Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and an electronic device. A negative pole piece comprises a negative active material layer facing a positive pole piece, and the negative active material layer is provided with a first groove. A part of the negative pole lug is arranged in the first groove, and the other part of the negative pole lug extends out of the negative pole piece along the first direction; the positive pole piece comprises a positive pole active material layer facing the negative pole active material layer, a first adhesive layer is arranged on the positive pole piece, the positive pole active material layer comprises a first area, a deactivating area and a main body part, the first area is overlapped with the first groove when being observed along a third direction, and the deactivating area is arranged between the main body part and the first area. And along the first direction, the length of the deactivation area in the second direction is increased. Along the third direction, the average thickness of the deactivation area is H1, the thickness of the main body part is H2, and H1 is smaller than H2. Lithium precipitation can be reduced, and the energy density of the secondary battery can be 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] Secondary batteries such as lithium-ion batteries are widely used in electronic devices such as smartphones, portable notebooks, wearable devices, and smart homes due to their high energy density and environmental protection advantages. Lithium-ion batteries include positive and negative electrodes, and usually require positive and negative electrodes to lead out the positive and negative electrodes of the lithium-ion battery. For example, a groove is provided on the active material layer of the negative electrode to connect the negative electrode ear to lead out the negative electrode. However, the lithium ions released from the groove corresponding to the negative electrode ear in the active material layer of the positive electrode may be difficult to embed into the negative electrode active material layer, which can easily lead to lithium precipitation. Summary of the invention

[0003] The present application aims to provide a secondary battery and an electronic device, aiming to reduce the risk of lithium plating in the secondary battery.

[0004] In order to solve the technical problem, the embodiment of the present application adopts the following technical solution:

[0005] In the first aspect, the present application proposes a secondary battery, comprising a positive electrode sheet, a separator, a negative electrode sheet and a negative electrode tab, wherein a separator is stacked between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet comprises a negative electrode active material layer facing the positive electrode sheet, and the negative electrode active material layer is provided with a first groove. A portion of the negative electrode tab is provided in the first groove, and another portion of the negative electrode tab extends out of the negative electrode sheet along a first direction. The positive electrode sheet comprises a positive electrode active material layer facing the negative electrode active material layer, and the positive electrode active material layer comprises a first portion and a main portion. In a third direction, a first portion is provided on the positive electrode active material layer adjacent to the first groove. The first portion comprises a first region and a deactivated region, and when viewed along the third direction, the positive projection of the first region on the negative electrode sheet coincides with the first groove, and a first glue layer is provided on the surface of the first region facing the negative electrode sheet, and a deactivated region is provided between the main portion and the first region. In the first direction, the first portion comprises a first section and a second section connected in sequence, and compared with the second section, the positive projection of the first section on the negative electrode sheet is away from the first groove. In the first direction, the width of the first segment is W a The width of the second segment is W b , 0.95≤W a / W b ≤1.05. In the second direction, the average length of the first segment is L a , the average length of the second segment is L b , L a <L bAlong the third direction, the average thickness of the deactivated area is H1, the thickness of the main part is H2, and H1<H2. The third direction is the thickness direction of the positive electrode sheet, and the first direction, the second direction and the third direction are perpendicular to each other.

[0006] In the above technical solution, the portion with higher current density can be covered by the deactivated region, and the positive electrode active material layer in the deactivated region is less, which can reduce the accumulation of lithium ions near the first groove, thereby reducing the occurrence of lithium precipitation. Moreover, compared with extending the first glue layer, by setting the deactivated region, the space occupied by the first glue layer can be effectively reduced, which is beneficial to improving the energy density of the secondary battery. At the same time, the deactivated region can allow a small amount of lithium ions to be transmitted, which is beneficial to the full utilization of the active material layer, and can further improve the energy density of the secondary battery.

[0007] In addition, along the first direction, the length of the deactivation region in the second direction is increased, and the length gradient of the deactivation region is set according to the current density, which can optimize the distribution of the reaction zones of the positive electrode active material layer and the negative electrode active material layer, and can reduce lithium plating while improving the utilization rate of the positive electrode active material layer and the negative electrode active material layer, thereby improving the energy density of the secondary battery.

[0008] In some embodiments, along the second direction, the deactivated region includes a first subregion and a second subregion, and the first region is located between the first subregion and the second subregion. In the direction away from the first region, the width of the first subregion in the first direction decreases, and the width of the second subregion in the first direction decreases. Along the first direction, the length of the first part in the second direction increases. According to the current density, the shape of the deactivated region is set accordingly, which can reduce lithium plating while improving the energy density of the secondary battery.

[0009] In some embodiments, the deactivated region is set by removing part of the positive electrode active material layer from the positive electrode plate, which can reduce the amount of lithium removed from the positive electrode active material layer, so that the negative electrode active material layer has enough residual amount to embed lithium ions, thereby reducing the occurrence of lithium precipitation.

[0010] In some embodiments, 20%≤H1 / H2≤80%, that is, the main body can provide more lithium ions, which is beneficial to the ion exchange of the secondary battery during normal charge and discharge. The deactivated area provides fewer lithium ions, which can facilitate the negative electrode active material layer to have enough margin to embed the lithium ions released from the positive electrode active material layer per unit time, and can facilitate the deactivated area to be fully utilized, which is beneficial to reduce the occurrence of lithium precipitation while improving the energy density of the secondary battery. Preferably, 30%≤H1 / H2≤60%.

[0011] In some embodiments, when observed along the third direction, the deactivated region is at least partially arranged around the first region, the current density near the first groove is relatively large, and the lithium ion deintercalation reaction is violent. By setting the deactivated region around the first region, the detachment amount around the first groove can be effectively reduced, thereby reducing the occurrence of lithium plating.

[0012] In some embodiments, along the second direction, the deactivated region includes a first sub-region and a second sub-region, and the first region is located between the first sub-region and the second sub-region. Along the second direction, the maximum length of the first sub-region is L m1 , the maximum length of the second sub-region is L m2 , the length of the first groove is L1, 13mm≤L m1 +L m2 +L1≤35mm, which can reduce the loss of secondary battery energy density and balance the occurrence of lithium plating.

[0013] In some embodiments, along the first direction, the maximum width of the first sub-region and the maximum width of the second sub-region are both equal to the width of the first region.

[0014] In some embodiments, 20 mm ≤ L m1 +L m2 +L1≤28mm, according to the current density, setting the maximum length of the first sub-region and the second sub-region can reduce the occurrence of lithium plating and reduce the loss of secondary battery energy density. Among them, along the second direction, the maximum length L of the first sub-region m1 1.5mm≤L can be selected m1 ≤12.5mm, for example, any value between 1.5mm and 12.5mm. Preferably, 6mm≤L m1 ≤9mm, which can further reduce lithium plating and reduce the energy density loss of secondary batteries.

[0015] In some embodiments, along the second direction, the first sub-region is divided into a first segment and a second segment of equal length, and the first segment is located between the second segment and the first region; along the first direction, the maximum width of the first segment is W m11 , the maximum width of the second segment is W m12 , W m12 <W m11 Along the third direction, the average thickness of the first section is H 11 , the average thickness of the second segment is H 12 , H 12 >H 11The first section has a larger current density and a smaller thickness, which can reduce the amount of lithium removed from the first section and reduce the occurrence of lithium deposition. The second section has a smaller current density and a larger thickness, which can reduce lithium deposition while allowing more lithium ions to participate in the electrochemical reaction and increase the energy density of the secondary battery. For example, 20% ≤ H 11 / H2≤50%,50%≤H 12 / H2≤80%.

[0016] In some embodiments, the thickness of the first sub-region increases gradually from the first region to the first sub-region, which is beneficial for reducing lithium plating while improving the energy density of the secondary battery.

[0017] In some embodiments, the deactivated region further includes a third sub-region, and along the first direction, the third sub-region and the first region are sequentially arranged, and the third sub-region is connected between the first region and the main body. Along the first direction, the maximum width of the third sub-region is W m3 , 3mm≤W m3 ≤15mm. Adjusting the shape of the third sub-region according to the current density and selecting the maximum width of the third sub-region can reduce the energy density loss of the secondary battery while reducing lithium plating. Preferably, 4.5mm≤W m3 ≤12mm, which can further reduce the occurrence of lithium plating and reduce the energy density loss of secondary batteries.

[0018] In some embodiments, along the first direction, the third sub-region is divided into a third segment and a fourth segment of equal width, and the third segment is located between the first region and the fourth segment; along the second direction, the maximum length of the third segment is L m31 , the maximum length of the fourth segment is L m32 , L m32 <L m31 It is beneficial to reduce lithium plating and improve the energy density of secondary batteries. Along the third direction, the average thickness of the third section is H 31 , the average thickness of the fourth segment is H 32 , H 32 >H 31 The third section has a larger current density and a smaller thickness, which can reduce the amount of lithium removed from the third section and reduce the occurrence of lithium deposition. The fourth section has a smaller current density and a larger thickness, which can reduce lithium deposition while allowing more lithium ions to participate in the electrochemical reaction and improve the energy density of the secondary battery.

[0019] In some embodiments, the thickness of the third sub-region decreases along the direction from the first region to the third sub-region, which is beneficial for reducing lithium plating while improving the energy density of the secondary battery.

[0020] In some embodiments, the first adhesive layer covers the first groove, so that the positive electrode active material layer corresponding to the first groove is isolated by the first adhesive layer, thereby reducing the occurrence of lithium plating.

[0021] In some embodiments, along the second direction, the length of the first groove is L1, the length of the first adhesive layer is L2, 1mm≤L2-L1≤10mm, reducing the space occupied by the first adhesive layer, improving the energy density of the secondary battery, and facilitating the adhesive application. Preferably, 1mm≤L2-L1≤6mm.

[0022] In some embodiments, along the second direction, the deactivated region includes a first sub-region and a second sub-region, and the first region is located between the first sub-region and the second sub-region. Along the second direction, the negative electrode active material layer includes a first end and a second end that are oppositely disposed. Along the third direction, the projection of the first sub-region on the negative electrode active material layer is located between the first groove and the first end, and the projection of the second sub-region on the negative electrode active material layer is located between the first groove and the second end. Along the second direction, the distance from the first groove to the first end is L3, and the distance from the first groove to the second end is L4. Along the second direction, the maximum length of the first sub-region is L m1 , the maximum length of the second sub-region is L m2 . L3>L4,L m1 >L m2 ; or, L3<L4, L m1 <L m2 By reasonably setting the lengths of the first sub-region and the second sub-region, the risk of lithium plating can be reduced while reducing the size of the deactivated region, thereby increasing the energy density of the secondary battery.

[0023] In some embodiments, the deactivated region is provided with a plurality of second grooves, at least some of which are provided around the first region. The provision of the second grooves allows the portion with a higher current density to be covered by the deactivated region. The deactivated region has fewer layers of positive electrode active material, which can reduce the accumulation of lithium ions near the first grooves, thereby reducing the occurrence of lithium precipitation. Moreover, compared with extending the first glue layer, by providing the deactivated region, the space occupied by the first glue layer can be effectively reduced, which is beneficial to improving the energy density of the secondary battery. At the same time, the deactivated region allows a small amount of lithium ions to be transmitted, which is beneficial to the full utilization of the active material layer, and can further improve the energy density of the secondary battery.

[0024] In some embodiments, along the third direction, the average depth of the second groove is T, the thickness of the main part is H2, 25% ≤ T / H2 ≤ 90%, that is, the main part can provide more lithium ions, which is beneficial to the ion exchange of the secondary battery during normal charging and discharging. The deactivated area provides fewer lithium ions, which can facilitate the negative electrode active material layer to have enough margin to embed the lithium ions released from the positive electrode active material layer per unit time, and can facilitate the deactivated area to be fully utilized, which is beneficial to reduce the occurrence of lithium plating while improving the energy density of the secondary battery. For example, 12.5μm ≤ T ≤ 45μm.

[0025] In some embodiments, when observed along the third direction, the average width of the second groove is W3, 0.5mm≤W3≤1.5mm, which is beneficial to reduce the amount of lithium desorption from the positive electrode active material layer, reduce the occurrence of lithium plating, and is beneficial to fully utilize the positive electrode active material and improve the energy density of the secondary battery.

[0026] In some embodiments, when observed along the third direction, the straight-line distance between two adjacent second grooves is D, 0.3mm≤D≤1mm, which is conducive to full utilization of the positive electrode active material layer, improving the energy density of the secondary battery, and facilitating the uniform diffusion of lithium ions, reducing excessive local lithium ion concentration, and thereby reducing the risk of lithium plating.

[0027] In some embodiments, the deactivated region includes a fourth sub-region, and along the second direction, the fourth sub-region is located between the first region and the main body. Along the second direction, the fourth sub-region is divided into a fifth segment and a sixth segment of equal length, and the fifth segment is located between the sixth segment and the first region; along the first direction, the maximum width of the fifth segment is W m41 , the maximum width of the sixth segment is W m42 , W m42 <W m41 Along the third direction, the average depth of the second groove in the fifth section is T m41 , the average depth of the second groove in the sixth segment is T m42 , T m42 <T m41 The current density corresponding to the fifth section is relatively large, and the depth of the second groove in the fifth section is larger, which can reduce the amount of lithium removal in the fifth section and reduce the occurrence of lithium deposition. The current density corresponding to the sixth section is relatively small, and the depth of the second groove in the sixth section is relatively small, which can reduce lithium deposition while allowing more lithium ions to participate in the electrochemical reaction, thereby improving the energy density of the secondary battery.

[0028] In some embodiments, along the first direction, a maximum width of the fourth sub-region is equal to a width of the first region.

[0029] In some embodiments, the deactivation region further includes a sixth sub-region. Along the first direction, the sixth sub-region and the first region are sequentially arranged, and the sixth sub-region is connected between the first region and the main body. Along the first direction, the sixth sub-region is divided into a seventh segment and an eighth segment of equal width, and the seventh segment is located between the first region and the eighth segment; along the second direction, the maximum length of the seventh segment is L m61 , the maximum length of the eighth segment is L m62 , L m62 <L m61 Along the third direction, the average depth of the second groove in the seventh segment is T m61 , the average depth of the second groove in the eighth segment is T m62 , T m62 <T m61 .

[0030] 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.

[0031] 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

[0032] 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.

[0033] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0034] Figure 2 A schematic diagram of the winding structure of an electrode assembly in some embodiments of the present application;

[0035] Figure 3 A schematic diagram of the stacked structure of an electrode assembly according to some embodiments of the present application;

[0036] Figure 4 A schematic diagram of the stacked structure of a positive electrode sheet, a separator and a negative electrode sheet in some embodiments of the present application;

[0037] Figure 5 A schematic diagram of the current density of the negative electrode active material layer at the first groove in some embodiments of the present application;

[0038] Figure 6 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0039] Figure 7Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0040] Figure 8 A schematic diagram of a portion of the structure of a positive electrode active material layer located in a deactivated region in some embodiments of the present application;

[0041] Fig. 9 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0042] Fig.10 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0043] Fig.11 A schematic diagram of the structure of a positive electrode active material layer and a negative electrode active material layer according to another embodiment of the present application;

[0044] Fig.12 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0045] Fig.13 A schematic diagram of a portion of the structure of a positive electrode active material layer located in a deactivated region in some embodiments of the present application;

[0046] Fig.14 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0047] Fig.15 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0048] Fig.16 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0049] Fig.17 A schematic diagram of the structure of the negative electrode plate and the deactivated region of some embodiments of the present application;

[0050] Fig.18 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0051] Fig.19 A schematic diagram of the structure of the deactivation area of ​​some embodiments of the present application;

[0052] Fig. 20 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0053] Fig.21Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0054] Fig. 22 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0055] Fig.23 Schematic diagram of the structure of the positive electrode active material layer and the negative electrode active material layer in some embodiments of the present application;

[0056] Fig.24 Schematic diagram of the structure of the negative electrode plate and the deactivation area of ​​some embodiments of the present application.

[0057] Description of reference numerals:

[0058] 1000. Secondary battery;

[0059] 100. Electrode assembly;

[0060] 10. positive electrode sheet; 11. positive electrode current collector; 111. first surface; 112. second surface; 12. positive electrode active material layer; 121. main body; 121a. first part; 121a1. first section; 121a2. second section; 122. deactivated region; 122a. second groove; 1221. first sub-region; 1221a. first section; 1221b. second section; 1222. second sub-region; 1223. third sub-region; 1223a. third section; 1223b. fourth section; 1224. fourth sub-region; 1224a. fifth section; 1224b. sixth section; 1225. fifth sub-region; 1226. sixth sub-region; 1226a. seventh section; 1226b. eighth section; 123. first region;

[0061] 20, negative electrode plate; 20a, first end; 20b, second end; 21, negative electrode current collector; 211, third surface; 212, fourth surface; 22, negative electrode active material layer; 221, first groove; 222, first edge;

[0062] 30. Isolation film;

[0063] 40. Negative electrode tab;

[0064] 50, first adhesive layer; 60, second adhesive layer;

[0065] 200, housing;

[0066] X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0067] 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.

[0068] 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.

[0069] 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.

[0070] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. 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.

[0071] 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.

[0072] In the first aspect, the present application proposes a secondary battery 1000, please refer to Figure 1 and Figure 2 The secondary battery 1000 includes an electrode assembly 100 , a shell 200 and an electrolyte (not shown in the figure). The shell 200 can accommodate the electrode assembly 100 and the electrolyte. The electrolyte infiltrates the electrode assembly 100 in the shell 200 .

[0073] For the electrode assembly 100, please refer to Figure 2 and Figure 3 The electrode assembly 100 includes a positive electrode sheet 10, a negative electrode sheet 20 and a separator 30. The positive electrode sheet 10, the separator 30 and the negative electrode sheet 20 are stacked and wound, wherein Figure 2 The winding structure of the electrode assembly 100 is shown, for example, the positive electrode sheet 10 and / or the negative electrode sheet 20 are stacked in the thickness direction and wound in the length direction thereof to form a wound electrode assembly 100. In some other embodiments, the electrode assembly 100 may also adopt a laminated structure, wherein Figure 3The stacking structure of the electrode assembly 100 is shown. Along the third direction Z (the thickness direction of the positive electrode sheets 10 and / or the negative electrode sheets 20 ), a plurality of positive electrode sheets 10 and a plurality of negative electrode sheets 20 are alternately stacked, and an isolation film 30 is arranged between adjacent positive electrode sheets 10 and negative electrode sheets 20 .

[0074] It should be noted that, in the embodiment of the present application, the first direction X is the width direction of the positive electrode sheet 10 and / or the negative electrode sheet 20, the second direction Y is the length direction of the positive electrode sheet 10 and / or the negative electrode sheet 20, and the third direction Z is the thickness direction of the positive electrode sheet 10 and / or the negative electrode sheet 20. The first direction X, the second direction Y, and the third direction Z are perpendicular to each other. In the laminated electrode assembly 100, the first direction X may also be the width direction of the positive electrode sheet 10 and / or the negative electrode sheet 20, and the second direction Y may also be the length direction of the positive electrode sheet 10 and / or the negative electrode sheet 20.

[0075] Please refer to Figure 4 The positive electrode sheet 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode current collector 11 may be an overall flat aluminum foil, titanium foil, nickel foil or stainless steel foil. The positive electrode active material layer 12 may be arranged on at least one surface of the positive electrode current collector 11 in the thickness direction, for example, along the third direction Z. The positive electrode current collector 11 includes a first surface 111 and a second surface 112 arranged opposite to each other. The positive electrode active material layer 12 may be arranged on the first surface 111 and / or the second surface 112. The positive electrode active material layer 12 includes a positive electrode active material, a conductive agent and an adhesive. The above-mentioned material components are mixed, stirred evenly and applied to the first surface 111 and / or the second surface 112, so as to obtain the positive electrode active material layer 12. 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.

[0076] Please refer to Figure 4 The negative electrode sheet 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 may be an integrally flat copper foil, titanium foil, nickel foil, stainless steel foil or silver foil. The negative electrode active material layer 22 may be disposed on at least one surface of the negative electrode current collector 21 in the thickness direction, for example, along the third direction Z, the negative electrode current collector 21 includes a third surface 211 and a fourth surface 212 disposed opposite to each other, and the negative electrode active material layer 22 may be disposed on the third surface 211 and / or the fourth surface 212. The negative electrode active material layer 22 includes a negative electrode active material, a conductive agent, and an adhesive, etc. Such materials are mixed, stirred evenly, and coated on the third surface 211 and / or the fourth surface 212, thereby obtaining the negative electrode active material layer 22. Among them, the negative electrode active material includes one or more of graphite, soft carbon, hard carbon, elemental silicon, silicon oxide, silicon alloy, etc.

[0077] The secondary battery 1000 further includes a negative electrode tab 40, see Figure 4 The negative electrode tab 40 is connected to the negative electrode sheet 20. For example, a first groove 221 is provided in the negative electrode active material layer 22, so that the negative electrode current collector 21 is exposed from the first groove 221. A part of the negative electrode tab 40 is provided in the first groove 221 and connected to the negative electrode current collector 21. The connection method includes but is not limited to welding or conductive adhesive bonding. A second adhesive layer 60 can be provided to cover part of the negative electrode tab 40 to isolate the burrs on the negative electrode tab 40 and reduce the risk of the burrs piercing the separator 30. Another part of the negative electrode tab 40 extends out of the negative electrode active material layer 22 along the first direction X.

[0078] The secondary battery 1000 further includes a first adhesive layer 50, see Figure 4 , the first glue layer 50 is disposed on the surface of the positive electrode active material layer 12 facing the negative electrode active material layer 22. Along the third direction Z, the first glue layer 50 covers the first groove 221, so that the portion of the positive electrode active material layer 12 corresponding to the first groove 221 is covered by the first glue layer 50, which can reduce or prevent the release of lithium ions from the portion, thereby allowing the negative electrode active material layer 22 to have sufficient residual amount to embed lithium ions, thereby reducing the risk of lithium precipitation.

[0079] The inventors of this application have found that the negative electrode active material at the first groove 221 may form a solid electrolyte interface (SEI) film, which further hinders the insertion of lithium ions and aggravates the occurrence of lithium precipitation. The inventors of this application have concluded through analysis that there is a problem of uneven current density at the first groove 221 of the negative electrode active material layer 22. Please refer to Figure 5 , Figure 5 Schematic diagram showing the current density of the negative electrode active material layer 22 near the first groove 221, the darker the color, the greater the current density. Figure 5 It can be seen that the closer to the first groove 221, the greater the current density. When the current density of the negative electrode active material layer 22 is large, a large number of lithium ions reach the surface of the negative electrode active material layer 22 per unit time, which easily leads to the aggregation of lithium ions on the surface of the negative electrode active material layer 22, thereby causing lithium precipitation. In addition, high current density will cause the local polarization of the negative electrode active material layer 22 to increase (the potential in the local area deviates from the equilibrium potential), which may reduce the negative electrode potential. When the negative electrode potential is lower than the potential of lithium ions reduced to metallic lithium, it may cause lithium precipitation problems.

[0080] To reduce the above problems, in the embodiments of this application, please refer to Figures 6 to 8The positive electrode active material layer 1212 includes a first portion 121a and a main portion 121. In the third direction Z, the first portion 121a is provided on the positive electrode active material layer 12 adjacent to the first groove 221. The first portion 121a includes a first region 123 and a deactivated region 122. When viewed along the third direction Z, the positive projection of the first region 123 on the negative electrode sheet 20 coincides with the first groove 221. The surface of the first region 123 facing the negative electrode sheet 20 is provided with a first glue layer 50. The deactivated region 122 is provided between the main portion 121 and the first region 123. The deactivated region 122 is realized by removing part of the positive electrode active material layer 12 on the positive electrode sheet 10, while the positive electrode active material layer 12 of the main portion 121 is not removed, so that the amount of positive electrode active material per unit area in the deactivated region 122 is less than that in the main portion 121.

[0081] Along the first direction X, the first portion 121a includes a first section 121a1 and a second section 121a2 connected in sequence. Compared with the second section 121a2, the positive projection of the first section 121a1 on the negative electrode sheet 20 is farther away from the first groove 221. In the first direction X, the width of the first section 121a1 is W a , the width of the second section 121a2 is W b , 0.95≤W a / W b ≤1.05; in the second direction Y, the average length of the first section 121a1 is L a , the average length of the second section 121a2 is L b , L a <L b That is, along the first direction X, the length of the first portion 121a in the second direction Y is increased. Along the third direction Z, the average thickness of the deactivated region 122 is H1, and the thickness of the main portion 121 is H2, where H1<H2.

[0082] The portion with a higher current density can be covered by the deactivated region 122, and the positive electrode active material layer 12 in the deactivated region 122 is less, which can reduce the accumulation of lithium ions near the first groove 221, thereby reducing the occurrence of lithium precipitation. In addition, compared with extending the first glue layer 50, by setting the deactivated region 122, the space occupied by the first glue layer 50 can be effectively reduced, which is beneficial to improving the energy density of the secondary battery 1000. At the same time, the deactivated region 122 can allow a small amount of lithium ions to be transmitted, which is beneficial to the full utilization of the active material layer, and can further improve the energy density of the secondary battery 1000.

[0083] In addition, extending the first glue layer 50 increases the contact area between the first glue layer 50 and the electrolyte. After long-term use, the aging and viscosity reduction of the glue layer may cause it to move and break at the edge, causing the positive electrode active material covered by the extended area of ​​the first glue layer 50 to re-participate in the reaction, increasing the risk of lithium precipitation. The deactivated area 122 is provided to fundamentally reduce the amount of lithium removed from the positive electrode active material layer 12, and there is no problem of the isolated positive electrode active material re-participating in the reaction, which is conducive to extending the service life of the secondary battery 1000.

[0084] In addition, along the first direction X, the length of the deactivated region 122 in the second direction Y is increased, and the length gradient of the deactivated region 122 is set according to the current density, which can optimize the distribution of the reaction areas of the positive electrode active material layer 12 and the negative electrode active material layer 22, and can reduce lithium plating while improving the utilization rate of the positive electrode active material layer 12 and the negative electrode active material layer 22, thereby improving the energy density of the secondary battery 1000.

[0085] The inventor of the present application also unexpectedly discovered that by limiting H1<H2, the local polarization of the negative electrode active material layer 22 is reduced, the decomposition of the electrolyte can be reduced, and the generation of the solid electrolyte interface film can be reduced, which can further reduce lithium precipitation. In addition, the heat concentration at the first groove 221 can be alleviated, the occurrence of side reactions can be reduced, and the charge and discharge performance of the secondary battery 1000 can be improved.

[0086] In some embodiments, along the second direction Y, the deactivated region 122 includes a first sub-region 1221 and a second sub-region 1222, and the first region 123 is located between the first sub-region 1221 and the second sub-region 1222. Along the direction away from the first region 123, the width of the first sub-region 1221 in the first direction X decreases, and the width of the second sub-region 1222 in the first direction X decreases. Along the first direction X, the length of the first portion 121a in the second direction Y increases. According to the current density, the shape of the deactivated region 122 is set accordingly, which can reduce lithium deposition while improving the energy density of the secondary battery 1000.

[0087] The inventors of the present application have found that the current density of the negative electrode active material layer 22 near the first groove 221 is relatively high, and the risk of lithium deposition is relatively high, but near the first groove 221, there is still a part of the negative electrode active material layer 22 that can undergo electrochemical reactions and exert capacity for the secondary battery 1000. Under the premise that lithium deposition does not occur under the same conditions, the part with a higher current density can receive fewer lithium ions than the part with a lower current density.

[0088] In the embodiment of the present application, 20%≤H1 / H2≤80%. That is, the main body 121 can provide more lithium ions, which is beneficial to the ion exchange of the secondary battery 1000 during normal charging and discharging. The deactivated region 122 provides fewer lithium ions, which can facilitate the negative electrode active material layer 22 to have sufficient margin to embed the lithium ions released from the positive electrode active material layer 12 per unit time, and can facilitate the deactivated region 122 to be fully utilized, which is beneficial to reduce the occurrence of lithium plating while improving the energy density of the secondary battery 1000. Preferably, 30%≤H1 / H2≤60%, which can further reduce the occurrence of lithium plating and reduce the energy density loss of the secondary battery.

[0089] For the measurement of the average thickness H1 of the above-mentioned deactivated region 122, please refer to Fig. 9 , along the length direction of the positive electrode sheet 10 (the second direction Y), five points at different positions are randomly selected on one side of the first region 123. When the positive electrode sheet 10 and the negative electrode sheet 20 are stacked, the projections of the five points are located on the extension line of the midline M in the width direction of the first groove 221. Along the length direction of the positive electrode sheet 10 (the second direction Y), five points at different positions are randomly selected on the other side of the first region 123. When the positive electrode sheet 10 and the negative electrode sheet 20 are stacked, the projections of the five points are located on the extension line of the midline M in the width direction of the first groove 221. Along the width direction of the positive electrode sheet 10 (the first direction X), five points at different positions are randomly selected again. When the positive electrode sheet 10 and the negative electrode sheet 20 are stacked, the projections of the five points are located on the extension line of the midline N in the length direction of the first groove 221. The above-mentioned deactivated region 122 is cut to obtain a cross section with each point, and the cross section is observed by SEM to obtain the thickness of the above-mentioned 15 points, and then the average thickness H1 is calculated.

[0090] In some other embodiments, when the first groove 221 is cleaned, the first region 123 may also be cleaned at the same time, and then the first adhesive layer 50 is bonded, which can further reduce the space occupied by the first adhesive layer 50 and improve the energy density of the secondary battery 100 .

[0091] In some embodiments, please refer to Fig.10 , observed along the third direction Z, the deactivated region 122 is arranged around the first region 123, and may be arranged around half a circle, 3 / 4 of a circle, or a full circle, etc. The current density near the first groove 221 is relatively large, and the lithium ion deintercalation reaction is intense. By arranging the deactivated region 122 around the first region 123, the amount of detachment around the first groove 221 can be effectively reduced, thereby reducing the occurrence of lithium precipitation. Among them, observed along the third direction Z, the deactivated region 122 is also arranged around the first glue layer 50, and the first glue layer 50 can cover part of the deactivated region 122.

[0092] Please refer to Fig.10Along the first direction X, the negative electrode active material layer 22 has a first edge 222, and the first groove 221 may penetrate the first edge 222 or not penetrate the first edge 222. When it does not penetrate the first edge 222, the deactivated region 122 may surround the first region 123, that is, surround the first groove 221, which can effectively reduce the amount of lithium desorption around the first groove 221, thereby reducing the occurrence of lithium deposition.

[0093] The inventor of the present application sets the maximum length of the deactivated region 122 according to the current density of the negative electrode active material layer 22 at the first groove 221. In the embodiment of the present application, along the second direction Y, the deactivated region 122 includes a first sub-region 1221 and a second sub-region 1222, and the first region 123 is located between the first sub-region 1221 and the second sub-region 1222. Along the first direction X, the maximum width of the first sub-region and the maximum width of the second sub-region can be equal to the width of the first region. For example, the width of the first sub-region 1221 is W m1 , the width of the first region 123 is W2, that is, W m1 =W2, and the second sub-region 1222 is similar. Along the second direction, the maximum length of the first sub-region is L m1 , the maximum length of the second sub-region is L m2 , the length of the first groove is L1, that is, L m =L m1 +L m2 +L1. Satisfied, 13mm≤L m1 +L m2 +L1≤35mm, which can reduce the loss of energy density of the secondary battery 100 and reduce the occurrence of lithium plating.

[0094] It is understood that, in some embodiments, the width of the first region 123 is similar to that of the first groove 221, that is, W2 = W1. In some embodiments, 20 mm ≤ L m1 +L m2 +L1≤28mm, according to the current density, the maximum length of the first sub-region 1221 and the second sub-region 1222 is set to reduce the occurrence of lithium plating and reduce the loss of energy density of the secondary battery 1000. m1 1.5mm≤L can be selected m1 ≤12.5mm, for example, any value between 1.5mm and 12.5mm. Preferably, 6mm≤L m1 ≤9mm, which can further reduce lithium plating and reduce the energy density loss of secondary batteries.

[0095] In some embodiments, please refer to Fig.12, along the second direction Y, the first sub-region 1221 is divided into a first segment 1221a and a second segment 1221b of equal length. For example, the length of the first segment 1221a is L m11 , the length of the second segment 1221b is L m12 , that is, L m11 =L m12 The first section 1221a is located between the second section 1221b and the first region 123. Along the first direction X, the maximum width of the first section 1221a is W m11 , the maximum width of the second segment 1221b is W m12 , W m12 <W m11 The first section 1221a is closer to the first groove 221, and the corresponding current density is more concentrated, while the current density corresponding to the second section 1221b is relatively small, which limits W m12 <W m11 , which is beneficial to improving the energy density of the secondary battery 1000 while reducing lithium plating.

[0096] In some embodiments, along the third direction Z, the average thickness of the first segment 1221a is H. 11 , the average thickness of the second section 1221b is H 12 , H 12 >H 11 The first section 1221a has a larger current density and a smaller thickness, which can reduce the amount of lithium removed from the first section 1221a and reduce the occurrence of lithium deposition. The second section 1221b has a smaller current density and a larger thickness, which can reduce lithium deposition while allowing more lithium ions to participate in the electrochemical reaction, thereby increasing the energy density of the secondary battery 1000. For example, 20%≤H 11 / H2≤50%,50%≤H 12 / H2≤80%.

[0097] The average thickness of the first section 1221a can be measured by taking five points on the midline of the width direction of the first section 1221a and five points on the midline of the length direction of the first section 1221a, measuring the thickness of the ten points and taking the average value. The following types of average thickness can be measured according to this method.

[0098] Optional, see Fig.13 , along the direction from the first region 123 to the first sub-region 1221, the thickness of the first sub-region 1221 increases, according to Figure 5 It can be seen that the current density gradually decreases along the direction from the first region 123 to the first sub-region 1221 , so the first sub-region 1221 can be correspondingly set to a structure with increasing thickness, which is beneficial to reduce lithium plating while improving the energy density of the secondary battery 1000 .

[0099] For the second sub-region 1222 , along the second direction Y, the first region 123 is located between the first sub-region 1221 and the second sub-region 1222 , and the second sub-region 1222 can be configured similarly to the first sub-region 1221 .

[0100] As for the width of the deactivated region 122, along the first direction X, the side of the first groove 221 away from the first edge 222, the closer to the center of the first groove 221, the greater the current density. The inventor of the present application sets the maximum width of the deactivated region 122 according to the current density in the width direction, please refer to Fig.10 , along the first direction X, the maximum width of the deactivated region 122 is W m The width of the first groove 221 is W1. The deactivated region 122 includes a third sub-region 1223. The third sub-region 1223 and the first region 123 are arranged in sequence along the first direction X. The third sub-region 1223 is connected between the first region 123 and the main body 121. The maximum width of the third sub-region 1223 along the first direction X is W m3 , that is, W m =W1+W m3 . 3mm≤W can be selected m3 ≤15mm, adjusting the shape of the third sub-region 1223 according to the current density, and selecting the maximum width of the third sub-region 1223 can reduce the energy density loss of the secondary battery 1000 while reducing lithium plating. m3 ≤12mm, which can further reduce the occurrence of lithium plating and reduce the energy density loss of the secondary battery 1000.

[0101] In some embodiments, please refer to Fig.15 , along the first direction X, the third sub-region 1223 is divided into a third segment 1223a and a fourth segment 1223b with equal widths. For example, the width of the third segment 1223a is W m31 , the width of the fourth segment 1223b is W m32 , that is, W m31 =W m32 , the third section 1223a is located between the first region 123 and the fourth section 1223b. Along the second direction Y, the maximum length of the third section 1223a is L m31 , the maximum length of the fourth segment 1223b is L m32 , L m32 <L m31 The third section 1223a is closer to the first groove 221, and the corresponding current density is more concentrated, while the fourth section 1223b corresponds to a relatively small current density, which limits L m32 <L m31, which is beneficial to improving the energy density of the secondary battery 1000 while reducing lithium plating.

[0102] Along the third direction Z, the average thickness of the third segment 1223a is H 31 , the average thickness of the fourth segment 1223b is H 32 , H 32 >H 31 The third section 1223a has a larger current density and a smaller thickness, which can reduce the amount of lithium removed from the third section 1223a and reduce the occurrence of lithium deposition. The fourth section 1223b has a smaller current density and a larger thickness, which can reduce lithium deposition while allowing more lithium ions to participate in the electrochemical reaction, thereby increasing the energy density of the secondary battery 1000.

[0103] Optionally, along the direction from the first region 123 to the third sub-region 1223, the thickness of the third sub-region 1223 increases gradually. Figure 5 It can be seen that the current density gradually decreases along the direction from the first region 123 to the third sub-region 1223. Therefore, the third sub-region 1223 can be set to a structure with increasing thickness, which is beneficial to reduce lithium plating and improve the energy density of the secondary battery 1000.

[0104] In some embodiments, the first glue layer 50 may overlap with the first region 123 , or the first glue layer 50 may cover the first groove 221 , so that the positive electrode active material layer 12 corresponding to the first groove 221 is isolated by the first glue layer 50 , thereby reducing lithium plating.

[0105] Since the positive electrode active material layer 12 is provided with the deactivated region 122, the lithium ion transmission around the first groove 221 can be reduced, thereby reducing the occurrence of lithium deposition. Therefore, the length of the first glue layer 50 can be adaptively reduced. For example, please refer to Fig.16 , along the second direction Y, the length of the first groove 221 is L1, the length of the first adhesive layer 50 is L2, 1mm≤L2-L1≤10mm. The space occupied by the first adhesive layer 50 can be reduced, the energy density of the secondary battery 1000 can be improved, and the adhesive bonding operation can be facilitated. Preferably, 1mm≤L2-L1≤6mm, which can further reduce the impact of the first adhesive layer 50 on the internal space of the secondary battery 1000, further improve the energy density of the secondary battery 1000, and facilitate the adhesive bonding operation.

[0106] In some embodiments, please refer to Fig.17, along the second direction Y, the deactivated region 122 includes a first sub-region 1221 and a second sub-region 1222, and the first region 123 is located between the first sub-region 1221 and the second sub-region 1222. Along the second direction Y, the negative electrode active material layer 22 includes a first end 20a and a second end 20b that are oppositely arranged. Along the third direction Z, the projection of the first sub-region 1221 on the negative electrode active material layer 22 is located between the first groove 221 and the first end 20a, and the projection of the second sub-region 1222 on the negative electrode active material layer 22 is located between the first groove 221 and the second end 20b. Along the second direction Y, the distance from the first groove 221 to the first end 20a is L3, and the distance from the first groove 221 to the second end 20b is L4.

[0107] The inventors of the present application have found that, for the negative electrode sheet 20, the larger L3 is, the larger the amount of the negative electrode active material layer 22 participating in the electrochemical reaction is, and the greater the current density between the first groove 221 and the first end 20a is. The inventors of the present application set the length difference between the first sub-region 1221 and the second sub-region 1222 according to the length L3 from the first groove 221 to the first end 20a and the length L4 from the first groove 221 to the second end 20b.

[0108] For example, along the second direction Y, the maximum length of the first sub-region 1221 is L m1 , the maximum length of the second sub-region 1222 is L m2 When L3>L4, it indicates that the current density between the first groove 221 and the first end 20a is relatively large, and L m1 >L m2 When L3<L4, it indicates that the current density between the first groove 221 and the second end 20b is relatively large, and L m1 <L m2 By reasonably setting the lengths of the first sub-region 1221 and the second sub-region 1222, the risk of lithium deposition can be reduced while reducing the size of the deactivated region 122, thereby increasing the energy density of the secondary battery 1000. When L3=L4, L m1 With L m2 Set to be approximately equal, for example |L m2 -L m1 |≤0.5mm.

[0109] Please refer to Fig.18 and Fig.19, the deactivated region 122 is provided with a plurality of second grooves 122a, for example, a plurality of second grooves 122a are formed in the deactivated region 122 by laser drilling, mechanical punching and other processes, and at least part of the second grooves 122a are arranged around the first glue layer 50. The portion with a larger current density can be covered by the deactivated region 122, and the positive electrode active material layer 12 in the deactivated region 122 is less, which can reduce the aggregation of lithium ions near the first groove 221, thereby reducing the occurrence of lithium precipitation. Moreover, compared with extending the first glue layer 50, by setting the deactivated region 122, the space occupied by the first glue layer 50 can be effectively reduced, which is beneficial to improving the energy density of the secondary battery 1000. At the same time, the deactivated region 122 can allow a small amount of lithium ions to be transmitted, which is beneficial to the full utilization of the active material layer, and can further improve the energy density of the secondary battery 1000.

[0110] Moreover, along the first direction X, the length of the deactivated region 122 in the second direction Y is increased. The length gradient of the deactivated region 122 is set according to the above-mentioned current density, which can optimize the distribution of the reaction areas of the positive electrode active material layer 12 and the negative electrode active material layer 22, and can reduce lithium plating while improving the utilization rate of the positive electrode active material layer 12 and the negative electrode active material layer 22, thereby improving the energy density of the secondary battery 1000.

[0111] In some embodiments, along the third direction Z, the average depth of the second groove 122a is T, the thickness of the main part 121 is H2, and 25%≤T / H2≤90%. That is, the main part 121 can provide more lithium ions, which is beneficial to the ion exchange of the secondary battery 1000 during normal charging and discharging. The deactivated region 122 provides fewer lithium ions, which can facilitate the negative electrode active material layer 22 to have sufficient margin to embed the lithium ions released from the positive electrode active material layer 12 per unit time, and can facilitate the deactivated region 122 to be fully utilized, which is beneficial to reduce the occurrence of lithium precipitation while improving the energy density of the secondary battery 1000. For example, 12.5μm≤T≤45μm.

[0112] The measurement of the average depth of the second grooves 122a can be similar to the measurement of the average thickness of the deactivated area 122 in the first aspect mentioned above, except that the five points are replaced by five second grooves 122a. If the number of second grooves 122a is small, three second grooves 122a can also be used to measure the average depth.

[0113] Regarding the width of the second groove 122a, if the width is small, the reduction of the amount of lithium removal from the positive electrode active material layer 12 is limited, which is not conducive to reducing the risk of lithium deposition. If the width is large, it may cause the energy density loss of the secondary battery 1000. In the embodiment of the present application, please refer to Fig.19, observed along the third direction Z, the average width of the second groove 122a is W3, 0.5mm≤W3≤1.5mm, which is beneficial to reducing the amount of lithium desorption of the positive electrode active material layer 12, reducing the occurrence of lithium plating, and is beneficial to fully utilizing the positive electrode active material, thereby improving the energy density of the secondary battery 1000.

[0114] For the distance between two adjacent second grooves 122a, if the distance is small, it may cause excessive loss of the positive active material layer, affecting the energy density of the secondary battery 1000. If the distance is large, it may cause uneven diffusion of lithium ions, which may cause excessive local lithium ion concentration and also cause the risk of lithium precipitation. Fig.19 , observed along the third direction Z, the average distance between two adjacent second grooves 122a is D, 0.3mm≤D≤1mm, which is conducive to full utilization of the positive electrode active material layer 12, improving the energy density of the secondary battery 1000, and is conducive to the uniform diffusion of lithium ions, reducing the excessive local lithium ion concentration, and thus reducing the risk of lithium plating.

[0115] In some embodiments, please refer to Fig. 20 , the deactivated region 122 includes a fourth sub-region 1224. Along the first direction X, the maximum width of the fourth sub-region 1224 may be equal to the width of the first region 123. For example, the width of the fourth sub-region 1224 is W m4 , the width of the first region 123 is W2, that is, W m4 =W2. Along the second direction Y, the fourth sub-region 1224 is connected between the main portion 121 and the first region 123, the length of the first groove 221 is L1, and the maximum length of the fourth sub-region 1224 is L m4 , can choose 1.5mm≤L m4 ≤12.5mm, for example, any value between 1.5mm and 12.5mm. Preferably, 6mm≤L m4 ≤9mm, which can further reduce lithium plating and reduce the energy density loss of the secondary battery 1000.

[0116] In some embodiments, please refer to Fig.21 , along the second direction Y, the fourth sub-region 1224 is divided into a fifth segment 1224a and a sixth segment 1224b of equal length. For example, the length of the fifth segment 1224a is L m41 , the length of the sixth segment 1224b is L m42 , that is, L m41 =L m42 The fifth segment 1224a is located between the sixth segment 1224b and the first region 123. Along the first direction X, the maximum width of the fifth segment 1224a is W m41 , the maximum width of the sixth segment 1224b is W m42 , Wm42 <W m41 The fifth section 1224a is closer to the first groove 221, and the corresponding current density is more concentrated, while the current density corresponding to the sixth section 1224b is relatively small, which limits W m42 <W m41 , which is beneficial to improving the energy density of the secondary battery 1000 while reducing lithium plating.

[0117] In some embodiments, along the third direction Z, the average depth of the second groove 122a in the fifth segment 1224a is T m41 , the average depth of the second groove 122a in the sixth section 1224b is T m42 , T m42 <T m41 The current density corresponding to the fifth section 1224a is relatively large, and the depth of the second groove 122a in the fifth section 1224a is relatively large, which can reduce the amount of lithium removed from the fifth section 1224a and reduce the occurrence of lithium deposition. The current density corresponding to the sixth section 1224b is relatively small, and the depth of the second groove 122a in the sixth section 1224b is relatively small, which can reduce lithium deposition while allowing more lithium ions to participate in the electrochemical reaction, thereby improving the energy density of the secondary battery 1000.

[0118] In some embodiments, the deactivated region 122 further includes a fifth sub-region 1225 . Along the second direction Y, the first region 123 is located between the fourth sub-region 1224 and the fifth sub-region 1225 . The fifth sub-region 1225 can be configured similarly to the fourth sub-region 1224 .

[0119] In some embodiments, please refer to Fig. 22 , the deactivated region 122 includes a sixth sub-region 1226. Along the first direction X, the sixth sub-region 1226 and the first region 123 are sequentially arranged. The sixth sub-region 1226 is connected between the first region 123 and the main body 121. Along the first direction X, the maximum width of the sixth sub-region 1226 is W m6 The width of the first groove 221 is W1, and 3 mm ≤ W m6 ≤15mm. Adjusting the shape of the sixth sub-region 1226 according to the current density and selecting the maximum width of the sixth sub-region 1226 can reduce the energy density loss of the secondary battery 1000 while reducing lithium plating. Preferably 4.5mm≤W m6 ≤12mm, which can further reduce the occurrence of lithium plating and reduce the energy density loss of the secondary battery 1000.

[0120] In some embodiments, please refer to Fig.23, along the first direction X, the sixth sub-region 1226 is divided into a seventh segment 1226a and an eighth segment 1226b of equal width. For example, the width of the seventh segment 1226a is W m61 , the width of the eighth segment 1226b is W m62 , that is, W m61 =W m62 The seventh section 1226a is located between the first region 123 and the eighth section 1226b. Along the second direction Y, the maximum length of the seventh section 1226a is L m61 , the maximum length of the eighth segment 1226b is L m62 , L m62 <L m61 The seventh section 1226a is closer to the first groove 221, and the corresponding current density is more concentrated, while the eighth section 1226b corresponds to a relatively small current density, which limits L m62 <L m61 , which is beneficial to improving the energy density of the secondary battery 1000 while reducing lithium plating.

[0121] In some embodiments, along the third direction Z, the average depth of the second groove 122a in the seventh segment 1226a is T m61 , the average depth of the second groove 122a in the eighth section 1226b is T m62 , T m62 <T m61 The current density corresponding to the seventh section 1226a is relatively large, and the depth of the second groove 122a in the seventh section 1226a is larger, which can reduce the amount of lithium removed from the seventh section 1226a and reduce the occurrence of lithium deposition. The current density corresponding to the eighth section 1226b is relatively small, and the depth of the second groove 122a in the eighth section 1226b is relatively small, which can reduce lithium deposition while allowing more lithium ions to participate in the electrochemical reaction, thereby improving the energy density of the secondary battery 1000.

[0122] In the third aspect, the present application also proposes an electronic device, including a secondary battery 1000 as in any embodiment of the first aspect or the second aspect described 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, for example, game consoles, electric car toys, electric ship toys, electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecrafts.

[0123] Example 1-1

[0124] Preparation of positive electrode:

[0125] The positive electrode active material is lithium cobalt oxide, 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 5 ) are mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) is added as a solvent, and a positive electrode slurry with a solid content of 75wt% is prepared, and the mixture is stirred evenly under a vacuum mixer. An aluminum foil with a thickness of 8μm and a length of 1000mm is selected as the positive electrode current collector, and the positive electrode slurry is 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. After that, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer, and the single-sided coating thickness H2 is 50μm.

[0126] Preparation of negative electrode sheet:

[0127] The negative electrode active material graphite powder, silicon powder, conductive agent conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 87.5:10:1:1.5, 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 an empty foil area without negative electrode slurry is reserved on the 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 double-sided coating of the negative electrode active material layer, and the single-sided coating thickness is 55μm.

[0128] Preparation of isolation membrane:

[0129] 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.

[0130] Electrolyte preparation:

[0131] 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 solvent, and 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.

[0132] Preparation of lithium-ion secondary batteries:

[0133] By laser cleaning, a first groove of 10 mm (L1) × 15 mm (W1) is cleaned in the above-mentioned negative electrode active material layer, and a nickel sheet is selected as the negative electrode tab, and the negative electrode tab is welded and connected to the negative electrode sheet in the first groove.

[0134] Through laser cleaning, a deactivated area is cleaned on the positive electrode active material layer. Along the width direction of the positive electrode sheet, the length of the deactivated area in the length direction of the positive electrode sheet is increased to form a special-shaped structure similar to the current density concentration area. The uncleaned part is the main part, and the average thickness H1 of the deactivated area is 45μm. The maximum length L of the deactivated area m 20mm, maximum width W m It is 20mm. After the positive electrode sheet is welded to the positive electrode ear, polyethylene terephthalate is selected as the base material layer, and epoxy resin is used as the adhesive layer to prepare a first adhesive layer with a length and width of 11mm (L2) × 16mm. The first adhesive layer is bonded to the deactivated area of ​​the positive electrode active material layer. The isolation film, positive electrode sheet, isolation film, and negative electrode sheet prepared above are stacked in order and wound to obtain an electrode assembly. Observing along the thickness direction of the positive electrode sheet, the first adhesive layer is located in the deactivated area and covers the first groove. The first area (the area corresponding to the first groove) is flanked by the first sub-area and the second sub-area, respectively. The width L of the first sub-area m1 and the width L of the second sub-region m2 Consistent or nearly consistent, L m1 5mm, L m2 The deactivated area exceeds the first adhesive layer in the width direction of the isolation film, and the exceeding part forms the third sub-area with a width of W m3 It is 4.5mm.

[0135] Different from Example 1-1, the relevant parameters in Examples 1-2 to 1-27 and Comparative Example 1-1 are shown in Table 1 below, wherein the first sub-region is divided into a first segment and a second segment of equal length, and the first segment is located between the second segment and the first region. The average thickness of the first segment is H 11 , the average thickness of the second segment is H 12 In Comparative Example 1-1, the positive electrode active material layer was not laser cleaned, and there was no deactivated region in the positive electrode active material layer.

[0136] Lithium deposition test method:

[0137] Place the lithium-ion secondary battery at a test temperature of 25°C for 30 minutes and perform step-by-step charging according to the following charging steps:

[0138] (1) 5C constant current charging to 4.23V, constant voltage charging to 4C;

[0139] (2) 4C constant current charging to 4.3V, constant voltage charging to 3C;

[0140] (3) 3C constant current charging to 4.4V, constant voltage charging to 2C;

[0141] (4) 2C constant current charging to 4.5V, constant voltage charging to 0.05C;

[0142] After standing for 10 minutes, discharge according to the following steps:

[0143] 0.2C DC discharge to 3V.

[0144] The above charge and discharge process is one cycle. After repeating 100 cycles, when the lithium-ion secondary battery is in a fully charged state (the battery is designed to have a maximum voltage of 4.5V), the secondary battery is disassembled to obtain the positive electrode sheet, the separator and the negative electrode sheet. If the lithium deposition area near the negative electrode ear is greater than or equal to 2mm 2 , then it is judged as lithium deposition. Each group tests 20 lithium-ion batteries, the number of lithium deposition is X, and the lithium deposition rate is X / 20.

[0145] Table 1

[0146]

[0147]

[0148] According to the above Table 1, combined with Examples 1-1 to 1-27 and Comparative Example 1-1, it can be seen that when a deactivated region is provided at the first groove corresponding to the positive electrode active material layer, the occurrence of lithium deposition can be effectively reduced. This is because the portion with a larger current density can be covered by the deactivated region, and the positive electrode active material layer in the deactivated region is less, which can reduce the aggregation of lithium ions near the first groove, thereby reducing the occurrence of lithium deposition. Therefore, in the embodiment of the present application, H1<H2 can be selected.

[0149] In Example 1-1, the thickness of the deactivated region is still large, and the positive electrode active material layer still releases a large number of lithium ions per unit time, which may make it difficult for the negative electrode active material layer to embed lithium ions in time, and there is still a certain risk of lithium precipitation. In Example 1-8, the thickness of the deactivated region is small, and the lithium precipitation rate is similar to that of Example 1-7, but the diffusion and migration of lithium ions in Example 1-8 are hindered, which can easily cause the positive electrode active material layer that can normally participate in the electrochemical reaction to be removed, resulting in a large loss of energy density of the lithium ion battery. Therefore, in the embodiment of the present application, 20%≤H1 / H2≤80% can be selected, which can reduce lithium precipitation while allowing more lithium ions to participate in the electrochemical reaction normally, thereby improving the energy density of the secondary battery. In Examples 1-4 to 1-6, the lithium precipitation rate is low, and it is convenient for more lithium ions to fully participate in the electrochemical reaction, which is beneficial to improving the energy density of the secondary battery. Considering the improvement of energy density while reducing the occurrence of lithium precipitation, in the embodiment of the present application, 30%≤H1 / H2≤60% can be selected.

[0150] In combination with Examples 1-5, 1-9 to 1-13, in Example 1-13, H 11 >H 12 , and the current density is greater closer to the first groove, and the first section is closer to the first groove, so in Examples 1-13, the risk of lithium deposition is higher. 12 >H 11 .

[0151] In Example 1-9, the thickness of the first section is relatively small, which may cause energy density loss, and the thickness of the second section is relatively large, and the risk of lithium deposition is higher than that of Examples 1-10 to 1-12 and Example 1-5. Therefore, in the embodiments of the present application, 20%≤H 11 / H2≤50%,50%≤H 12 / H2≤80%.

[0152] In combination with Examples 1-5 and Examples 1-14 to 1-21, in Example 1-14, L m1 +L m2 + L1 is small, it is difficult to effectively cover the area with high current density, and the risk of lithium deposition is high. In Examples 1-15 to 1-21, the risk of lithium deposition is low. In the examples of this application, 13 mm ≤ L m1 +L m2 In Examples 1-5 and 1-17 to 1-19, the lithium plating rate is small, and the lengths of the first sub-region and the second sub-region are smaller, which can further reduce the energy density loss of the secondary battery. Considering the reduction of energy density loss and lithium plating, 20 mm ≤ L m1 +L m2 +L1≤28mm.

[0153] As for the length of the first sub-region, in combination with Embodiments 1-4 and 1-15 to 1-21, 1.5 mm ≤ L may be selected. m1 In Examples 1-17 to 1-19, the lithium deposition rate is small, and the lengths of the first sub-region and the second sub-region are smaller. In the embodiments of the present application, 6 mm ≤ L m1 ≤9mm.

[0154] In combination with Example 1-5 and Example 1-22 to Example 1-27, in Example 1-22 to Example 1-23, the width of the third sub-region is small, it is difficult to effectively block lithium ions, and the risk of lithium precipitation is high. In Example 1-24 to Example 1-27, the lithium precipitation rate is low, so in the embodiment of the present application, 3mm≤W can be selected. m3 ≤15mm.

[0155] Similarly, in Examples 1-5 and Examples 1-25 to 1-26, the lithium precipitation rate is further reduced than that in Example 1-24, and the lithium precipitation rate in Example 1-27 is similar to that in Example 1-26. In Example 1-26, the width of the third sub-region is smaller, which can reduce the energy density loss of the secondary battery. Therefore, in the embodiments of the present application, it is preferred that 4.5 mm ≤ W m3 ≤12mm.

[0156] Different from Example 1-5, the relevant parameters in Examples 2-1 to 2-7 are shown in Table 3 below, wherein the length of the first adhesive layer is L2, and the length of the first groove is L1.

[0157] Table 2

[0158]

[0159]

[0160] In combination with Example 1-5 and Examples 2-1 to 2-7, when a square hot pressing area is used, in Example 2-1, the length of the first glue layer is small, and the current density near the first groove is large, which may cause the first glue layer to be difficult to effectively cover the part, the lithium ion deintercalation reaction is still violent, and the risk of lithium precipitation is still high. In combination with Example 2-4 and Examples 2-8 to 2-14, when a special-shaped hot pressing area is used, in Example 2-8, the length of the first glue layer is small, and the current density near the first groove is large, which may also cause the first glue layer to be difficult to effectively cover the part, the lithium ion deintercalation reaction is still violent, and the risk of lithium precipitation is still high. Therefore, in the embodiments of the present application, 1mm≤L2-L1≤10mm can be selected.

[0161] When a square hot pressing area is used, the lithium precipitation rate of Example 2-5 is similar to that of Examples 2-6 to 2-7, but in Example 2-5, the length of the first glue layer is smaller, and the energy density loss of the secondary battery is smaller. When a special-shaped hot pressing area is used, the lithium precipitation rate of Example 2-12 is similar to that of Examples 2-13 to 2-14, but in Example 2-12, the length of the first glue layer is smaller, and the energy density loss of the secondary battery is smaller. Therefore, in the embodiments of the present application, it is preferred that 1mm≤L2-L1≤6mm.

[0162] Different from Example 1-1, in Examples 3-1 to 3-18, a plurality of second grooves are formed on the positive electrode active material layer by a laser grooving process, and the areas where the second grooves are located together form a deactivated area. The average width of each second groove is W3, and the distance between two adjacent second grooves is D. The relevant parameters are shown in Table 2 below.

[0163] Table 3

[0164]

[0165]

[0166] According to the above Table 3, combined with Examples 3-1 to 3-8 and Comparative Example 1-1, it can be seen that when a deactivated region having a plurality of second grooves is provided at the positive electrode active material layer corresponding to the first groove, the occurrence of lithium deposition can also be effectively reduced. This is because the portion with a larger current density can be covered by the deactivated region, and the positive electrode active material layer in the deactivated region is less, which can reduce the aggregation of lithium ions near the first groove, thereby reducing the occurrence of lithium deposition.

[0167] In Example 3-1, the depth of the second groove is relatively small, and the positive electrode active material layer still releases a large amount of lithium ions per unit time, which may make it difficult for the negative electrode active material layer to embed lithium ions in time, and the risk of lithium precipitation is relatively high. In Example 3-8, the thickness of the deactivated area is relatively small, and the lithium precipitation rate is similar to that of Example 3-7, but the depth of the second groove in Example 3-8 is relatively large, resulting in the removal of lithium ions that can normally participate in the electrochemical reaction, resulting in a serious loss of energy density of the lithium-ion battery. Therefore, in the embodiments of the present application, 25% ≤ T / H2 ≤ 90% can be selected, that is, 12.5μm ≤ T ≤ 45μm, which can reduce lithium precipitation while allowing more lithium ions to normally participate in the electrochemical reaction and improve the energy density of the secondary battery.

[0168] In combination with Example 3-5 and Examples 3-9 to 3-14, in Example 3-9, the width of the second groove is relatively small, that is, the positive electrode active material layer still releases a large amount of lithium ions per unit time, and the risk of lithium precipitation is relatively high. In Example 3-14, the lithium precipitation rate is similar to that of Example 3-13, but in Example 3-14, the width of the second groove is relatively large, resulting in the removal of lithium ions that can normally participate in the electrochemical reaction, resulting in a serious loss of energy density of the lithium-ion battery. Therefore, in the embodiments of the present application, 0.5mm≤W3≤1.5mm can be selected, which can reduce the energy density loss of the lithium-ion battery while reducing lithium precipitation.

[0169] In combination with Example 3-5 and Examples 3-15 to 3-19, in Example 3-19, the distance between two adjacent second grooves is large, that is, the positive electrode active material layer still releases more lithium ions per unit time, and the risk of lithium precipitation is high. In Example 3-15, the lithium precipitation rate is similar to that of Example 3-16, but in Example 3-15, the distance between two adjacent second grooves is small, resulting in the removal of lithium ions that can normally participate in the electrochemical reaction, resulting in a serious loss of energy density of the lithium-ion battery. Therefore, in the embodiments of the present application, 0.3mm≤D≤1mm can be selected, which can reduce the energy density loss of the lithium-ion battery while reducing lithium precipitation.

[0170] 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 positive electrode sheet, a separator, a negative electrode sheet and a negative electrode tab, wherein the separator is stacked between the positive electrode sheet and the negative electrode sheet; the negative electrode sheet comprises a negative electrode active material layer facing the positive electrode sheet, and the negative electrode active material layer is provided with a first groove; a portion of the negative electrode tab is provided in the first groove, and another portion of the negative electrode tab extends out of the negative electrode sheet along a first direction; the positive electrode sheet comprises a positive electrode active material layer facing the negative electrode active material layer, characterized in that: The positive electrode active material layer includes a first portion and a main portion. In the third direction, the first portion is arranged on the positive electrode active material layer adjacent to the first groove. The first portion includes a first region and a deactivated region. When viewed along the third direction, the orthographic projection of the first region on the negative electrode sheet coincides with the first groove. A first glue layer is arranged on a surface of the first region facing the negative electrode sheet. The deactivated region is arranged between the main portion and the first region. Along the first direction, the first portion includes a first section and a second section connected in sequence, and compared with the second section, the positive projection of the first section on the negative electrode sheet is away from the first groove; in the first direction, the width of the first section is W a , the width of the second section is W b , 0.95≤W a / W b ≤1.05; in the second direction, the average length of the first segment is L a , the average length of the second segment is L b , L a <L b ; Along the third direction, the average thickness of the deactivated area is H1, the thickness of the main body is H2, and H1<H2; The third direction is the thickness direction of the positive electrode sheet, and the first direction, the second direction and the third direction are perpendicular to each other.

2. The secondary battery according to claim 1, characterized in that: Along the second direction, the deactivated region includes a first sub-region and a second sub-region, and the first region is located between the first sub-region and the second sub-region; along a direction away from the first region, a width of the first sub-region in the first direction decreases gradually, and a width of the second sub-region in the first direction decreases gradually; Along the first direction, the length of the first portion in the second direction increases gradually.

3. The secondary battery according to claim 1, characterized in that: The deactivated region is provided by removing a portion of the positive electrode active material layer from the positive electrode sheet.

4. The secondary battery according to claim 1, characterized in that: 20%≤H1 / H2≤80%.

5. The secondary battery according to claim 4, characterized in that: 30%≤H1 / H2≤60%.

6. The secondary battery according to claim 1, characterized in that: When viewed along the third direction, the deactivation region is disposed around the first region.

7. The secondary battery according to claim 1, characterized in that: Along the second direction, the deactivation region includes a first sub-region and a second sub-region, and the first region is located between the first sub-region and the second sub-region; Along the second direction, the maximum length of the first sub-region is L m1 , the maximum length of the second sub-region is L m2 , the length of the first groove is L1, 13mm≤L m1 +L m2 +L1≤35mm.

8. The secondary battery according to claim 7, characterized in that: 20mm≤L m1 +L m2 +L1≤28mm。 9. The secondary battery according to claim 7, characterized in that: 1.5mm≤L m1 ≤12.5mm。 10. The secondary battery according to claim 9, characterized in that: 6mm≤L m1 ≤9mm。 11. The secondary battery according to any one of claims 7 to 10, characterized in that: Along the second direction, the first sub-region is divided into a first segment and a second segment of equal length, and the first segment is located between the second segment and the first region; along the first direction, the maximum width of the first segment is W m11 , the maximum width of the second segment is W m12 , W m12 <W m11 ; Along the third direction, the average thickness of the first segment is H 11 , the average thickness of the second segment is H 12 , H 12 >H 11 .

12. The secondary battery according to claim 11, characterized in that: 20%≤H 11 / H2≤50%,50%≤H 12 / H2≤80%。 13. The secondary battery according to claim 12, characterized in that: Along the direction from the first region to the first sub-region, the thickness of the first sub-region increases gradually.

14. The secondary battery according to claim 1, characterized in that: The deactivation area further includes a third sub-area, and along the first direction, the third sub-area and the first area are arranged in sequence, and the third sub-area is connected between the first area and the main body; Along the first direction, the maximum width of the third sub-region is W m3 , 3mm≤W m3 ≤15mm.

15. The secondary battery according to claim 14, characterized in that: 4.5mm≤W m3 ≤12mm。 16. The secondary battery according to claim 15, characterized in that: Along the first direction, the third sub-region is divided into a third segment and a fourth segment of equal width, and the third segment is located between the first region and the fourth segment; along the second direction, the maximum length of the third segment is L m31 , the maximum length of the fourth segment is L m32 , L m32 <L m31 ; Along the third direction, the average thickness of the third section is H 31 , the average thickness of the fourth section is H 32 , H 32 >H 31 .

17. The secondary battery according to claim 16, characterized in that: Along the direction from the first region to the third sub-region, the thickness of the third sub-region decreases gradually.

18. The secondary battery according to claim 1, characterized in that: The first adhesive layer covers the first groove.

19. The secondary battery according to claim 1, characterized in that: Along the second direction, the length of the first groove is L1, the length of the first adhesive layer is L2, and 1mm≤L2-L1≤10mm.

20. The secondary battery according to claim 19, characterized in that: 1mm≤L2-L1≤6mm.

21. The secondary battery according to claim 1, characterized in that: Along the second direction, the deactivation region includes a first sub-region and a second sub-region, and the first region is located between the first sub-region and the second sub-region; Along the second direction, the negative electrode active material layer includes a first end and a second end that are oppositely arranged, and along the third direction, a projection of the first sub-region on the negative electrode active material layer is located between the first groove and the first end, and a projection of the second sub-region on the negative electrode active material layer is located between the first groove and the second end; Along the second direction, the distance from the first groove to the first end is L3, and the distance from the first groove to the second end is L4; Along the second direction, the maximum length of the first sub-region is L m1 , the maximum length of the second sub-region is L m2 ; L3>L4,L m1 >L m2 ; or, L3<L4, L m1 <L m2 .

22. The secondary battery according to claim 1, characterized in that: The deactivation area is provided with a plurality of second grooves, and at least some of the second grooves are arranged around the first area.

23. The secondary battery according to claim 22, characterized in that: Along the third direction, an average depth of the second groove is T, a thickness of the main body portion is H2, and 25%≤T / H2≤90%.

24. The secondary battery according to claim 23, characterized in that: 12.5μm≤T≤45μm.

25. The secondary battery according to claim 22, characterized in that: When viewed along the third direction, the average width of the second groove is W3, and 0.5 mm≤W3≤1.5 mm.

26. The secondary battery according to claim 22, characterized in that: When viewed along the third direction, a straight-line distance between two adjacent second grooves is D, and 0.3 mm ≤ D ≤ 1 mm.

27. The secondary battery according to claim 22, characterized in that: The deactivation region includes a fourth sub-region, and along the second direction, the fourth sub-region is located between the first region and the main body; Along the second direction, the fourth sub-region is divided into a fifth segment and a sixth segment of equal length, the fifth segment is located between the sixth segment and the first region; along the first direction, the maximum width of the fifth segment is W m41 , the maximum width of the sixth segment is W m42 , W m42 <W m41 ; Along the third direction, the average depth of the second groove in the fifth section is T m41 , the average depth of the second groove in the sixth section is T m42 , T m42 <T m41 .

28. The secondary battery according to claim 27, characterized in that: The deactivation area further includes a sixth sub-area, which is arranged in sequence with the first area along the first direction, and is connected between the first area and the main body; Along the first direction, the sixth sub-area is divided into a seventh segment and an eighth segment of equal width, and the seventh segment is located between the first area and the eighth segment; along the second direction, the maximum length of the seventh segment is L m61 , the maximum length of the eighth segment is L m62 , L m62 <L m61 ; Along the third direction, the average depth of the second groove in the seventh section is T m61 , the average depth of the second groove in the eighth section is T m62 , T m62 <T m61 .

29. An electronic device, characterized in that: Includes the secondary battery according to any one of claims 1 to 28.

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