Secondary battery and electronic device

Abstract

The invention relates to a secondary battery and electronic equipment, the secondary battery comprises a negative plate, a positive plate and a diaphragm, the positive plate comprises a positive current collector, a first positive active layer and a positive tab, and the first positive active layer is arranged on one surface of the positive current collector along the thickness direction of the positive current collector. The first positive electrode active layer is provided with a first groove, and the positive electrode tab is arranged in the first groove and electrically connected with the positive electrode current collector. A first positive electrode insulating layer is arranged on the surface, facing the negative plate, of the first positive electrode active layer and covers the first groove, and a first negative electrode insulating layer is arranged on the surface, facing the first positive electrode active layer, of the negative plate and covers the first groove in the direction perpendicular to the surface of the first negative electrode insulating layer; the projection of the first negative electrode insulating layer on the first positive electrode active layer covers the first groove. A first hole is formed in one side of the first negative electrode insulating layer in the width direction of the first groove. According to the secondary battery and the electronic equipment provided by the invention, the lithium precipitation problem of the negative plate in the tab middle-arranged structure of the positive plate 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] As the power source of electronic devices, secondary batteries are the key to ensuring the normal use of electronic devices. At present, in order to achieve faster charging speed, secondary batteries often adopt a central-ear structure (welding the ear to the middle area of ​​the active material layer of the pole piece), and set a first protective glue on the surface of the active material layer to cover the welding burrs in the welding area to prevent the welding burrs from piercing the diaphragm and contacting the opposite pole piece with the opposite polarity and causing a short circuit. In order to improve the protection effect, the current technology also often sets a second protective glue on the surface of the active material layer of the opposite polarity pole piece to prevent the welding burrs from piercing the first protective glue and the diaphragm and contacting the active material layer of the opposite polarity pole piece and causing a short circuit.

[0003] However, for the structure of the positive electrode with the lug in the middle, during the charging process, the lithium ions in the positive electrode active material covered by the first protective glue will still bypass the first protective glue and move to the opposite negative electrode under the action of the electric potential. Since the second protective glue covers part of the negative electrode active material, the local position of the negative electrode cannot absorb excessive lithium ions, resulting in excessive lithium ion concentration in the local position of the negative electrode. Excessive lithium ions accumulate in the negative electrode active layer near the edge of the second protective glue, causing lithium precipitation problems. Therefore, it is necessary to improve the above problems. Summary of the invention

[0004] The purpose of the present application is to provide a secondary battery and an electronic device, aiming to improve the lithium plating problem of the negative electrode sheet in the structure of the middle-positioned tab of the positive electrode sheet.

[0005] According to the first aspect of the present application, a secondary battery is provided, comprising a negative electrode sheet, a positive electrode sheet and a separator, wherein a separator is provided between adjacent negative electrode sheets and positive electrode sheets, the positive electrode sheet comprises a positive electrode collector, a first positive electrode active layer and a positive electrode tab, and the first positive electrode active layer is provided on one surface of the positive electrode collector along the thickness direction of the positive electrode collector. The first positive electrode active layer is provided with a first groove, and the positive electrode tab is provided in the first groove and is electrically connected to the positive electrode collector. A first positive electrode insulating layer is provided on the surface of the first positive electrode active layer facing the negative electrode sheet, and the first positive electrode insulating layer covers the first groove, and a first negative electrode insulating layer is provided on the surface of the negative electrode sheet facing the first positive electrode active layer, and along a direction perpendicular to the surface of the first negative electrode insulating layer, the projection of the first negative electrode insulating layer on the first positive electrode active layer covers the first groove. A first hole is provided on one side of the first negative electrode insulating layer along the width direction of the first groove.

[0006] In the above technical solution, the positive electrode tab is arranged in the first groove opened in the first positive active layer to form a tab-centered structure of the positive electrode sheet, thereby achieving a faster charging speed. The first positive electrode insulation layer covering the first groove is arranged on the surface of the first positive active layer facing the negative electrode sheet to cover the positive electrode tab welding burr and the positive electrode current collector exposed in the first groove, thereby reducing the possibility of the positive electrode tab welding burr piercing the diaphragm and contacting the negative electrode sheet, and reducing the possibility of the positive electrode current collector exposed in the first groove contacting the negative electrode sheet. The first negative electrode insulation layer is arranged on the surface of the negative electrode sheet facing the first positive active layer to project and cover the first groove, so as to further reduce the possibility of the welding burr piercing the diaphragm and contacting the negative electrode sheet. By opening a first hole on one side of the first negative electrode insulation layer, the lithium ions on one side of the first negative electrode insulation layer can be absorbed by the negative electrode sheet through the first hole, thereby reducing the possibility of excessive lithium ions accumulating in the negative electrode sheet close to the first negative electrode insulation layer and causing lithium precipitation.

[0007] In some preferred embodiments, the first negative electrode insulating layer includes a first punching portion and a first main body portion. Along the width direction of the first groove, the first punching portion is connected to one side of the first main body portion, and the first punching portion is provided with a first hole. Along the direction perpendicular to the surface of the first negative electrode insulating layer, the projection of the first main body portion on the first positive electrode active layer covers the first groove. By limiting the projection of the first main body portion without the first hole on the first positive electrode active layer to cover the first groove, the first main body portion blocks the first groove, and then blocks the welding burr of the positive electrode tab, so as to reduce the possibility of the welding burr piercing the diaphragm and contacting the negative electrode sheet.

[0008] In some preferred embodiments, along the width direction of the first groove, the width of the first main body is 0.5mm to 6mm greater than the width of the first groove. By limiting the first main body to be not less than 0.5mm and not more than 6mm greater than the width of the first groove, the first negative electrode insulating layer can have sufficient bonding force to adhere to the negative electrode sheet, so that the first main body can cover the first groove while the first main body is not too wide, so as to improve the excessive reduction of the energy density of the secondary battery.

[0009] In some preferred embodiments, the first negative electrode insulating layer satisfies at least one of the following characteristics: (1) The ratio of the area of ​​the first perforated portion to the area of ​​the first main body is 0.01:1 to 0.5:1, so as to reduce the accumulation of excess lithium ions in the negative electrode sheet close to the first negative electrode insulating layer and cause lithium deposition, while the area of ​​the first perforated portion will not be too large, so as to improve the effect of the first perforated portion with a larger area on the adhesion of the first main body to the negative electrode sheet. (2) The minimum diameter of the circumscribed circle of the contour of the first hole is 0.2mm to 1.0mm, so that lithium ions can be better absorbed by the negative electrode sheet through the first hole. (3) The first perforated portion is provided with a plurality of first holes, and the spacing between two adjacent first holes is 0.2mm to 0.5mm, so that lithium ions can be evenly absorbed by the negative electrode sheet through the plurality of first holes, thereby better preventing local lithium deposition. (4) Along the width direction of the first groove, the distance between the first hole near the edge of the first perforated portion and the edge of the first perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the first perforated portion in the width direction of the first groove and better prevent local lithium deposition. (5) Along the length direction of the first groove, the distance between the first hole near the edge of the first perforated portion and the edge of the first perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the first perforated portion in the length direction of the first groove and better prevent local lithium deposition. (6) The shape of the first hole is at least one of a circle, an ellipse or a polygon.

[0010] In some preferred embodiments, the first negative electrode insulating layer includes a second perforated portion, and along the width direction of the first groove, the second perforated portion is connected to the other side of the first main body away from the first perforated portion, and the second perforated portion is provided with a second hole. By providing perforated portions on both sides of the first groove in the width direction, the possibility of lithium deposition on the other side of the first groove in the width direction of the first groove can be further reduced.

[0011] In some preferred embodiments, the first negative electrode insulating layer satisfies at least one of the following characteristics: (7) The ratio of the area of ​​the second perforated portion to the area of ​​the first main body is 0.01:1 to 0.5:1, so as to reduce the accumulation of excess lithium ions in the negative electrode sheet near the other side of the first negative electrode insulating layer to cause lithium deposition, while the area of ​​the second perforated portion will not be too large, so as to improve the effect of the second perforated portion with a larger area on the adhesion between the first main body and the negative electrode sheet. (8) The minimum diameter of the circumscribed circle of the contour of the second hole is 0.2mm to 1.0mm, so that the lithium ions can be better absorbed by the negative electrode sheet through the second hole. (9) The second perforated portion is provided with a plurality of second holes, and the spacing between two adjacent second holes is 0.2mm to 0.5mm, so that the lithium ions can be evenly absorbed by the negative electrode sheet through the plurality of second holes, so as to better prevent local lithium deposition. (10) Along the width direction of the first groove, the distance between the second hole near the edge of the second perforated portion and the edge of the second perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the second perforated portion in the width direction of the first groove and better prevent local lithium deposition. (11) Along the length direction of the first groove, the distance between the second hole near the edge of the second perforated portion and the edge of the second perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the second perforated portion in the length direction of the first groove and better prevent local lithium deposition. (12) The shape of the second hole is at least one of a circle, an ellipse or a polygon.

[0012] In some preferred embodiments, the first negative electrode insulating layer includes a third punching portion, and along the length direction of the first groove, the third punching portion is connected to the side of the first main body close to the bottom of the first groove, and the third punching portion is provided with a third hole. By connecting the third punching portion provided with the third hole to the side of the first main body close to the bottom of the first groove, the possibility of lithium deposition on the side of the first negative electrode insulating layer close to the bottom of the first groove is reduced.

[0013] In some preferred embodiments, the first negative electrode insulating layer satisfies at least one of the following characteristics: (13) The ratio of the area of ​​the third perforated portion to the area of ​​the first main body is 0.001:1 to 0.2:1, so as to reduce the lithium deposition on the side of the first negative electrode insulating layer close to the bottom of the first groove while the area of ​​the third perforated portion is not too large, so as to improve the effect of the third perforated portion with a larger area on the adhesion of the first main body to the negative electrode sheet. (14) The minimum diameter of the circumscribed circle of the contour of the third hole is 0.2mm to 1.0mm, so that lithium ions can be better absorbed by the negative electrode sheet through the third hole. (15) The third perforated portion is provided with a plurality of third holes, and the spacing between two adjacent third holes is 0.2mm to 0.5mm, so that lithium ions can be evenly absorbed by the negative electrode sheet through the plurality of third holes, so as to better prevent local lithium deposition. (16) Along the length direction of the first groove, the distance between the third hole close to the edge of the third perforated portion and the edge of the third perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the third perforated portion in the length direction of the first groove and better prevent local lithium deposition. (17) Along the width direction of the first groove, the distance between the third hole close to the edge of the third perforated portion and the edge of the third perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the third perforated portion in the width direction of the first groove and better prevent local lithium deposition. (18) The shape of the third hole is at least one of a circle, an ellipse or a polygon.

[0014] In some preferred embodiments, along the width direction of the first groove, the width of the first negative electrode insulating layer is smaller than the width of the first positive electrode insulating layer, so that the first positive electrode insulating layer with a larger width can block more positive electrode active materials, thereby reducing the amount of positive electrode active materials that can participate in the electrochemical reaction, thereby reducing the possibility of lithium plating in the negative electrode sheet.

[0015] In some preferred embodiments, the first positive electrode insulating layer includes a fourth punching portion and a second main body portion, and along the width direction of the first groove, the fourth punching portion is connected to one side of the second main body portion, and the fourth punching portion is provided with a fourth hole. In a direction perpendicular to the surface of the first positive electrode insulating layer, the fourth punching portion at least partially overlaps with the first positive electrode active layer. By connecting the fourth punching portion provided with the fourth hole on one side of the second main body portion, the positive electrode active material covered by the first positive electrode insulating layer can release lithium ions through the fourth hole, so as to reduce the possibility of lithium ions in the positive electrode active material covered by the first positive electrode insulating layer bypassing the first positive electrode insulating layer and moving to the opposite negative electrode sheet, thereby reducing the possibility of lithium precipitation due to excessive lithium ion concentration at a local position of the negative electrode sheet, and improving the utilization rate of the positive electrode active material of the positive electrode sheet, thereby improving the energy density.

[0016] In some preferred embodiments, the second main body covers the first groove in a direction perpendicular to the surface of the first positive electrode insulating layer, so that the second main body blocks the welding burrs of the positive electrode tab to reduce the possibility of the welding burrs piercing the diaphragm and contacting the negative electrode sheet. In the width direction of the first groove, the width of the second main body is 0.5 mm to 6 mm larger than the width of the first groove, so that the second main body is not too wide while the second main body blocks the first groove, so as to improve the excessive reduction of the energy density of the secondary battery.

[0017] In some preferred embodiments, the first positive electrode insulating layer satisfies at least one of the following characteristics: (19) The ratio of the area of ​​the fourth perforated portion to the area of ​​the second main body portion is 0.01:1 to 0.5:1, so as to reduce the possibility of lithium deposition due to excessive lithium ion concentration at the local position of the negative electrode sheet, while the area of ​​the fourth perforated portion will not be too large, so as to improve the energy density of the secondary battery caused by the large fourth perforated portion. (20) The minimum diameter of the circumscribed circle of the contour of the fourth hole is 0.2mm to 1.0mm, so that the positive electrode active material blocked by the first positive electrode insulating layer can better release lithium ions through the fourth hole. (21) The fourth perforated portion is provided with a plurality of fourth holes, and the spacing between two adjacent fourth holes is 0.2mm to 0.5mm, so that the positive electrode active material blocked by the first positive electrode insulating layer can evenly release lithium ions through the plurality of fourth holes, so as to better prevent local lithium deposition. (22) Along the width direction of the first groove, the distance between the fourth hole near the edge of the fourth perforated portion and the edge of the fourth perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer bypassing the edge of the fourth perforated portion in the width direction of the first groove and being released, so as to better prevent local lithium deposition. (23) Along the length direction of the first groove, the distance between the fourth hole near the edge of the fourth perforated portion and the edge of the fourth perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer bypassing the edge of the fourth perforated portion in the length direction of the first groove and being released, so as to better prevent local lithium deposition. (24) The shape of the fourth hole is at least one of a circle, an ellipse or a polygon.

[0018] In some preferred embodiments, the first positive electrode insulating layer includes a fifth punching portion, and along the width direction of the first groove, the fifth punching portion is connected to the side of the second main body away from the fourth punching portion, and the fifth punching portion is provided with a fifth hole. By connecting the fifth punching portion provided with the fifth hole to the other side of the second main body along the width direction of the first groove, the positive electrode active material covered by the first positive electrode insulating layer can release lithium ions through the fifth hole, so as to reduce the possibility of lithium ions in the positive electrode active material covered by the first positive electrode insulating layer bypassing the first positive electrode insulating layer and moving to the opposite negative electrode sheet, thereby reducing the possibility of lithium precipitation due to excessive lithium ion concentration at a local position of the negative electrode sheet, and improving the utilization rate of the positive electrode active material of the positive electrode sheet, thereby improving the energy density.

[0019] In some preferred embodiments, the first positive electrode insulating layer satisfies at least one of the following characteristics: (25) The ratio of the area of ​​the fifth perforated portion to the area of ​​the second main body portion is 0.01:1 to 0.5:1, so as to reduce the possibility of lithium deposition due to excessive lithium ion concentration at a local position of the negative electrode sheet, while the area of ​​the fifth perforated portion will not be too large, so as to improve the loss of the larger energy density of the secondary battery due to the fifth perforated portion with a larger area. (26) The minimum diameter of the circumscribed circle of the contour of the fifth hole is 0.2mm to 1.0mm, so that the positive electrode active material blocked by the first positive electrode insulating layer can better release lithium ions through the fifth hole. (27) The fifth perforated portion is provided with a plurality of fifth holes, and the spacing between two adjacent fifth holes is 0.2mm to 0.5mm, so that the positive electrode active material blocked by the first positive electrode insulating layer can evenly release lithium ions through the plurality of fifth holes, so as to better prevent local lithium deposition. (28) Along the width direction of the first groove, the distance between the fifth hole near the edge of the fifth perforated portion and the edge of the fifth perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer bypassing the edge of the fifth perforated portion in the width direction of the first groove and being released, so as to better prevent local lithium deposition. (29) Along the length direction of the first groove, the distance between the fifth hole near the edge of the fifth perforated portion and the edge of the fifth perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer bypassing the edge of the fifth perforated portion in the length direction of the first groove and being released, so as to better prevent local lithium deposition. (30) The shape of the fifth hole is at least one of a circle, an ellipse or a polygon.

[0020] In some preferred embodiments, the first positive electrode insulating layer includes a sixth punching portion, and along the length direction of the first groove, the sixth punching portion is connected to the side of the second main body close to the bottom of the first groove, and the sixth punching portion is provided with a sixth hole. By connecting the sixth punching portion provided with the sixth hole to the side of the second main body close to the bottom of the first groove, the positive electrode active material covered by the first positive electrode insulating layer can release lithium ions through the sixth hole, so as to reduce the possibility of lithium ions in the positive electrode active material covered by the first positive electrode insulating layer bypassing the first positive electrode insulating layer and moving to the opposite negative electrode sheet, thereby reducing the possibility of lithium deposition due to excessive lithium ion concentration at a local position of the negative electrode sheet, and improving the utilization rate of the positive electrode active material of the positive electrode sheet, thereby improving the energy density.

[0021] In some preferred embodiments, the first positive electrode insulating layer satisfies at least one of the following characteristics: (31) The ratio of the area of ​​the sixth perforated portion to the area of ​​the second main body portion is 0.001:1 to 0.2:1, so as to reduce the possibility of lithium deposition due to excessive lithium ion concentration at a local position of the negative electrode sheet, while the area of ​​the sixth perforated portion will not be too large, so as to improve the energy density of the secondary battery caused by the large sixth perforated portion. (32) The minimum diameter of the circumscribed circle of the contour of the sixth hole is 0.2mm to 1.0mm, so that the positive electrode active material blocked by the first positive electrode insulating layer can better release lithium ions through the sixth hole. (33) The sixth perforated portion is provided with a plurality of sixth holes, and the spacing between two adjacent sixth holes is 0.2mm to 0.5mm, so that the positive electrode active material blocked by the first positive electrode insulating layer can evenly release lithium ions through the plurality of sixth holes, so as to better prevent local lithium deposition. (34) Along the length direction of the first groove, the distance between the sixth hole near the edge of the sixth perforated portion and the edge of the sixth perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer bypassing the edge of the sixth perforated portion in the length direction of the first groove and being released, so as to better prevent local lithium deposition. (35) Along the width direction of the first groove, the distance between the sixth hole near the edge of the sixth perforated portion and the edge of the sixth perforated portion is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer bypassing the edge of the sixth perforated portion in the width direction of the first groove and being released, so as to better prevent local lithium deposition. (36) The shape of the sixth hole is at least one of a circle, an ellipse or a polygon.

[0022] In some preferred embodiments, the positive electrode sheet includes a second positive electrode active layer, and the second positive electrode active layer is provided on the surface of the positive electrode collector away from the first positive electrode active layer along the thickness direction of the positive electrode collector. The second positive electrode active layer is provided with a second groove, and the second groove is used to provide a receiving space for the equipment for welding the positive electrode tab. The surface of the second positive electrode active layer facing the negative electrode sheet is provided with a second positive electrode insulating layer, and the second positive electrode insulating layer covers the second groove to reduce the possibility of the positive electrode collector exposed by the second groove contacting the negative electrode sheet. The surface of the negative electrode sheet facing the second positive electrode active layer is provided with a second negative electrode insulating layer, and the projection of the second negative electrode insulating layer on the second positive electrode active layer covers the second groove in a direction perpendicular to the surface of the second negative electrode insulating layer to reduce the possibility of the metal burrs of the positive electrode collector piercing the diaphragm and contacting the negative electrode sheet. Along the width direction of the second groove, a seventh hole is provided on one side of the second negative electrode insulating layer to reduce the possibility of lithium deposition of the negative electrode sheet on one side of the second negative electrode insulating layer.

[0023] In some preferred embodiments, the secondary battery satisfies at least one of the following characteristics: (37) The thickness of the first positive electrode insulating layer is H1, 4 μm ≤ H1 ≤ 30 μm, so that the first positive electrode insulating layer has good anti-puncture performance and the first positive electrode insulating layer is not too thick, so as to improve the excessive reduction of the energy density of the secondary battery. (38) The thickness of the first negative electrode insulating layer is H2, 4 μm ≤ H2 ≤ 30 μm, so that the first negative electrode insulating layer has good anti-puncture performance and the first negative electrode insulating layer is not too thick, so as to improve the excessive reduction of the energy density of the secondary battery. (39) The first positive electrode insulating layer includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide, so that the first positive electrode insulating layer has good insulation performance. (40) The first negative electrode insulating layer includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide, so that the first negative electrode insulating layer has good insulating properties.

[0024] 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.

[0025] In the present application, the lug-center structure has protective glue disposed on both the surface of the positive electrode active layer and the surface of the opposite negative electrode sheet, which can better reduce the risk of the lug welding burrs piercing the diaphragm and contacting the opposite electrode sheet with the opposite polarity to cause a short circuit. However, for the lug-center structure of the positive electrode sheet, during the charging process, there will be a lithium deposition problem at the edge of the protective glue on the surface of the negative electrode sheet. By opening holes in the protective glue on the surface of the negative electrode sheet, the lithium ions near the protective glue on the surface of the negative electrode sheet can be absorbed by the negative electrode sheet through the holes, thereby reducing the lithium deposition problem at the edge of the protective glue on the surface of the negative electrode sheet.

[0026] 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

[0027] 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 unless otherwise stated, the dimensions in the drawings do not constitute proportional limitations.

[0028] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0029] Figure 2 This is a schematic diagram of the structure of the electrode assembly of some embodiments of the present application;

[0030] Figure 3 for Figure 2 A partial enlarged view of the middle part;

[0031] Figure 4 This is a schematic structural diagram of the first negative electrode insulating layer of some embodiments of the present application;

[0032] Figure 5 This is a schematic structural diagram of the negative electrode sheet of some embodiments of the present application observed along a direction perpendicular to the surface of the first negative electrode insulating layer;

[0033] Figure 6 This is a schematic structural diagram of a first positive electrode insulating layer in some embodiments of the present application;

[0034] Figure 7 This is a schematic structural diagram of the positive electrode sheet of some embodiments of the present application observed along a direction perpendicular to the surface of the first positive electrode insulating layer;

[0035] Figure 8 This is a schematic diagram of the structure of the electrode assembly of some embodiments of the present application;

[0036] Fig. 9 for Figure 8 A partial enlarged view of point B in the middle;

[0037] Fig.10 This is a schematic structural diagram of the second negative electrode insulating layer of some embodiments of the present application;

[0038] Fig.11 This is a schematic structural diagram of the negative electrode sheet of some embodiments of the present application observed in a direction perpendicular to the surface of the second negative electrode insulating layer;

[0039] Fig.12 This is a schematic structural diagram of a second positive electrode insulating layer in some embodiments of the present application;

[0040] Fig.13 This is a schematic structural diagram of the positive electrode sheet of some embodiments of the present application observed along a direction perpendicular to the surface of the second positive electrode insulating layer.

[0041] Description of reference numerals:

[0042] 100, secondary battery; X, first direction; Y, second direction;

[0043] 10. Shell;

[0044] 20. Electrode assembly;

[0045] 21, positive electrode sheet; 211, positive electrode current collector; 212, first positive electrode active layer; 2121, first groove; 213, positive electrode ear; 214, second positive electrode active layer; 2141, second groove;

[0046] 22, negative electrode sheet; 221, negative electrode current collector; 222, first negative electrode active layer; 223, second negative electrode active layer;

[0047] 23. Diaphragm;

[0048] 24, first positive electrode insulating layer; 241, second main body; 242, fourth punching portion; 2421, fourth hole; 243, fifth punching portion; 2431, fifth hole; 244, sixth punching portion; 2441, sixth hole;

[0049] 25, first negative electrode insulating layer; 251, first main body; 252, first punching portion; 2521, first hole; 253, second punching portion; 2531, second hole; 254, third punching portion; 2541, third hole;

[0050] 26, second positive electrode insulating layer; 261, fourth main body; 262, tenth punching portion; 2621, tenth hole; 263, eleventh punching portion; 2631, eleventh hole; 264, twelfth punching portion; 2641, twelfth hole;

[0051] 27. second negative electrode insulating layer; 271. third main body; 272. seventh punching portion; 2721. seventh hole; 273. eighth punching portion; 2731. eighth hole; 274. ninth punching portion; 2741. ninth hole. DETAILED DESCRIPTION

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] In the first aspect, the embodiment of the present application provides a secondary battery 100, please refer to Figure 1 The secondary battery 100 includes a shell 10 and an electrode assembly 20 . The shell 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte infiltrates the electrode assembly 20 in the shell 10 .

[0058] For the electrode assembly 20, please refer to Figure 2 , Figure 2 The winding structure of the electrode assembly 20 is shown. The electrode assembly 20 includes a positive electrode sheet 21, a separator 23 and a negative electrode sheet 22. A separator 23 is arranged between the adjacent negative electrode sheets 22 and the positive electrode sheets 21. The positive electrode sheets 21, the separator 23 and the negative electrode sheets 22 are stacked and wound. Exemplarily, along the thickness direction of the positive electrode sheet 21 and / or the negative electrode sheet 22, the positive electrode sheet 21, the separator 23 and the negative electrode sheet 22 are stacked in sequence and then wound to form a wound electrode assembly 20. In the embodiment of the present application, the electrode assembly 20 is taken as an example for explanation as a winding structure. In some other embodiments, the electrode assembly 20 may also be a laminated structure. For example, along the thickness direction of the positive electrode sheet 21 and / or the negative electrode sheet 22, the positive electrode sheet 21, the separator 23 and the negative electrode sheet 22 are stacked in sequence to form a laminated electrode assembly 20.

[0059] For the positive electrode sheet 21, please refer to Figure 3The positive electrode sheet 21 includes a positive electrode current collector 211, a first positive electrode active layer 212 and a positive electrode tab 213. The first positive electrode active layer 212 is disposed on one surface of the positive electrode current collector 211 along the thickness direction of the positive electrode current collector 211. The first positive electrode active layer 212 is provided with a first groove 2121. The positive electrode tab 213 is disposed in the first groove 2121 and is electrically connected to the positive electrode current collector 211 to form a tab-centered structure, so that the secondary battery 100 can be charged faster.

[0060] For the positive electrode current collector 211, the positive electrode current collector 211 may be a composite current collector (a composite structure of metal-polymer-metal), for example, the positive electrode current collector 211 includes a polymer layer and a metal layer disposed on two opposite surfaces of the polymer layer, the polymer layer as the main mechanical support layer of the positive electrode current collector 211, may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), the metal layer may include at least one of aluminum, copper, nickel, titanium, and silver, the positive electrode current collector 211 uses the polymer layer as the main mechanical support layer, the metal layer may be thinned, thereby reducing the metal burrs caused by mechanical damage to the secondary battery 100, and reducing the mass of the positive electrode current collector 211, thereby improving the mass energy density of the secondary battery 100. In some other embodiments, the positive electrode current collector 211 may also be a single-layer metal foil, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0061] As for the first positive electrode active layer 212, the first positive electrode active layer 212 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The first positive electrode active layer 212 includes a first positive electrode active material, a conductive agent, a binder, etc. The above materials are mixed and stirred evenly and coated on a surface of the positive electrode current collector 211 to obtain the first positive electrode active layer 212. The first positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium iron manganese phosphate.

[0062] In the present application, the positive electrode tab 213 is a metal conductor led out from the positive electrode sheet 21, and the positive electrode tab 213 is used to connect in series or in parallel with other parts of the secondary battery 100. The present application has no particular restrictions on the material of the positive electrode tab 213, as long as the purpose of the present application can be achieved, for example, the material of the positive electrode tab 213 known in the art can be used. The present application has no particular restrictions on the formation method of the first groove 2121, and a formation method known in the art can be used, as long as the purpose of the present application can be achieved, for example, by laser cleaning in the corresponding first positive active layer 212 area, or by first pasting foam paper on the positive current collector 211, coating the first positive active layer 212 and drying, and peeling off the foam paper to obtain the first groove 2121.

[0063] The negative electrode sheet 22 comprises a negative electrode collector 221 and a first negative electrode active layer 222 . Along the thickness direction of the negative electrode collector 221 , the first negative electrode active layer 222 is disposed on the surface of the negative electrode collector 221 facing the first positive electrode active layer 212 .

[0064] For the negative electrode current collector 221, the negative electrode current collector 221 may be a composite current collector (a composite structure of metal-polymer-metal), for example, the negative electrode current collector 221 includes a polymer layer and a metal layer disposed on two opposite surfaces of the polymer layer, the polymer layer as the main mechanical support layer of the negative electrode current collector 221, may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), the metal layer may include at least one of aluminum, copper, nickel, titanium, and silver, the negative electrode current collector 221 uses the polymer layer as the main mechanical support layer, the metal layer may be thinned, thereby reducing the metal burrs caused by mechanical damage to the secondary battery 100, and reducing the mass of the negative electrode current collector 221, thereby improving the mass energy density of the secondary battery 100. In some other embodiments, the negative electrode current collector 221 may be a single-layer metal foil, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0065] For the first negative electrode active layer 222, the first negative electrode active layer 222 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The first negative electrode active layer 222 includes a first negative electrode active material, a conductive agent, an adhesive, etc. The above materials are mixed and stirred evenly and coated on the surface of the negative electrode current collector 221 facing the first positive electrode active layer 212, thereby obtaining the first negative electrode active layer 222. The first negative electrode active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0066] In some embodiments, a first positive electrode insulating layer 24 is disposed on the surface of the first positive electrode active layer 212 facing the negative electrode sheet 22, and the first positive electrode insulating layer 24 covers the first groove 2121 to cover the welding burrs of the positive electrode tab 213 and the positive electrode current collector 211 exposed in the first groove 2121, thereby reducing the possibility of the welding burrs piercing the separator 23 and contacting the negative electrode sheet 22, and reducing the possibility of the positive electrode current collector 211 exposed in the first groove 2121 contacting the negative electrode sheet 22. A first negative electrode insulating layer 25 is disposed on the surface of the first negative electrode active layer 222 facing the first positive electrode active layer 212, and the projection of the first negative electrode insulating layer 25 on the first positive electrode active layer 212 covers the first groove 2121 in a direction perpendicular to the surface of the first negative electrode insulating layer 25, so as to further reduce the possibility of the welding burrs piercing the separator 23 and contacting the negative electrode sheet 22. However, during the charging process of the secondary battery 100, the lithium ions in the first positive electrode active material covered by the first positive electrode insulating layer 24 will bypass the first positive electrode insulating layer 24 and move to the first negative electrode active layer 222 of the opposite negative electrode sheet 22 under the action of the electric potential, causing the lithium ion concentration at a local position of the first negative electrode active layer 222 to be too high. Since the first negative electrode insulating layer 25 covers part of the negative electrode active material, the local position of the first negative electrode active layer 222 cannot absorb excessive lithium ions, and the excess lithium ions accumulate in the negative electrode active layer near the edge of the first negative electrode insulating layer 25, causing lithium precipitation problems.

[0067] To improve the above problems, in the embodiments of this application, please refer to Figure 3 , Figure 4 and Figure 5 Along the width direction of the first groove 2121 (the first direction X), a first hole 2521 is opened on one side of the first negative electrode insulating layer 25, so that the lithium ions on one side of the first negative electrode insulating layer 25 can be absorbed by the first negative electrode active layer 222 through the first hole 2521, thereby reducing the possibility of excessive lithium ions accumulating in the first negative electrode active layer 222 close to the first negative electrode insulating layer 25 and causing lithium precipitation.

[0068] For the first negative electrode insulating layer 25, the first negative electrode insulating layer 25 includes a first punching portion 252 and a first main body portion 251. The first punching portion 252 is connected to one side of the first main body portion 251 along the width direction of the first groove 2121, and the first punching portion 252 is provided with a first hole 2521. In a direction perpendicular to the surface of the first negative electrode insulating layer 25, the projection of the first main body portion 251 on the first positive electrode active layer 212 covers the first groove 2121, so that the first main body portion 251 blocks the first groove 2121, and further blocks the welding burrs of the positive electrode tab 213, so as to reduce the possibility that the welding burrs pierce the diaphragm 23 and contact the negative electrode sheet 22.

[0069] Preferably, along the width direction of the first groove 2121, the width of the first main body 251 is 0.5mm to 6mm greater than the width of the first groove 2121. By limiting the first main body 251 to be not less than 0.5mm and not more than 6mm greater than the width of the first groove 2121, the first main body 251 is not too wide while the first groove 2121 is shielded, so as to improve the excessive reduction of the energy density of the secondary battery 100. Along the length direction of the first groove 2121, the length of the first main body 251 is 0.1mm to 4mm greater than the length of the first groove 2121, so as to meet the first main body 251 shielding the first groove 2121, while the first main body 251 is not too long, so as to improve the excessive reduction of the energy density of the secondary battery 100.

[0070] In some embodiments, the first negative electrode insulating layer 25 satisfies at least one of the following characteristics: (1) the ratio of the area of ​​the first perforated portion 252 to the area of ​​the first main body 251 is 0.01:1 to 0.5:1, so as to reduce the accumulation of excess lithium ions in the first negative electrode active layer 222 close to the first negative electrode insulating layer 25 and cause lithium deposition, while the area of ​​the first perforated portion 252 is not too large, so as to improve the effect of the first perforated portion 252 with a larger area on the adhesion of the first main body 251 to the negative electrode sheet 22. The shapes of the first perforated portion 252 and the first main body 251 are preferably rectangular, and the lengths of the first perforated portion 252 and the first main body 251 along the length direction (second direction Y) of the first groove 2121 are the same, so the ratio of the area of ​​the first perforated portion 252 to the first main body 251 is equal to the ratio of the width of the first perforated portion 252 to the width of the first groove 2121. (2) The minimum diameter of the circumscribed circle of the contour of the first hole 2521 is 0.2 mm to 1.0 mm, so that lithium ions can be better absorbed by the negative electrode sheet 22 through the first hole 2521. (3) The first perforated portion 252 is provided with a plurality of first holes 2521, and the spacing between two adjacent first holes 2521 is 0.2 mm to 0.5 mm, so that lithium ions can be uniformly absorbed by the negative electrode sheet 22 through the plurality of first holes 2521. Assuming that the spacing between two adjacent first holes 2521 is A1, the distance between the centers of the circumscribed circles of the contours of two adjacent first holes 2521 is B1, and the radius of the circumscribed circle of the contours of the first holes 2521 is R1, then A1 = B1-2*R1. (4) Along the width direction of the first groove 2121, the distance between the first hole 2521 close to the edge of the first perforated portion 252 and the edge of the first perforated portion 252 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the first perforated portion 252 in the width direction of the first groove 2121. Assuming that the distance between the first hole 2521 and the edge of the first perforated portion 252 along the width direction of the first groove 2121 is C1, the distance between the center of the circumscribed circle of the contour of the first hole 2521 and the edge of the first perforated portion 252 along the width direction of the first groove 2121 is D1, and C1=D1-R1. (5) Along the length direction of the first groove 2121, the distance between the first hole 2521 close to the edge of the first perforated portion 252 and the edge of the first perforated portion 252 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the first perforated portion 252 in the length direction of the first groove 2121. Assuming that the distance between the first hole 2521 and the edge of the first perforated portion 252 along the length direction of the first groove 2121 is E1, the distance between the center of the circumscribed circle of the contour of the first hole 2521 and the edge of the first perforated portion 252 along the length direction of the first groove 2121 is F1, E1 = F1-R1. (6) The shape of the first hole 2521 is at least one of a circle, an ellipse or a polygon.

[0071] In some embodiments, the first negative electrode insulating layer 25 includes a second perforated portion 253, and along the width direction of the first groove 2121, the second perforated portion 253 is connected to the other side of the first main body 251 away from the first perforated portion 252 (that is, the first perforated portion 252 and the second perforated portion 253 are respectively provided on both sides of the first main body 251 in the width direction of the first groove 2121), and the second perforated portion 253 is provided with a second hole 2531. By connecting the second perforated portion 253 provided with the second hole 2531 on the other side of the first main body 251 away from the first perforated portion 252, the possibility of lithium deposition of the first negative electrode insulating layer 25 on the other side in the width direction of the first groove 2121 is reduced.

[0072] In some embodiments, the first negative electrode insulating layer 25 satisfies at least one of the following features: (7) The ratio of the area of ​​the second perforated portion 253 to the area of ​​the first main body 251 is 0.01:1 to 0.5:1, so as to reduce the accumulation of excess lithium ions in the negative electrode sheet 22 near the other side of the first negative electrode insulating layer 25 and cause lithium deposition, while the area of ​​the second perforated portion 253 is not too large, so as to improve the effect of the second perforated portion 253 with a larger area on the adhesion of the first main body 251 to the negative electrode sheet 22. The second perforated portion 253 and the first main body 251 are preferably rectangular in shape, and the second perforated portion 253 and the first main body 251 have the same length along the length direction of the first groove 2121, so the ratio of the area of ​​the second perforated portion 253 to the first main body 251 is equal to the ratio of the width of the second perforated portion 253 to the width of the first groove 2121. (8) The minimum diameter of the circumscribed circle of the second hole 2531 is 0.2 mm to 1.0 mm, so that lithium ions can be better absorbed by the negative electrode sheet 22 through the second hole 2531. (9) The second perforated portion 253 is provided with a plurality of second holes 2531, and the spacing between two adjacent second holes 2531 is 0.2 mm to 0.5 mm, so that lithium ions can be uniformly absorbed by the negative electrode sheet 22 through the plurality of second holes 2531. Assuming that the spacing between two adjacent second holes 2531 is A2, the distance between the centers of the circumscribed circles of the contours of two adjacent second holes 2531 is B2, and the radius of the circumscribed circle of the contours of the second holes 2531 is R2, then A2 = B2-2*R2. (10) Along the width direction of the first groove 2121, the distance between the second hole 2531 close to the edge of the second perforated portion 253 and the edge of the second perforated portion 253 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the second perforated portion 253 in the width direction of the first groove 2121. Assuming that the distance between the second hole 2531 and the edge of the second perforated portion 253 along the width direction of the first groove 2121 is C2, the distance between the center of the circumscribed circle of the contour of the second hole 2531 and the edge of the second perforated portion 253 along the width direction of the first groove 2121 is D2, C2 = D2-R2. (11) Along the length direction of the first groove 2121, the distance between the second hole 2531 close to the edge of the second perforated portion 253 and the edge of the second perforated portion 253 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the second perforated portion 253 in the length direction of the first groove 2121. Assuming that the distance between the second hole 2531 and the edge of the second perforated portion 253 along the length direction of the first groove 2121 is E2, the distance between the center of the circumscribed circle of the contour of the second hole 2531 and the edge of the second perforated portion 253 along the length direction of the first groove 2121 is F2, E2 = F2-R2. (12) The shape of the second hole 2531 is at least one of a circle, an ellipse or a polygon.

[0073] In some embodiments, the first negative electrode insulating layer 25 includes a third punching portion 254. Along the length direction of the first groove 2121, the third punching portion 254 is connected to the side of the first main body 251 close to the bottom of the first groove 2121, and the third punching portion 254 is provided with a third hole 2541. By connecting the third punching portion 254 with the third hole 2541 on the side of the first main body 251 close to the bottom of the first groove 2121, the possibility of lithium deposition on the side of the first negative electrode insulating layer 25 close to the bottom of the first groove 2121 is reduced. In the present application, the boundaries of the regions in the first main body 251, the first punching portion 252, the second punching portion 253 and the third punching portion 254 are as follows: Figure 4 The dashed line shown in .

[0074] In some embodiments, the first negative electrode insulating layer 25 satisfies at least one of the following characteristics: (13) The ratio of the area of ​​the third perforated portion 254 to the area of ​​the first main body 251 is 0.001:1 to 0.2:1, so as to reduce the lithium deposition on the side of the first negative electrode insulating layer 25 close to the bottom of the first groove 2121 while the area of ​​the third perforated portion 254 is not too large, so as to improve the effect of the larger area of ​​the third perforated portion 254 on the adhesion of the first main body 251 to the negative electrode sheet 22. The shapes of the third punching portion 254 and the first main body 251 are preferably rectangular, and along the width direction of the first groove 2121, the width of the third punching portion 254 is equal to the sum of the width of the first main body 251, the width of the first punching portion 252 and the width of the second punching portion 253. Since the width of the first punching portion 252 and the width of the second punching portion 253 are both smaller than the width of the first main body 251, the width of the first punching portion 252 and the width of the second punching portion 253 can be ignored, that is, the width of the third punching portion 254 is approximately equal to the width of the first main body 251, so the ratio of the area of ​​the third punching portion 254 to the first main body 251 is approximately equal to the ratio of the length of the third punching portion 254 to the length of the first main body 251 along the length direction of the first groove 2121. (14) The minimum diameter of the circumscribed circle of the contour of the third hole 2541 is 0.2 mm to 1.0 mm, so that lithium ions can be better absorbed by the negative electrode sheet 22 through the third hole 2541. (15) The third perforated portion 254 is provided with a plurality of third holes 2541, and the spacing between two adjacent third holes 2541 is 0.2 mm to 0.5 mm, so that lithium ions can be uniformly absorbed by the negative electrode sheet 22 through the plurality of third holes 2541. Assuming that the spacing between two adjacent third holes 2541 is A3, the distance between the centers of the circumscribed circles of the contours of two adjacent third holes 2541 is B3, and the radius of the circumscribed circle of the contours of the third holes 2541 is R3, then A3 = B3-2*R3. (16) Along the length direction of the first groove 2121, the distance between the third hole 2541 close to the edge of the third perforated portion 254 and the edge of the third perforated portion 254 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the third perforated portion 254 in the length direction of the first groove 2121. Assuming that the distance between the third hole 2541 and the edge of the third perforated portion 254 along the length direction of the first groove 2121 is C3, the distance between the center of the circumscribed circle of the contour of the third hole 2541 and the edge of the third perforated portion 254 along the length direction of the first groove 2121 is D3, C3 = D3-R3. (17) Along the width direction of the first groove 2121, the distance between the third hole 2541 close to the edge of the third perforated portion 254 and the edge of the third perforated portion 254 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium deposition at the edge of the third perforated portion 254 in the width direction of the first groove 2121.Assuming that the distance between the third hole 2541 and the edge of the third punching portion 254 along the width direction of the first groove 2121 is E3, the distance between the center of the circumscribed circle of the contour of the third hole 2541 and the edge of the third punching portion 254 along the width direction of the first groove 2121 is F3, E3 = F3 - R3. (18) The shape of the third hole 2541 is at least one of a circle, an ellipse or a polygon.

[0075] In some embodiments, along the width direction of the first groove 2121, the width of the first negative electrode insulation layer 25 is smaller than the width of the first positive electrode insulation layer 24, so that the first positive electrode insulation layer 24 with a larger width can block more positive electrode active materials, thereby reducing the amount of positive electrode active materials that can participate in the electrochemical reaction, thereby reducing the possibility of lithium deposition in the negative electrode sheet 22.

[0076] In some embodiments, please refer to Figure 3 , Figure 6 and Figure 7 The first positive electrode insulating layer 24 includes a fourth perforated portion 242 and a second main body portion 241. Along the width direction of the first groove 2121, the fourth perforated portion 242 is connected to one side of the second main body portion 241, and the fourth perforated portion 242 is provided with a fourth hole 2421. Along the direction perpendicular to the surface of the first positive electrode insulating layer 24, the fourth perforated portion 242 at least partially overlaps with the first positive electrode active layer 212, so that the positive electrode active material covered by the first positive electrode insulating layer 24 can release lithium ions through the fourth hole 2421, so as to reduce the possibility of lithium ions in the positive electrode active material covered by the first positive electrode insulating layer 24 bypassing the first positive electrode insulating layer 24 and moving to the opposite negative electrode sheet 22, thereby reducing the possibility of lithium deposition due to excessive lithium ion concentration at a local position of the negative electrode sheet 22, and improving the utilization rate of the positive electrode active material of the positive electrode sheet 21, thereby improving the energy density.

[0077] In some embodiments, along the direction perpendicular to the surface of the first positive electrode insulating layer 24, the second main body 241 covers the first groove 2121, so that the second main body 241 blocks the welding burrs of the positive electrode tab 213, so as to reduce the possibility of the welding burrs piercing the separator 23 and contacting the negative electrode sheet 22. Along the width direction of the first groove 2121, the width of the second main body 241 is 0.5mm to 6mm larger than the width of the first groove 2121, so as to meet the second main body 241 shielding the first groove 2121, while the second main body 241 is not too wide, so as to improve the excessive reduction of the energy density of the secondary battery 100. Along the length direction of the first groove 2121, the length of the second main body 241 is 0.1mm to 4mm larger than the length of the first groove 2121, so as to meet the second main body 241 shielding the first groove 2121, while the second main body 241 is not too long, so as to improve the excessive reduction of the energy density of the secondary battery 100.

[0078] In some embodiments, the first positive electrode insulating layer 24 satisfies at least one of the following characteristics: (19) The ratio of the area of ​​the fourth perforated portion 242 to the area of ​​the second main body 241 is 0.01:1 to 0.5:1, so as to reduce the possibility of lithium deposition due to excessive lithium ion concentration at a local position of the negative electrode sheet 22, while the area of ​​the fourth perforated portion 242 is not too large, so as to improve the energy density of the secondary battery 100 caused by the fourth perforated portion 242 with a larger area. The shape of the fourth perforated portion 242 and the second main body 241 is preferably rectangular, and the length of the fourth perforated portion 242 and the second main body 241 along the length direction of the first groove 2121 is the same, so the ratio of the area of ​​the fourth perforated portion 242 to the second main body 241 is equal to the ratio of the width of the fourth perforated portion 242 to the second main body 241 along the width direction of the first groove 2121. (20) The minimum diameter of the circumscribed circle of the contour of the fourth hole 2421 is 0.2 mm to 1.0 mm, so that the positive electrode active material blocked by the first positive electrode insulating layer 24 can release lithium ions through the fourth hole 2421. (21) The fourth perforated portion 242 is provided with a plurality of fourth holes 2421, and the spacing between two adjacent fourth holes 2421 is 0.2 mm to 0.5 mm, so that the positive electrode active material blocked by the first positive electrode insulating layer 24 can release lithium ions uniformly through the plurality of fourth holes 2421. Assuming that the spacing between two adjacent fourth holes 2421 is A4, the distance between the centers of the circumscribed circles of the contours of two adjacent fourth holes 2421 is B4, and the radius of the circumscribed circle of the contours of the fourth holes 2421 is R4, then A4=B4-2*R4. (22) Along the width direction of the first groove 2121, the distance between the fourth hole 2421 close to the edge of the fourth perforated portion 242 and the edge of the fourth perforated portion 242 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer 24 bypassing the edge of the fourth perforated portion 242 in the width direction of the first groove 2121 and being released. Assuming that the distance between the fourth hole 2421 and the edge of the fourth perforated portion 242 along the width direction of the first groove 2121 is C4, the distance between the center of the circumscribed circle of the contour of the fourth hole 2421 and the edge of the fourth perforated portion 242 along the width direction of the first groove 2121 is D4, and C4 = D4-R4. (23) Along the length direction of the first groove 2121, the distance between the fourth hole 2421 close to the edge of the fourth punching portion 242 and the edge of the fourth punching portion 242 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer 24 bypassing the edge of the fourth punching portion 242 in the length direction of the first groove 2121 and being released.Assuming that the distance between the fourth hole 2421 and the edge of the fourth perforated portion 242 along the length direction of the first groove 2121 is E4, the distance between the center of the circumscribed circle of the contour of the fourth hole 2421 and the edge of the fourth perforated portion 242 along the length direction of the first groove 2121 is F4, and E4=F4-R4. (24) The shape of the fourth hole 2421 is at least one of a circle, an ellipse, or a polygon.

[0079] In some embodiments, the first positive electrode insulating layer 24 includes a fifth punching portion 243, and along the width direction of the first groove 2121, the fifth punching portion 243 is connected to the side of the second main body 241 away from the fourth punching portion 242, and the fifth punching portion 243 is provided with a fifth hole 2431. By connecting the fifth punching portion 243 provided with the fifth hole 2431 to the other side of the second main body 241 along the width direction of the first groove 2121, the positive electrode active material covered by the first positive electrode insulating layer 24 can release lithium ions through the fifth hole 2431, so as to reduce the possibility of lithium ions in the positive electrode active material covered by the first positive electrode insulating layer 24 bypassing the first positive electrode insulating layer 24 and moving to the opposite negative electrode sheet 22, thereby reducing the possibility of lithium deposition due to excessive lithium ion concentration at a local position of the negative electrode sheet 22, and improving the utilization rate of the positive electrode active material of the positive electrode sheet 21, thereby improving the energy density.

[0080] In some embodiments, the first positive electrode insulating layer 24 satisfies at least one of the following characteristics: (25) The ratio of the area of ​​the fifth perforated portion 243 to the area of ​​the second main body 241 is 0.01:1 to 0.5:1, so as to reduce the possibility of lithium deposition due to excessive lithium ion concentration at a local position of the negative electrode sheet 22, while the area of ​​the fifth perforated portion 243 is not too large, so as to improve the loss of the energy density of the secondary battery 100 caused by the fifth perforated portion 243 with a larger area. The shape of the fifth perforated portion 243 and the second main body 241 is preferably rectangular, and the length of the fifth perforated portion 243 and the second main body 241 along the length direction of the first groove 2121 is the same, so the ratio of the area of ​​the fifth perforated portion 243 to the second main body 241 is equal to the ratio of the width of the fifth perforated portion 243 to the second main body 241 along the width direction of the first groove 2121. (26) The minimum diameter of the circumscribed circle of the contour of the fifth hole 2431 is 0.2 mm to 1.0 mm, so that the positive electrode active material blocked by the first positive electrode insulating layer 24 can release lithium ions through the fifth hole 2431. (27) The fifth perforated portion 243 is provided with a plurality of fifth holes 2431, and the spacing between two adjacent fifth holes 2431 is 0.2 mm to 0.5 mm, so that the positive electrode active material blocked by the first positive electrode insulating layer 24 can release lithium ions uniformly through the plurality of fifth holes 2431. Assuming that the spacing between two adjacent fifth holes 2431 is A5, the distance between the centers of the circumscribed circles of the contours of two adjacent fifth holes 2431 is B5, and the radius of the circumscribed circle of the contour of the fifth hole 2431 is R5, then A5 = B5-2*R5. (28) Along the width direction of the first groove 2121, the distance between the fifth hole 2431 close to the edge of the fifth perforated portion 243 and the edge of the fifth perforated portion 243 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer 24 bypassing the edge of the fifth perforated portion 243 in the width direction of the first groove 2121 and being released. Assuming that the distance between the fifth hole 2431 and the edge of the fifth perforated portion 243 along the width direction of the first groove 2121 is C5, the distance between the center of the circumscribed circle of the contour of the fifth hole 2431 and the edge of the fifth perforated portion 243 along the width direction of the first groove 2121 is D5, and C5=D5-R5. (29) Along the length direction of the first groove 2121, the distance between the fifth hole 2431 close to the edge of the fifth punching portion 243 and the edge of the fifth punching portion 243 is 0.2 mm to 0.5 mm, so as to reduce the possibility of lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer 24 bypassing the edge of the fifth punching portion 243 in the length direction of the first groove 2121 and being released.Assuming that the distance between the fifth hole 2431 and the edge of the fifth punching portion 243 along the length direction of the first groove 2121 is E5, the distance between the center of the circumscribed circle of the contour of the fifth hole 2431 and the edge of the fifth punching portion 243 along the length direction of the first groove 2121 is F5, E5 = F5 - R5. (30) The shape of the fifth hole 2431 is at least one of a circle, an ellipse or a polygon.

[0081] In some embodiments, the first positive electrode insulating layer 24 includes a sixth punching portion 244. Along the length direction of the first groove 2121, the sixth punching portion 244 is connected to one side of the second main body 241 close to the bottom of the first groove 2121. The sixth punching portion 244 is provided with a sixth hole 2441, so that the positive electrode active material covered by the first positive electrode insulating layer 24 can release lithium ions through the sixth hole 2441, so as to reduce the possibility of lithium ions in the positive electrode active material covered by the first positive electrode insulating layer 24 bypassing the first positive electrode insulating layer 24 and moving to the opposite negative electrode sheet 22, thereby reducing the possibility of lithium precipitation due to excessive lithium ion concentration at a local position of the negative electrode sheet 22, and improving the utilization rate of the positive electrode active material of the positive electrode sheet 21, thereby improving the energy density. In the present application, the boundaries of the regions in the second main body 241, the fourth punching portion 242, the fifth punching portion 243 and the sixth punching portion 244 are as follows: Figure 6 The dashed line shown in .

[0082] In some embodiments, the first positive electrode insulating layer 24 satisfies at least one of the following characteristics: (31) the ratio of the area of ​​the sixth perforated portion 244 to the area of ​​the second main portion 241 is 0.001:1 to 0.2:1, so as to reduce the possibility of lithium deposition due to excessive lithium ion concentration in local positions of the negative electrode sheet 22, while the area of ​​the sixth perforated portion 244 will not be too large, so as to improve the energy density of the secondary battery 100 caused by the larger area of ​​the sixth perforated portion 244. Among them, the shapes of the sixth punching portion 244 and the second main body portion 241 are preferably rectangular, and along the width direction of the first groove 2121, the width of the sixth punching portion 244 is equal to the sum of the width of the second main body portion 241, the width of the fourth punching portion 242 and the width of the fifth punching portion 243. Since the width of the fourth punching portion 242 and the width of the fifth punching portion 243 are both smaller than the width of the second main body portion 241, the width of the fourth punching portion 242 and the width of the fifth punching portion 243 can be ignored, that is, the width of the sixth punching portion 244 is approximately equal to the width of the second main body portion 241, so the ratio of the area of ​​the sixth punching portion 244 to the second main body portion 241 is approximately equal to the ratio of the length of the sixth punching portion 244 to the second main body portion 241 along the length direction of the first groove 2121. (32) The minimum diameter of the circumscribed circle of the contour of the sixth hole 2441 is 0.2 mm to 1.0 mm, so that the positive electrode active material blocked by the first positive electrode insulating layer 24 can release lithium ions through the sixth hole 2441. (33) The sixth perforated portion 244 is provided with a plurality of sixth holes 2441, and the spacing between two adjacent sixth holes 2441 is 0.2 mm to 0.5 mm, so that the positive electrode active material blocked by the first positive electrode insulating layer 24 can release lithium ions uniformly through the plurality of sixth holes 2441. Assuming that the spacing between two adjacent sixth holes 2441 is A6, the distance between the centers of the circumscribed circles of the contours of two adjacent sixth holes 2441 is B6, and the radius of the circumscribed circle of the contours of the sixth holes 2441 is R6, then A6 = B6-2*R6. (34) Along the length direction of the first groove 2121, the distance between the sixth hole 2441 close to the edge of the sixth perforated portion 244 and the edge of the sixth perforated portion 244 is 0.2 mm to 0.5 mm, so as to reduce the possibility that the lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer 24 bypass the edge of the sixth perforated portion 244 along the length direction of the first groove 2121 and are released. Assuming that the distance between the sixth hole 2441 and the edge of the sixth perforated portion 244 along the length direction of the first groove 2121 is C6, the distance between the center of the circumscribed circle of the contour of the sixth hole 2441 and the edge of the sixth perforated portion 244 along the length direction of the first groove 2121 is D6, and C6=D6-R6.(35) Along the width direction of the first groove 2121, the distance between the sixth hole 2441 close to the edge of the sixth perforated portion 244 and the edge of the sixth perforated portion 244 is 0.2 mm to 0.5 mm, so as to reduce the possibility that the lithium ions of the positive electrode active material blocked by the first positive electrode insulating layer 24 bypass the edge of the sixth perforated portion 244 in the width direction of the first groove 2121 and are released. It is assumed that the distance between the sixth hole 2441 and the edge of the sixth perforated portion 244 along the width direction of the first groove 2121 is E6, and the distance between the center of the circumscribed circle of the contour of the sixth hole 2441 and the edge of the sixth perforated portion 244 along the width direction of the first groove 2121 is F6, and E6 = F6-R6. (36) The shape of the sixth hole 2441 is at least one of a circle, an ellipse or a polygon.

[0083] In some embodiments, please refer to Figure 8 and Fig. 9 The positive electrode sheet 21 includes a second positive electrode active layer 214. Along the thickness direction of the positive electrode current collector 211, the surface of the positive electrode current collector 211 away from the first positive electrode active layer 212 is provided with the second positive electrode active layer 214. The second positive electrode active layer 214 is provided with a second groove 2141, and the second groove 2141 is used to provide a receiving space for the equipment for welding the positive electrode tab 213. The surface of the second positive electrode active layer 214 facing the negative electrode sheet 22 is provided with a second positive electrode insulating layer 26, and the second positive electrode insulating layer 26 covers the second groove 2141 to reduce the possibility of the positive electrode current collector 211 exposed in the second groove 2141 contacting the negative electrode sheet 22. The negative electrode sheet 22 includes a second negative electrode active layer 223, the surface of the negative electrode current collector 221 facing away from the first negative electrode active layer 222 is provided with the second negative electrode active layer 223, and the surface of the second negative electrode active layer 223 facing the second positive electrode active layer 214 is provided with a second negative electrode insulating layer 27, and along the direction perpendicular to the surface of the second negative electrode insulating layer 27, the projection of the second negative electrode insulating layer 27 on the second positive electrode active layer 214 covers the second groove 2141, so as to reduce the possibility of the metal burrs of the positive electrode current collector 211 piercing the separator 23 and contacting the negative electrode sheet 22. Along the width direction (first direction X) of the second groove 2141, a seventh hole 2721 is opened on one side of the second negative electrode insulating layer 27, so as to reduce the possibility of lithium deposition of the negative electrode sheet 22 on one side of the second negative electrode insulating layer 27.

[0084] As for the second positive electrode active layer 214, the second positive electrode active layer 214 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The second positive electrode active layer 214 includes a second positive electrode active material, a conductive agent, a binder, etc. The above materials are mixed and stirred evenly and coated on the surface of the positive current collector 211 away from the first positive electrode active layer 212, thereby obtaining the second positive electrode active layer 214. The second positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0085] As for the second negative electrode active layer 223, the second negative electrode active layer 223 is infiltrated by the electrolyte in the shell 10 to generate an electrochemical reaction. The second negative electrode active layer 223 includes a second negative electrode active material, a conductive agent, an adhesive, etc. The above materials are mixed and stirred evenly and coated on the surface of the negative electrode current collector 221 away from the first negative electrode active layer 222, thereby obtaining the second negative electrode active layer 223. The second negative electrode active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0086] In some embodiments, see Fig. 9 , Fig.10 and Fig.11 The second negative electrode insulating layer 27 includes a seventh punching portion 272 and a third main body portion 271. Along the width direction of the second groove 2141, the seventh punching portion 272 is connected to one side of the third main body portion 271, and the seventh punching portion 272 is provided with a seventh hole 2721. Along the direction perpendicular to the surface of the second negative electrode insulating layer 27, the projection of the third main body portion 271 on the second positive electrode active layer 214 covers the second groove 2141, so that the third main body portion 271 blocks the second groove 2141, and further blocks the metal burrs of the positive electrode current collector 211, so as to reduce the possibility of the metal burrs piercing the separator 23 and contacting the negative electrode sheet 22. Preferably, the second negative electrode insulating layer 27 includes an eighth punching portion 273, along the width direction of the second groove 2141, the eighth punching portion 273 is connected to the other side of the third main body 271 away from the seventh punching portion 272, and the eighth punching portion 273 is provided with an eighth hole 2731 to reduce the possibility of lithium deposition on the other side of the second negative electrode insulating layer 27 in the width direction of the second groove 2141. Preferably, the second negative electrode insulating layer 27 includes a ninth punching portion 274, along the length direction of the second groove 2141 (the second direction Y), the ninth punching portion 274 is connected to the side of the third main body 271 close to the bottom of the second groove 2141, and the ninth punching portion 274 is provided with a ninth hole 2741 to reduce the possibility of lithium deposition on the side of the second negative electrode insulating layer 27 close to the bottom of the second groove 2141. In the present application, the boundaries of the regions in the third main body 271, the seventh punching portion 272, the eighth punching portion 273 and the ninth punching portion 274 are as follows: Fig.10 The dashed line shown in .

[0087] In some embodiments, see Fig. 9 , Fig.12 and Fig.13 The second positive electrode insulating layer 26 includes a tenth punching portion 262 and a fourth main body portion 261. Along the width direction of the second groove 2141, the tenth punching portion 262 is connected to one side of the fourth main body portion 261. The tenth punching portion 262 is provided with a tenth hole 2621, so that the positive electrode active material covered by the second positive electrode insulating layer 26 can release lithium ions through the tenth hole 2621, so as to reduce the possibility that the lithium ions in the positive electrode active material covered by the second positive electrode insulating layer 26 bypass the second positive electrode insulating layer 26 and move to the opposite negative electrode sheet 22. Along the direction perpendicular to the surface of the second positive electrode insulating layer 26, the projection of the fourth main body portion 261 on the second positive electrode active layer 214 covers the second groove 2141, so that the fourth main body portion 261 blocks the second groove 2141, and further blocks the metal burrs of the positive electrode current collector 211, so as to reduce the possibility that the metal burrs pierce the separator 23 and contact the negative electrode sheet 22. Preferably, the second positive electrode insulating layer 26 includes an eleventh punching portion 263, and along the width direction of the second groove 2141, the eleventh punching portion 263 is connected to the other side of the fourth main body 261 away from the tenth punching portion 262, and the eleventh punching portion 263 is provided with an eleventh hole 2631, so that the positive electrode active material covered by the second positive electrode insulating layer 26 can release lithium ions through the eleventh hole 2631, so as to reduce the possibility of lithium ions in the positive electrode active material covered by the second positive electrode insulating layer 26 bypassing the second positive electrode insulating layer 26 and moving to the opposite negative electrode sheet 22. Preferably, the second positive electrode insulating layer 26 includes a twelfth punching portion 264. Along the length direction of the second groove 2141, the twelfth punching portion 264 is connected to the side of the fourth main body 261 close to the bottom of the second groove 2141. The twelfth punching portion 264 is provided with a twelfth hole 2641, so that the positive electrode active material covered by the second positive electrode insulating layer 26 can release lithium ions through the twelfth hole 2641, so as to reduce the possibility that the lithium ions in the positive electrode active material covered by the second positive electrode insulating layer 26 bypass the second positive electrode insulating layer 26 and move to the opposite negative electrode sheet 22. In the present application, the boundaries of the regions in the fourth main body 261, the tenth punching portion 262, the eleventh punching portion 263 and the twelfth punching portion 264 are as follows: Fig.12 The dashed line shown in .

[0088] In some embodiments, the secondary battery 100 satisfies at least one of the following features: (37) The thickness of the first positive electrode insulating layer 24 is H1, 4 μm ≤ H1 ≤ 30 μm, so that the first positive electrode insulating layer 24 has good anti-puncture performance and the first positive electrode insulating layer 24 is not too thick, so as to improve the excessive reduction of the energy density of the secondary battery 100. (38) The thickness of the first negative electrode insulating layer 25 is H2, 4 μm ≤ H2 ≤ 30 μm, so that the first negative electrode insulating layer 25 has good anti-puncture performance and the first negative electrode insulating layer 25 is not too thick, so as to improve the excessive reduction of the energy density of the secondary battery 100. (39) The first positive electrode insulating layer 24 includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide, so that the first positive electrode insulating layer 24 has good insulation performance. (40) The first negative electrode insulating layer 25 includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide, so that the first negative electrode insulating layer 25 has good insulating properties.

[0089] Preferably, the thickness of the second positive electrode insulating layer 26 is H3, 4μm≤H3≤30μm, so that the second positive electrode insulating layer 26 has good anti-puncture performance, and the second positive electrode insulating layer 26 is not too thick, so as to improve the excessive reduction of the energy density of the secondary battery 100. The thickness of the second negative electrode insulating layer 27 is H4, 4μm≤H4≤30μm, so that the second negative electrode insulating layer 27 has good anti-puncture performance, and the second negative electrode insulating layer 27 is not too thick, so as to improve the excessive reduction of the energy density of the secondary battery 100. The second positive electrode insulating layer 26 includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide, so that the second positive electrode insulating layer 26 has good insulation performance. The second negative electrode insulating layer 27 includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide, so that the second negative electrode insulating layer 27 has good insulation performance.

[0090] Preferably, the first positive electrode insulating layer 24, the first negative electrode insulating layer 25, the second positive electrode insulating layer 26 and the second negative electrode insulating layer 27 all include a glue layer and a substrate layer, the glue layer is disposed on one surface of the substrate layer, the glue layer comprises polyolefin and / or modified polyolefin, and an elastomer, a filler and an antioxidant, the elastomer comprises at least one of styrene-ethylene-butylene-styrene block copolymer, polyurethane, polyamide, polybutadiene or polyisobutylene, the filler comprises at least one of titanium dioxide, talcum powder, white carbon black or calcium carbonate, the antioxidant comprises at least one of diphenylamine, trimethyl phosphite, triethyl phosphite or distearyl thiodipropionate. The substrate layer comprises at least one of polyethylene terephthalate, polyimide or polypropylene.

[0091] In the second aspect of the present application, an electronic device is also proposed, including a secondary battery 100 as in any embodiment of the first 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, and the like. Among them, electric toys can include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys, electric airplane toys, and the like, and spacecraft can include airplanes, rockets, space shuttles, spacecraft, and the like.

[0092] Test part:

[0093] 1. Lithium analysis test:

[0094] Lithium deposition test of lithium-ion batteries at 45°C: At 45°C, let the lithium-ion battery stand for 5 minutes, charge to 4.25V at a constant current of 1.5C, then charge to 4.48V at a constant current of 1.2C, then charge to 0.02C at a constant voltage of 4.48V; let stand for 5 minutes, discharge to 3.4V at a constant current of 1C, then discharge to 3.0V at a constant current of 0.2C. Repeat the above steps 700 times, let stand for 5 minutes, then charge to 4.48V at a constant current of 1C, then charge to 0.02C at a constant voltage of 4.48V, finally let stand for 5 minutes, disassemble and observe the degree of lithium deposition at the edge of the first negative electrode insulation layer and the second negative electrode insulation layer.

[0095] Among them, for the calculation method of the lithium deposition degree at the edge of the first negative electrode insulating layer, the lithium deposition area at the edge of the first negative electrode insulating layer without perforations is S11, the lithium deposition area at the edge of the first negative electrode insulating layer of any embodiment or comparative example is S12, and the lithium deposition degree at the edge of the first negative electrode insulating layer of any embodiment or comparative example is V1, then V1 = S12 / S11. For the calculation method of the lithium deposition degree at the edge of the second negative electrode insulating layer, the lithium deposition area at the edge of the second negative electrode insulating layer without perforations is S21, the lithium deposition area at the edge of the second negative electrode insulating layer of any embodiment or comparative example is S22, and the lithium deposition degree at the edge of the second negative electrode insulating layer of any embodiment or comparative example is V2, then V2 = S22 / S21.

[0096] 2. Adhesion test:

[0097] The insulating layer of each embodiment and the adhesive tape in the comparative example are respectively pasted on the aluminum foil, and the aluminum foil pasted with the adhesive tape is cut into strip samples of 20mm×60mm, and hot-pressed at a temperature of 85°C and a pressure of 1MPa for 40min. Then, after being immersed in an electrolyte at 85°C for 4h, the sample is pasted on a steel plate with a double-sided tape (Nitto 5000NS) (the adhesion length is not less than 40mm), and the steel plate is fixed to the corresponding position of a high-speed rail tensile testing machine. The other end of the sample that is not adhered to the steel plate is pulled up, and the sample is clamped in a chuck, wherein the pulled-up sample part has an angle of 180° with the steel plate in space, and the chuck is pulled at a speed of 50mm / min. Finally, the average tensile force in the stable area is measured and recorded as the bonding force after immersion in the electrolyte.

[0098] Among them, the organic solvents of the electrolyte are ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate (EP), and the mass ratio is EC:PC:DEC:EP=3:1:3:3, the solute is lithium hexafluorophosphate (LiPF6), and the concentration of LiPF6 is 1 mol / L.

[0099] Example 1

[0100] <Preparation of positive electrode sheet>:

[0101] The positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride are mixed in a mass ratio of 96:2.0:2.0, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry is 75wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 9μm, and the aluminum foil is dried at 85°C to obtain a positive electrode sheet with a coating thickness of 110μm and a single-sided coating of a positive electrode active material layer. The above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material on both sides. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 85°C for 8h to obtain a positive electrode sheet with a specification of 74mm×851mm. Among them, the positive electrode sheet includes a positive electrode ear. And the first groove is set by laser cleaning.

[0102] <Preparation of negative electrode sheet>:

[0103] The negative electrode active material artificial graphite, the conductive agent Super P, the thickener sodium carboxymethyl cellulose (CMC-Na), and the binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 97.4:1.2:0.7:0.7, deionized water is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry is 70wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm, and the copper foil is dried at 110°C to obtain a negative electrode sheet with a coating thickness of 130μm and a single-sided coating of a negative electrode active material layer. The above steps are repeated on the other surface of the aluminum foil to obtain a negative electrode sheet with a double-sided coating of negative electrode active materials. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 120°C for 12h to obtain a negative electrode sheet with a specification of 76mm×867mm.

[0104] <Preparation of diaphragm>:

[0105] A polyethylene porous polymer film is used as the separator.

[0106] <Electrolyte Preparation>:

[0107] In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), propylene carbonate (PC) and ethyl propionate (EP) were uniformly mixed in a mass ratio of 1:1:1 to form a basic solvent, and finally LiPF6 was added to dissolve and stirred evenly to form an electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the remainder was the basic solvent.

[0108] <Preparation of insulating layer>:

[0109] The insulating layer includes a glue layer arranged on one surface of the base material layer, wherein the thickness of the insulating layer is 20 μm, the thickness of the glue layer is 10 μm, and the thickness of the base material layer is 10 μm.

[0110] Polypropylene, elastomer polyurethane, filler titanium dioxide, and antioxidant diphenylamine are mixed evenly in a mass ratio of 60:25:7.5:7.5, and then coated on a substrate layer and dried at 120° C. to obtain an insulating layer. The substrate layer is a polyethylene terephthalate film.

[0111] The insulating layer is divided into a first punching portion and a first main body portion in the width direction, the ratio of the area of ​​the first punching portion to the area of ​​the first main body portion is 0.5:1, and circular holes are punched in the first punching portion with a hole spacing of 0.5 mm and a hole diameter of 1 mm by laser punching to obtain a first negative electrode insulating layer.

[0112] The non-perforated insulating layer is selected as the first positive electrode insulating layer.

[0113] <Preparation of lithium-ion batteries>:

[0114] The first positive electrode insulating layer is pasted on the surface of the first positive electrode active layer and covers the first groove, and the first negative electrode insulating layer is pasted on the surface of the first negative electrode active layer, and the pasting position is opposite to the position of the first groove. Then the positive electrode sheet, the diaphragm, and the negative electrode sheet are stacked in order, so that the diaphragm is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and the electrode assembly is wound. The electrode assembly is placed in an aluminum-plastic film packaging bag, and the electrolyte is injected after drying. After vacuum packaging, standing, formation, capacity, degassing, trimming and other processes, a lithium-ion battery is obtained. Among them, the formation conditions are to charge to 3.3V at a constant current of 0.02C, then charge to 3.6V at a constant current of 0.1C, and finally charge to 4.45V at a constant current of 0.2C.

[0115] The relevant parameters in Comparative Example 1 and Examples 2 to 6 are shown in Table 1 below.

[0116] Wherein, the first negative electrode insulating layer and the first positive electrode insulating layer in Comparative Example 1 are not perforated.

[0117] The first negative electrode insulating layer in Example 2 is divided into a first perforated portion, a first main portion and a second perforated portion in sequence along the width direction. The ratio of the area of ​​the first perforated portion to the area of ​​the first main portion is 0.5:1, and the ratio of the area of ​​the second perforated portion to the area of ​​the first main portion is 0.5:1. By using the laser punching method, circular holes are punched in the first perforated portion and the second perforated portion with a hole spacing of 0.5 mm and a hole diameter of 1 mm.

[0118] The first negative electrode insulating layer in Example 3 is divided into a first perforated portion, a first main portion and a second perforated portion in sequence along the width direction, and a third perforated portion is divided on one side of the first negative electrode insulating layer along the length direction, the ratio of the area of ​​the first perforated portion to the area of ​​the first main portion is 0.5:1, the ratio of the area of ​​the second perforated portion to the area of ​​the first main portion is 0.5:1, the ratio of the area of ​​the third perforated portion to the area of ​​the first main portion is 0.2:1, and circular holes are punched in the first perforated portion, the second perforated portion and the third perforated portion by laser punching with a hole spacing of 0.5 mm and a hole diameter of 1 mm.

[0119] The first positive electrode insulating layer in Example 4 is divided into a fourth punching portion and a second main body portion along the width direction, and the ratio of the area of ​​the fourth punching portion to the area of ​​the second main body portion is 0.5:1. Using the laser punching method, circular holes are punched in the fourth punching portion with a hole spacing of 0.5 mm and a hole diameter of 1 mm.

[0120] The first positive electrode insulating layer in Example 5 is divided into a fourth perforated portion, a second main portion and a fifth perforated portion in sequence along the width direction. The ratio of the area of ​​the fourth perforated portion to the area of ​​the second main portion is 0.5:1, and the ratio of the area of ​​the fifth perforated portion to the area of ​​the second main portion is 0.5:1. By using the laser punching method, circular holes are punched in the fourth perforated portion and the fifth perforated portion with a hole spacing of 0.5 mm and a hole diameter of 1 mm.

[0121] The first positive electrode insulating layer in Example 6 is divided into a fourth punching portion, a second main body portion and a fifth punching portion in sequence along the width direction, and a sixth punching portion is divided on one side of the first positive electrode insulating layer along the length direction, the ratio of the area of ​​the fourth punching portion to the area of ​​the second main body portion is 0.5:1, the ratio of the area of ​​the fifth punching portion to the area of ​​the second main body portion is 0.5:1, the ratio of the area of ​​the sixth punching portion to the area of ​​the second main body portion is 0.2:1, and circular holes are punched in the fourth punching portion, the fifth punching portion and the sixth punching portion by using a laser punching method with a hole spacing of 0.5 mm and a hole diameter of 1 mm.

[0122] Table 1

[0123]

[0124] According to the above Table 1, combined with Comparative Example 1 and Examples 1 to 3, it can be seen that the lithium ion battery in the embodiment of the present application can effectively improve the lithium plating problem of the lithium ion battery by drilling holes in the first negative electrode insulating layer.

[0125] In combination with Examples 1 to 6, it can be seen that the lithium ion battery in the embodiment of the present application can further improve the lithium plating problem of the lithium ion battery by punching holes in the first negative electrode insulating layer and the first positive electrode insulating layer at the same time.

[0126] The relevant parameters in Examples 7 to 12 are shown in Table 2 below, wherein Examples 7 to 12 only test the first negative electrode insulating layer, and the first negative electrode insulating layer only includes a first main body portion and a first perforated portion that are connected.

[0127] Table 2

[0128]

[0129] According to the above Table 2, combined with Examples 7 to 12, it can be seen that when the ratio of the area of ​​the perforated portion to the area of ​​the main body of the insulating layer in the embodiment of the present application is greater than 7.5:15, the insulating layer cannot obtain good adhesion. At the same time, in actual applications, when the ratio of the area of ​​the perforated portion to the area of ​​the main body is lower than 0.15:15, it is difficult to effectively reduce the degree of lithium plating at the edge of the first negative electrode insulating layer.

[0130] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A secondary battery, comprising a negative electrode sheet, a positive electrode sheet and a separator, wherein the separator is disposed between the adjacent negative electrode sheet and the positive electrode sheet, the positive electrode sheet comprises a positive electrode collector, a first positive electrode active layer and a positive electrode tab, and along the thickness direction of the positive electrode collector, one surface of the positive electrode collector is provided with the first positive electrode active layer; the first positive electrode active layer is provided with a first groove, the positive electrode tab is disposed in the first groove and is electrically connected to the positive electrode collector; characterized in that: A first positive electrode insulating layer is provided on the surface of the first positive electrode active layer facing the negative electrode sheet, and the first positive electrode insulating layer covers the first groove; a first negative electrode insulating layer is provided on the surface of the negative electrode sheet facing the first positive electrode active layer, and along a direction perpendicular to the surface of the first negative electrode insulating layer, a projection of the first negative electrode insulating layer on the first positive electrode active layer covers the first groove; along the width direction of the first groove, a first hole is opened on one side of the first negative electrode insulating layer.

2. The secondary battery according to claim 1, characterized in that: The first negative electrode insulating layer includes a first punching portion and a first main body portion. Along the width direction of the first groove, the first punching portion is connected to one side of the first main body portion, and the first punching portion is provided with the first hole; along the direction perpendicular to the surface of the first negative electrode insulating layer, the projection of the first main body portion on the first positive electrode active layer covers the first groove.

3. The secondary battery according to claim 2, characterized in that: Along the width direction of the first groove, the width of the first body portion is 0.5 mm to 6 mm greater than the width of the first groove.

4. The secondary battery according to claim 2, characterized in that: The first cathode insulating layer satisfies at least one of the following characteristics: (1) A ratio of an area of ​​the first perforated portion to an area of ​​the first main body portion is 0.01:1 to 0.5:1; (2) The shape of the first hole is at least one of circular, elliptical or polygonal.

5. The secondary battery according to claim 2, characterized in that: The first negative electrode insulating layer includes a second perforated portion. Along the width direction of the first groove, the second perforated portion is connected to the other side of the first main body away from the first perforated portion. The second perforated portion is provided with a second hole.

6. The secondary battery according to claim 5, characterized in that: The first cathode insulating layer satisfies at least one of the following characteristics: (3) The ratio of the area of ​​the second perforated portion to the area of ​​the first main body portion is 0.01:1 to 0.5:1; (4) The second hole has a shape of at least one of a circle, an ellipse or a polygon.

7. The secondary battery according to claim 2, characterized in that: The first negative electrode insulating layer includes a third punching portion. Along the length direction of the first groove, the third punching portion is connected to a side of the first main body portion close to the bottom of the first groove. The third punching portion is provided with a third hole.

8. The secondary battery according to claim 7, characterized in that: The first cathode insulating layer satisfies at least one of the following characteristics: (5) The ratio of the area of ​​the third perforated portion to the area of ​​the first main body portion is 0.001:1 to 0.2:1; (6) The shape of the third hole is at least one of circular, elliptical or polygonal.

9. The secondary battery according to claim 1, characterized in that: Along the width direction of the first groove, the width of the first negative electrode insulating layer is smaller than the width of the first positive electrode insulating layer.

10. The secondary battery according to claim 1, characterized in that: The first positive electrode insulating layer includes a fourth punching portion and a second main body portion. Along the width direction of the first groove, the fourth punching portion is connected to one side of the second main body portion, and the fourth punching portion is provided with a fourth hole. Along the direction perpendicular to the surface of the first positive electrode insulating layer, the fourth punching portion at least partially overlaps with the first positive electrode active layer.

11. The secondary battery according to claim 10, characterized in that: Along a direction perpendicular to the surface of the first positive electrode insulating layer, the second main body covers the first groove; along a width direction of the first groove, the width of the second main body is 0.5 mm to 6 mm greater than the width of the first groove.

12. The secondary battery according to claim 10, characterized in that: The first positive electrode insulating layer satisfies at least one of the following characteristics: (7) A ratio of an area of ​​the fourth perforated portion to an area of ​​the second main body portion is 0.01:1 to 0.5:1; (8) The shape of the fourth hole is at least one of circular, elliptical or polygonal.

13. The secondary battery according to claim 10, characterized in that: The first positive electrode insulating layer includes a fifth punching portion. Along the width direction of the first groove, the fifth punching portion is connected to a side of the second main body away from the fourth punching portion. The fifth punching portion is provided with a fifth hole.

14. The secondary battery according to claim 13, characterized in that: The first positive electrode insulating layer satisfies at least one of the following characteristics: (9) The ratio of the area of ​​the fifth perforated portion to the area of ​​the second main body portion is 0.01:1 to 0.5:1; (10) The shape of the fifth hole is at least one of circular, elliptical or polygonal.

15. The secondary battery according to claim 10, characterized in that: The first positive electrode insulating layer includes a sixth punching portion, and along the length direction of the first groove, the sixth punching portion is connected to a side of the second main body portion close to the bottom of the first groove, and the sixth punching portion is provided with a sixth hole.

16. The secondary battery according to claim 15, characterized in that: The first positive electrode insulating layer satisfies at least one of the following characteristics: (11) A ratio of an area of ​​the sixth perforated portion to an area of ​​the second main body portion is 0.001:1 to 0.2:1; (12) The shape of the sixth hole is at least one of a circle, an ellipse or a polygon.

17. The secondary battery according to claim 1, characterized in that: The positive electrode sheet comprises a second positive electrode active layer, and along the thickness direction of the positive electrode current collector, the surface of the positive electrode current collector away from the first positive electrode active layer is provided with the second positive electrode active layer; the second positive electrode active layer is provided with a second groove; A second positive electrode insulating layer is provided on the surface of the second positive electrode active layer facing the negative electrode sheet, and the second positive electrode insulating layer covers the second groove; a second negative electrode insulating layer is provided on the surface of the negative electrode sheet facing the second positive electrode active layer, and along the direction perpendicular to the surface of the second negative electrode insulating layer, the projection of the second negative electrode insulating layer on the second positive electrode active layer covers the second groove; along the width direction of the second groove, a seventh hole is opened on one side of the second negative electrode insulating layer.

18. The secondary battery according to any one of claims 1 to 17, characterized in that: The secondary battery satisfies at least one of the following characteristics: (13) The thickness of the first positive electrode insulating layer is H1, 4 μm≤H1≤30 μm; (14) The thickness of the first negative electrode insulating layer is H2, 4 μm≤H2≤30 μm; (15) The first positive electrode insulating layer includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide; (16) The first negative electrode insulating layer includes at least one of polypropylene, modified polypropylene, styrene-isoprene-styrene copolymer, polyolefin, polyethylene terephthalate, and polyimide.

19. An electronic device, characterized in that: Comprising the secondary battery as claimed in any one of claims 1 to 18.

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