Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and electronic equipment, and a first active material layer comprises a first edge along the extension direction of a first tab. The first active material layer is provided with a first groove, the first active material layer comprises a first area, and the part, located between the first groove and the first edge, of the first active material layer forms the first area. A part of the first tab is arranged in the first groove, and the first tab is welded with the first current collector to form a first welding part; the first current collector is provided with a first surface facing the first tab, the height of the first welding part on the first surface is H1, the thickness of the first tab is Ta, and H1-Ta is more than or equal to 10 microns and less than or equal to 60 microns. The other part of the first tab is arranged on the surface, deviating from the first current collector, of the first region, and the other part of the first tab extends out of the first pole piece from the first region. Therefore, the damage and tearing of the first tab can be reduced, and the anti-falling and anti-impact properties of the secondary battery are improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] The tab is used as a bridge for the battery to be electrically connected to the external circuit. It is usually made of metal material. One part of the tab is welded to the current collector inside the battery, and the other part extends out of the shell, which allows the tab to be connected to the electrode assembly inside the battery, thereby achieving the purpose of transmitting current. However, when the battery is dropped or impacted, the tab or the area around the tab is prone to damage and tearing, which can easily lead to battery failure. Summary of the invention

[0003] The present application aims to provide a secondary battery and an electronic device, aiming to prevent damage and tearing of the tab or the area around the tab, thereby reducing the technical problem of easy failure of the battery.

[0004] The embodiment of the present application adopts the following technical solutions:

[0005] In the first aspect, the present application proposes a secondary battery, comprising a first pole ear, a shell and an electrode assembly, wherein the electrode assembly is arranged in the shell, and the electrode assembly includes a first pole sheet, one end of the first pole ear is connected to the first pole sheet, and the other end of the first pole ear extends out of the shell. The first pole sheet includes a first current collector and a first active material layer arranged on at least one surface of the first current collector, and along the extending direction of the first pole ear, the first active material layer includes a first edge. The first active material layer is provided with a first groove, and the first active material layer includes a first region, and 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 pole ear is arranged in the first groove, and the first pole ear is welded to the first current collector to form a first welding portion. The first current collector has a first surface facing the first pole ear, and along the thickness direction of the first pole sheet, the height of the first welding portion on the first surface is H 1 , the thickness of the first tab is T a , 10μm≤H 1 -T a ≤60 μm. Another portion of the first pole tab is disposed on a surface of the first region away from the first current collector and extends out of the first region from the first pole piece.

[0006] In the above technical solution, by setting a higher first welding portion and limiting 10μm≤H 1 -T a≤60μm, so that the welding between the first pole ear and the first current collector is more thorough, which can provide a stronger mechanical connection, enhance the bonding force between the first pole ear and the first current collector, and make the first pole ear and the surrounding area of ​​the first pole ear stronger, reduce the damage and tearing around the first pole ear and the second pole ear, and reduce the welding disconnection of the first pole ear and the first current collector caused by the secondary battery falling, impact, etc. It can also reduce the contact resistance between the first pole ear and the first current collector, thereby improving the conductivity between the first pole ear and the first current collector, which is beneficial to improving the charge and discharge rate of the secondary battery. At the same time, H 1 -T a ≤60μm, which can reduce the influence of the first welding portion on the thickness of the first pole piece and reduce the burrs on the first welding portion from piercing the isolation film, thereby reducing the occurrence of short circuits.

[0007] In addition, the portion of the first pole ear located at the first edge is supported by the first region, so that the first region can buffer the first pole ear and disperse the stress and shear force exerted on the first pole ear, thereby effectively reducing the damage and tearing of the first pole ear, reducing the poor contact between the first pole ear and the first current collector, and improving the drop resistance and impact resistance of the secondary battery.

[0008] At the same time, the first pole ear is in direct contact with the first region (first active material layer), and electrons can be directly transferred from the first active material layer to the first pole ear, reducing the electron transmission resistance in the intermediate link and improving the electron transmission efficiency. Combined with the first welding portion of the above height, the first pole ear can have a higher tear resistance and a higher current carrying capacity, which can improve the collision resistance of the secondary battery while increasing the charge and discharge rate of the secondary battery.

[0009] In some embodiments, the first electrode is a positive electrode, 10 μm ≤ H 1 -T a ≤40μm. This is beneficial to optimizing the space utilization rate inside the secondary battery. Alternatively, the first electrode is a negative electrode, 35μm≤H 1 -T a ≤60μm to accommodate the expansion of the negative electrode active material and reduce contact resistance.

[0010] In some embodiments, the first electrode is a positive electrode, the first current collector and the first electrode tab are made of aluminum, 15 μm ≤ H 1 -T a ≤30μm. Aluminum has good ductility, limited to 15μm≤H 1 -T a ≤30μm, which can reduce the damage and tearing of the first electrode ear and the first current collector.

[0011] In some embodiments, along the thickness direction of the first pole piece, the thickness of the first pole tab is Ta , 70μm≤T a ≤110μm, so that the first pole ear has higher strength and reduces the damage and tearing of the first pole ear.

[0012] In some embodiments, when observed along the thickness direction of the first pole sheet, on the surface of the first pole ear away from the first current collector, the area of ​​the first welding portion is S 1 , 30mm 2 ≤S 1 ≤70mm 2 The resistance between the first current collector and the first pole ear can be reduced, heat concentration can be alleviated, and the connection strength between the first pole ear and the first current collector can be improved. At the same time, the welding process can be simplified, and the burrs can be reduced from piercing the isolation film, thereby reducing the occurrence of short circuits.

[0013] In some embodiments, when observed along the thickness direction of the first pole piece, on the surface of the first pole ear away from the first current collector: along the extension direction of the first pole ear, the maximum length of the first welding portion is L, 9mm≤L≤15mm. Along the length direction of the first pole piece, the maximum width of the first welding portion is W, 3mm≤W≤5mm. This allows a better welding area between the first pole ear and the first current collector, improves the connection strength between the first pole ear and the first current collector, and reduces the contact resistance between the first pole ear and the first current collector.

[0014] In some embodiments, when viewed along the thickness direction of the first pole piece, along the extension direction of the first pole ear, the width of the portion where the first pole ear overlaps the first region is W. 1 , 2mm≤W 1 ≤4mm, the first region can have higher strength, effectively support the first pole ear, fully disperse stress and shear force, thereby reducing the tearing of the first pole ear, and reducing material costs.

[0015] In some embodiments, the first pole piece further includes a third active material layer, and the third active material layer is disposed on a surface of the first current collector away from the first active material layer. Along the extension direction of the first pole ear, 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, and a 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 pole piece, the projection of the first region partially overlaps with the third groove. The first pole ear can be smoothly transitioned to the first region, reducing the influence of excessive thickness mutation on the welding of the first pole ear and the first current collector.

[0016] In some embodiments, when viewed along the thickness direction of the first pole piece and along the extension direction of the first pole ear, the width of the portion where the first pole ear overlaps with the third region is W. 3 , 1mm≤W 3≤2mm, which can improve the damage and tear resistance of the first pole piece while reducing the influence of the third region on the energy density of the secondary battery, and can facilitate the welding of the first pole ear and the first current collector and improve the welding accuracy.

[0017] In some embodiments, the first electrode sheet is a positive electrode sheet, and along the thickness direction of the first electrode sheet, the thickness of the first active material layer is T 1 , the thickness of the third active material layer is T 3 35μm≤T 1 ≤55μm, and / or, 35μm≤T 3 ≤55μm. It can effectively support the first pole ear, fully disperse the stress and shear force, and reduce the disconnection of the welding between the first pole ear and the first current collector.

[0018] In some embodiments, the first electrode sheet is a negative electrode sheet, and along the thickness direction of the first electrode sheet, the thickness of the first active material layer is T 1 , the thickness of the third active material layer is T 3 40μm≤T 1 ≤60μm, and / or, 40μm≤T 3 ≤60μm. It can effectively support the first pole ear, fully disperse the stress and shear force, and reduce the disconnection of the welding between the first pole ear and the first current collector.

[0019] In some embodiments, the secondary battery further includes a first glue layer, which is disposed on the first active material layer. Along the thickness direction of the first electrode sheet, the first glue layer covers the first groove and part of the first electrode tab. The first glue layer includes a first portion, which extends 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 W 5 , 0.5mm≤W 5 ≤2mm, which can reduce the damage and tearing of the first tab and reduce the impact of the first adhesive layer on the energy density of the secondary battery.

[0020] In some embodiments, the electrode assembly further includes a second pole piece and a separator, and a separator is disposed between the first pole piece and the second pole piece. The secondary battery further includes a second pole piece, one end of the second pole piece is connected to the second pole piece, and the other end extends out of the shell. The second pole piece includes a second current collector and a second active material layer disposed on at least one surface of the second current collector, and the second active material layer includes a second edge along the extension direction of the second pole piece. The second active material layer is provided with a second groove, and the second active material layer includes a second region, and 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 pole piece is disposed in the second groove, and the second pole piece is welded to the second current collector so that the second pole piece and the second current collector jointly form a second welding portion. The second current collector has a second surface facing the second pole piece, and the height of the second welding portion on the second surface along the thickness direction of the second pole piece is H. 2 , the thickness of the second tab is T b , 10μm≤H 2 -T b ≤60 μm. Another portion of the second pole tab is disposed on a surface of the second region away from the second current collector and extends out of the second region from the second pole piece.

[0021] The welding between the second pole ear and the second current collector can be made more thorough, a stronger mechanical connection can be provided, the bonding force between the second pole ear and the second current collector can be enhanced, and the strength of the second pole ear and the surrounding of the second pole ear can be improved, the damage and tearing of the second pole ear and the surrounding of the second pole ear can be reduced, and the welding disconnection of the second pole ear and the second current collector caused by the secondary battery falling, impact, etc. can be reduced. At the same time, a larger contact area can be provided, thereby improving the conductive performance between the second pole ear and the second current collector, reducing the contact resistance, and being conducive to improving the charge and discharge rate of the secondary battery.

[0022] The portion of the second pole ear located at the second edge is supported by the second area, so that the second area can buffer the second pole ear and disperse the stress and shear force exerted on the second pole ear, thereby effectively reducing the damage and tearing of the second pole ear and improving the drop resistance and impact resistance of the secondary battery.

[0023] At the same time, the second pole ear is in direct contact with the second region (second active material layer), and electrons can be directly transferred from the second active material layer to the second pole ear, reducing the electron transmission resistance in the intermediate link and improving the electron transmission efficiency. Combined with the above-mentioned second welding portion, the second pole ear can have higher tear resistance and higher current carrying capacity, which can improve the collision resistance of the secondary battery while increasing the charge and discharge rate of the secondary battery.

[0024] In some embodiments, when observed along the thickness direction of the second pole piece, on the surface of the second pole ear away from the second current collector, the area of ​​the second welding portion is S 2, 30mm 2 ≤S 2 ≤70mm 2 The resistance between the second current collector and the second pole ear can be reduced, heat concentration can be alleviated, and the connection strength between the second pole ear and the second current collector can be improved. At the same time, the welding process can be simplified, and the burrs can be reduced from piercing the isolation film, thereby reducing the occurrence of short circuits.

[0025] In some embodiments, when viewed along the thickness direction of the second pole piece, along the extension direction of the second pole ear, the width of the portion where the second pole ear overlaps the second region is W. 2 , 2mm≤W 2 ≤4mm, which can make the second region have higher strength, effectively support the second pole ear, fully disperse the stress and shear force, thereby reducing the tearing of the second pole ear, and further reducing the material cost.

[0026] In some embodiments, the second pole piece further includes a fourth active material layer, and the fourth active material layer is disposed on a surface of the second current collector that is away from the second active material layer. Along the extension direction of the second pole ear, 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, and a 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 pole piece, the projection of the second region partially overlaps with the fourth groove. The second pole ear can be smoothly transitioned to the second region, reducing the influence of excessive thickness mutation on the welding of the second pole ear and the second current collector.

[0027] In some embodiments, when viewed along the thickness direction of the second pole piece and along the extension direction of the second pole ear, the width of the portion where the second pole ear overlaps the fourth region is W. 4 , 1mm≤W 4 ≤2mm. It can improve the damage and tear resistance of the second pole piece while reducing the influence of the fourth region on the energy density of the secondary battery, and can facilitate the welding of the second pole ear and the second current collector and improve the welding accuracy.

[0028] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery as in any embodiment of the first aspect above.

[0029] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and the figures in the drawings do not constitute proportional limitations unless otherwise stated.

[0031] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0032] Figure 2 A schematic diagram of a stacked structure of a first pole piece, an isolation film, and a second pole piece in some embodiments of the present application;

[0033] Figure 3 This is a schematic structural diagram of a first pole piece in some embodiments of the present application;

[0034] Figure 4 for Figure 2 AA section view and BB section view (excluding the first adhesive layer and the second adhesive layer);

[0035] Figure 5 This is a schematic structural diagram of the first pole piece located at the first groove in some embodiments of the present application;

[0036] Figure 6 for Figure 2 AA section view and BB section view (including the first adhesive layer and the second adhesive layer);

[0037] Figure 7 This is a schematic structural diagram of the portion of the first pole piece located in the first groove in some embodiments of the present application.

[0038] Description of reference numerals:

[0039] 100. Secondary battery;

[0040] 10. Shell;

[0041] 20. Electrode assembly;

[0042] 21, first pole piece; 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;

[0043] 22, second pole piece; 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;

[0044] 23. Isolation film;

[0045] 30. first pole ear; 40. second pole ear;

[0046] 50, first welding portion; 60, second welding portion;

[0047] 70, first adhesive layer; 80, second adhesive layer;

[0048] X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0050] Reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0051] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0052] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0053] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0054] In the first aspect, the present application proposes a secondary battery 100, please refer to Figure 1 , the secondary battery 100 includes a shell 10, an electrode assembly 20, a first pole tab 30 and a second pole tab 40. The shell 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure), and the electrolyte infiltrates the electrode assembly 20 in the shell 10, so that an electrochemical reaction occurs. One end of the first pole tab 30 is connected to the electrode assembly 20 in the shell 10, and the other end of the first pole tab 30 extends out of the shell 10. One end of the second pole tab 40 is connected to the electrode assembly 20 in the shell 10, and the other end of the second pole tab 40 extends out of the shell 10. The first pole tab 30 and the second pole tab 40 have opposite polarities and are used to lead out the positive and negative electrodes of the secondary battery 100.

[0055] For the electrode assembly 20, please refer to Figure 1 and Figure 2 , the electrode assembly 20 includes a first pole piece 21, a second pole piece 22 and a separator 23. The electrode assembly 20 may adopt a laminated structure, for example, along the thickness direction (third direction Z) of the first pole piece 21, a plurality of first pole pieces 21 and a plurality of second pole pieces 22 are alternately stacked, and a separator 23 is provided between two adjacent first pole pieces 21 and second pole pieces 22. In some other embodiments, the electrode assembly 20 may also adopt a winding structure, along the thickness direction (third direction Z) of the first pole piece 21, the first pole piece 21, the separator 23 and the second pole piece 22 are stacked and wound along the length direction (first direction X) of the first pole piece 21, thereby forming a wound electrode assembly 20.

[0056] Please refer to Figure 2 , taking the first electrode sheet 21 as a positive electrode sheet as an example, the first electrode sheet 21 includes a first current collector 211 and a first active material layer 212. The first current collector 211 is a conductive substrate of the first electrode sheet 21, and can be an overall flat aluminum foil. Aluminum foil has high conductivity and low resistance, and can improve the charge and discharge rate of the secondary battery 100. The first active material layer 212 can be arranged 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 an adhesive. The above-mentioned material components are mixed and stirred evenly and applied to the surface of the first current collector 211, thereby obtaining 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 iron manganese phosphate.

[0057] Please refer to Figure 2 , taking the second pole piece 22 as the negative pole piece as an example, the second pole piece 22 includes a second current collector 221 and a second active material layer 222. The second current collector 221 is used as the conductive substrate of the second pole piece 22, and a whole flat copper foil can be used. 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 arranged 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 an adhesive. After mixing, these materials are stirred evenly and coated on the surface of the second current collector 221, thereby obtaining 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.

[0058] The first pole tab 30 is a metal conductor that draws out the current from the first pole piece 21 , and can be made of aluminum, copper or nickel. The first pole tab 30 is welded to the first current collector 211 so that the first pole tab 30 and the first pole piece 21 are in conduction.

[0059] In the embodiments of this application, please refer to Figure 3 and Figure 4 The first active material layer 212 has a first edge 212a, for example, the first edge 212a is located at one side of the width direction (second direction Y) of the first pole piece 21. To facilitate the electrical connection between the first pole 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 foaming process. The first current collector 211 can be exposed from the first groove 214, and a part of the first pole tab 30 can be placed in the first groove 214 to weld the first pole tab 30 and the first current collector 211, and the other part of the first pole tab 30 extends out of the first pole piece 21 from the first edge 212a.

[0060] The second pole tab 40 is a metal conductor that draws out the current from the second pole piece 22 , and can also be made of aluminum, copper or nickel. The second pole tab 40 is welded to the second current collector 221 to make the second pole tab 40 and the second pole piece 22 conductive.

[0061] In the embodiments of this application, please refer to Figure 4 The second active material layer 222 has a second edge 222a, for example, the second edge 222a is located on one side of the second electrode sheet 22 in the width direction. 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, and a part of the second electrode tab 40 can be placed in the second groove 224 to weld the second electrode tab 40 and the second current collector 221, and the other part of the second electrode tab 40 extends out of the housing 10 from the second edge 222a.

[0062] The inventors of the present application have discovered that in order to improve the sealing performance of the shell 10, the pole ear is fixed to the shell 10. During the process of the secondary battery 100 being dropped or impacted, the electrode assembly 20 is prone to relative displacement with the shell 10, causing the electrode assembly 20 to pull the pole ear, which may easily cause the pole ear or part of the current collector around the pole ear to be damaged or torn, and may easily cause the electrical connection between the pole ear and the current collector to be disconnected, resulting in failure of the secondary battery.

[0063] To reduce the above problems, in the embodiment of the present application, the welding of the first pole ear 30 and the first pole piece 21 is taken as an example, please refer to Figure 4and Figure 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 of the first electrode sheet 21 (the third direction Z), the height of the first welding portion 50 on the first surface 2111 is H. 1 , the thickness of the first electrode tab 30 is T a , 10μm≤H 1 -T a ≤60μm.

[0064] By adopting the first welding portion 50 with a larger height and limiting the 1 -T a ≤60μm, so that the welding between the first pole tab 30 and the first current collector 211 is more thorough, a stronger mechanical connection can be provided, the bonding force between the first pole tab 30 and the first current collector 211 can be enhanced, and the strength of the first pole tab 30 and the surrounding of the first pole tab 30 can be improved, and the damage and tearing of the first pole tab 30 and the first current collector 211 around the first pole tab 30 can be reduced, and the welding disconnection of the first pole tab 30 and the first current collector 211 caused by the secondary battery 100 falling, impacting, etc. can be reduced. And the contact resistance between the first pole tab 30 and the first current collector 211 can be reduced, thereby improving the conductivity between the first pole tab 30 and the first current collector 211, which is conducive to improving the charge and discharge rate of the secondary battery 100.

[0065] At the same time, the inventor of the present application has found that if the height of the first welding portion 50 is too large, it will affect the thickness of the first pole piece 21, resulting in uneven thickness of the first pole piece 21. Moreover, if the height is too large, it is easy for some welding burrs on the first welding portion 50 to pierce the isolation film 23, which may cause the first pole piece 21 to contact with the second pole piece 22 and cause a short circuit. In the present application, H is defined as 1 -T a ≤60 μm, which can reduce the influence of the first welding portion 50 on the thickness of the first pole piece 21 and reduce the burrs on the first welding portion 50 from piercing the isolation film 23, thereby reducing the occurrence of short circuits.

[0066] The surface of the first welding portion 50 may be uneven, and the height of each part of the first welding portion 50 is ensured to be within 10 μm ≤ H 1 -T a ≤60μm. For measuring the height of the first welding portion 50, a laser displacement sensor can be used to measure the three-dimensional morphology of the surface of the first welding portion 50, and the height of the first welding portion 50 can be obtained through the high-precision measurement function of the sensor.

[0067] Regarding the thickness of the first pole tab 30 , in some embodiments, along the thickness direction (third direction Z) of the first pole piece 21 , the thickness of the first pole tab 30 is T . a , 70μm≤T a ≤110 μm, the first pole tab 30 can have a higher strength and reduce the damage and tearing of the first pole tab 30. The thickness of the first pole tab 30 refers to the thickness of the unwelded area of ​​the first pole tab 30.

[0068] Regarding the welding method of the first electrode tab 30 and the first current collector 211, in some embodiments, the welding method is ultrasonic welding, and the ultrasonic welding device includes a welding head. The first welding portion 50 with different welding heights can be welded by setting different depths of the grooves on the welding head. It is also possible to weld the first welding portion 50 with different heights by controlling the energy of the welding head. Alternatively, the energy transfer during the welding process is adjusted by adjusting the ultrasonic frequency, thereby adjusting the height of the first welding portion 50. The height of the first welding portion 50 can also be adjusted by adjusting the welding time, welding pressure, amplitude, etc.

[0069] In some embodiments, the welding method is laser welding, and the height of the first welding portion 50 can be adjusted in the following ways. (1) Laser power: The laser power directly affects the temperature and melting depth of the welding area. When the power is high, the height of the first welding portion 50 increases; when the power is low, the height of the first welding portion 50 decreases. (2) Laser pulse width: The laser pulse width affects the energy transfer during the welding process. When the pulse width is long, the height of the first welding portion 50 increases; when the pulse width is too short, the height of the first welding portion 50 decreases. (3) Laser spot size: The laser spot size affects the concentration of the welding area. When the spot is large, the height of the first welding portion 50 increases; when the spot is too small, the height of the first welding portion 50 decreases.

[0070] It is understandable that in some other embodiments, resistance welding, electron beam welding, cold pressure welding, etc. may also be used.

[0071] The inventors of the present application have also discovered that due to the use of a first welding portion 50 with a relatively large height, the gap between the first pole ear 30 and the first edge 212a may be too large, and part of the first pole ear 30 may be in a suspended state. During the process of the secondary battery 100 falling or impacting, the first pole ear 30 may repeatedly impact the first edge 212a, which may cause the stress and shear force of the first pole ear 30 at the first edge 212a to concentrate, resulting in damage and tearing of the first pole ear 30.

[0072] To reduce the above problems, in the embodiments of this application, please refer to Figure 4 and Figure 5, the first active material layer 212 includes a first region 2121, and a portion of the first active material layer 212 located between the first groove 214 and the first edge 212a forms the first region 2121. Another portion of the first pole tab 30 is disposed on a surface of the first region 2121 that is away from the first current collector 211, and another portion of the first pole tab 30 extends out of the first pole sheet 21 from the first region 2121. The portion of the first pole tab 30 located at the first edge 212a is supported by the first region 2121, so that the first region 2121 can buffer the first pole tab 30, disperse the stress and shear force on the first pole tab 30, and thereby effectively reduce the damage and tearing of the first pole tab 30, and improve the drop resistance and impact resistance of the secondary battery 100.

[0073] At the same time, the first pole tab 30 is in direct contact with the first region 2121 (first active material layer 212), and electrons can be directly transferred from the first active material layer 212 to the first pole tab 30, reducing the electron transmission resistance in the intermediate link and improving the electron transmission efficiency. Combined with the first welding portion 50 of the above height, the first pole tab 30 can have a higher tear resistance and a higher current carrying capacity, which can improve the collision resistance of the secondary battery 100 while improving the charge and discharge rate of the secondary battery 100.

[0074] In the embodiment of the present application, the first electrode sheet 21 is a positive electrode sheet, and along the thickness direction (third direction Z) of the first electrode sheet 21, the height of the first welding portion 50 satisfies 10 μm ≤ H 1 -T a ≤40μm. Alternatively, the first electrode sheet 21 may also be a negative electrode sheet, 35μm≤H 1 -T a ≤60μm. During the charge and discharge process of the secondary battery 100, the expansion coefficient of the negative electrode active material is usually greater than that of the positive electrode active material, and lithium ions will be embedded in the negative electrode active material layer, resulting in the volume expansion of the negative electrode active material layer. The negative electrode adopts a higher welding part, which is more conducive to adapting to the volume change of the negative electrode active material layer and reducing the fracture of the welding part due to the expansion of the negative electrode active material layer. In addition, compared with the positive electrode, the negative electrode generates more heat, and the use of a higher welding part means that the welding is more thorough, which can reduce resistance and reduce heat generation.

[0075] The positive electrode active material usually has a higher potential and a relatively stable structure, its volume change is small, and the electron conduction is relatively regular; and the heat generated by the positive electrode is usually less than that of the negative electrode. The use of a smaller welding part in the positive electrode is more conducive to optimizing the space utilization inside the secondary battery 100.

[0076] When the first electrode sheet 21 is a positive electrode sheet, the material of the first current collector 211 and the first electrode tab 30 is aluminum. Preferably, 15 μm ≤ H 1 -Ta ≤30μm. The first pole ear 30 and the first current collector 211 made of aluminum have high strength and ductility, and are limited to 15μm≤H 1 -T a ≤30 μm can reduce the damage and tearing of the first electrode tab 30 and the first current collector 211 , thereby improving the drop resistance and impact resistance of the secondary battery 100 .

[0077] For the thickness of the active material layer, in some embodiments, please refer to Figure 2 The first electrode sheet 21 is a positive electrode sheet. Along the thickness direction of the first electrode sheet 21 (the third direction Z), the thickness of the first active material layer 212 is T 1 , 35μm≤T 1 ≤55μm. If the thickness of the first active material layer 212 is too small, it may be difficult to effectively support the first electrode tab 30, and the stress and shear force are not dispersed sufficiently. If the thickness is too large, the thickness of the first electrode tab 30 may change too much when it is extended, which may affect the welding strength between the first electrode tab 30 and the first current collector 211, and may cause the welding between the first electrode tab 30 and the first current collector 211 to be disconnected. Limit 35μm≤T 1 ≤55 μm, which can effectively support the first electrode tab 30, fully disperse stress and shear force, and reduce the disconnection of the welding between the first electrode tab 30 and the first current collector 211. Similarly, the thickness of the third active material layer 213 is T 3 , 35μm≤T 3 ≤55μm.

[0078] The first electrode sheet 21 may also be a negative electrode sheet. Along the thickness direction (third direction Z) of the first electrode sheet 21, 40 μm ≤ T 1 ≤60μm, 40μm≤T 3 ≤60 μm, which can effectively support the second electrode tab 40, fully disperse stress and shear force, and reduce the disconnection of the welding between the second electrode tab 40 and the second current collector 221. Similarly, the thickness of the fourth active material layer 223 is T 4 , 40μm≤T 4 ≤60μm. At the same time, the thickness of the second active material layer 222 and the thickness of the fourth active material layer 223 are slightly greater than the thickness of the first active material layer 212 and the thickness of the third active material layer 213, corresponding to the different welding heights of the positive and negative electrodes, and allowing the negative electrode to have enough margin to embed the lithium ions released from the positive electrode, reducing the occurrence of lithium plating.

[0079] In the embodiment of the present application, the second electrode tab 40 may also be configured similarly. Figure 4The second electrode tab 40 is welded to the second current collector 221 to form a second welding portion 60. The second current collector 221 has a second surface 2211 facing the second electrode tab 40. Along the thickness direction of the second electrode sheet 22 (the third direction Z), the height of the second welding portion 60 on the second surface 2211 is H 2 , the thickness of the second electrode tab 40 is T b , 10μm≤H 2 -T b ≤60μm.

[0080] By adopting a higher second welding portion 60 and limiting 10 μm ≤ H 2 -T b ≤60μm, so that the welding between the second pole tab 40 and the second current collector 221 is more thorough, a stronger mechanical connection can be provided, the bonding force between the second pole tab 40 and the second current collector 221 can be enhanced, and the strength of the second pole tab 40 and the second pole tab 40 can be improved, and the second pole tab 40 and the second current collector 221 around the second pole tab 40 can be reduced. The damage and tearing of the second pole tab 40 and the second current collector 221 around the second pole tab 40 are reduced, and the electrical connection between the second pole tab 40 and the second current collector 221 caused by the secondary battery 100 falling, impacting, etc. is reduced. And it can provide a larger contact area, thereby improving the conductive performance between the second pole tab 40 and the second current collector 221, reducing the contact resistance, which is conducive to improving the charge and discharge rate of the secondary battery 100. The welding method of the second welding part 60 can refer to the above-mentioned first welding part 60.

[0081] In addition, in the embodiment of the present application, the second active material layer 222 includes a second region 2221, and a 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 pole tab 40 is disposed on a surface of the second region 2221 away from the second current collector 221, and another portion of the second pole tab 40 extends out of the second pole sheet 22 from the second region 2221. The portion of the second pole tab 40 located at the second edge 222a is supported by the second region 2221, so that the second region 2221 can buffer the second pole tab 40, disperse the stress and shear force on the second pole tab 40, and thereby effectively reduce the damage and tearing of the second pole tab 40, and improve the drop resistance and impact resistance of the secondary battery 100.

[0082] At the same time, the second pole tab 40 is in direct contact with the second region 2221 (the second active material layer 222), and electrons can be directly transferred from the second active material layer 222 to the second pole tab 40, reducing the electron transmission resistance in the intermediate link and improving the electron transmission efficiency. Combined with the higher second welding portion 60, the second pole tab 40 can have a higher tear resistance and a higher current carrying capacity, which can improve the collision resistance of the secondary battery 100 while improving the charge and discharge rate of the secondary battery 100.

[0083] Regarding the thickness of the second pole tab 40 , in some embodiments, along the thickness direction of the second pole sheet 22 (the third direction Z), the thickness of the second pole tab 40 can also be set to 70 μm to 110 μm, which can make the second pole tab 40 have higher strength and reduce the damage and tearing of the second pole tab 40 .

[0084] For the welding area of ​​the first welding portion 50, if the welding area is too small, the resistance between the first current collector 211 and the first electrode tab 30 is large, which easily leads to heat concentration and may cause insufficient connection strength between the first electrode tab 30 and the first current collector 211. If the welding area is too large, the welding time is prolonged, the production cost is increased, and more welding burrs may be generated, resulting in an increased risk of burrs piercing the separator 23.

[0085] In the embodiment of the present application, when observed along the thickness direction (third direction Z) of the first pole sheet 21, on the surface of the first pole ear 30 away from the first current collector 211, the area of ​​the first welding portion 50 is S 1 , 30mm 2 ≤S 1 ≤70mm 2 , the resistance between the first current collector 211 and the first electrode tab 30 can be reduced, heat concentration can be alleviated, and the connection strength between the first electrode tab 30 and the first current collector 211 can be improved. At the same time, the welding process can be simplified, and the burrs can be reduced from piercing the isolation film 23, thereby reducing the occurrence of short circuits.

[0086] For example, see Figure 5 , observed along the thickness direction of the first pole piece 21 (third direction Z), on the surface of the first pole ear 30 away from the first current collector 211: along the extension direction of the first pole ear 30 (second direction Y), the maximum length of the first welding portion 50 is L, 9mm≤L≤15mm, along the length direction of the first pole piece 21 (first direction X), the maximum width of the first welding portion 50 is W, 3mm≤W≤5mm. This can provide a better welding area between the first pole ear 30 and the first current collector 211, improve the connection strength between the first pole ear 30 and the first current collector 211, and reduce the contact resistance between the first pole ear 30 and the first current collector 211

[0087] Based on the same inventive concept, when observed along the thickness direction (third direction Z) of the second pole sheet 22, on the surface of the second pole ear 40 away from the second current collector 221, the area of ​​the second welding portion 60 is S 2 , 30mm 2 ≤S 2 ≤70mm 2 , which can reduce the resistance between the second current collector 221 and the second pole ear 40, relieve heat concentration, and improve the connection strength between the second pole ear 40 and the second current collector 221. At the same time, the welding process can be simplified, and the burrs can be reduced from piercing the isolation film 23, thereby reducing the occurrence of short circuits. For example, along the thickness direction (third direction Z) of the second pole piece 22, on the surface of the second pole ear 40 away from the second current collector 221: along the second direction Y, the maximum length of the second welding portion 60 is 9mm to 15mm, and along the first direction X, the maximum width of the second welding portion 60 is 3mm to 5mm.

[0088] Regarding the area test method of the first welding portion 50: the first welding portion 50 can be observed using an optical microscope or an electron microscope, and after the first welding portion 50 is magnified to a suitable multiple, an image is taken, and then the area of ​​the first welding portion 50 is measured using image analysis software.

[0089] As for the width of the first region 2121, the inventor of the present application has found that if the width of the first region 2121 is too small, the mechanical strength of the first region 2121 is insufficient, and the first region 2121 may lose powder due to the edge effect, and it is difficult to effectively support the first pole ear 30, and it is difficult to fully disperse the stress and shear force, and the risk of the first pole ear 30 being torn is high. If the width of the first region 2121 is too large, the part covered by the first pole ear 30 is difficult to occur or cannot participate in the electrochemical reaction, and the excessive width means that more materials are used, which wastes costs and occupies too much space.

[0090] In the embodiments of this application, please refer to Figure 4 and Figure 5 , observed along the thickness direction (third direction Z) of the first pole piece 21, along the extension direction (second direction Y) of the first pole tab 30, the width of the portion where the first pole tab 30 overlaps with the first region 2121 is W 1 , 2mm≤W 1 ≤4mm, the first region 2121 can have higher strength, effectively support the first pole ear 30, fully disperse stress and shear force, thereby reducing the tearing of the first pole ear 30, and reducing material costs.

[0091] Based on the same inventive concept, when observed along the thickness direction (third direction Z) of the second pole piece 22, along the extension direction (second direction Y) of the second pole tab 40, the width of the portion where the second pole tab 40 overlaps with the second region 2221 is W2 , 2mm≤W 2 ≤4mm. The second region 2221 can have a higher strength, effectively support the second pole tab 40, fully disperse stress and shear force, thereby reducing the tearing of the second pole tab 40, and further reducing material costs.

[0092] 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 in the first groove 214 area, and can resist the damage and tearing of the first current collector 211 in the first groove 214 area, thereby improving the drop resistance and impact resistance of the secondary battery 100. The second region 2221 is similar, and can also reduce the tearing of the second current collector 221.

[0093] In some embodiments, please refer to Figure 2 and Figure 4 , the first pole piece 21 further includes a third active material layer 213, and the third active material layer 213 is arranged on the surface of the first current collector 211 away from the first active material layer 212. The first pole piece 21 adopts double-sided active material layers, which can improve the energy density of the secondary battery 100. Along the extension direction of the first pole ear 30 (the second direction Y), the third active material layer 213 includes a third edge 213a, and the third active material layer 213 is provided with a third groove 215. For example, when welding the first pole ear 30, the welding seat supports the first current collector 211 in the third groove 215, and the welding head welds the first pole ear 30 and the first current collector 211 in the first groove 214.

[0094] The third active material layer 213 includes a third region 2131 . The portion of the third active material layer 213 between the third groove 215 and the third edge 213 a forms the third region 2131 . The setting of the third region 2131 can further reduce the tearing of the first current collector 211 and improve the flatness of the first pole piece 21 .

[0095] The inventors of the present application have found that when the first pole ear 30 is arranged in the first region 2121, in the thickness direction of the first pole sheet 21 (the third direction Z), the first region 2121 corresponds to the third region 2131, that is, the first pole ear 30 is supported by two layers of active material layers. If the thickness mutation is too large, it may affect the welding of the first pole ear 30 and the first current collector 211.

[0096] To reduce the above problems, in the embodiment of the present application, along the thickness direction (third direction Z) of the first pole piece 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 pole tab 30 extends out of the first pole piece 21 from the first region 2121, the first sub-region 2121a first contacts and supports the first pole tab 30. In the thickness direction (third direction Z) of the first pole piece 21, the first sub-region 2121a has no third active material layer 213 corresponding to it, and only one layer of active material layer supports the first pole tab 30, so that the first pole tab 30 can smoothly transition to the first region 2121, reducing the influence of excessive thickness mutation on the welding of the first pole tab 30 and the first current collector 211.

[0097] In some embodiments, when viewed along the thickness direction (third direction Z) of the first pole piece 21 and along the extension direction (second direction Y) of the first pole tab 30, the width of the portion where the first pole tab 30 overlaps with the third region 2131 is W. 3 , 1mm≤W 3 ≤2mm, by partially staggering the first area 2121 and the third area 2131, the damage and tear resistance of the first pole piece 21 can be improved while reducing the influence of the third area 2131 on the energy density of the secondary battery 100, and sufficient empty foil can be reserved to facilitate the welding of the first pole tab 30 and the first current collector 211, thereby improving the welding accuracy.

[0098] Based on the same concept, the second pole piece 22 further includes a fourth active material layer 223. Along the extension direction (second direction Y) of the second pole ear 40, the fourth active material layer 223 includes a fourth edge 223a, and the fourth active material layer 223 is provided with a fourth groove 225. The fourth active material layer 223 includes a fourth region 2231, and 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 provision of the fourth region 2231 can further reduce the tearing of the second current collector 221 and improve the flatness of the second pole piece 22.

[0099] Along the thickness direction (third direction Z) of the second pole piece 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 pole tab 40 extends out of the second pole piece 22 from the second region 2221, the second sub-region 2221a first contacts and supports the second pole tab 40. In the thickness direction (third direction Z) of the second pole piece 22, the second sub-region 2221a has no fourth active material layer 223 corresponding to it, and only one layer of active material layer supports the second pole tab 40, so that the second pole tab 40 can smoothly transition to the second region 2221, reducing the influence of excessive thickness mutation on the welding of the second pole tab 40 and the second current collector 221.

[0100] In some embodiments, when viewed along the thickness direction (third direction Z) of the second pole piece 22 and along the extension direction (second direction Y) of the second pole tab 40, the width of the fourth region 2231 is W. 4 , 1mm≤W 4 ≤2mm, by partially staggering the second region 2221 and the fourth region 2231, the damage and tear resistance of the second pole sheet 22 can be improved while reducing the influence of the fourth region 2231 on the energy density of the secondary battery 100, and the welding of the second pole tab 40 and the second current collector 221 can be facilitated to improve the welding accuracy.

[0101] For the thickness of each active material layer, in some embodiments, please refer to Figure 2 The first electrode sheet 21 is a positive electrode sheet. Along the thickness direction of the first electrode sheet 21 (the third direction Z), the thickness of the first active material layer 212 is T 1 , 35μm≤T 1 ≤55μm. If the thickness of the first active material layer 212 is too small, it may be difficult to effectively support the first electrode tab 30, and the stress and shear force are not dispersed sufficiently. If the thickness is too large, the thickness of the first electrode tab 30 may change too much when it is extended, which may affect the welding strength between the first electrode tab 30 and the first current collector 211, and may cause the welding between the first electrode tab 30 and the first current collector 211 to be disconnected. Limit 35μm≤T 1 ≤55 μm, which can effectively support the first electrode tab 30, fully disperse stress and shear force, and reduce the disconnection of the welding between the first electrode tab 30 and the first current collector 211. Similarly, the thickness of the third active material layer 213 is T 3 , 35μm≤T 3 ≤55μm.

[0102] The first electrode 21 may also be a negative electrode, then 40 μm ≤ T 1 ≤60μm, 40μm≤T 3Alternatively, the first electrode sheet 21 is a positive electrode sheet, the second electrode sheet 22 is a negative electrode sheet, and along the thickness direction of the second electrode sheet 22 (the third direction Z), the thickness of the second active material layer 222 is T 2 , 40μm≤T 2 ≤60 μm, which can effectively support the second electrode tab 40, fully disperse stress and shear force, and reduce the disconnection of the welding between the second electrode tab 40 and the second current collector 221. Similarly, the thickness of the fourth active material layer 223 is T 4 , 40μm≤T 4 ≤60μm. At the same time, the thickness of the second active material layer 222 and the thickness of the fourth active material layer 223 are slightly greater than the thickness of the first active material layer 212 and the thickness of the third active material layer 213, corresponding to the different welding heights of the positive and negative electrodes, and allowing the negative electrode to have enough margin to embed the lithium ions released from the positive electrode, reducing the occurrence of lithium plating.

[0103] In the embodiments of this application, please refer to Figure 6 and Figure 7 The secondary battery 100 further includes a first adhesive layer 70, which is disposed on the first active material layer 212. Along the thickness direction (third direction Z) of the first pole piece 21, the first adhesive layer 70 covers the first groove 214 and part of the first pole tab 30. The first adhesive layer 70 can cover the welding burrs between the first pole tab 30 and the first current collector 211, reduce the burrs piercing the isolation film 23, and thus reduce the occurrence of short circuits. In addition, the first adhesive layer 70 can fix and protect the first pole tab 30, improve the connection strength between the first pole tab 30 and the first current collector 211, and reduce the welding disconnection between the first pole tab 30 and the first current collector 211.

[0104] The first adhesive layer 70 includes a first portion 71. Along the extending direction (second direction Y) of the first pole tab 30, the first portion 71 exceeds the first edge 212a, so that the first adhesive layer 70 covers the portion of the first pole tab 30 located at the first edge 212a, which can disperse the stress and shear force of the portion, and the first adhesive layer 70 can resist the tearing of the first pole tab 30, further improving the drop resistance and impact resistance of the secondary battery 100.

[0105] In the embodiment of the present application, along the extension direction (second direction Y) of the first electrode tab 30, the width of the first portion is W 5 , 0.5mm≤W 5 ≤2 mm, which can reduce the damage and tearing of the first electrode tab 30 and reduce the influence of the first adhesive layer 70 on the energy density of the secondary battery 100.

[0106] Based on the same invention concept, please refer to Figure 6The secondary battery 100 further includes a second adhesive layer 80, which is disposed on the second active material layer 222. Along the thickness direction (third direction Z) of the second pole piece 22, the second adhesive layer 80 covers the second groove 224 and part of the second pole tab 40. The second adhesive layer 80 can cover the welding burrs between the second pole tab 40 and the second current collector 221, reduce the burrs piercing the isolation film 23, and thus reduce the occurrence of short circuits. In addition, the second adhesive layer 80 can fix and protect the second pole tab 40, improve the connection strength between the second pole tab 40 and the second current collector 221, and reduce the welding disconnection between the second pole tab 40 and the second current collector 221.

[0107] The second adhesive layer 80 includes a second portion 81. Along the extending direction (second direction Y) of the second pole tab 40, the second portion 81 exceeds the second edge 222a, so that the second adhesive layer 80 covers the portion of the second pole tab 40 located at the second edge 222a, which can disperse the stress and shear force of the portion, and the second adhesive layer 80 can resist the tearing of the second pole tab 40, further improving the drop resistance and impact resistance of the secondary battery 100.

[0108] In the embodiment of the present application, along the extension direction (second direction Y) of the second electrode tab 40, the width of the second portion is W 6 , 0.5mm≤W 6 ≤2mm, which can reduce the damage and tearing of the second electrode tab 40 and reduce the influence of the second adhesive layer 80 on the energy density of the secondary battery 100.

[0109] In the second aspect, the present application also proposes an electronic device, including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device of the embodiment of the present application is not particularly limited, and it 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, electric tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecrafts, etc.

[0110] Example 1-1:

[0111] <Preparation of positive electrode sheet>

[0112] The positive electrode active material lithium iron phosphate, the positive electrode conductive agent acetylene black, and the positive electrode binder polyvinylidene fluoride (PVDF, weight average molecular weight 5×10 5) were mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) was added as a solvent, and a positive electrode slurry with a solid content of 75wt% was prepared, and the mixture was stirred evenly in a vacuum mixer. An aluminum foil with a thickness of 8μm and a length of 1000mm was selected as the positive electrode current collector, and the positive electrode slurry was evenly coated on one surface of the positive electrode current collector aluminum foil, and dried at 110°C to obtain a positive electrode sheet with a single-sided positive electrode active material layer. Afterwards, the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer.

[0113] <Welding of positive electrode tab>

[0114] A first groove is cleaned out in a positive electrode active material layer by a laser cleaning process. The first groove and the edge (edge ​​in the width direction) of the positive electrode active material layer form a first region. The width of the first region is W 1 The width is 6mm and the thickness is T a The aluminum sheet with a thickness of 70 μm is used as the positive electrode tab. The positive electrode tab is welded to the positive electrode current collector in the first groove by ultrasonic welding to form a first welding portion with an approximately rectangular shape. The welding parameters are as follows: 20KHz ultrasonic welding head, the diameter of the ultrasonic welding head is about 2mm 、 The welding pressure was 200 N and the amplitude of the ultrasonic wave was 20 μm. On the surface of the positive electrode tab facing away from the positive electrode current collector (first surface), the height H of the first welding portion was 1 80μm, H 1 -T a =80 μm-70 μm=10 μm, the length L of the first welding portion is 12 mm, and the width W is 4 mm. Another portion of the positive electrode tab is supported by the first region and extends out of the positive electrode tab.

[0115] <Preparation of negative electrode sheet>

[0116] The negative electrode active material graphite powder, silicon powder, conductive carbon black (Super P), and binder styrene-acrylic rubber (SD-3) are mixed in a weight ratio of 89.5:8:1:1.5, and then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 50wt%, and stirred evenly. A copper foil with a thickness of 5μm and a length of 1050mm is selected as the negative electrode current collector, and the negative electrode slurry is evenly coated on one surface of the negative electrode current collector copper foil, and dried at 90°C to obtain a single-sided negative electrode sheet. After the above steps are completed, the single-sided coating of the negative electrode sheet has been completed. After that, the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a negative electrode active material layer coated on both sides. A second groove is cleaned out in a negative electrode active material layer by a laser cleaning process, and a part of the negative electrode ear is welded to the negative electrode current collector in the second groove.

[0117] <Preparation of Separator Film>

[0118] Polyethylene is selected as a 7 μm substrate layer, and polyvinylidene fluoride is selected as an adhesive layer. An alumina ceramic layer with a thickness of 2 μm is arranged on the side of the adhesive layer away from the substrate layer to prepare a porous isolation membrane.

[0119] <Electrolyte Preparation>

[0120] In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium salt 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.

[0121] <Preparation of lithium-ion batteries>

[0122] The prepared separator, positive electrode sheet, separator, and negative electrode sheet are stacked in order and wound to obtain an electrode assembly; the aluminum-plastic film formed by punching holes is placed in an assembly fixture with the pit surface facing upward, and the electrode assembly is placed in the pit and pressed tightly with external force. Then another aluminum-plastic film formed by punching holes is covered on the electrode assembly with the pit surface facing downward, and after packaging, liquid injection, hot pressing, shaping and other processes, a lithium-ion secondary battery is obtained.

[0123] Different from 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. The energy of the welding head can be controlled to be different, so as to weld the first welding parts of different heights. Alternatively, the energy transfer during the welding process can be adjusted by adjusting the ultrasonic frequency, so as to adjust the height of the first welding part. The height, area, length and width of the first welding part can also be adjusted by adjusting the welding time, welding pressure, amplitude, etc.

[0124] Drop test method: Under the environmental condition of 25±5℃, charge the lithium-ion secondary battery to 100% SOC, and test the voltage of the lithium-ion secondary battery before the drop test. Put the lithium-ion secondary battery into the fixture compartment, and use the automatic drop device to drop the bottom, side, and top of the lithium-ion secondary battery from the position of 1.8m to the steel plate in turn, for a total of 6 rounds, i.e. 18 times. After the drop, let it stand at room temperature for 24 hours, and measure and record the voltage of the lithium-ion secondary battery. Disassemble the lithium-ion secondary battery, observe whether the positive electrode ear is broken, observe whether the positive electrode ear is separated from the positive electrode collector, and whether the first current collector around the positive electrode ear is torn. If the voltage drop of the lithium-ion secondary battery is greater than 30mV, and the positive electrode ear or the area around the positive electrode ear is damaged or torn, the lithium-ion secondary battery fails the drop test. Each group tests 20, the number of failures is N, and the drop failure rate is N / 20.

[0125] Table 1

[0126]

[0127]

[0128] According to the above Table 1, combined with Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-5, it can be seen that when the first region is set and 10 μm ≤ H 1 -T a ≤60μm, which can effectively reduce the risk of drop failure. This is because the limit of 10μm≤H 1 -T a ≤60μm, which makes the welding between the positive electrode tab and the positive electrode collector more thorough, can provide a stronger mechanical connection, enhance the bonding force between the positive electrode tab and the positive electrode collector, improve the strength of the positive electrode tab and the surrounding area of ​​the positive electrode tab, reduce the damage and tearing of the positive electrode tab and the surrounding area of ​​the positive electrode tab, and reduce the welding disconnection between the positive electrode tab and the positive electrode collector caused by the secondary battery falling, impact, etc.

[0129] In addition, the positive electrode tab is supported by the first region, so that the first region can buffer the positive electrode tab, disperse the stress and shear force on the positive electrode tab, and thus effectively reduce the damage and tearing of the positive electrode tab, thereby improving the drop resistance and impact resistance of the secondary battery. 1 -T a If the size is too large, there is a risk of burrs piercing the isolation membrane. In addition, in Comparative Examples 1-4, the first area is not set, which will lead to the concentration of stress and shear force on the positive electrode ear, which may easily cause the positive electrode ear to be damaged and torn, and the risk of falling failure is further increased.

[0130] In addition, in Examples 1-1 to 1-5, the risk of drop failure is low, and the height of the first welding portion is smaller than that of 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 isolation membrane is lower. In the embodiment of the present application, 10 μm ≤ H 1 -T a ≤40μm. Further, in Examples 1-2 to 1-4, the risk of drop failure is further reduced. Preferably, 15μm≤H 1 -T a ≤30μm.

[0131] In combination with Example 1-4 and Examples 1-8 to 1-11, the risk of falling failure in Example 1-4 and Examples 1-9 to 1-10 is relatively low. This is because in Example 1-4 and Examples 1-9 to 1-10, the width of the first region is better, which can effectively support and buffer the positive electrode ear, fully disperse the stress and shear force on the positive electrode ear, and reduce the tearing of the positive electrode ear. In Example 1-10, if the width of the overlap between the positive electrode ear and the first region is too small, it is difficult to effectively disperse the stress and shear force. In Example 1-13, if the width of the overlap between the positive electrode ear and the first region is too large, it may affect the welding quality and easily cause welding separation. Therefore, in the embodiments of the present application, the width of the first region can be selected to be 2mm≤W 1 ≤4mm.

[0132] In combination with Examples 1-4 and Examples 1-12 to 1-19, in Examples 1-4 and Examples 1-12 to 1-18, the drop failure rate is less than that in Example 1-19. This is because the length of the first welding portion is better, which can reduce welding burrs while improving the connection strength between the positive electrode tab and the positive electrode collector, thereby reducing the burrs from piercing the separator, and can reduce the drop failure rate of the lithium-ion secondary battery. In Example 1-19, if the length of the first welding portion is too small, the connection strength between the positive electrode tab and the positive electrode collector may be low, which may easily cause damage and tearing of the positive electrode tab and the surrounding area. In Example 1-18, if the length of the first welding portion is too large, it may cause more burrs, piercing the separator and causing a short circuit, and the need to set a first groove with a larger length for welding the positive electrode tab will result in a loss of energy density of the lithium-ion secondary battery. Therefore, in combination with Examples 1-4 and Examples 1-12 to 1-17, in the embodiments of the present application, the length of the first welding portion can be selected to be 9mm≤L≤15mm.

[0133] In combination with Examples 1-4 and Examples 1-20 to 1-23, in Examples 1-4 and Examples 1-21 to 1-22, the drop failure rate is reduced. This is because the width of the first welding portion is better, which can reduce welding burrs while improving the connection strength between the positive electrode tab and the positive electrode collector, thereby reducing the burrs from piercing the separator, and can reduce the drop failure rate of the lithium-ion secondary battery. In Example 1-20, the width of the first welding portion is small, which may result in a low connection strength between the positive electrode tab and the positive electrode collector, resulting in easy separation between the positive electrode tab and the positive electrode collector. In Example 1-23, the width of the first welding portion is large, and the edge position of the positive electrode tab is prone to cause a cold weld, which is also prone to cause a low connection strength between the positive electrode tab and the positive electrode collector. Therefore, in the embodiments of the present application, in combination with Examples 1-4 and Examples 1-21 to 1-22, the width of the first welding portion can be selected to be 3mm≤W≤5mm.

[0134] Further combined with Examples 1-24 to 1-26, in Examples 1-24 to 1-25, the risk of drop failure is reduced. In Example 1-23, the welding area is too large, which is easy to cause cold welding and affect the welding strength. In Example 1-26, the welding area is small, which is easy to cause low welding strength. Under the condition of satisfying 9mm≤L≤15mm and 3mm≤W≤5mm, combined with Examples 1-24 to 1-25, in the embodiments of the present application, 30mm can be selected. 2 ≤S 1 ≤70mm 2 , which can improve the connection strength between the first pole ear and the first current collector, reduce the number of burrs piercing the isolation membrane, reduce the occurrence of short circuits, and thus improve the drop resistance and impact resistance of the lithium-ion secondary battery.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Under the concept of the present application, the technical features in the above embodiments or different embodiments may also be combined, the steps may be implemented in any order, and there are many other changes in different aspects of the present application as described above, which are not provided in detail for the sake of simplicity. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary battery, comprising a first pole ear, a shell and an electrode assembly, wherein the electrode assembly is disposed in the shell, the electrode assembly comprises a first pole piece, one end of the first pole ear is connected to the first pole piece, and the other end of the first pole ear extends out of the shell; the first pole piece comprises a first current collector and a first active material layer disposed on at least one surface of the first current collector, and along the extending direction of the first pole ear, the first active material layer comprises a first edge, characterized in that: The first active material layer is provided with a first groove, the first active material layer includes a first region, and a 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 welding portion; The first current collector has a first surface facing the first pole tab. Along the thickness direction of the first pole sheet, the height of the first welding portion on the first surface is H1, and the thickness of the first pole tab is T a , 10μm≤H1-T a ≤60μm; Another portion of the first electrode tab is disposed on a surface of the first region away from the first current collector and extends out of the first region from the first electrode sheet.

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

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

4. The secondary battery according to claim 1, characterized in that: 70μm≤T a ≤110μm。 5. The secondary battery according to claim 1, characterized in that: Observed along the thickness direction of the first pole piece, on the surface of the first pole ear away from the first current collector, the area of ​​the first welding portion is S1,30mm 2 ≤S1≤70mm 2 .

6. The secondary battery according to claim 1, characterized in that: Observed along the thickness direction of the first pole sheet, on the surface of the first pole ear facing away from the first current collector: Along the extension direction of the first electrode tab, the maximum length of the first welding portion is L, 9 mm ≤ L ≤ 15 mm; Along the length direction of the first pole piece, the maximum width of the first welding portion is W, 3mm≤W≤5mm.

7. The secondary battery according to claim 1, characterized in that: Observed along the thickness direction of the first pole sheet and along the extending direction of the first pole tab, the width of the portion where the first pole tab overlaps with the first region is W1, and 2 mm ≤ W1 ≤ 4 mm.

8. The secondary battery according to claim 1, characterized in that: The first pole piece further includes a third active material layer, and the third active material layer is disposed on a surface of the first current collector away from the first active material layer; Along the extending 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, the third active material layer includes a third region, and a 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 pole piece, a projection of the first region partially overlaps with the third groove.

9. The secondary battery according to claim 8, characterized in that: Observed along the thickness direction of the first pole sheet and along the extending direction of the first pole tab, the width of the portion where the first pole tab overlaps with the third region is W3, and 1 mm ≤ W3 ≤ 2 mm.

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

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

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The electrode assembly further includes a second pole piece and a separation film, wherein the separation film is disposed between the first pole piece and the second pole piece; The secondary battery further comprises a second pole lug, one end of the second pole lug is connected to the second pole piece, and the other end thereof extends out of the housing; The second pole piece includes a second current collector and a second active material layer disposed on at least one surface of the second current collector, and along the extension direction of the second pole ear, the second active material layer includes a second edge; The second active material layer is provided with a second groove, the second active material layer includes a second region, and a 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 welding portion; The second current collector has a second surface facing the second pole tab. Along the thickness direction of the second pole sheet, the height of the second welding portion on the second surface is H2, and the thickness of the second pole tab is T b , 10μm≤H2-T b ≤60μm; Another portion of the second pole tab is disposed on a surface of the second region away from the second current collector and extends out of the second region from the second pole piece.

13. The secondary battery according to claim 12, characterized in that: Observed along the thickness direction of the second pole piece, on the surface of the second pole ear away from the second current collector, the area of ​​the second welding portion is S2,30mm 2 ≤S2≤70mm 2 and / or, Observed along the thickness direction of the second pole piece and along the extension direction of the second pole tab, the width of the portion where the second pole tab overlaps with the second region is W2, and 2 mm ≤ W2 ≤ 4 mm.

14. The secondary battery according to claim 12, characterized in that: The second pole piece further includes a fourth active material layer, and the fourth active material layer is disposed on a surface of the second current collector away from the second active material layer; Along the extending 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, the fourth active material layer includes a fourth region, and a 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 pole piece, the projection of the second region partially overlaps with the fourth groove; Observed along the thickness direction of the second pole sheet and along the extending direction of the second pole tab, the width of the portion where the second pole tab overlaps with the fourth region is W4, and 1 mm≤W4≤2 mm.

15. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 14.

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