figure 2, the first electrode 21 is a positive electrode. Along the thickness direction (third direction Z) of the first electrode 21, the thickness of the first active material layer 212 is T1, 35μm≤T1≤55μm. If the thickness of the first active material layer 212 is too small, it may be difficult to effectively support the first tab 30, resulting in insufficient stress and shear force dispersion. If the thickness is too large, it may cause excessive thickness abruptness when the first tab 30 extends, affecting the welding strength between the first tab 30 and the first current collector 211, potentially leading to weld breakage between the first tab 30 and the first current collector 211. Limiting the thickness to 35μm≤T1≤55μm can effectively support the first tab 30, fully disperse stress and shear force, and reduce the likelihood of weld breakage between the first tab 30 and the first current collector 211. Similarly, the thickness of the third active material layer 213 is T3, 35μm≤T3≤55μm.

[0080] The first electrode 21 can also be a negative electrode. Along the thickness direction (third direction Z) of the first electrode 21, 40μm≤T1≤60μm, 40μm≤T3≤60μm, it can effectively support the second electrode tab 40, fully disperse stress and shear force, and reduce the possibility of the second electrode tab 40 breaking off from the weld with the second current collector 221. Similarly, the thickness of the fourth active material layer 223 is T4, 40μm≤T4≤60μm. At the same time, the thickness of the second active material layer 222 and the fourth active material layer 223 are slightly greater than the thickness of the first active material layer 212 and the third active material layer 213, corresponding to the different weld heights of the positive and negative electrodes, and ensuring that the negative electrode has sufficient margin to embed lithium ions extracted from the positive electrode, reducing lithium plating.

[0081] In the embodiments of this application, the second electrode tab 40 can also be similarly configured. Referring to Figure 4, the second electrode tab 40 is welded to the second current collector 221 to form a second welded portion 60. The second current collector 221 has a second surface 2211 facing the second electrode tab 40. Along the thickness direction (third direction Z) of the second electrode 22, the height of the second welded portion 60 on the second surface 2211 is H2, and the thickness of the second electrode tab 40 is T. b 10μm≤H2-T b ≤60μm.

[0082] By employing a higher second weld portion 60, and limiting 10μm≤H2-T bThe weld width is ≤60μm, allowing for a more thorough weld between the second tab 40 and the second current collector 221. This provides a stronger mechanical connection, enhances the bonding force between the second tab 40 and the second current collector 221, and improves the strength of the second tab 40 and its surrounding area. It also reduces the risk of breakage or tearing of the second tab 40 and the surrounding second current collector 221, and minimizes the risk of electrical disconnection between the second tab 40 and the second current collector 221 during drops or impacts of the secondary battery 100. Furthermore, it provides a larger contact area, thereby improving the conductivity between the second tab 40 and the second current collector 221, reducing contact resistance, and contributing to a higher charge / discharge rate for the secondary battery 100. The welding method of the second weld portion 60 can be referenced from that of the first weld portion 60 described above.

[0083] In addition, in the embodiments of this application, the second active material layer 222 includes a second region 2221, and the portion of the second active material layer 222 located between the second groove 224 and the second edge 222a forms the second region 2221. Another portion of the second tab 40 is disposed on the surface of the second region 2221 facing away from the second current collector 221, and the other portion of the second tab 40 extends from the second region 2221 out of the second electrode 22. The portion of the second tab 40 located at the second edge 222a is supported by the second region 2221, allowing the second region 2221 to buffer the second tab 40, dispersing the stress and shear force experienced by the second tab 40, thereby effectively reducing the risk of breakage and tearing of the second tab 40 and improving the drop and impact resistance of the secondary battery 100.

[0084] Simultaneously, the second tab 40 is in direct contact with the second region 2221 (second active material layer 222), allowing electrons to be directly transferred from the second active material layer 222 to the second tab 40. This reduces electron transport resistance in intermediate stages and improves electron transport efficiency. Combined with the aforementioned higher second weld portion 60, the second tab 40 exhibits higher tear resistance and current carrying capacity, thereby improving the impact resistance of the secondary battery 100 while also increasing its charge / discharge rate.

[0085] Regarding the thickness of the second tab 40, in some embodiments, the thickness of the second tab 40 can also be set to 70μm to 110μm along the thickness direction (third direction Z) of the second electrode 22, which can make the second tab 40 have higher strength and reduce the second tab 40 from breaking and tearing.

[0086] If the welding area of ​​the first welding part 50 is too small, the resistance between the first current collector 211 and the first tab 30 will be large, which will easily lead to heat concentration and may result in insufficient connection strength between the first tab 30 and the first current collector 211. If the welding area is too large, the welding time will be longer, the production cost will increase, and more welding burrs may be generated, which will increase the risk of burrs piercing the separator 23.

[0087] In the embodiments of this application, when viewed along the thickness direction (third direction Z) of the first electrode 21, the area of ​​the first welding portion 50 on the surface of the first electrode tab 30 facing away from the first current collector 211 is S1, 30mm. 2 ≤S1≤70mm 2 This reduces the resistance between the first current collector 211 and the first tab 30, alleviating heat concentration and improving the connection strength between the first tab 30 and the first current collector 211. Simultaneously, it simplifies the welding process, reduces burrs piercing the isolation membrane 23, and thus reduces the occurrence of short circuits.

[0088] For example, referring to Figure 5, observing along the thickness direction (third direction Z) of the first electrode 21, on the surface of the first electrode tab 30 facing away from the first current collector 211: along the extension direction of the first electrode tab 30 (second direction Y), the maximum length of the first weld portion 50 is L, 9mm ≤ L ≤ 15mm; along the length direction of the first electrode 21 (first direction X), the maximum width of the first weld portion 50 is W, 3mm ≤ W ≤ 5mm. This allows for a better welding area between the first electrode tab 30 and the first current collector 211, improving the connection strength between them while reducing the contact resistance.

[0089] Based on the same inventive concept, viewed along the thickness direction (third direction Z) of the second electrode 22, on the surface of the second electrode tab 40 opposite to the second current collector 221, the area of ​​the second weld portion 60 is S2, 30mm. 2 ≤S2≤70mm 2 This reduces the resistance between the second current collector 221 and the second tab 40, alleviates heat concentration, and improves the connection strength between the second tab 40 and the second current collector 221. Simultaneously, it simplifies the welding process, reduces burrs piercing the separator 23, and thus reduces the occurrence of short circuits. For example, viewed along the thickness direction (third direction Z) of the second electrode 22, on the surface of the second tab 40 opposite to the second current collector 221: along the second direction Y, the maximum length of the second weld portion 60 is 9 mm to 15 mm, and along the first direction X, the maximum width of the second weld portion 60 is 3 mm to 5 mm.

[0090] For the method of testing the area of ​​the first welded part 50: the first welded part 50 can be observed using an optical microscope or an electron microscope. After magnifying the first welded part 50 to a suitable magnification, an image is taken, and then the area of ​​the first welded part 50 is measured using image analysis software.

[0091] Regarding the width of the first region 2121, the inventors of this application have found that if the width of the first region 2121 is too small, the mechanical strength of the first region 2121 will be insufficient. Due to the edge effect, the first region 2121 may shed powder and fall off, and it will be difficult to effectively support the first tab 30, and it will be difficult to fully disperse stress and shear force, resulting in a higher risk of tearing of the first tab 30. If the width of the first region 2121 is too large, the part covered by the first tab 30 will be difficult to participate in or unable to participate in the electrochemical reaction. An excessively large width means the use of more material, wasting costs and occupying too much space.

[0092] In the embodiments of this application, please refer to Figures 4 and 5. Observing along the thickness direction (third direction Z) of the first electrode 21, along the extension direction (second direction Y) of the first electrode tab 30, the width of the portion overlapping the first electrode tab 30 and the first region 2121 is W1, where 2mm≤W1≤4mm. This allows the first region 2121 to have high strength, effectively supporting the first electrode tab 30, fully dispersing stress and shear force, thereby reducing tearing of the first electrode tab 30, and reducing material costs.

[0093] Based on the same inventive concept, viewed along the thickness direction (third direction Z) of the second electrode 22, and along the extension direction (second direction Y) of the second electrode tab 40, the width of the overlapping portion between the second electrode tab 40 and the second region 2221 is W2, where 2mm ≤ W2 ≤ 4mm. This allows the second region 2221 to have higher strength, effectively supporting the second electrode tab 40, fully dispersing stress and shear force, thereby reducing tearing of the second electrode tab 40, and further reducing material costs.

[0094] In addition, the first region 2121 can provide support for the first current collector 211, and can also disperse the shear force of the first current collector 211 located in the first groove 214 region, and can resist the breakage and tearing of the first current collector 211 in the first groove 214 region, thereby improving the drop resistance and impact resistance of the secondary battery 100. The second region 2221 is similar, and can also reduce tearing of the second current collector 221.

[0095] In some embodiments, referring to Figures 2 and 4, the first electrode 21 further includes a third active material layer 213, which is disposed on the surface of the first current collector 211 facing away from the first active material layer 212. The first electrode 21 employs an active material layer on both sides, which can improve the energy density of the secondary battery 100. Along the extension direction (second direction Y) of the first tab 30, the third active material layer 213 includes a third edge 213a and a third groove 215. For example, when welding the first tab 30, the welding socket supports the first current collector 211 in the third groove 215, and the welding head welds the first tab 30 and the first current collector 211 in the first groove 214.

[0096] The third active material layer 213 includes a third region 2131. The portion of the third active material layer 213 located between the third groove 215 and the third edge 213a forms the third region 2131. The arrangement of the third region 2131 can further reduce tearing of the first current collector 211 and improve the flatness of the first electrode 21.

[0097] The inventors of this application have discovered that when the first tab 30 is disposed in the first region 2121, the first region 2121 corresponds to the third region 2131 in the thickness direction (third direction Z) of the first electrode 21. That is, the first tab 30 is supported by two layers of active material. If the thickness change is too large, it may affect the welding of the first tab 30 and the first current collector 211.

[0098] To mitigate the aforementioned issues, in the embodiments of this application, along the thickness direction (third direction Z) of the first electrode 21, the projection of the first region 2121 partially overlaps with the third groove 215. For example, the portion overlapping with the third groove 215 is defined as the first sub-region 2121a. When the first tab 30 extends from the first region 2121 out of the first electrode 21, the first sub-region 2121a first contacts and supports the first tab 30. In the thickness direction (third direction Z) of the first electrode 21, the first sub-region 2121a does not have a corresponding third active material layer 213; only one active material layer supports the first tab 30. This allows the first tab 30 to smoothly transition to the first region 2121, reducing the impact of excessive thickness abruptness on the welding of the first tab 30 and the first current collector 211.

[0099] In some embodiments, when viewed along the thickness direction (third direction Z) of the first electrode 21, the width of the overlapping portion of the first electrode 30 and the third region 2131 along the extension direction (second direction Y) of the first electrode tab 30 is W3, where 1mm≤W3≤2mm. By partially misaligning the first region 2121 and the third region 2131, the resistance of the first electrode 21 to breakage and tearing can be improved, while the impact of the third region 2131 on the energy density of the secondary battery 100 can be reduced. Sufficient empty foil can also be reserved to facilitate the welding of the first electrode tab 30 and the first current collector 211, thereby improving the welding accuracy.

[0100] Based on the same concept, the second electrode 22 also includes a fourth active material layer 223. Along the extension direction of the second electrode tab 40 (second direction Y), the fourth active material layer 223 includes a fourth edge 223a and a fourth groove 225. The fourth active material layer 223 includes a fourth region 2231. The portion of the fourth active material layer 223 located between the fourth groove 225 and the fourth edge 223a forms the fourth region 2231. The fourth region 2231 can further reduce tearing of the second current collector 221 and improve the flatness of the second electrode 22.

[0101] Along the thickness direction (Z-direction) of the second electrode 22, the projection of the second region 2221 partially overlaps with the fourth groove 225. For example, the portion overlapping with the fourth groove 225 is defined as the second sub-region 2221a. When the second electrode tab 40 extends from the second region 2221 out of the second electrode 22, the second sub-region 2221a first contacts and supports the second electrode tab 40. In the thickness direction (Z-direction) of the second electrode 22, the second sub-region 2221a does not have a corresponding fourth active material layer 223. Only one active material layer supports the second electrode tab 40, which allows the second electrode tab 40 to smoothly transition to the second region 2221, reducing the impact of excessive thickness abruptness on the welding of the second electrode tab 40 and the second current collector 221.

[0102] In some embodiments, when viewed along the thickness direction (third direction Z) of the second electrode 22, the width of the fourth region 2231 along the extension direction (second direction Y) of the second tab 40 is W4, where 1mm≤W4≤2mm. By partially misaligning the second region 2221 and the fourth region 2231, the resistance of the second electrode 22 to breakage and tearing can be improved, while the impact of the fourth region 2231 on the energy density of the secondary battery 100 can be reduced. It can also facilitate the welding of the second tab 40 and the second current collector 221 and improve the welding accuracy.

[0103] Regarding the thickness of each of the above-mentioned active material layers, in some embodiments, referring to Figure 2, the first electrode 21 is a positive electrode. Along the thickness direction of the first electrode 21 (third direction Z), the thickness of the first active material layer 212 is T1, 35μm≤T1≤55μm. If the thickness of the first active material layer 212 is too small, it may be difficult to effectively support the first tab 30, and the stress and shear force will not be sufficiently dispersed. If the thickness is too large, it may cause too large a change in thickness when the first tab 30 extends, which will affect the welding strength between the first tab 30 and the first current collector 211, and may cause the weld between the first tab 30 and the first current collector 211 to break. Limiting it to 35μm≤T1≤55μm can effectively support the first tab 30, fully disperse stress and shear force, and reduce the possibility of the weld between the first tab 30 and the first current collector 211 breaking. Similarly, the thickness of the third active material layer 213 is T3, 35μm≤T3≤55μm.

[0104] The first electrode 21 can also be a negative electrode, in which case 40μm≤T1≤60μm and 40μm≤T3≤60μm. Alternatively, the first electrode 21 can be a positive electrode, and the second electrode 22 can be a negative electrode. Along the thickness direction of the second electrode 22 (third direction Z), the thickness of the second active material layer 222 is T2, 40μm≤T2≤60μm. This effectively supports the second electrode tab 40, fully disperses stress and shear force, and reduces the risk of breakage of the weld between the second electrode tab 40 and the second current collector 221. Similarly, the thickness of the fourth active material layer 223 is T4, 40μm≤T4≤60μm. Furthermore, the thicknesses of the second active material layer 222 and the fourth active material layer 223 are slightly greater than the thicknesses of the first active material layer 212 and the third active material layer 213, corresponding to the different weld heights of the positive and negative electrodes, and ensuring that the negative electrode has sufficient margin to embed lithium ions extracted from the positive electrode, thus reducing lithium plating.

[0105] In the embodiments of this application, referring to Figures 6 and 7, the secondary battery 100 further includes a first adhesive layer 70. The first adhesive layer 70 is disposed on the first active material layer 212, along the thickness direction (third direction Z) of the first electrode 21, and covers the first groove 214 and part of the first tab 30. The first adhesive layer 70 can cover the welding burrs between the first tab 30 and the first current collector 211, reducing the burrs from piercing the separator 23, thereby reducing the occurrence of short circuits. Furthermore, the first adhesive layer 70 can fix and protect the first tab 30, improve the connection strength between the first tab 30 and the first current collector 211, and reduce the breakage of the weld between the first tab 30 and the first current collector 211.

[0106] The first adhesive layer 70 includes a first portion 71 extending beyond the first edge 212a along the extension direction (second direction Y) of the first tab 30. This allows the first adhesive layer 70 to cover the portion of the first tab 30 located at the first edge 212a, thereby dispersing the stress and shear force of that portion. Furthermore, the first adhesive layer 70 can resist tearing of the first tab 30, further improving the drop resistance and impact resistance of the secondary battery 100.

[0107] In the embodiments of this application, along the extension direction of the first tab 30 (second direction Y), the width of the first part is W5, 0.5mm≤W5≤2mm, which can reduce the damage and tearing of the first tab 30 while reducing the impact of the first adhesive layer 70 on the energy density of the secondary battery 100.

[0108] Based on the same inventive concept, referring to Figure 6, the secondary battery 100 further includes a second adhesive layer 80. The second adhesive layer 80 is disposed on the second active material layer 222, along the thickness direction (third direction Z) of the second electrode 22, and covers the second groove 224 and part of the second tab 40. The second adhesive layer 80 can cover the welding burrs between the second tab 40 and the second current collector 221, reducing the burrs from piercing the separator 23, thereby reducing the occurrence of short circuits. Furthermore, the second adhesive layer 80 can fix and protect the second tab 40, improve the connection strength between the second tab 40 and the second current collector 221, and reduce the breakage of the weld between the second tab 40 and the second current collector 221.

[0109] The second adhesive layer 80 includes a second portion 81 extending beyond the second edge 222a along the extension direction (second direction Y) of the second tab 40. This allows the second adhesive layer 80 to cover the portion of the second tab 40 located at the second edge 222a, thereby dispersing stress and shear force in that portion. Furthermore, the second adhesive layer 80 can resist tearing of the second tab 40, further improving the drop resistance and impact resistance of the secondary battery 100.

[0110] In the embodiments of this application, along the extension direction (second direction Y) of the second tab 40, the width of the second part is W6, 0.5mm≤W6≤2mm, which can reduce the damage and tearing of the second tab 40 while reducing the impact of the second adhesive layer 80 on the energy density of the secondary battery 100.

[0111] Secondly, this application also proposes an electronic device, including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art. For example, electronic devices include, but are not limited to, Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0112] Example 1-1:

[0113] <Preparation of the positive electrode>

[0114] The positive electrode active material is lithium iron phosphate, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10⁻⁶). 5 The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone (NMP) added as a solvent to prepare a positive electrode slurry with a solid content of 75 wt%, and stirred evenly under vacuum. An aluminum foil with a thickness of 8 μm and a length of 1000 mm was selected as the positive electrode current collector. The positive electrode slurry was uniformly coated on one surface of the aluminum foil and dried at 110°C to obtain a positive electrode sheet with a single-sided coating of positive active material. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material.

[0115] <Welding of the positive electrode tab>

[0116] A first groove is created in a positive electrode active material layer using laser cleaning technology. This first groove, along with the edge (width direction) of the positive electrode active material layer, forms a first region with a width W1 of 3 mm. A material with a width of 6 mm and a thickness T is selected. a A 70mm aluminum sheet is used as the positive electrode tab. The positive electrode tab is welded to the positive current collector within the first groove using ultrasonic welding, forming a roughly rectangular first welded part. The welding parameters are as follows: 20kHz ultrasonic welding head, approximately 2mm diameter, welding pressure of 200N, and ultrasonic amplitude of 20μm. On the surface of the positive electrode tab away from the positive current collector (the first surface), the height H1 of the first welded part is 80μm, and H1-T... a =80μm-70μm=10μm, the length L of the first welded part is 12mm, and the width W is 4mm. The other part of the positive electrode tab is supported by the first region and extends out of the positive electrode plate.

[0117] <Preparation of Negative Electrode Sheets>

[0118] A negative electrode active material (graphite powder), silicon powder, conductive carbon black (Super P), and binder (styrene-acrylic rubber (SD-3)) were mixed in a weight ratio of 89.5:8:1:1.5. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 50 wt%, and the mixture was stirred evenly. A copper foil with a thickness of 5 mm and a length of 1050 mm was selected as the negative electrode current collector. The negative electrode slurry was uniformly coated onto one surface of the copper foil and dried at 90°C to obtain a single-sided negative electrode sheet. This completes the single-sided coating of the negative electrode sheet. The above steps were then repeated on the other surface of the negative electrode sheet to obtain a double-sided coated negative electrode active material layer. A second groove was created in one of the negative electrode active material layers using a laser cleaning process. A portion of the negative electrode tab was then welded to the negative electrode current collector within the second groove.

[0119] <Preparation of the separating membrane>

[0120] A porous separator membrane was prepared by using polyethylene as a 7μm substrate layer and polyvinylidene fluoride as an adhesive layer, with an alumina ceramic layer of 2μm thickness placed on the side of the adhesive layer away from the substrate layer.

[0121] <Electrolyte Preparation>

[0122] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0123] <Preparation of Lithium-ion Batteries>

[0124] The separator, positive electrode, separator, and negative electrode prepared above are stacked in sequence and wound to obtain an electrode assembly. A punched aluminum-plastic film is placed in an assembly fixture with the punched surface facing upwards, and the electrode assembly is placed in the punched surface and pressed firmly. Then, another punched aluminum-plastic film is placed on the electrode assembly with the punched surface facing downwards. After encapsulation, electrolyte injection, hot pressing formation, and shaping processes, a lithium-ion secondary battery is obtained.

[0125] Unlike Example 1-1, the relevant parameters in Examples 1-2 to 1-26 and Comparative Examples 1-1 to 1-5 are shown in Table 1 below. Different heights of the first welded part can be welded by controlling the energy of the welding head. Alternatively, the height of the first welded part can be adjusted by adjusting the ultrasonic frequency and thus the energy transfer during the welding process. The height, area, length, and width of the first welded part can also be adjusted by adjusting the welding time, welding pressure, amplitude, etc.

[0126] Drop Test Method: Under ambient conditions of 25±5℃, the lithium-ion secondary battery is charged to 100% SOC. The voltage of the lithium-ion secondary battery is measured before the drop test. The lithium-ion secondary battery is placed in a clamping chamber, and an automatic drop device is used to drop the bottom, side, and top surfaces of the lithium-ion secondary battery sequentially from a position of 1.8 m onto a steel plate, for a total of 6 rounds (18 drops). After the drop test, the battery is left to stand at room temperature for 24 hours, and the voltage of the lithium-ion secondary battery is measured and recorded. The lithium-ion secondary battery is disassembled, and the positive electrode tab is observed to be broken, detached from the positive current collector, and the first current collector around the positive electrode tab is observed to be torn. If the voltage drop of the lithium-ion secondary battery is greater than 30mV, or if the positive electrode tab or the area around the positive electrode tab is damaged or torn, the lithium-ion secondary battery fails the drop test. Each group consists of 20 batteries, with N batteries failing, resulting in a drop failure rate of N / 20.

[0127] Table 1

[0128] H1-Ta (μm) Positive electrode tab is located on the surface of the first region. W1 (mm) S1 (mm2) L (mm) W (mm) Drop failure rate. Comparative Example 1-16 No / 48 12 416 / 20. Comparative Example 1-26 Yes 348 12 49 / 20. Comparative Example 1-330 No / 48 12 411 / 20. Comparative Example 1-465 No / 48 12 415 / 20. Comparative Example 1-565 Yes 348 12 410 / 20. Example 1-110 Yes 348 12 43 / 20 Examples 1-215 is 3481240 / 20 Examples 1-320 is 3481241 / 20 Examples 1-430 is 3481241 / 20 Examples 1-540 is 3481242 / 20 Examples 1-650 is 3481244 / 20 Examples 1-760 is 3481244 / 20 Examples 1-830 is 1481246 / 20 Examples 1-930 is 2481243 / 20 Examples 1-103 0 is 4481243 / 20 Example 1-1130 is 5481246 / 20 Example 1-1230 is 336943 / 20 Example 1-1330 is 3401044 / 20 Example 1-1430 is 3441143 / 20 Example 1-1530 is 3521342 / 20 Example 1-1630 is 3561441 / 20 Example 1-1730 is 3601541 / 20 Example 1-1830 is 364 1642 / 20 Example 1-1930 is 332846 / 20 Example 1-2030 is 3241225 / 20 Example 1-2130 is 3361234 / 20 Example 1-2230 is 3601251 / 20 Example 1-2330 is 3721265 / 20 Example 1-2430 is 3301033 / 20 Example 1-2530 is 3701454 / 20 Example 1-2630 is 327936 / 20

[0129] According to Table 1 above, and in conjunction with Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-5, it can be seen that when a first region is set, and the condition 10μm≤H1-T is met... a A thickness of ≤60μm effectively reduces the risk of drop failure. This is because the limit is 10μm ≤H1-T. a With a thickness of ≤60μm, the welding between the positive electrode tab and the positive current collector is more thorough, providing a stronger mechanical connection, enhancing the bonding force between the positive electrode tab and the positive current collector, improving the strength of the positive electrode tab and the area around it, reducing damage and tearing of the positive electrode tab and the area around it, and reducing the welding disconnection between the positive electrode tab and the positive current collector caused by drops, impacts, etc. of the secondary battery.

[0130] Furthermore, the positive electrode tab is supported by the first region, which buffers the positive electrode tab and disperses the stress and shear force it experiences, thereby effectively reducing the risk of breakage and tearing, and improving the drop and impact resistance of the secondary battery. In Comparative Examples 1-4 to 1-5, H1-T a If the size is too large, there is a risk that the burrs will puncture the separator. Furthermore, in Comparative Examples 1-4, the absence of a first zone will lead to stress and shear force concentration on the positive electrode tab, which may cause the positive electrode tab to break or tear, further increasing the risk of drop failure.

[0131] Furthermore, in Examples 1-1 to 1-5, the risk of drop failure is lower, and the height of the first welded portion is smaller than in Examples 1-6 to 1-7. In Examples 1-1 to 1-5, the process is simpler, and the risk of welding burrs piercing the release membrane is lower. In the embodiments of this application, 10μm≤H1-T can be selected. a ≤40μm. Furthermore, in Examples 1-2 to 1-4, the risk of drop failure is further reduced; preferably, 15μm ≤H1-T. a ≤30μm.

[0132] In conjunction with Examples 1-4 and Examples 1-8 to 1-11, and Examples 1-4 and 1-9 to 1-10, the risk of drop failure is low. This is because in Examples 1-4 and 1-9 to 1-10, the width of the first region is optimal, effectively supporting and buffering the positive electrode tab, fully dispersing the stress and shear force on the positive electrode tab, and reducing the risk of tearing. In Examples 1-10, if the overlap between the positive electrode tab and the first region is too small, it will be difficult to effectively disperse stress and shear force. In Examples 1-13, if the overlap between the positive electrode tab and the first region is too large, it may affect the welding quality and easily cause weld separation. Therefore, in the embodiments of this application, the width of the first region can be selected as 2mm ≤ W1 ≤ 4mm.

[0133] In conjunction with Examples 1-4 and Examples 1-12 to 1-19, the drop failure rate in Examples 1-4 and Examples 1-12 to 1-18 is lower than that in Example 1-19. This is because the length of the first weld portion is optimal, which can improve the connection strength between the positive electrode tab and the positive electrode current collector while reducing welding burrs, thereby reducing burr penetration of the separator and lowering the drop failure rate of the lithium-ion secondary battery. In Examples 1-19, if the length of the first weld portion is too small, the connection strength between the positive electrode tab and the positive electrode current collector may be low, easily leading to damage and tearing of the positive electrode tab and its surroundings. In Examples 1-18, if the length of the first weld portion is too large, it may result in more burrs, increasing the risk of short circuit due to puncture of the separator. Furthermore, a longer first groove is required for welding the positive electrode tab, leading to energy density loss in the lithium-ion secondary battery. Therefore, in conjunction with Examples 1-4 and Examples 1-12 to 1-17, in the embodiments of this application, the length of the first weld portion can be selected as 9mm ≤ L ≤ 15mm.

[0134] In conjunction with Examples 1-4 and Examples 1-20 to 1-23, and Examples 1-4 and 1-21 to 1-22, the drop failure rate is reduced. This is because the width of the first weld portion is optimal, which can improve the connection strength between the positive electrode tab and the positive current collector while reducing welding burrs, thereby reducing burr penetration of the separator and lowering the drop failure rate of the lithium-ion secondary battery. In Examples 1-20, the width of the first weld portion is small, which may lead to low connection strength between the positive electrode tab and the positive current collector, making them prone to separation. In Examples 1-23, the width of the first weld portion is large, which may easily cause incomplete soldering at the edge of the positive electrode tab, also leading to low connection strength between the positive electrode tab and the positive current collector. Therefore, in the embodiments of this application, in conjunction with Examples 1-4 and Examples 1-21 to 1-22, the width of the first weld portion can be selected to be 3mm ≤ W ≤ 5mm.

[0135] Furthermore, in conjunction with Examples 1-24 to 1-26, the risk of drop failure is reduced in Examples 1-24 to 1-25. In Examples 1-23, an excessively large welding area easily leads to incomplete welds, affecting welding strength. In Examples 1-26, a small welding area easily results in low welding strength. Under the conditions of satisfying 9mm≤L≤15mm and 3mm≤W≤5mm, and in conjunction with Examples 1-24 to 1-25, in the embodiments of this application, 30mm can be selected. 2 ≤S1≤70mm 2 This can improve the connection strength between the first tab and the first current collector, reduce burrs piercing the separator, reduce short circuits, and thus improve the drop and impact resistance of lithium-ion secondary batteries.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A secondary battery, comprising a first tab, a housing, and an electrode assembly, wherein the electrode assembly is disposed within the housing, the electrode assembly includes a first electrode plate, one end of the first tab is connected to the first electrode plate, and the other end of the first tab extends outside the housing; the first electrode plate includes a first current collector and a first active material layer disposed on at least one surface of the first current collector, and the first active material layer includes a first edge along the extension direction of the first tab, characterized in that: The first active material layer is provided with a first groove, and the first active material layer includes a first region, wherein the portion of the first active material layer located between the first groove and the first edge forms the first region; A portion of the first electrode tab is disposed in the first groove, and the first electrode tab is welded to the first current collector to form a first welded portion; The first current collector has a first surface facing the first electrode tab. Along the thickness direction of the first electrode sheet, the height of the first weld portion on the first surface is H1, and the thickness of the first electrode tab is T. a 10μm≤H1-T a ≤60μm; Another portion of the first electrode tab is disposed on the surface of the first region away from the first current collector and extends out of the first region from the first electrode plate.

2. The secondary battery according to claim 1, characterized in that, The first electrode is a positive electrode, with 10μm ≤ H1-T a ≤40μm; or, The first electrode is a negative electrode, with 35μm ≤ H1-T a ≤60μm.

3. The secondary battery according to claim 2, characterized in that, The first electrode is a positive electrode, and the first current collector and the first tab are made of aluminum with a diameter of 15μm ≤ H1-T. a ≤30μm.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, 70μm≤T a ≤110μm。 5. The secondary battery according to any one of claims 1 to 4, characterized in that, Viewed along the thickness direction of the first electrode sheet, on the surface of the first electrode tab facing away from the first current collector, the area of ​​the first welded portion is S1, 30 mm. 2 ≤S1≤70mm 2 .

6. The secondary battery according to any one of claims 1 to 5, characterized in that, Viewed along the thickness direction of the first electrode, on the surface of the first electrode tab facing away from the first current collector: Along the extension direction of the first electrode tab, the maximum length of the first welded part is L, 9mm≤L≤15mm; Along the length of the first electrode, the maximum width of the first welded portion is W, where 3mm ≤ W ≤ 5mm.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, Viewed along the thickness direction of the first electrode sheet, and along the extension direction of the first electrode tab, the width of the portion of the first electrode tab overlapping with the first region is W1, where 2mm≤W1≤4mm.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The first electrode further includes a third active material layer, which is disposed on the surface of the first current collector opposite to the first active material layer; Along the extension direction of the first tab, the third active material layer includes a third edge; The third active material layer is provided with a third groove, and the third active material layer includes a third region. The portion of the third active material layer located between the third groove and the third edge forms the third region. Along the thickness direction of the first electrode, the projection of the first region overlaps with the portion of the third groove.

9. The secondary battery according to claim 8, characterized in that, Viewed along the thickness direction of the first electrode sheet, along the extension direction of the first electrode tab, the width of the portion of the first electrode tab overlapping with the third region is W3, where 1mm≤W3≤2mm.

10. The secondary battery according to claim 8, characterized in that, Along the thickness direction of the first electrode, the thickness of the first active material layer is T1, and the thickness of the third active material layer is T3; The first electrode is a positive electrode, with 35μm≤T1≤55μm and 35μm≤T3≤55μm; or, The first electrode is a negative electrode, with 40μm≤T1≤60μm and 40μm≤T3≤60μm.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The secondary battery further includes a first adhesive layer, which is disposed on the first active material layer and covers the first groove and part of the first tab along the thickness direction of the first electrode sheet. The first adhesive layer includes a first portion extending beyond the first edge along the extension direction of the first electrode tab; Along the extension direction of the first electrode tab, the width of the first portion is W5, 0.5mm≤W5≤2mm.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The electrode assembly further includes a second electrode and a separator, wherein the separator is disposed between the first electrode and the second electrode; The secondary battery also includes a second tab, one end of which is connected to the second electrode plate, and the other end extends out of the casing; The second electrode includes a second current collector and a second active material layer disposed on at least one surface of the second current collector. Along the extension direction of the second electrode tab, the second active material layer includes a second edge. The second active material layer is provided with a second groove, and the second active material layer includes a second region, wherein the portion of the second active material layer located between the second groove and the second edge forms the second region; A portion of the second electrode tab is disposed in the second groove, and the second electrode tab is welded to the second current collector to form a second welded portion; The second current collector has a second surface facing the second electrode tab. Along the thickness direction of the second electrode sheet, the height of the second weld portion on the second surface is H2, and the thickness of the second electrode tab is T. b 10μm≤H2-T b ≤60μm; Another portion of the second electrode tab is disposed on the surface of the second region opposite to the second current collector and extends out of the second region from the second electrode plate.

13. The secondary battery according to claim 12, characterized in that, Viewed along the thickness direction of the second electrode sheet, on the surface of the second electrode tab opposite to the second current collector, the area of ​​the second welded portion is S2, 30mm. 2 ≤S2≤70mm 2 ; and / or, Viewed along the thickness direction of the second electrode sheet, along the extension direction of the second electrode tab, the width of the portion of the second electrode tab overlapping with the second region is W2, where 2mm≤W2≤4mm.

14. The secondary battery according to claim 12, characterized in that, The second electrode also includes a fourth active material layer, which is disposed on the surface of the second current collector opposite to the second active material layer; Along the extension direction of the second electrode tab, the fourth active material layer includes a fourth edge; The fourth active material layer is provided with a fourth groove, and the fourth active material layer includes a fourth region. The portion of the fourth active material layer located between the fourth groove and the fourth edge forms the fourth region. Along the thickness direction of the second electrode, the projection of the second region overlaps with the fourth groove portion; Viewed along the thickness direction of the second electrode sheet, and along the extension direction of the second electrode tab, the width of the portion of the second electrode tab overlapping with the fourth region is W4, where 1mm ≤ W4 ≤ 2mm.

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

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