Secondary battery and electronic device

Abstract

A secondary battery (1000) and an electronic device. A negative electrode sheet (20) comprises a negative electrode active material layer (22) facing a positive electrode sheet (10), and the positive electrode sheet (10) comprises a positive electrode active material layer (12) facing the negative electrode active material layer (22). The secondary battery (1000) further comprises a negative electrode tab (40), the negative electrode active material layer (22) is provided with a first slot (221), one part of the negative electrode tab (40) is arranged in the first slot (221), and the other part of the negative electrode tab (40) extends out of the negative electrode sheet (20) in a first direction. The secondary battery (1000) further comprises a first adhesive layer (50), the first adhesive layer (50) is arranged on the surface of the positive electrode active material layer (12) facing the negative electrode sheet (20), and in a third direction, the first adhesive layer (50) covers the first slot (221). In a second direction, the length of the first adhesive layer (50) is L, the length of the first slot (221) is L1, and 1.2≤L / L1≤3. By setting the length of the first adhesive layer (50) on the basis of the current density of the negative electrode active material layer (22) at the first slot (221), the occurrence of lithium precipitation can be reduced, and the impact of the first adhesive layer (50) on the energy density of the secondary battery (1000) can be reduced.

Description

Secondary battery and electronic device TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and an electronic device. BACKGROUND

[0002] Secondary batteries such as lithium ion batteries are widely used in electronic devices such as smart phones, portable notebooks, wearable devices, and smart homes due to their high energy density, environmental protection, and other advantages. A lithium ion battery includes a positive electrode sheet and a negative electrode sheet, and usually needs to set a positive electrode tab and a negative electrode tab to lead out the positive and negative electrodes of the lithium ion battery. For example, a recess is formed on the active material layer of the negative electrode sheet to connect the negative electrode tab to lead out the negative electrode. However, lithium ions extracted at the groove position of the positive electrode tab corresponding to the negative electrode tab may be difficult to be inserted into the negative electrode active material layer, which is easy to cause lithium precipitation at the groove position of the negative electrode tab.

[0003] SUMMARY

[0004] The present application aims to provide a secondary battery and an electronic device, and aims to reduce the risk of lithium precipitation of the secondary battery.

[0005] In order to solve the technical problems of the present application, the following technical solutions are adopted:

[0006] In a first aspect, the present application provides a secondary battery, including a positive electrode sheet, a separator film and a negative electrode sheet which are stacked or stacked and wound. The negative electrode sheet includes a negative electrode active material layer facing the positive electrode sheet, and the positive electrode sheet includes a positive electrode active material layer facing the negative electrode active material layer. The secondary battery further includes a negative electrode tab, the negative electrode active material layer is provided with a first recess, and a part of the negative electrode tab is arranged in the first recess. Another part of the negative electrode tab extends out of the negative electrode sheet along a first direction. The secondary battery further includes a first adhesive layer, which is arranged on the surface of the positive electrode active material layer facing the negative electrode sheet, and covers the first recess along a third direction. Along a second direction, the length of the first adhesive layer is L, and the length of the first recess is L1, and 1.2≤L / L1≤3. The third direction is the thickness direction of the positive electrode sheet and / or the negative electrode sheet, and the first direction, the second direction and the third direction are perpendicular to each other.

[0007] In the technical solution, the length of the first adhesive layer is set according to the current density of the negative active material layer at the first groove, and the condition 1.2≤L / L1≤3 is limited, so that the part with large current density is isolated by the first adhesive layer, the lithium ion aggregation near the first groove is reduced, and the lithium precipitation is reduced. In addition, the condition 1.2≤L / L1≤3 can reduce the loss of energy density of the secondary battery, and facilitate the balance between reducing lithium precipitation and reducing energy density loss. At the same time, the local polarization of the negative active material layer is reduced, the electrolyte decomposition is reduced, the generation of the solid electrolyte interface (SEI) film is reduced, and the lithium precipitation is further reduced. In addition, the heat concentration at the first groove can be alleviated, the side reaction can be reduced, and the charge and discharge performance of the secondary battery can be improved.

[0008] In some embodiments, 2≤L / L1≤2.6, which can further reduce lithium precipitation and reduce the impact of the first adhesive layer on energy density.

[0009] In some embodiments, along the first direction, the width of the first adhesive layer is W, the width of the first groove is W1, and 1.06≤W / W1≤2, which can reduce the loss of energy density while reducing lithium precipitation. In other embodiments, 1.2≤W / W1≤1.5, which can further reduce the loss of energy density while reducing lithium precipitation.

[0010] In some embodiments, 16mm≤W≤30mm, preferably 18mm≤W≤22.5mm.

[0011] In some embodiments, 8mm≤L1≤20mm.

[0012] In some embodiments, along the second direction, the first adhesive layer comprises a first part and a second part arranged in sequence, and the second part is connected with the first part and arranged integrally. Along the second direction, the first part comprises a first edge and a second edge arranged oppositely, and the first groove comprises a third edge and a fourth edge arranged oppositely. The extension direction of the third edge is consistent with that of the first edge, and the extension direction of the fourth edge is consistent with that of the second edge. Along the third direction, the third edge overlaps with the first edge, and the fourth edge overlaps with the second edge. Along the second direction, the length of the second part is L2, and 0.1≤L2 / L1≤1. This can reduce lithium precipitation on one side of the first groove in the length direction and reduce the loss of energy density of the secondary battery.

[0013] In some embodiments, the third edge and the fourth edge extend along the first direction.

[0014] In some embodiments, 0.5≤L2 / L1≤0.8, which can reduce lithium precipitation on one side of the first groove in the length direction and reduce the loss of energy density of the secondary battery. Optionally, 5mm≤L2≤8mm.

[0015] In some embodiments, the second portion is provided with first through holes in the third direction. The first through holes expose part of the positive active material layer, and lithium ion deintercalation reaction can occur between the part of the exposed positive active material layer and the part of the negative active material layer capable of exhibiting capacity, thereby improving utilization of the positive active material layer and the negative active material layer and further improving the energy density of the secondary battery.

[0016] In some embodiments, the area of the second portion is S1, the sum of the areas of all the first through holes on the second portion is S2, and 40%≤S2 / S1≤60% when viewed in the third direction. This can reduce the risk of lithium precipitation while improving utilization of the negative active material layer and the positive active material layer, thereby further improving the energy density of the secondary battery.

[0017] In some embodiments, the radius of the first through hole is R1, and 0.1mm≤R1≤1mm. This can reduce the risk of lithium precipitation while improving utilization of the negative active material layer, thereby further improving the energy density of the secondary battery.

[0018] In some embodiments, the second portion includes a first region and a second region, and the first region is located between the first portion and the second region in the second direction. When viewed in the third direction, the area of the first region is S 11 , the sum of the areas of all the first through holes in the first region is S 21 . When viewed in the third direction, the area of the second region is S 12 , and the sum of the areas of all the first through holes in the second region is S 22 . S 21 / S 11 <S 22 / S 12 .

[0019] The negative active material layer corresponding to the first region has a high current density and a high risk of lithium precipitation, and has less negative active material capable of exhibiting capacity. By setting a smaller hole density in the first region, the amount of lithium removed from the first region can be reduced, thereby reducing the risk of lithium precipitation in the negative active material layer. The negative active material layer corresponding to the second region has a low current density and a low risk of lithium precipitation, and has more negative active material capable of exhibiting capacity. By setting a larger hole density in the second region, the amount of lithium removed from the second region can be increased, thereby facilitating more negative active material to participate in electrochemical reactions and improving the energy density of the secondary battery. By reasonably setting the distribution of the first through holes in the second portion, the risk of lithium precipitation can be reduced while improving the energy density of the secondary battery.

[0020] In some embodiments, the widths of the first region and the second region are equal in the second direction.

[0021] In some embodiments, the number of the first through holes in the first region is N1, and the number of the first through holes in the second region is N2, N1

[0022] In some embodiments, the distance between two adjacent first through holes in the first region is D1, and the distance between two adjacent first through holes in the second region is D2, D1

[0023] In some embodiments, the first adhesive layer further comprises a third portion, the third portion, the first portion and the second portion are sequentially arranged along the second direction, and the third portion is connected with the first portion and arranged integrally. The length of the third portion along the second direction is L3, and 0.5≤L3 / L1≤0.8. The lithium precipitation on the other side of the first groove in the length direction can be reduced, and the loss of the energy density of the secondary battery can be reduced. Optionally, 5mm≤L3≤8mm.

[0024] In some embodiments, the third portion is provided with a second through hole along the third direction, so that part of the positive active material layer is exposed. The lithium ion deintercalation reaction between the exposed part of the positive active material layer and the part of the negative active material layer capable of exerting capacity can also occur, further improving the utilization rate of the negative active material layer and the energy density of the secondary battery.

[0025] In some embodiments, the third portion comprises a third region and a fourth region, and the fourth region is located between the first portion and the third region along the second direction. The area of the third region observed along the third direction is S 31 , and the sum of the areas of all the second through holes in the third region observed along the third direction is S 41 . The area of the fourth region observed along the third direction is S 32 , and the sum of the areas of all the second through holes in the fourth region observed along the third direction is S 42 , S 41 / S 31 >S 42 / S 32 .

[0026] The fourth region corresponds to the negative active material layer, the current density is relatively large, the risk of lithium precipitation is relatively high, and the negative active material capable of exerting capacity is relatively small. By setting the hole density of the first region to be relatively small, the amount of lithium extraction of the fourth region can be reduced, thereby reducing the risk of lithium precipitation of the negative active material layer. The third region corresponds to the negative active material layer, the current density is relatively small, the risk of lithium precipitation is relatively low, and the negative active material capable of exerting capacity is relatively large. By setting the hole density of the third region to be relatively large, the amount of lithium extraction of the third region can be increased, so that more negative active material can participate in the electrochemical reaction, thereby improving the energy density of the secondary battery. By reasonably setting the distribution of the first through hole in the second part, the energy density of the secondary battery can be improved while reducing the risk of lithium precipitation.

[0027] In some embodiments, along the second direction, the first adhesive layer comprises a third part, a first part and a second part arranged in sequence, the third part is connected and arranged integrally with the first part, and the second part is connected and arranged integrally with the first part. Along the second direction, the negative active material layer comprises a first end portion and a second end portion arranged oppositely, the second part is located between the first groove and the first end portion, and the third part is located between the first groove and the second end portion. Along the second direction, the length from the first groove to the first end portion is L4, and the length from the first groove to the second end portion is L5. Along the second direction, the length of the second part is L2, and the length of the third part is L3. L4>L5, L2>L3; or L4

[0028] In some embodiments, along the third direction, the thickness of the positive active material layer covered by the first adhesive layer is H1, the thickness of the positive active material layer not covered by the first adhesive layer is H2, and H1

[0029] In some embodiments, along the third direction, the thickness of the first adhesive layer is H3, and H1+H3≤H2, so that the first adhesive layer does not occupy the thickness of the positive active material layer, the energy density of the secondary battery is sufficiently improved, and the occurrence of lithium precipitation can be reduced.

[0030] In some embodiments, the first adhesive layer includes a substrate layer and an adhesive layer, and the adhesive layer is arranged on the surface of the substrate layer facing the positive active material layer. The material of the substrate layer includes at least one of polyethylene terephthalate or polyimide, so that the substrate layer has good insulation performance, mechanical strength and high temperature resistance, and can provide structural support for the adhesive layer, so that the entire first adhesive layer can maintain a stable shape inside the secondary battery. The material of the adhesive layer includes at least one of polyethylene, polypropylene, polyurethane, epoxy resin, styrene butadiene rubber, polyvinylidene fluoride or polyacrylic acid, and the adhesive layer has good initial adhesion and holding adhesion, and can be tightly combined with the positive active material layer.

[0031] In a second aspect, the present application further provides an electronic device comprising the secondary battery according to any one of the embodiments of the first aspect.

[0032] Additional aspects and advantages of the embodiments of the present application will be described, shown, or illustrated in part in the following description, or will be apparent from the embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0033] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are schematic and not intended to be limiting of the embodiments, and in which like reference numerals designate similar items in the figures, and wherein the drawings are not necessarily to scale.

[0034] FIG. 1 is a schematic structural diagram of a secondary battery according to some embodiments of the present application;

[0035] FIG. 2 is a schematic diagram of a winding structure of an electrode assembly according to some embodiments of the present application;

[0036] FIG. 3 is a schematic diagram of a laminated structure of an electrode assembly according to some embodiments of the present application;

[0037] FIG. 4 is a schematic diagram of a laminated structure of a positive electrode sheet and a negative electrode sheet according to some embodiments of the present application;

[0038] FIG. 5 is a schematic cross-sectional diagram of a first adhesive layer according to some embodiments of the present application;

[0039] FIG. 6 is a schematic diagram of the current density of a part of the negative active material layer at the first groove according to some embodiments of the present application;

[0040] FIG. 7 is a schematic diagram of a part of the negative active material layer (including the first groove) and the first adhesive layer according to some embodiments of the present application;

[0041] FIG. 8 is a schematic diagram of a part of the negative active material layer (including the first groove) and a part of the positive active material layer (including the first adhesive layer) according to some embodiments of the present application;

[0042] FIG. 9 is a schematic structural view of a partial negative active material layer (including a first groove) and a partial positive active material layer (including a first adhesive layer) according to some embodiments of the present application;

[0043] FIG. 10 is a schematic structural view of a first adhesive layer according to an embodiment of the present application (top view);

[0044] FIG. 11 is a schematic structural view of a partial negative active material layer (including a first groove) and a partial positive active material layer (including a first adhesive layer) according to some embodiments of the present application;

[0045] FIG. 12 is a schematic structural view of a negative electrode tab and a first adhesive layer according to some embodiments of the present application;

[0046] FIG. 13 is a schematic structural view of a positive electrode tab according to some embodiments of the present application.

[0047] Legend of reference signs: 1000, secondary battery; 100, electrode assembly; 10, positive electrode tab; 11, positive current collector; 111, first surface; 112, second surface; 12, positive active material layer; 121, edge region; 20, negative electrode tab; 20a, first end portion; 20b, second end portion; 21, negative current collector; 211, third surface; 212, fourth surface; 22, negative active material layer; 221, first groove; 2211, third edge; 2212, fourth edge; 222, edge; 30, separator; 40, negative tab; 50, first adhesive layer; 50a, base material layer; 50b, adhesive layer; 51, first portion; 511, first edge; 512, second edge; 52, second portion; 523, first through hole; 521, first region; 522, second region; 53, third portion; 531, third region; 532, fourth region; 533, second through hole; 60, second adhesive layer; 200, housing; X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0048] In order to make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application.

[0049] Reference herein to “an embodiment” in the embodiments of the present application means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive or alternative embodiments to other embodiments.

[0050] 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 two or more, unless otherwise explicitly specified.

[0051] In the description of the embodiments of the present application, the term "and / or" is only used to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects have an "or" relationship.

[0052] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict between them.

[0053] In a first aspect, the present application provides a secondary battery 1000, please refer to FIG. 1, the secondary battery 1000 includes an electrode assembly 100, a shell 200 and an electrolyte (not marked in the figure), the shell 200 can accommodate the electrode assembly 100 and the electrolyte, the electrolyte is soaked in the electrode assembly 100 in the shell 200.

[0054] For the above-mentioned electrode assembly 100, please refer to FIG. 2 and FIG. 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 FIG. 2 shows the winding structure of the electrode assembly 100, for example, stacked along the thickness direction of the positive electrode sheet 10 and / or the negative electrode sheet 20 and wound along the length direction thereof, to form a wound electrode assembly 100. In some other embodiments, the electrode assembly 100 can also adopt a laminated structure, wherein FIG. 3 shows the laminated structure of the electrode assembly 100, a plurality of positive electrode sheets 10 and a plurality of negative electrode sheets 20 are alternately stacked along the third direction Z (the thickness direction of the positive electrode sheet 10 and / or the negative electrode sheet 20), and the separator 30 is arranged between adjacent positive electrode sheet 10 and negative electrode sheet 20.

[0055] It should be noted that in the embodiments 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, the first direction X can also be the width direction of the positive electrode sheet 10 and / or the negative electrode sheet 20, and the second direction Y can also be the length direction of the positive electrode sheet 10 and / or the negative electrode sheet 20.

[0056] Referring to FIG. 4, the positive electrode tab 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode current collector 11 serves as an electrically conductive base material of the positive electrode tab 10 and can be a whole flat aluminum foil. The aluminum foil has high electrical conductivity and small electrical resistance, which can improve the charge-discharge rate of the secondary battery 1000. In addition, the aluminum foil has certain strength and ductility, and is not prone to breakage or deformation in production processes such as winding or stacking, so as to ensure the structural integrity of the positive electrode tab 10. At the same time, the positive electrode of the secondary battery 1000 is at a high potential during the charge-discharge process, and the aluminum foil is relatively stable at this potential and is not prone to chemical reaction, thereby improving the charge-discharge stability of the secondary battery 1000. In other embodiments, the positive electrode current collector 11 can also be a titanium foil, a nickel foil, or a stainless steel foil, etc.

[0057] The positive electrode active material layer 12 can be arranged on at least one surface of the positive electrode current collector 11 in the thickness direction of the positive electrode current collector 11, for example, along the third direction Z. The positive electrode current collector 11 includes oppositely arranged first and second surfaces 111 and 112, and the positive electrode active material layer 12 can 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 a binder, etc. After the above-mentioned material components are mixed and stirred uniformly, the positive electrode active material layer 12 is obtained by coating the first surface 111 and / or the second surface 112. The positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium manganese iron phosphate, etc.

[0058] Referring to FIG. 4, the negative electrode tab 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 serves as an electrically conductive base material of the negative electrode tab 20 and can be a whole flat copper foil. The copper foil has high electrical conductivity and small electrical resistance, which can improve the charge-discharge rate of the secondary battery 1000. In addition, the copper foil has certain strength and ductility, and is not prone to breakage or deformation in production processes such as winding or stacking, so as to ensure the structural integrity of the negative electrode tab 20. At the same time, the negative electrode of the secondary battery 1000 is at a low potential during the charge-discharge process, and the copper foil is relatively stable at this potential and is not prone to chemical reaction, thereby improving the charge-discharge stability of the secondary battery 1000. In other embodiments, the negative electrode current collector 21 can also be a titanium foil, a nickel foil, a stainless steel foil, or a silver foil, etc.

[0059] The negative active material layer 22 can be arranged on at least one surface of the negative current collector 21 in the thickness direction, for example, in the third direction Z. The negative current collector 21 includes a third surface 211 and a fourth surface 212 arranged oppositely, and the negative active material layer 22 can be arranged on the third surface 211 and / or the fourth surface 212. The negative active material layer 22 includes a negative active material, a conductive agent, and a binder, and the like. After mixing and stirring, the materials are uniformly coated on the third surface 211 and / or the fourth surface 212 to obtain the negative active material layer 22. The negative active material includes one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxide compounds, silicon alloys, and the like.

[0060] The secondary battery 1000 further includes a negative tab 40. Referring to FIG. 4, the negative tab 40 is connected to the negative tab 20 described above. For example, a first groove 221 is arranged on the negative active material layer 22 described above, so that the negative current collector 21 is exposed from the first groove 221. A portion of the negative tab 40 is arranged in the first groove 221 and connected to the negative current collector 21. The connection mode includes, but is not limited to, welding or conductive adhesive bonding, and the like. Another portion of the negative tab 40 extends out of the negative active material layer 22 in the first direction X.

[0061] During charging, an external power source delivers current to the electrode assembly 100 through the tab, causing lithium ions to be released from the positive tab 10 and inserted into the negative tab 20. The present inventors have found that because the first groove 221 is arranged on the negative active material layer 22 described above, the amount of the negative active material layer 22 is reduced. In the portion of the positive active material layer 12 facing the first groove 221, the released lithium ions are difficult to insert into the negative active material layer 22, which can easily lead to lithium precipitation. Lithium precipitation can form lithium metal dendrites, which can pierce the separator, causing positive and negative short circuits, triggering safety problems, and also reducing the capacity and cycle life of the secondary battery 1000.

[0062] To reduce the above problems, in an embodiment of the present application, referring to FIG. 4, the secondary battery 1000 further includes a first adhesive layer 50 arranged on the surface of the positive active material layer 12 facing the negative tab 20. In the third direction Z, the first adhesive layer 50 covers the first groove 221, so that the portion of the positive active material layer 12 corresponding to the first groove 221 is covered by the first adhesive layer 50. This can reduce the release or inability to release lithium ions in this portion, so that the negative active material layer 22 has sufficient capacity to insert lithium ions, thereby reducing the risk of lithium precipitation.

[0063] In some other embodiments, the second adhesive layer 60 can be provided on the negative active material layer 22 and cover the first recess 221 when the negative tab 40 is welded to the negative current collector 21, so as to reduce the occurrence of short circuit caused by the welding burr piercing the separator 30. When the second adhesive layer 60 is provided, the length of the first adhesive layer 50 can be greater than that of the second adhesive layer 60, and the width of the first adhesive layer 50 can be greater than that of the second adhesive layer 60, so that the negative active material layer 22 has sufficient excess to embed the lithium ions released from the positive active material layer 12, thereby reducing the occurrence of lithium precipitation. For example, the projection of the second adhesive layer 60 in the third direction Z is located within the projection of the first adhesive layer 50.

[0064] For the material of the first adhesive layer 50, in some embodiments, referring to FIGS. 4 and 5, the first adhesive layer 50 includes a substrate layer 50a and an adhesive layer 50b provided on the surface of the substrate layer 50a facing the positive active material layer 12. The material of the substrate layer 50a includes at least one of polyethylene terephthalate or polyimide. The substrate layer 50a has good insulation performance, mechanical strength and high temperature resistance, and can provide structural support for the adhesive layer 50b, so that the entire first adhesive layer 50 can maintain a stable shape inside the secondary battery 1000. The material of the adhesive layer 50b includes at least one of polyethylene, polypropylene, polyurethane, epoxy resin, styrene butadiene rubber, polyvinylidene fluoride or polyacrylic acid. The adhesive layer 50b has good initial adhesion and holding adhesion, and can be tightly combined with the positive active material layer 12.

[0065] The inventors of the present application have found that the negative active material at the first recess 221 can form a solid electrolyte interface (SEI) film, further hindering the embedding of lithium ions and exacerbating the occurrence of lithium precipitation. The inventors have found through analysis that there is a problem of uneven current density at the first recess 221 of the negative active material layer 22. Referring to FIG. 6, FIG. 6 shows a schematic diagram of the current density of the negative active material layer 22 near the first recess 221, and the darker the color, the greater the current density. As can be seen from FIG. 6, the closer to the first recess 221, the greater the current density. When the current density of the negative active material layer 22 is large, a large amount of lithium ions reaches the surface of the negative active material layer 22 per unit time, which easily leads to the aggregation of lithium ions on the surface of the negative active material layer 22, thereby causing lithium precipitation. Moreover, high current density can cause local polarization of the negative active material layer 22 to increase (the potential in the local area deviates from the equilibrium potential), which can cause the negative potential to decrease, and when the negative potential is lower than the potential at which lithium ions are reduced to metallic lithium, lithium precipitation can occur.

[0066] The inventor of the present application sets the length of the first adhesive layer 50 according to the current density of the negative active material layer 22 at the first groove 221. In the embodiments of the present application, referring to FIG. 7, the length of the first adhesive layer 50 is L, the length of the first groove 221 is L1, and 1.2≤L / L1≤3 in the second direction Y, so that the part with a larger current density is isolated by the first adhesive layer 50, the lithium ions are reduced to gather near the first groove 221, and the lithium precipitation is reduced. In addition, limiting 1.2≤L / L1≤3 can reduce the loss of energy density of the secondary battery 1000, and facilitate to achieve the balance between reducing lithium precipitation and reducing energy density loss.

[0067] Meanwhile, the inventor of the present application accidentally found that by limiting 1.2≤L / L1≤3, the local polarization of the negative active material layer 22 is reduced, the electrolyte decomposition is reduced, the generation of the solid electrolyte interface (SEI) film is reduced, and the lithium precipitation is further reduced. In addition, the heat concentration at the first groove 221 is alleviated, the side reaction is reduced, and the charge and discharge performance of the secondary battery 1000 is improved. Optionally, 8mm≤L1≤20mm can reduce lithium precipitation.

[0068] In other embodiments, 2≤L / L1≤2.6 can be selected to further reduce lithium precipitation and the impact of the first adhesive layer 50 on energy density.

[0069] As for the width of the first adhesive layer 50, referring to FIGS. 6 and 7, the current density is larger near the first groove 221 in the width direction (the first direction X) of the first groove 221 and away from the edge 222, but the current density is relatively smaller on both sides in the length direction (the second direction Y) of the first groove 221. In the embodiments of the present application, the width of the first adhesive layer 50 is W, the width of the first groove 221 is W1, and 1.06≤W / W1≤2, preferably 1.2≤W / W1≤1.5, so that lithium precipitation is reduced while the loss of energy density is reduced. For example, 16mm≤W≤30mmm, and preferably 18mm≤W≤22.5mmm.

[0070] In some embodiments, referring to FIG. 8, along the second direction Y, the first adhesive layer 50 includes a first portion 51 and a second portion 52 arranged in sequence, and the second portion 52 is connected with the first portion 51 and arranged integrally. Along the third direction Z, the first portion 51 overlaps the first groove 221, that is, the length of the first portion 51 along the second direction Y can be L1. For example, along the second direction Y, the first portion 51 includes a first edge 511 and a second edge 512 arranged oppositely, and the first groove 221 includes a third edge 2211 and a fourth edge 2212 arranged oppositely. The third edge 2211 is consistent with the extension direction of the first edge 511, and the fourth edge 2212 is consistent with the extension direction of the second edge 512. Along the third direction Z, the third edge 2211 overlaps the first edge 511, and the fourth edge 2212 overlaps the second edge 512. Optionally, the third edge 2211 and the third edge 2212 both extend along the first direction X. It can be understood that the first adhesive layer 50 is an integral component, the first portion 51 and the second portion 52 are arranged integrally, and the first edge 511 and the second edge 512 are virtual edges for dividing the first adhesive layer 50.

[0071] Along the second direction Y, the length of the second portion 52 is L2, and 0.1≤L2 / L1≤1, which can reduce the lithium precipitation on one side of the length direction (the second direction Y) of the first groove 221 and reduce the loss of the energy density of the secondary battery 1000.

[0072] Among them, along the second direction Y, the length L2 of the second portion 52 is selected as 1mm≤L2≤10mm, which can be selected as any value between 1mm and 10mm, for example, L2 is selected from 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm, etc. In some other embodiments, preferably, 0.5≤L2 / L1≤0.8.

[0073] The present inventors have found that the current density of the negative active material layer 22 near the first groove 221 is relatively large, and the risk of lithium precipitation is relatively high. However, near the first groove 221, part of the negative active material layer 22 can still undergo an electrochemical reaction and provide capacity for the secondary battery 1000. Under the premise of not precipitating lithium under the same conditions, compared with the part with a smaller current density, the part with a larger current density can receive less lithium ions, but not no lithium ions. Both the part with a larger current density and the part with a smaller current density can still provide a certain capacity. The present inventors have found that the part of the positive active material layer 12 exposed by the through hole in the second part 52 can undergo a lithium ion deintercalation reaction with the part of the negative active material layer 22 that can provide capacity, thereby improving the utilization of the positive active material layer 12 and the negative active material layer 22, and further improving the energy density of the secondary battery 1000.

[0074] For the area ratio of the first through hole 523 on the second part 52, the present inventors have found that if the area ratio of the first through hole 523 on the second part 52 is too large, the positive active material layer 12 can release more lithium ions, which can easily lead to insufficient amount of the negative active material layer 22, and further cause lithium precipitation. If the area ratio of the first through hole 523 on the second part 52 is too small, the part of the negative active material layer 22 that can provide capacity cannot fully provide capacity, resulting in a loss of energy density of the secondary battery 1000.

[0075] In the embodiments of the present application, the area of the second part 52 is S1, the sum of the areas of all the first through holes 523 on the second part 52 is S2, and 40%≤S2 / S1≤60% along the third direction Z. This can reduce the risk of lithium precipitation while improving the utilization of the negative active material layer 22 and the positive active material layer 12, and further improving the energy density of the secondary battery 1000.

[0076] For measuring the area ratio of the first through hole 523 on the second part 52, an image analysis method can be used. First, the second part 52 is separated on the first adhesive layer 50, and then the image of the first adhesive layer 50 is scanned or taken and imported into an image analysis software such as Adobe Photoshop. The contrast and brightness of the image are adjusted to make the boundary of the second part 52 and the first through hole 523 clearer. The threshold adjustment tool is used to convert the image into a binary image, i.e., the adhesive part is white and the through hole part is black. In the image analysis software, the measurement tool can be used to measure the total area of the second part 52 and the total area of the first through hole 523.

[0077] The inventor of the present application found that the closer to the first groove 221, the greater the current density, and the distribution density gradient of the first through holes 523 in the first adhesive layer 50 can be set according to the size of the current density. For example, referring to FIGS. 9 and 10, the second part 52 includes a first region 521 and a second region 522, and the first region 521 is located between the first part 51 and the second region 522 along the second direction Y. When viewed along the third direction Z, the area of the first region 521 is S 11 , and the sum of the areas of all the first through holes 523 in the first region 521 is S 21 . When viewed along the third direction Z, the area of the second region 522 is S 12 , and the sum of the areas of all the first through holes 523 in the second region 522 is S 22 , S 21 / S 11 <S 22 / S 12 .

[0078] The negative electrode active material layer 22 corresponding to the first region 521 has a larger current density, a higher risk of lithium precipitation, and less negative electrode active material capable of exerting capacity, and by setting the hole density of the first region 521 to be smaller, the amount of lithium precipitation of the first region 521 can be reduced, and the negative electrode active material layer 22 is less likely to precipitate lithium.

[0079] The negative electrode active material layer 22 corresponding to the second region 522 has a smaller current density, a lower risk of lithium precipitation, and more negative electrode active material capable of exerting capacity, and by setting the hole density of the second region 522 to be larger, the amount of lithium precipitation of the second region 522 can be increased, and more negative electrode active material can participate in the electrochemical reaction, thereby improving the energy density of the secondary battery 1000. By reasonably setting the distribution of the first through holes 523 in the second part 52, the energy density of the secondary battery 1000 can be improved while reducing lithium precipitation.

[0080] In some other embodiments, the number of first through holes 523 in the first region 521 is N1, and the number of first through holes 523 in the second region 522 is N2, and N1

[0081] For the radius of the first through hole 523, the present inventor has found that if the radius of the first through hole 523 is too large, more lithium ions per unit area of the positive active material layer 12 are likely to be released, which can easily lead to insufficient area of the negative active material layer 22, thereby causing lithium precipitation. If the radius of the first through hole 523 is too small, fewer lithium ions per unit area are released, which makes it difficult for the part of the negative active material layer 22 that can generate capacity to fully generate capacity, resulting in a loss of energy density of the secondary battery 1000. In the embodiments of the present application, the radius of the first through hole 523 is R1, and 0.1mm≤R1≤1mm, which can reduce the risk of lithium precipitation while improving the utilization rate of the negative active material layer 22, thereby improving the energy density of the secondary battery 1000. The radius of the first through hole 523 can be the radius of the first through hole 523 itself or the radius of the fitting circle in which the first through hole 523 is located.

[0082] In some embodiments, referring to FIG. 8, the first adhesive layer 50 further includes a third portion 53, which is sequentially arranged along the second direction Y with the first portion 51 and the second portion 52, and is connected with and integrally arranged with the first portion 51. The length of the third portion 53 along the second direction Y is L3, which can be selected as 0.1≤L3 / L1≤1, which can reduce lithium precipitation on the other side of the first groove 221 in the length direction (second direction Y) and reduce the loss of energy density of the secondary battery 1000.

[0083] In some embodiments, referring to FIG. 8, the first adhesive layer 50 further includes a third portion 53, which is sequentially arranged along the second direction Y with the first portion 51 and the second portion 52, and is connected with and integrally arranged with the first portion 51. The length of the third portion 53 along the second direction Y is L3, which can be selected as 0.1≤L3 / L1≤1, which can reduce lithium precipitation on the other side of the first groove 221 in the length direction (second direction Y) and reduce the loss of energy density of the secondary battery 1000.

[0084] Referring to FIGS. 9 and 10, the third portion 53 is provided with a second through hole 533 along the third direction Z, and the second through hole 533 exposes part of the positive active material layer 12. The part of the positive active material layer 12 exposed in this way can also react with the part of the negative active material layer 22 that can generate capacity to release and insert lithium ions, thereby further improving the utilization rate of the negative active material layer 22 and the energy density of the secondary battery 1000.

[0085] For the area ratio of the second through hole 533 on the third portion 53, in the embodiments of the present application, the area of the third portion 53 along the third direction Z is S3, and the sum of the areas of all the second through holes 533 on the third portion 53 is S4, and 40%≤S4 / S3≤60%, which can reduce the risk of lithium precipitation while improving the utilization rate of the negative active material layer 22, thereby improving the energy density of the secondary battery 1000.

[0086] In some embodiments, referring to FIGS. 9 and 10, the third portion 53 includes a third region 531 and a fourth region 532, and the fourth region 532 is located between the first portion 51 and the third region 531 along the second direction Y. The area of the third region 531 viewed along the third direction Z is S 31 , and the sum of the areas of all the second through holes 533 in the third region 531 is S 41 . The area of the fourth region 532 viewed along the third direction Z is S 32 , and the sum of the areas of all the second through holes 533 in the fourth region 532 is S 42 , S 41 / S 31 >S 42 / S 32 .

[0087] The fourth region 532 corresponds to the negative electrode active material layer 22, and has a relatively large current density, a relatively high risk of lithium precipitation, and a relatively small amount of negative electrode active material capable of exerting capacity. By setting a smaller hole density in the first region 521, the amount of lithium extraction in the fourth region 532 can be reduced, and the risk of lithium precipitation in the negative electrode active material layer 22 can be reduced.

[0088] The third region 531 corresponds to the negative electrode active material layer 22, and has a relatively small current density, a relatively low risk of lithium precipitation, and a relatively large amount of negative electrode active material capable of exerting capacity. By setting a larger hole density in the third region 531, the amount of lithium extraction in the third region 531 can be increased, and more negative electrode active material can be involved in electrochemical reactions, thereby improving the energy density of the secondary battery 1000. By reasonably setting the distribution of the first through holes 523 in the second portion 52, the energy density of the secondary battery 1000 can be improved while reducing the risk of lithium precipitation.

[0089] In some embodiments, the number of second through holes 533 in the fourth region 532 is N4, the number of second through holes 533 in the third region 531 is N3, and N4

[0090] For the radius of the second through hole 533, similar to the first through hole 523, in the embodiments of the present application, the radius of the second through hole 533 is R2, 0.1mm≤R2≤1mm, which can reduce the risk of lithium precipitation while improving the utilization rate of the negative active material layer 22, thereby improving the energy density of the secondary battery 1000.

[0091] For the formation of the first through hole 523 and the second through hole 533, it can be formed on the first adhesive layer 50 through mechanical punching, laser punching and the like. For example, by using the nail roller punching method in mechanical punching, the radius of each first through hole 523 and each second through hole 533 can be made to approach the same, which can facilitate the above-mentioned setting of the hole density according to the current density.

[0092] The present inventors have found that at the position close to the edge 222 of the negative active material layer 22, the current density is large, as shown in FIG. 6, the risk of lithium precipitation is large at the edge 222, and the heat generation is high, which is prone to cause side reactions. To reduce this problem, in the embodiments of the present application, please refer to FIG. 11, on one side of the extension direction (first direction X) of the negative tab 40, the positive active material layer 12 has an edge region 121, after the positive tab 10 and the negative tab 20 are stacked, the edge region 121 coincides or approaches to coincide with the edge 222 of the negative active material layer 22, or the edge 222 exceeds part along the first direction X. The first adhesive layer 50 covers part of the edge region 121, which can reduce the accumulation of lithium ions at the edge 222 of the negative active material layer 22, reduce the occurrence of lithium precipitation, and reduce the occurrence of side reactions.

[0093] In some embodiments, along the second direction Y, the first adhesive layer 50 includes a third portion 53, a first portion 51 and a second portion 52 arranged in sequence, the third portion 53 is connected and arranged integrally with the first portion 51, and the second portion 52 is connected and arranged integrally with the first portion 51. Please refer to FIG. 12, along the second direction Y, the negative active material layer 22 includes a first end portion 20a and a second end portion 20b arranged oppositely, the second portion 52 is located between the first recess 221 and the first end portion 20a, and the third portion 53 is located between the first recess 221 and the second end portion 20b. Along the second direction Y, the length of the first recess 221 to the first end portion 20a is L4, and the length of the first recess 221 to the second end portion 20b is L5.

[0094] The present inventors have found that for the negative tab 20, the larger the L4 is, the larger the amount of negative active material layer 22 participating in the electrochemical reaction is, and the larger the current density between the first recess 221 and the first end portion 20a is. According to the length L4 of the first recess 221 to the first end portion 20a and the length L5 of the first recess 221 to the second end portion 20b, the present inventors set the length difference between the second portion 52 and the third portion 53.

[0095] For example, along the second direction Y, the length of the second portion 52 is L2, and the length of the third portion 53 is L3. When L4 > L5, it indicates that the current density between the first groove 221 and the first end 20a is larger, and L2 > L3 can be set. When L4 < L5, it indicates that the current density between the first groove 221 and the second end 20b is larger, and L2 < L3 can be set. By reasonably setting the lengths of the second portion 52 and the third portion 53, the energy density of the secondary battery 1000 can be improved while reducing the risk of lithium precipitation. When L4 = L5, L3 and L2 can be set to be approximately equal, for example, |L3-L2|≤0.5mm.

[0096] In some embodiments, referring to FIG. 13, along the third direction Z, the thickness of the positive electrode active material layer 12 covered by the first adhesive layer 50 is H1, and the thickness of the positive electrode active material layer 12 not covered by the first adhesive layer 50 is H2, H1 < H2. Reducing the amount of the positive electrode active material layer 12 covered by the first adhesive layer 50 can reduce the impact of the first adhesive layer 50 on the energy density of the secondary battery 1000.

[0097] When the second portion 52 is provided with the first through hole 523 and / or the third portion 53 is provided with the second through hole 533, by reducing the amount of the positive electrode active material layer 12 covered, the lithium ion can be reduced, and the lithium precipitation can be reduced.

[0098] When the second portion 52 is not provided with the first through hole 523 and / or the third portion 53 is not provided with the second through hole 533, the positive electrode active material layer 12 covered is difficult or even impossible to participate in the electrochemical reaction, and the first adhesive layer 50 can be set not to exceed the positive electrode active material layer 12 not covered, for example, along the third direction Z, the thickness of the first adhesive layer 50 is H3, H1+H3≤H2, so that the first adhesive layer 50 does not occupy the thickness of the positive electrode active material layer 12, fully improving the energy density of the secondary battery 1000, and reducing the occurrence of lithium precipitation.

[0099] In a second aspect, the present application also provides an electronic device comprising the secondary battery 1000 according to any one of the embodiments of the first aspect. The electronic device of the embodiments of the present application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device includes but is not limited to a Bluetooth headset, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric car, a ship, a spacecraft, etc. Among them, the electric toy can include a fixed or mobile electric toy, for example, a game console, an electric car toy, an electric ship toy, and an electric plane toy, etc., and the spacecraft can include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0100] Experiment 1: Lithium precipitation test of lithium ion battery

[0101] Example A1:

[0102] Preparation of the positive electrode sheet

[0103] The positive electrode active material lithium iron phosphate, the positive electrode conductive agent acetylene black, and the positive electrode binder polyvinylidene fluoride (PVDF, weight average molecular weight 5 x 10 5 ) were mixed in a mass ratio of 94:3:3, N-methyl pyrrolidone (NMP) was added as a solvent, a positive electrode slurry with a solid content of 75wt% was prepared, and the positive electrode slurry was stirred uniformly in a vacuum stirrer. An aluminum foil with a thickness of 8pm and a length of 1000mm was selected as the positive electrode current collector, the positive electrode slurry was uniformly coated on one surface of the positive electrode current collector aluminum foil, and the positive electrode active material layer was dried at 110°C. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with positive electrode active material on both sides.

[0104] Preparation of the negative electrode sheet

[0105] The negative electrode active material graphite powder, silicon powder, conductive agent conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) were mixed in a weight ratio of 87.5:10:1:1.5, deionized water was then added as a solvent, a negative electrode slurry with a solid content of 50wt% was prepared, and the negative electrode slurry was stirred uniformly. A copper foil with a thickness of 5pm and a length of 1050mm was selected as the negative electrode current collector, the negative electrode slurry was uniformly coated on one surface of the negative electrode current collector copper foil, and the copper foil was reserved as a blank foil area without negative electrode slurry, and the negative electrode active material layer was dried at 90°C. The above steps were repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with negative electrode active material on both sides.

[0106] Preparation of the separator film

[0107] A polyethylene (PE) porous film with a thickness of 7pm was used as the separator film.

[0108] Preparation of the electrolyte

[0109] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solvent, lithium salt lithium hexafluorophosphate was then added to the organic solvent and dissolved and mixed uniformly to obtain an electrolyte with a lithium salt concentration of 1.15mol / L.

[0110] Preparation of the lithium ion battery

[0111] The first groove of 10 mm (L1) x 15 mm (W1) is cleaned out on the negative active material layer by laser cleaning, and a nickel sheet is selected as the negative tab, and the negative tab is welded and connected with the negative tab in the first groove. After the positive tab is welded with the positive tab, polyethylene terephthalate is selected as the base material layer, and epoxy resin is used as the adhesive layer to prepare a first adhesive layer of 12 mm (L) x 20 mm (W), and the first adhesive layer is arranged on the positive active material layer. The separator, the positive tab, the separator, and the negative tab are stacked in order to obtain an electrode assembly. The first adhesive layer corresponds to the first groove, and the first adhesive layer exceeds 1 mm on one side of the length direction of the positive tab (second part L2) and exceeds 1 mm on the other side (third part L3). The electrode assembly is placed in the shell, and the positive and negative tabs are led out, packaged and injected with electrolyte.

[0112] Lithium precipitation test

[0113] The secondary battery is placed in an environment with a test temperature of 25°C for 30 min, and is charged to 4.5V in the following charging steps:

[0114] (1) 5C constant current charging to 4.23V;

[0115] (2) 4C constant current charging to 4.3V;

[0116] (3) 3C constant current charging to 4.5V;

[0117] (4) 2C constant current charging to 4.5V, constant voltage charging to 0.05C;

[0118] After standing for 10 min, discharge according to the following steps:

[0119] 0.2C direct current discharge to 3V.

[0120] The above charging and discharging process is one cycle, and after 100 cycles, when the battery is in a full charge state (the maximum voltage of the battery is designed to be 4.5V), the secondary battery is disassembled to obtain the negative tab, and if the lithium deposition area of the negative active material layer near the negative tab is greater than or equal to 2 mm 2 , it is determined to be lithium precipitation. Each group of tests 20 batteries, and the number of lithium precipitation is X, and the lithium precipitation rate is X / 20.

[0121] Different from example A1, the related parameters in examples A2 to A38 and comparative examples A1 to A5 are shown in table 1.

[0122] Table 1

[0123] According to Table 1, in the comparative example A3, the first adhesive layer is too long, and in the case where the length L1 of the first groove is only 10 mm, the range of the positive active material layer covered is large, which leads to a loss of energy density compared with the example A8. As can be seen from the examples A1-A8, examples 20-38 and comparative examples A1-A5, when 1.2≤L / L1≤3 is adopted, the risk of lithium precipitation can be effectively reduced. By limiting 1.2≤L / L1≤3, the part with large current density can be isolated by the first adhesive layer, the lithium ions are reduced to gather near the first groove, and thus the lithium precipitation is reduced. At the same time, the local polarization of the negative active material layer is reduced, the electrolyte decomposition is reduced, and thus the generation of the solid electrolyte interface (SEI) film is reduced, which can further reduce the lithium precipitation. Preferably, 2≤L / L1≤2.6 can further reduce the lithium precipitation and the impact on the energy density. As for the length of the first part and the length of the second part, 0.1≤L2 / L1≤1 and 0.1≤L3 / L1≤10 can be selected. As can be seen from the examples A4-A6, preferably, 0.5≤L2 / L1≤0.8 and 0.5≤L3 / L1≤0.8 can reduce the risk of lithium precipitation. Compared with the comparative example A4, the lithium precipitation rate in the example A20 is lower, compared with the comparative example A5, the lithium precipitation rate in the example A27 is lower, compared with the comparative example A6, the lithium precipitation rate in the example A33 is lower. Moreover, in the examples A20-A38, within the range of 1.2≤L / L1≤3, the variation rule of the small lithium precipitation rate is met.

[0124] As can be seen from the examples A9-A19, the lithium precipitation risk in the examples A11-A18 is lower than that in the examples A9, A10 and A19. If the width of the first adhesive layer is too small, it can be difficult to effectively cover the part with large current density, and if the width of the first adhesive layer is too large, it can hinder the diffusion and transmission of lithium ions in the positive electrode, interfere with the transmission path of lithium ions, and not only exist the risk of lithium precipitation, but also affect the energy density. Therefore, in the examples of the present application, 1.06≤W / W1≤2 is selected. As can be seen from the examples A13-A15, preferably, 1.2≤W / W1≤1.5 can further reduce the risk of lithium precipitation and the impact on the energy density.

[0125] Different from the example A8, the related parameters in the examples B1-B7 are shown in Table 2. The size of the first adhesive layer is 30 mm x 20 mm, the length of the first part L1 is 10 mm, and the length of the second part L2 is 10 mm. The first through hole with a radius of 0.8 mm is formed on the second part by means of pin roller punching, and the second through hole with a radius of 0.8 mm is formed on the third part.

[0126] Table 2

[0127] According to Table 2 above, in combination with Examples B1 to B7, when 40%≤S4 / S3≤60% is selected, the lithium precipitation rate can be further reduced. By providing the first through hole and the second through hole, part of the positive electrode active material layer is exposed. The part of the positive electrode active material layer exposed can undergo lithium ion deintercalation reaction with the part of the negative electrode active material layer capable of exhibiting capacity. The utilization rate of the positive electrode active material layer and the negative electrode active material layer can be improved, and thus the energy density of the secondary battery can be improved. Further, 40%≤S2 / S1≤60% is preferred, which can further improve the energy density.

[0128] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; under the idea of the present application, the technical features in the above examples or different examples can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above, which are not provided in details for simplicity; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate 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, and a negative electrode sheet which are stacked or stacked and wound, the negative electrode sheet comprising a negative electrode active material layer facing the positive electrode sheet, the positive electrode sheet comprising a positive electrode active material layer facing the negative electrode active material layer, the secondary battery further comprising a negative electrode tab, the negative electrode active material layer being provided with a first recess, a portion of the negative electrode tab being disposed in the first recess, another portion of the negative electrode tab protruding from the negative electrode sheet in a first direction, characterized in that, The secondary battery further comprises a first adhesive layer; The first adhesive layer is arranged on a surface of the positive active material layer facing the negative electrode tab, and covers the first groove along a third direction; Along a second direction, a length of the first adhesive layer is L, and a length of the first groove is L1, and 1.2≤L / L1≤3; The third direction is a thickness direction of the positive electrode tab, 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 by 2≤L / L1≤2.

6.

3. The secondary battery according to claim 1, characterized by Along the first direction, a width of the first adhesive layer is W, and a width of the first groove is W1, and 1.06≤W / W1≤2.

4. The secondary battery according to claim 3, characterized by 1.2≤W / W1≤1.

5.

5. The secondary battery according to claim 4, characterized by 16mm≤W≤30mmm.

6. The secondary battery according to claim 5, characterized by 18mm≤W≤22.5mmm.

7. The secondary battery according to claim 1, characterized by 8mm≤L1≤20mm.

8. The secondary battery according to any one of claims 1 to 7, characterized by, Along the second direction, the first adhesive layer comprises a first part and a second part, and the second part is connected with and arranged integrally with the first part; Along the second direction, the first part comprises a first edge and a second edge arranged oppositely, and the first groove comprises a third edge and a fourth edge arranged oppositely; the third edge is consistent with an extension direction of the first edge, and the fourth edge is consistent with an extension direction of the second edge; Along the third direction, the third edge overlaps with the first edge, and the fourth edge overlaps with the second edge; Along the second direction, a length of the second part is L2, and 0.1≤L2 / L1≤1.

9. The secondary battery according to claim 8, characterized by The third edge and the fourth edge extend along the first direction.

10. The secondary battery according to claim 8 or 9, characterized by 1mm≤L2≤10mm.

11. The secondary battery according to claim 8 or 9, characterized by 0.5≤L2 / L1≤0.

8.

12. The secondary battery according to claim 11, characterized by 5mm≤L2≤8mm.

13. The secondary battery according to any one of claims 8 to 12, characterized by Along the third direction, the second part is provided with a first through hole.

14. The secondary battery according to claim 13, characterized by When viewed along the third direction, an area of the second part is S1, and a sum of areas of all the first through holes is S2, and 40%≤S2 / S1≤60%.

15. The secondary battery according to claim 13 or 14, characterized by A radius of the first through hole is R1, and 0.1mm≤R1≤1mm.

16. The secondary battery according to any one of claims 13 to 15, characterized by The second part comprises a first region and a second region, and along the second direction, the first region is located between the first part and the second region; S is the area of the first region as viewed in the third direction 11 S is the sum of the areas of all the first through holes of the first region as viewed in the third direction 21 ; When viewed along the third direction, the area of ​​the second region is S. 12 The sum of the areas of all the first through holes in the second region is S. 22 S 21 / S 11 <S 22 / S 12 .

17. The secondary battery according to claim 16, characterized by Along the second direction, a width of the first region is equal to a width of the second region.

18. The secondary battery according to claim 16, characterized by In the first region, a number of the first through holes is N1, and in the second region, a number of the first through holes is N2, and N1 19. The secondary battery according to any one of claims 16 to 18, characterized by, In the first region, a distance between adjacent two first through holes is D1, and in the second region, a distance between adjacent two first through holes is D2, and D1>D2.

20. The secondary battery according to any one of claims 13 to 19, characterized by The first adhesive layer further comprises a third part, and along the second direction, the third part, the first part, and the second part are arranged in sequence, and the third part is connected with and arranged integrally with the first part; Along the second direction, a length of the third part is L3, and 0.5≤L3 / L1≤0.

8.

21. The secondary battery according to claim 20, characterized by 5mm≤L3≤8mm.

22. The secondary battery according to claim 20 or 21, characterized by Along the third direction, the third part is provided with a second through hole.

23. The secondary battery according to claim 22, characterized by The third portion includes a third region and a fourth region, and the fourth region is located between the first portion and the third region along the second direction; In a view along the third direction, the area of the third region is S 31 , the total of the third regions The sum of the areas of the second through holes is S 41 ; S 32 , the sum of the areas of all the second through holes in the fourth region is S 42 , S 41 / S 31 >S 42 / S 32 .

24. The secondary battery according to any one of claims 1 to 7, characterized by, The first adhesive layer includes a third portion, a first portion, and a second portion along the second direction, the third portion is connected with the first portion and arranged integrally, and the second portion is connected with the first portion and arranged integrally; The negative active material layer includes oppositely arranged first and second end portions along the second direction, the second portion is located between the first groove and the first end portion, and the third portion is located between the first groove and the second end portion; The length of the first groove to the first end portion is L4, and the length of the first groove to the second end portion is L5 along the second direction; The length of the second portion is L2, and the length of the third portion is L3 along the second direction; L4>L5, L2>L3, or L4 25. The secondary battery according to any one of claims 1 to 24, characterized by The thickness of the positive active material layer covered by the first adhesive layer is H1 along the third direction, and the thickness of the positive active material layer not covered by the first adhesive layer is H2, and H1 26. The secondary battery according to claim 25, characterized by The thickness of the first adhesive layer is H3 along the third direction, and H1+H3≤H2.

27. The secondary battery according to any one of claims 1 to 26, The first adhesive layer includes a substrate layer and an adhesive layer, and the adhesive layer is arranged on the surface of the substrate layer facing the positive active material layer; The material of the substrate layer includes at least one of polyethylene terephthalate or polyimide; The material of the adhesive layer includes at least one of polyethylene, polypropylene, polyurethane, epoxy resin, styrene butadiene rubber, polyvinylidene fluoride, or polyacrylic acid.

28. An electronic device, comprising: The secondary battery according to any one of claims 1 to 27.

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