Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and electronic equipment. A negative active material layer is provided with a first groove. The negative pole lug is partially arranged in the first groove, and the other part of the negative pole lug extends out of the negative pole piece. An isolating membrane is arranged on one side, facing the positive pole piece, of the first groove, and the positive pole piece comprises a positive active material layer facing the negative active material layer. The second adhesive layer is adhered to the isolating membrane and comprises a first area and a second area arranged around the first area. In the third direction, the first area coincides with the first groove. The second region includes a first portion and a third portion. The width of the first part is equal to that of the first area in the first direction; in the second direction, the first part is connected with the first area, the length of the first part is Lm1, and Lm1 is larger than or equal to 1 mm and smaller than or equal to 10 mm. In the first direction, the third part is connected with the first area, the width of the third part is Wm3, and Wm3 is larger than or equal to 2mm and smaller than or equal to 15mm. The lithium precipitation risk of the secondary battery is reduced, and the energy density loss of the secondary battery is reduced.

Description

Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in electronic devices such as smartphones, portable notebooks, wearable devices, and smart homes due to their high energy density and environmental advantages. Lithium-ion batteries include positive and negative electrodes, and positive and negative tabs are usually required to lead out the positive and negative electrodes of the lithium-ion battery. For example, grooves are provided on the negative active material layer to connect the negative tabs and lead out the negative electrode. However, the lithium ions released from the corresponding negative tab slots in the positive active material layer may be difficult to embed into the negative active material layer, which can easily lead to lithium plating. Summary of the Invention

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

[0004] In a first aspect, the present application proposes a secondary battery comprising a positive electrode sheet, a separator, a negative electrode sheet, and a negative electrode tab, with the separator interposed between the positive and negative electrode sheets. The negative electrode sheet includes a negative active material layer facing the positive electrode sheet, and the negative active material layer is provided with a first groove. The negative electrode tab is partially disposed in the first groove, with another portion of the negative tab extending out of the negative electrode sheet, with the direction from the negative electrode sheet to the extended portion of the negative tab being a first direction. The separator is disposed on the side of the first groove facing the positive electrode sheet. The positive electrode sheet includes a positive active material layer facing the negative active material layer, and a first adhesive layer is disposed on the surface of the positive active material layer facing the negative active material layer. The first adhesive layer covers the first groove along a third direction. The secondary battery also includes a second adhesive layer adhered to the separator. The second adhesive layer includes a first region and a second region surrounding the first region. The first region overlaps with the first groove along the third direction. The second region includes a first portion and a third portion. Along the first direction, the first portion has the same width as the first region; along the second direction, the first portion is connected to the first region, and the length of the first portion is L m1 , 1 mm≤L m1 ≤10mm. Along the first direction, the third part is connected to the first area, and the width of the third part is W m3 , 2mm≤W m3 ≤15mm. The third direction is the thickness direction of the positive electrode sheet, and the first direction, the second direction and the third direction are perpendicular to each other.

[0005] In the above technical solution, the second area is arranged around the first area, which can form a buffer zone around the first groove, isolating some lithium ions that may diffuse near the first groove, reducing the excessive accumulation of lithium ions near the first groove, and thus reducing the occurrence of lithium plating. In addition, it is limited to 1mm≤L m1 ≤10mm and 2mm≤W m3 ≤15mm, which enables the first part to form a transition area at the edge of the first groove. On the one hand, it can reduce the direct transmission of lithium ions to the first groove, and reduce the direct bypassing of lithium ions by the first area into the first groove or near the first groove, thereby reducing the occurrence of lithium plating; on the other hand, it helps to make the transmission path of lithium ions smoother and reduce the aggregation of lithium ions and transmission barriers caused by structural mutations.

[0006] In addition, the second adhesive layer is directly bonded to the separator, which can effectively reduce damage to the negative electrode active material layer and help improve the integrity and performance stability of the negative electrode active material layer. At the same time, the separator itself has a certain pore structure. Providing a second adhesive layer on it can better control the transmission path and distribution of lithium ions, reduce the lithium creep phenomenon in the first groove, and further reduce the uneven distribution of lithium ions on the surface of the negative electrode active material layer, reducing the risk of lithium plating. Furthermore, bonding the second adhesive layer to the separator can separate the preparation and bonding of the second adhesive layer from the preparation of the negative electrode active material layer, which is conducive to simplifying the secondary battery production process.

[0007] In some embodiments, the second region further includes a second portion, and along the second direction, the first region is connected between the first portion and the second portion; along the first direction, the width of the second portion is equal to the width of the first region. Along the second direction, the length of the first groove is L1, and the length of the second portion is L m2 , 12mm≤L m1 +L1+L m2 ≤35mm. It can reduce the loss of secondary battery energy density and reduce the occurrence of lithium plating. Further, 22mm≤L m1 +L1+L m2 ≤28mm, which can reduce the occurrence of lithium plating and further reduce the energy density loss of secondary batteries.

[0008] In some embodiments, 6 mm ≤ L m1 ≤9mm, which helps the first portion form an effective barrier along the length of the negative electrode sheet, significantly reducing the diffusion of lithium ions toward the vicinity of the first groove, thereby more effectively reducing the risk of lithium plating and improving battery safety and stability. Furthermore, it reduces the space occupied by the first portion and the transition barrier to lithium ions, thereby reducing the energy density loss of the secondary battery.

[0009] In some embodiments, the second region is provided with a plurality of through holes along the third direction. The average porosity of the second region is G2, with a range of 20% ≤ G2 ≤ ​​60%. This ensures that the second adhesive layer has sufficient pores to allow a suitable amount of lithium ions to pass through, maintaining normal charging and discharging of the secondary battery and improving the energy density of the secondary battery. At the same time, this also limits the passage rate of lithium ions, reducing the amount of lithium ions that reach the vicinity of the first groove, thereby reducing problems such as lithium plating caused by excessive lithium ion concentration, thereby improving the safety and stability of the secondary battery.

[0010] In some embodiments, along the second direction, the first portion is divided into a first section and a second section of equal length, and the first section is located between the second section and the first portion. Along the third direction, the first portion is provided with a plurality of through holes, and the average porosity of the first section is G m21 The average porosity of the second section is G m22 , G m21 <G m22 The closer to the first groove, the greater the current density. The first section is closer to the first groove, and the porosity G is set to be relatively small. m21 , which can appropriately limit the transmission speed and number of lithium ions, and reduce the problems such as lithium precipitation caused by excessive lithium ions in high current density areas. m22 The larger the size, the more lithium ions can pass through, so as to meet the demand for lithium ions in the area slightly away from the first groove, making the transmission of lithium ions in the first part of the second area more reasonable and improving the energy density of the secondary battery. m21 ≤40%, 40%≤G m22 ≤60%.

[0011] In some embodiments, the porosity of the first portion gradually increases from the first segment to the second segment, making the transmission of lithium ions throughout the first portion more reasonable, thereby reducing lithium plating and improving the energy density of the secondary battery.

[0012] In some embodiments, along the first direction, the width of the second adhesive layer is W m , 17mm≤W m ≤30mm, which can moderately block the rapid migration of lithium ions near the first groove, thereby reducing excessive aggregation of lithium ions near the first groove, effectively reducing the risk of lithium plating, and improving the safety and stability of the secondary battery.

[0013] In some embodiments, 19.5 mm ≤ W m ≤27mm, the transmission speed of lithium ions can be more reasonably adjusted, so that there will not be too many lithium ions gathered near the first groove to cause lithium deposition, and a certain amount of lithium ions can participate in the electrochemical reaction, and the space occupied by the second glue layer can be reduced, thereby improving the energy density of the secondary battery.

[0014] In some embodiments, 4.5 mm ≤ W m3 ≤12mm, which makes it easier for the third part to block part of the lithium ion transmission, reduce the local high concentration caused by excessive lithium ion transmission, and thus reduce the occurrence of lithium plating; at the same time, it can also reduce the transitional blocking of lithium ions and reduce the space occupied by the second glue layer, thereby improving the energy density of the secondary battery.

[0015] In some embodiments, along the first direction, the third portion is divided into a third section and a fourth section of equal width, and the third section is located between the fourth section and the first region. Along the third direction, the third portion is provided with a plurality of through holes; the average porosity of the third section is G m31 The average porosity of the fourth section is G m32 , G m31 <G m32 , which can reduce lithium plating while increasing the energy density of secondary batteries.

[0016] In some embodiments, the second adhesive layer covers the first adhesive layer along the third direction, reducing lithium ion accumulation near the first groove and reducing lithium plating. This reduces the space occupied by the first adhesive layer, improves the energy density of the secondary battery, and facilitates adhesive application. Furthermore, if 1mm≤L2-L1≤6mm, the impact of the first adhesive layer on the internal space of the secondary battery can be further reduced, further improving the energy density of the secondary battery and facilitating adhesive application. In some embodiments, along the second direction, the second adhesive layer further includes a second portion, and the first region is connected between the first portion and the second portion. Along the second direction, the negative electrode active material layer includes a first end portion and a second end portion that are oppositely disposed. Along the third direction, the projection of the first portion on the negative electrode active material layer is located between the first groove and the first end portion, and the projection of the second portion on the negative electrode active material layer is located between the first groove and the second end portion. Along the second direction, the distance from the first groove to the first end portion is L3, and the distance from the first groove to the second end portion is L4. Along the second direction, the length of the first portion is L m1 , the length of the second part is L m2 L3>L4, L m1 >L m2 ; or, L3 <L4,L m1 <L m2 While reducing the risk of lithium plating, the size of the second glue layer can be reduced, thereby increasing the energy density of the secondary battery.

[0017] In a second aspect, the present application further proposes an electronic device comprising a secondary battery as described in any embodiment of the first aspect above.

[0018] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the following description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] One or more embodiments are exemplarily described by the figures in the accompanying drawings, which are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0020] Figure 1 This is a schematic structural diagram of a secondary battery in some embodiments of the present application; Figure 2 Schematic diagram of the winding structure of the electrode assembly in some embodiments of the present application; Figure 3 Schematic diagram of the stacked structure of the electrode assembly of some embodiments of the present application; Figure 4 Schematic diagram of the stacked structure of the positive electrode sheet, the separator and the negative electrode sheet in some embodiments of the present application; Figure 5 Schematic diagram of the current density of the negative electrode active material layer at the first groove in some embodiments of the present application; Figure 6 Schematic diagram of the structure of the negative electrode plate and the separator in some embodiments of the present application; Figure 7 Schematic diagram of the structure of the negative electrode plate and the separator in some embodiments of the present application; Figure 8 Schematic diagram of the structure of the negative electrode plate and the separator in some embodiments of the present application; Figure 9 A schematic diagram of a portion of the structure of an isolation membrane according to some embodiments of the present application; Figure 10 A schematic diagram of a portion of the structure of an isolation membrane according to some embodiments of the present application; Figure 11 Schematic diagram of the structure of the negative electrode plate and the separator in some embodiments of the present application; Figure 12 Schematic diagram of the structure of the negative electrode sheet and the second adhesive layer in some embodiments of the present application.

[0021] Description of reference numerals: 1000. Secondary battery; 100. Electrode assembly; 10. Positive electrode sheet; 11. Positive electrode current collector; 111. First surface; 112. Second surface; 12. Positive electrode active material layer; 20, negative electrode plate; 20a, first end; 20b, second end; 21, negative electrode current collector; 211, third surface; 212, fourth surface; 22, negative electrode active material layer; 221, first groove; 222, first edge; 30. Isolation film; 40. Negative electrode tab; 50. First adhesive layer; 60, second adhesive layer; 61, first region; 62, second region; 621, first portion; 621a, first section; 621b, second section; 622, second portion; 623, third portion; 623a, third portion; 623b, fourth portion; 200, housing; X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0022] 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 combination 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.

[0023] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments.

[0024] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0025] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0026] 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.

[0027] In the first aspect, the present application proposes a secondary battery 1000, please refer to Figure 1 The secondary battery 1000 includes an electrode assembly 100 , a shell 200 and an electrolyte (not shown). The shell 200 can accommodate the electrode assembly 100 and the electrolyte. The electrolyte in the shell 200 soaks the electrode assembly 100 .

[0028] For the electrode assembly 100, please refer to Figures 1 to 3 The electrode assembly 100 includes a positive electrode sheet 10, a negative electrode sheet 20 and a separator 30. The positive electrode sheet 10, the separator 30 and the negative electrode sheet 20 are stacked and wound, wherein Figure 2 The winding structure of the electrode assembly 100 is shown, for example, the positive electrode sheet 10 and / or the negative electrode sheet 20 are stacked in the thickness direction and wound along the length direction thereof to form a wound electrode assembly 100. In some other embodiments, the electrode assembly 100 may also adopt a laminated structure, wherein Figure 3 The lamination structure of the electrode assembly 100 is shown. Along the third direction Z (the thickness direction of the positive electrode sheet 10 and / or the negative electrode sheet 20), multiple positive electrode sheets 10 and multiple negative electrode sheets 20 are alternately stacked, and an isolation film 30 is set between adjacent positive electrode sheets 10 and negative electrode sheets 20.

[0029] It should be noted that in the embodiments of the present application, the first direction X is the width direction of the positive electrode sheet 10 and / or the negative electrode sheet 20, the second direction Y is the length direction of the positive electrode sheet 10 and / or the negative electrode sheet 20, and the third direction Z is the thickness direction of the positive electrode sheet 10 and / or the negative electrode sheet 20. The first direction X, the second direction Y, and the third direction Z are perpendicular to each other. In the laminated electrode assembly 100, the first direction X may also be the width direction of the positive electrode sheet 10 and / or the negative electrode sheet 20, and the second direction Y may also be the length direction of the positive electrode sheet 10 and / or the negative electrode sheet 20.

[0030] Please refer to Figure 4 The positive electrode sheet 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode current collector 11 can be made of an overall flat aluminum foil, titanium foil, nickel foil, or stainless steel foil. The positive electrode active material layer 12 can be disposed on at least one surface of the positive electrode current collector 11 in the thickness direction, for example, along the third direction Z. The positive electrode current collector 11 includes a first surface 111 and a second surface 112 disposed opposite each other. The positive electrode active material layer 12 can be disposed on the first surface 111 and / or the second surface 112. The positive electrode active material layer 12 includes a positive electrode active material, a conductive agent, and a binder. The above-mentioned material components are mixed, stirred evenly, and coated on the first surface 111 and / or the second surface 112 to obtain the positive electrode active material layer 12. The positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium iron manganese phosphate.

[0031] Please refer to Figure 4The negative electrode sheet 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 can be made of a flat copper foil, titanium foil, nickel foil, stainless steel foil, or silver foil. The negative electrode active material layer 22 can be provided on at least one surface of the negative electrode current collector 21 in the thickness direction, for example, along the third direction Z. The negative electrode current collector 21 includes a third surface 211 and a fourth surface 212 that are arranged opposite to each other. The negative electrode active material layer 22 can be provided on the third surface 211 and / or the fourth surface 212. The negative electrode active material layer 22 includes a negative electrode active material, a conductive agent, and a binder. These materials are mixed, stirred, and evenly coated on the third surface 211 and / or the fourth surface 212 to obtain the negative electrode active material layer 22. The negative electrode active material includes one or more of graphite, soft carbon, hard carbon, elemental silicon, silicon oxides, silicon alloys, and the like.

[0032] In some embodiments, the separator 30 includes a substrate layer (not shown) and a ceramic layer (not shown). The substrate layer includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, polyimide, or polyamide, and the ceramic layer includes at least one of aluminum oxide, magnesium oxide, or zirconium oxide. This allows the separator 30 to adapt to the electrolyte environment within the secondary battery 1000, extending its service life.

[0033] In some other embodiments, the separator 30 may not require a ceramic layer, that is, the separator 30 may only include a substrate layer. A separator 30 without a ceramic layer has greater flexibility, which helps accommodate the expansion of the negative electrode plate 20. Furthermore, it has higher ionic conductivity, which can reduce the internal resistance of the secondary battery 1000 and improve the secondary cycle life. Furthermore, the separator 30 can have a lower thermal shrinkage rate, maintaining good dimensional stability under high temperature conditions, reducing the risk of internal short circuits in the secondary battery 1000 due to thermal shrinkage.

[0034] The secondary battery 1000 also includes a negative electrode tab 40, see Figure 4 The negative electrode tab 40 is connected to the negative electrode plate 20. For example, a first groove 221 is provided in the negative electrode active material layer 22. The first groove 221 can be cleaned out of the negative electrode active material layer 22 by laser cleaning, or a portion of the negative electrode active material layer 22 can be removed by a foaming process, thereby forming the first groove 221, so that the negative electrode current collector 21 is exposed from the first groove 221. A portion of the negative electrode tab 40 is provided in the first groove 221 and connected to the negative electrode current collector 21. The connection method includes but is not limited to welding or conductive adhesive bonding. The other portion of the negative electrode tab 40 extends out of the negative electrode plate 20, wherein the direction from the negative electrode plate 20 to the extended portion of the negative electrode tab 40 is the first direction X.

[0035] Please refer to Figure 4The secondary battery 1000 further includes a first adhesive layer 50 disposed on the surface of the positive electrode active material layer 12 facing the negative electrode active material layer 22. Along the third direction Z, the first adhesive layer 50 covers the first groove 221. The portion of the positive electrode active material layer 12 corresponding to the first groove 221 is covered by the first adhesive layer 50, thereby reducing or preventing the release of lithium ions from this portion of the positive electrode active material layer 12. This allows the negative electrode active material layer 22 to have sufficient residual lithium ions to be embedded, thereby reducing the risk of lithium plating.

[0036] The inventors of this application have found that there is a problem of uneven current density in the first groove 221 of the negative electrode active material layer 22. Figure 5 , Figure 5 A schematic diagram showing the current density of the negative electrode active material layer 22 near the first groove 221 is shown. The darker the color, the greater the current density. Figure 5 It can be seen that the closer to the first groove 221, the greater the current density. When the current density of the negative electrode active material layer 22 is large, a large number of lithium ions are released and reach the surface of the negative electrode active material layer 22 per unit time, which can easily cause lithium ions to accumulate on the surface of the negative electrode active material layer 22, thereby causing lithium plating. In addition, high current density can cause the local polarization of the negative electrode active material layer 22 to increase (the potential in the local area deviates from the equilibrium potential), which may cause the negative electrode potential to decrease. When the negative electrode potential is lower than the potential at which lithium ions are reduced to metallic lithium, lithium plating may occur. Lithium plating may cause safety issues such as internal short circuit and overheating of the secondary battery 1000.

[0037] To reduce the above problems, in the embodiments of this application, please refer to Figure 4 、 Figure 6 as well as Figure 7 The secondary battery 1000 further includes a second adhesive layer 60, which is bonded to the isolation film 30. The second adhesive layer 60 includes a first region 61 and a second region 62 disposed around the first region 61. Along the third direction Z, the first region 61 overlaps with the first groove 221. The second region 62 includes a first portion 621 and a third portion 623. Along the first direction X, the width of the first portion 621 is equal to that of the first region 61. For example, the width of the first portion 621 is W. m1 , the width of the first region 61 is the width W1 of the first groove 221, that is, W m1 =W1. Along the second direction Y, the first portion 621 is connected to the first region 61, and the length of the first portion 621 is L m1 , 1 mm≤L m1 ≤10mm. Along the first direction X, the third portion 623 is connected to the first region 61, and the width of the third portion 623 is W m3 , wherein the width range of the third portion 623 is 2mm≤Wm3 ≤15mm.

[0038] In the embodiment of the present application, the first region 61 overlaps with the first groove 221, so that the first region 61 can directly block part of the lithium ions from being transmitted to the first groove 221, thereby reducing the amount of lithium ions embedded near the first groove 221, thereby reducing the risk of lithium plating due to insufficient residual negative electrode active material layer 22 at the first groove 221. In addition, the second region 62 is arranged around the first region 61, which can further form a buffer zone around the first groove 221, isolating some lithium ions that may diffuse near the first groove 221, reducing excessive aggregation of lithium ions near the first groove 221, and thus reducing the occurrence of lithium plating. Among them, the second region 62 is arranged around the first region 61, and the second region 62 can surround the first region 61 for a full circle, or surround a portion of the first region 61, such as half a circle or 3 / 4 circle around the first region 61.

[0039] Please refer to Figure 6 Along the first direction X, the negative electrode active material layer 22 has a first edge 222, and the first groove 221 may penetrate the first edge 222 or not penetrate the first edge 222. When it does not penetrate the first edge 222, the second region 62 may surround the first region 61, that is, surround the first groove 221, which can effectively reduce the amount of lithium desorption around the first groove 221, thereby reducing the occurrence of lithium plating.

[0040] Furthermore, in the embodiment of the present application, the length of the first portion 621 in the second direction Y is also limited to L m1 , where 1mm≤L m1 ≤10mm, any value between 1mm and 10mm can be selected, for example, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm, etc., which can enable the first portion 621 to form a transition area at the edge of the first groove 221. On the one hand, it can reduce the direct transmission of lithium ions to the first groove 221, and reduce the direct bypassing of lithium ions by the first region 61 into the first groove 221 or near the first groove 221, thereby reducing the occurrence of lithium plating; on the other hand, it helps to make the transmission path of lithium ions smoother and reduce the aggregation of lithium ions and transmission barriers caused by structural mutations.

[0041] If L m1If it is larger, for example, greater than 10mm, it may excessively hinder the transmission of lithium ions, the lithium ion transmission path becomes longer and more complicated, and the migration resistance of electrons and ions inside the secondary battery 1000 increases, thereby increasing the internal resistance of the secondary battery 1000 and affecting the charge and discharge efficiency of the secondary battery 1000, such as causing the charging time of the secondary battery 1000 to be extended and the output current to be reduced during discharge. In addition, since it is difficult for lithium ions to reach the negative electrode active material layer 22, it may also make it difficult for the active material in some areas of the negative electrode active material layer 22 to fully participate in the electrochemical reaction, reducing the utilization rate of the active material. At the same time, the second glue layer 60 occupies a large space, which will directly cause the energy density of the secondary battery 1000 to lose. Furthermore, if the length of the second glue layer 60 is too large, lithium ion aggregation may also occur in the area of ​​the negative electrode active material layer 22 corresponding to the edge of the second glue layer 60, and there is also a certain risk of lithium plating.

[0042] If L m1 If the thickness of the first groove 221 is smaller, for example, less than 1 mm, it is difficult to form a sufficient buffer zone around the first groove 221, and it may be difficult to effectively prevent lithium ions from diffusing near the first groove 221. Lithium ions may still be excessively aggregated near the first groove 221, resulting in uneven distribution of lithium ions inside the secondary battery 1000, causing serious lithium creeping near the first groove 221, and making it difficult to effectively reduce the occurrence of lithium plating.

[0043] In the embodiment of the present application, the width of the third portion 623 in the first direction X is further defined as W. m3 , where 2mm≤W m3 ≤15mm, and any value between 2mm and 15mm can be selected, for example, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, or 15mm. Similarly, the third portion 623 can form a transition region at the edge of the first groove 221. On the one hand, it can reduce the direct transmission of lithium ions to the first groove 221 and reduce the direct bypass of the first region 61 by lithium ions into the first groove 221 or near the first groove 221; on the other hand, it helps to make the transmission path of lithium ions smoother and reduce the aggregation and transmission barriers of lithium ions caused by structural mutations. In addition, the third portion 623 and the first portion 621 work together to further reduce the aggregation of lithium ions near the first groove 221, further reducing the risk of lithium plating.

[0044] The first portion 621 has a length L m1 Similar, W m3 A larger value may excessively hinder the transmission of lithium ions, resulting in an increase in the internal resistance of the secondary battery 1000, affecting the charge and discharge efficiency of the secondary battery 1000, and causing a loss in the energy density of the secondary battery 1000. m3If the diameter is smaller, it is difficult to form a sufficient buffer zone around the first groove 221 , and it is difficult to effectively reduce the occurrence of lithium plating.

[0045] Furthermore, in the embodiments of the present application, the second adhesive layer 60 is directly bonded to the separator 30, effectively reducing damage to the negative electrode active material layer 22 (for example, directly bonding the second adhesive layer 60 to the negative electrode active material layer 22 may damage the negative electrode active material layer 22 during coating or other processes), thereby helping to improve the integrity and performance stability of the negative electrode active material layer 22. Furthermore, since the separator 30 itself has a certain porous structure, the provision of the second adhesive layer 60 thereon can better control the transmission path and distribution of lithium ions, reduce lithium creep in the first groove 221, further reduce the uneven distribution of lithium ions on the surface of the negative electrode active material layer 22, and reduce the risk of lithium plating.

[0046] Furthermore, by bonding the second adhesive layer 60 to the separator 30, the preparation and bonding of the second adhesive layer 60 can be separated from the preparation of the negative electrode active material layer 22, which is conducive to simplifying the production process of the secondary battery 1000. For example, the separator 30 can be glued first and then stacked and assembled with the negative electrode plate 20, which is conducive to controlling each link in the production process. For example, when the second adhesive layer 60 is bonded to the negative electrode active material layer 22, if the bonding position is improper, it will be difficult to adjust. Separating the second adhesive layer 60 from the negative electrode active material layer 22 will inevitably cause significant damage to the negative electrode active material layer 22. If the second adhesive layer 60 is bonded to the separator 30, the position of the second adhesive layer 60 can be adjusted by simply adjusting the stacking position of the separator 30 and the negative electrode plate 20, which is simpler and more convenient to operate.

[0047] Among them, the second adhesive layer 60 can be adhered to the surface of the isolation film 30 facing the positive electrode active material layer 12, and can also be adhered to the surface of the isolation film 30 facing the negative electrode active material layer 22. In the embodiment of the present application, it is preferred that the second adhesive layer 60 is adhered to the surface of the isolation film 30 facing the negative electrode active material layer 22, which can reduce the impact of burrs on the negative electrode tab 40 on the isolation film 30.

[0048] Regarding the material of the second adhesive layer 60 , the second adhesive layer 60 includes a second base material layer (not shown) and a second adhesive layer (not shown). The second adhesive layer is disposed on the surface of the second base material layer facing the isolation film 30 .

[0049] The material of the second substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyamide, spandex, or aramid. For example, polyimide, aramid, and the like have high strength and can withstand certain external impacts and stretching, thereby reducing the risk of cracking or damage to the second adhesive layer 60. Materials such as polyethylene and polypropylene have good flexibility, while materials such as polyethylene terephthalate have low thermal shrinkage and hygroscopic expansion. They can maintain stable dimensions under different temperature and humidity conditions, adapt to the volume changes of the negative electrode plate 20 during the charge and discharge process, and improve the porosity stability of the second adhesive layer 60. Furthermore, the above materials have good corrosion resistance and are not easily corroded or chemically reacted with the electrolyte, thereby improving the performance stability of the second adhesive layer 60. For example, in the case of long-term contact with the electrolyte, the second adhesive layer 60 will not dissolve or deteriorate, thereby extending the service life of the second adhesive layer 60.

[0050] The second adhesive layer is made of at least one of polyolefin, polyacrylate, epoxy resin, or polyacrylic acid. The polar groups on the molecular chains of polyacrylate and polyacrylic acid can interact with lithium ions, promoting their migration within the second adhesive layer 60. Polyolefin can synergize with other ion-conducting components to create a suitable microstructure, providing channels and space for lithium ion transmission, thereby improving the overall ion conductivity of the second adhesive layer 60.

[0051] In some embodiments, please refer to Figure 6 and Figure 7 The second region 62 further includes a second portion 622. Along the second direction Y, the first region 61 is connected between the first portion 621 and the second portion 622. Along the first direction X, the width of the second portion 622 is equal to the width of the first region 61. For example, the width of the second portion 622 is W. m2 , the width of the first region 61 is consistent with the width of the first groove 221, both are W1, then W m2 =W1.

[0052] Along the second direction Y, the length of the first groove 221 is L1, and the length of the second portion 622 is L m2 , 12mm≤L m1 +L1+L m2 ≤35mm, any value between 12mm and 35mm can be selected, for example, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 22mm, 24mm, 26mm, 28mm, 30mm, 32mm, 33mm or 35mm, etc. This can reduce the loss of energy density of the secondary battery 1000 and reduce the occurrence of lithium plating. Further, 22mm≤L m1 +L1+L m2≤28 mm, which can reduce the occurrence of lithium plating and further reduce the energy density loss of the secondary battery 1000.

[0053] In some embodiments, the length of the first portion 621 in the second direction Y is further selected to be 6 mm ≤ L m1 ≤9mm, which helps the first portion 621 form an effective barrier along the length of the negative electrode sheet 20, significantly reducing the diffusion of lithium ions toward the vicinity of the first groove 221, thereby more effectively reducing the risk of lithium plating and improving the safety and stability of the battery. Furthermore, it reduces the space occupied by the first portion 621 and reduces the transition barrier to lithium ions, thereby reducing the energy density loss of the secondary battery 1000.

[0054] The inventors of this application further discovered that the current density near the first groove 221 is higher, and the risk of lithium deposition is higher. However, near the first groove 221, part of the negative electrode active material layer 22 is still capable of undergoing electrochemical reactions. Under the same conditions, the part with higher current density can receive fewer lithium ions than the part with lower current density. Although this part can receive relatively fewer lithium ions, it is not completely unable to receive lithium ions. Both the part with higher current density and the part with lower current density can still exert a certain capacity.

[0055] Please refer to Figure 8 The inventors of the present application provide a plurality of through holes 62a in the second region 62 of the second adhesive layer 60, thereby allowing some lithium ions to be transmitted, thereby allowing the through holes 62a to provide a specific transmission path for the lithium ions. Although the second region 62 is mainly used to isolate the transmission of some lithium ions, the presence of the through holes 62a allows a small amount of lithium ions to pass through. Therefore, during the operation of the secondary battery 1000, some lithium ions can pass from the positive electrode active material layer 12 through the through holes 62a to the negative electrode active material layer 22. This can reduce the inability to fully utilize the local negative electrode active material layer 22 due to excessive isolation of lithium ions, thereby providing a certain capacity for the secondary battery 1000 and improving the energy density of the secondary battery 1000.

[0056] The average porosity of the second region 62 is G2, where 20% ≤ G2 ≤ ​​60%, and any value between 20% and 60% can be selected, such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%. This ensures that the second adhesive layer 60 has sufficient pores to allow a suitable amount of lithium ions to pass through, maintaining normal charging and discharging of the secondary battery 1000 and improving the energy density of the secondary battery 1000. At the same time, it also limits the passage rate of lithium ions, reducing the amount of lithium ions that reach the vicinity of the first groove 221, thereby reducing problems such as lithium plating caused by excessive lithium ion concentration, and helping to improve the safety and stability of the secondary battery 1000.

[0057] If G2 is large, for example, greater than 60%, the lithium ion passage rate will be high, and a large number of lithium ions will flow into the vicinity of the first groove 221, which may lead to excessively high local lithium ion concentration, increase the risk of lithium plating, reduce the safety of the secondary battery 1000, and easily cause uneven lithium ion distribution, affecting the charge and discharge efficiency and cycle stability of the secondary battery 1000. If G2 is small, for example, less than 20%, it may seriously hinder the passage of lithium ions through the second region 62, resulting in insufficient lithium ions reaching the vicinity of the first groove 221, making it difficult to fully utilize the negative electrode active material layer 22, and thus difficult to effectively utilize the capacity of the secondary battery 1000, resulting in a loss of energy density.

[0058] In some embodiments, please refer to Figure 9 , along the second direction Y, the first portion 621 is divided into a first segment 621a and a second segment 621b of equal length. For example, the length of the first segment 621a in the second direction Y is L m21 The length of the second segment 621b in the second direction Y is L m22 , that is, L m21 =L m22 .

[0059] The first section 621a is located between the second section 621b and the first portion 621. Along the third direction Z, the first portion 621 is provided with a plurality of through holes 62a. The average porosity of the first section 621a is G. m21 The average porosity of the second section 621b is G m22 , G m21 <G m22 Since the current density is higher closer to the first groove 221, the first section 621a is closer to the first groove 221 and a relatively small porosity G is set. m21 , which can appropriately limit the transmission speed and number of lithium ions, and reduce the problems of lithium precipitation caused by excessive lithium ions in high current density areas. m22 The larger the size, the more lithium ions can pass through to meet the lithium ion demand of the area slightly away from the first groove 221 , so that the lithium ion transmission in the first part 621 of the second region 62 is more reasonable, thereby improving the energy density of the secondary battery 1000 .

[0060] Further, 20%≤G m21 ≤40%, any value between 20% and 40% can be selected, for example, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38% or 40%, etc. And, 40%≤G m22 ≤60%, any value between 40% and 60% can be selected, for example, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 56%, 58% or 60%, etc.

[0061] For the first section 621a, the current density of the negative electrode active material layer 22 is relatively large. In the embodiment of the present application, it is limited to 20%≤G m21 The porosity range of ≤40% is conducive to precise adaptation to high current density. It can not only allow a certain amount of lithium ions to pass through to maintain the necessary electrochemical reaction, but also effectively control the lithium ion flow, reduce adverse reactions such as lithium plating caused by excessive lithium ions at high current density, and improve the safety and stability of the secondary battery 1000.

[0062] For the second segment 621b, the current density of the negative electrode active material layer 22 corresponding thereto is relatively low. In the embodiment of the present application, the current density is limited to 40%≤G m22 The porosity range of ≤60% can make the lithium ion passage rate relatively high, thereby meeting the lithium ion quantity requirement of the region at a lower current density, facilitating full utilization of the negative electrode active material layer 22 and improving the energy density of the secondary battery 1000 .

[0063] In some embodiments, the porosity of the first portion 621 gradually increases along the direction from the first section 621a to the second section 621b. Since the current density is high near the first groove 221, the risk of lithium deposition is higher. The smaller the porosity, the less lithium ions are transmitted, and the less lithium ions are aggregated near the first groove 221 to cause lithium deposition. The farther away from the first groove 221, the lower the current density. The gradually increased porosity can gradually increase the lithium ion transmission rate, meet the demand for the number of lithium ions at different locations, and make the transmission of lithium ions throughout the first portion 621 more reasonable, thereby reducing lithium deposition while increasing the energy density of the secondary battery 1000.

[0064] In some embodiments, please refer to Figure 9 , in the first direction X, the width of the second adhesive layer 60 is W m , 17mm≤W m ≤30mm, and can be any value between 17mm and 30mm, for example, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm, 23mm, 24mm, 25mm, 26mm, 27mm, 28mm, 29mm or 30mm. The second adhesive layer 60 has a certain barrier effect, and its width is 17mm≤W mWhen the thickness is ≤30 mm, the rapid migration of lithium ions toward the vicinity of the first groove 221 can be moderately blocked, thereby reducing excessive accumulation of lithium ions near the first groove 221, effectively reducing the risk of lithium plating, and improving the safety and stability of the secondary battery 1000. Furthermore, the capacity of the secondary battery 1000 is not affected by excessive space occupation and excessive lithium ion isolation, thereby allowing the secondary battery 1000 to fully utilize its internal active material while ensuring safety, thereby improving the energy density of the secondary battery 1000.

[0065] If W m If the width is too large, it will occupy too much internal space of the secondary battery 1000, and due to the barrier effect of the second adhesive layer 60 on lithium ions, it will be more difficult for lithium ions to bypass the second adhesive layer 60 when the width is large, which will increase the internal resistance of the secondary battery 1000, causing energy loss and affecting the energy density loss of the secondary battery 1000. In addition, lithium ions may also accumulate in the area of ​​the negative electrode active material layer 22 corresponding to the edge of the second adhesive layer 60, and there is also a certain risk of lithium plating. If W m If the thickness of the first groove 221 is too small, the blocking effect on the lithium ion transmission will be insufficient, which may cause the lithium ions to excessively accumulate near the first groove 221, making it impossible to effectively control the distribution of lithium ions and increasing the risk of lithium plating.

[0066] Furthermore, 19.5mm≤W m ≤27mm, which is conducive to more accurate blocking of lithium ions. Under this width, the transmission speed of lithium ions can be more reasonably adjusted, so that there will not be too many lithium ions gathering near the first groove 221 to cause lithium precipitation, and a certain amount of lithium ions can participate in the electrochemical reaction, and the space occupied by the second glue layer 60 can be reduced, thereby improving the energy density of the secondary battery 1000.

[0067] In some embodiments, the width of the third portion 623 may be selected to be 4.5 mm ≤ W m3 ≤12mm, which makes it easier for the third portion 623 to block part of the lithium ion transmission, reduce the local high concentration caused by excessive lithium ion transmission, and thus reduce the occurrence of lithium plating; at the same time, it can also reduce the transitional blocking of lithium ions and reduce the space occupied by the second adhesive layer 60, thereby improving the energy density of the secondary battery 1000.

[0068] In some embodiments, please refer to Figure 10 , along the first direction X, the third portion 623 is divided into a third segment 623a and a fourth segment 623b of equal width. For example, the width of the third segment 623a in the first direction X is W m31 The width of the fourth segment 623b in the first direction X is W m32 , that is, W m31 =W m32The third section 623a is located between the fourth section 623b and the first region 61. Along the third direction Z, the third portion 623 is provided with a plurality of through holes 62a. The average porosity of the third section 623a is G m31 The average porosity of the fourth segment 623b is G m32 , G m31 <G m32 .

[0069] Since the current density increases closer to the first groove 221, the risk of lithium deposition increases. The third section 623a is configured with a relatively small porosity to reduce the number of channels through which lithium ions can pass, thereby reducing the transmission speed of lithium ions. This reduces the excessive accumulation of lithium ions near the first groove 221, where the current density is high, and effectively reduces the risk of lithium deposition. The fourth section 623b is configured with a larger porosity because the current density gradually decreases with increasing distance from the first groove 221. A higher porosity is required to ensure the transmission efficiency of lithium ions, allowing lithium ions to smoothly pass through the fourth section 623b of the third portion 623 and participate in the electrochemical reaction, thereby maintaining the overall performance of the battery.

[0070] For the measurement of the porosity of each part, a scanning electron microscope (SEM) method can be used to observe the microstructure of the pores of the second adhesive layer 60. For example, the average porosity of the first part 621 can be measured. Figure 7 The center line P is the center line of the first portion 621 along the second direction Y, and the center line Q is the center line of the first portion 621 along the first direction X. Five measurement areas are evenly spaced along the center line P, and five measurement areas are evenly spaced along the center line Q. The porosity of each measurement area is determined using SEM and image analysis software. The average porosity of each measurement area is then calculated as the average porosity of the first portion 621. Other portions can be measured similarly, and the porosity of the second region 62 is calculated by calculating the average porosity of each portion.

[0071] To adjust the porosity, a template method can be used to adjust the porosity of the second adhesive layer 60. Solid particles (such as silica or carbon nanotubes) are used as a template. A polymerized adhesive layer is formed around the template. The template is then removed to form a second adhesive layer 60 with a specific pore size. The porosity of the second adhesive layer 60 can be adjusted by controlling the amount or size of the solid particles. Another method for adjusting the porosity is chemical crosslinking. Using chemical crosslinking agents or crosslinking reactions, the crosslinking density and pore size of the second adhesive layer 60 can be controlled.

[0072] In some embodiments, please refer to Figure 2 and Figure 11Along the third direction Z, the second adhesive layer 60 covers the first adhesive layer 50, which can reduce the accumulation of lithium ions near the first groove 221 and reduce the occurrence of lithium plating. Because the second adhesive layer 60 is bonded to the separator 30, the risk of lithium plating is further reduced. Therefore, the length of the first adhesive layer 50 can be adaptively reduced. For example, along the second direction Y, the length of the first groove 221 is L1, and the length of the first adhesive layer 50 is L2. 1mm≤L2-L1≤10mm, and any value between 1mm and 10mm can be selected, such as 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, or 10mm. This can reduce the space occupied by the first adhesive layer 50, improve the energy density of the secondary battery 1000, and facilitate the adhesive application operation. Preferably, 1mm≤L2-L1≤6mm can further reduce the impact of the first adhesive layer 50 on the internal space of the secondary battery 1000, further improve the energy density of the secondary battery 1000, and facilitate the adhesive application operation. In some embodiments, please refer to Figure 12 Along the second direction Y, the second adhesive layer 60 includes a first portion 621 and a second portion 622, with the first region 61 connecting the first portion 621 and the second portion 622. Along the second direction Y, the negative electrode active material layer 22 includes a first end portion 20a and a second end portion 20b that are opposite each other. Along the third direction Z, the projection of the first portion 621 on the negative electrode active material layer 22 is located between the first groove 221 and the first end portion 20a, while the projection of the second portion 622 on the negative electrode active material layer 22 is located between the first groove 221 and the second end portion 20b. Along the second direction Y, the distance from the first groove 221 to the first end portion 20a is L3, and the distance from the first groove 221 to the second end portion 20b is L4.

[0073] The inventors of this application have discovered that for the negative electrode sheet 20, the larger L3 is, the greater the amount of negative electrode active material layer 22 participating in the electrochemical reaction, and the greater the current density between the first groove 221 and the first end 20a. The inventors of this application set the length difference between the first portion 621 and the second portion 622 based on the length L3 from the first groove 221 to the first end 20a and the length L4 from the first groove 221 to the second end 20b.

[0074] For example, along the second direction Y, the length of the first portion 621 is L m1 , the length of the second portion 622 is L m2 When L3>L4, it indicates that the current density between the first groove 221 and the first end 20a is large, and L m1 >L m2 When L3<L4, it indicates that the current density between the first groove 221 and the second end 20b is large, and L m1 <L m2By reasonably setting the length of the first portion 621 and the second portion 622, the risk of lithium plating can be reduced while reducing the size of the second adhesive layer 60, thereby increasing the energy density of the secondary battery 1000. When L3=L4, L m1 With L m2 Set to approximately equal, for example |L m2 -L m1 |≤0.5mm.

[0075] In some other embodiments, when the first region 61 of the second adhesive layer 60 completely covers the first groove 221, the first adhesive layer 50 may not be required. That is, the first groove 221 can be directly isolated by the first region 61. This directly eliminates the space occupied by the first adhesive layer 50, which is beneficial to improving the energy density of the secondary battery 1000.

[0076] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, electronic devices include but are not limited to Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0077] Example 1-1 Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide, the positive electrode conductive agent acetylene black, the positive electrode binder polyvinylidene fluoride (PVDF, weight average molecular weight 5×10 5 ) were mixed in a mass ratio of 94:3:3, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 75wt%. This was then stirred evenly in a vacuum mixer. An aluminum foil with a thickness of 8μm and a length of 1000mm was used as the positive electrode current collector. The positive electrode slurry was evenly coated on one surface of the aluminum foil and dried at 110°C to obtain a positive electrode sheet coated on one side with a positive electrode active material layer. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode active material layer.

[0078] Preparation of negative electrode sheet: The negative electrode active materials, graphite powder, silicon powder, conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR), were mixed in a weight ratio of 87.5:10:1:1.5. Deionized water was then added as a solvent to create a negative electrode slurry with a solids content of 50 wt%, which was then stirred evenly. A copper foil with a thickness of 5 μm and a length of 1050 mm was used as the negative electrode current collector. The negative electrode slurry was evenly coated on one surface of the negative electrode current collector copper foil, leaving an uncoated area on the foil. The foil was then dried at 90°C to produce a single-sided negative electrode sheet. After completing these steps, the negative electrode sheet was coated on one side. The above steps were then repeated on the other side of the negative electrode sheet to produce a negative electrode sheet coated on both sides with the negative electrode active material layer.

[0079] Preparation of isolation membrane: Polyethylene was selected as a 7 μm substrate layer, and polyvinylidene fluoride was selected as an adhesive layer. An alumina ceramic layer with a thickness of 2 μm was set on the side of the adhesive layer away from the substrate layer to prepare a porous isolation membrane.

[0080] Preparation of the second adhesive layer Polyethylene terephthalate was selected as the second substrate layer, and polyacrylate was used as the second adhesive layer to prepare a 12 mm long and wide (L m1 +L1+L m2 )×17mm(W m ) and bond the second adhesive layer to the release film. Similarly, prepare a first adhesive layer with a length and width of 11 mm (L2) x 16 mm. Bond the second adhesive layer to the release film.

[0081] Electrolyte preparation: In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solvent, and then lithium hexafluorophosphate was added to the organic solvent to dissolve and mix uniformly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0082] Preparation of lithium-ion secondary batteries: By laser cleaning, a first groove of 10mm (L1) × 15mm (W1) is cleaned in the above-mentioned negative active material layer, and a nickel sheet is selected as the negative electrode tab, and the negative electrode tab is welded to the negative electrode sheet in the first groove. After the positive electrode sheet is welded to the positive electrode tab, the first adhesive layer is bonded to the positive active material layer. The isolation membrane, positive electrode sheet, isolation membrane, and negative electrode sheet prepared above are stacked in order and wound to obtain an electrode assembly. Observed along the thickness direction of the positive electrode sheet, the second adhesive layer and the first adhesive layer cover the first groove, the part of the second adhesive layer covering the first groove is the first area, and the part exceeding the first groove is the second area. Along the winding direction of the electrode assembly, both sides of the second adhesive layer exceed the first groove, and the part exceeding on one side is the first part, with a length of L m1 1mm; the part on the other side that exceeds is the second part, length L m2 Along the width direction of the negative electrode sheet, the second glue layer exceeds the second groove on the side of the first groove away from the edge. This part is the third part, with a width of W m3 2mm.

[0083] Unlike Example 1-1, the relevant parameters of Examples 1-2 to 1-26 and Comparative Examples 1-1 to 1-7 are shown in Table 1 below. In Comparative Example 1-1, no second adhesive layer is bonded to the isolation film. In Examples 1-14 to 1-26, the first portion is divided into a first segment and a second segment of equal length, the first segment being located between the second segment and the first portion, and the average porosity G of the first segment is 0.01%. m11 and the average porosity G of the second segment m12 As shown in Table 1 below.

[0084] Lithium deposition test method: Place the lithium-ion secondary battery at a test temperature of 25°C for 30 minutes and perform step-by-step charging according to the following charging steps: (1) 5C constant current charging to 4.23V, constant voltage charging to 4C; (2) 4C constant current charging to 4.3V, constant voltage charging to 3C; (3) 3C constant current charging to 4.4V, constant voltage charging to 2C; (4) 2C constant current charging to 4.5V, constant voltage charging to 0.05C; After standing for 10 minutes, discharge according to the following steps: 0.2C DC discharge to 3V.

[0085] The above charge and discharge process is one cycle. After 100 cycles, when the lithium-ion secondary battery is in a fully charged state (the battery is designed to have a maximum voltage of 4.5V), the secondary battery is disassembled to obtain the positive electrode sheet, the separator and the negative electrode sheet. If the lithium deposition area near the first groove is greater than or equal to 2mm 2, it is determined to be lithium deposition. Each group tests 20 lithium-ion batteries. The number of lithium depositions is X, and the lithium deposition rate is X / 20.

[0086] Table 1

[0087] According to Table 1 above, combined with Examples 1-1 to 1-13 and Comparative Examples 1-1 to 1-7, in Comparative Example 1-1, the second adhesive layer is not bonded to the isolation film, which easily causes lithium ions to accumulate near the first groove, resulting in a higher risk of lithium plating.

[0088] In Comparative Example 1-2, the length L of the first portion is m1 Small, it is difficult to form a sufficient buffer zone around the first groove, lithium ions tend to over-aggregate near the first groove, and the risk of lithium deposition is high. m1 The larger the size, the larger the space occupied, and the more the lithium ion transmission is hindered, which not only leads to the loss of energy density of the secondary battery, but also affects the charge and discharge efficiency of the secondary battery. m1 A larger size may also cause lithium ions to accumulate at the edge of the second glue layer, which may also lead to lithium plating to a certain extent.

[0089] In Comparative Examples 1-4, the width W of the third portion is m3 It is too small to form a sufficient buffer zone around the first groove, and it is difficult to effectively reduce the occurrence of lithium deposition. m3 The larger the W, the more likely it is to hinder the lithium ion transmission, resulting in an increase in the internal resistance of the secondary battery, affecting the charge and discharge efficiency of the secondary battery, and causing a loss in the energy density of the secondary battery. m1 A larger size may also cause lithium ions to accumulate at the edge of the second glue layer, which may also lead to lithium plating to a certain extent.

[0090] In Comparative Examples 1-6, the length L of the first portion m1 and the width W of the third part m3 The length L of the first part is relatively small, which makes it difficult to effectively limit the transmission of lithium ions and increases the risk of lithium deposition. m1 and the width W of the third part m3 They are all large, occupy a large space, and will excessively hinder the transmission of lithium ions, which will not only cause the loss of energy density of the secondary battery, but also cause lithium ions to accumulate at the edge of the second glue layer, and it is also easy to cause lithium plating.

[0091] Therefore, in the embodiments of the present application, in combination with embodiments 1-1 to 1-7, 1 mm≤L m1 ≤10mm; Combined with Examples 1-8 to 1-13, select 2mm≤W m3 ≤15mm. The first portion can form a transition region at the edge of the first groove. On the one hand, this can reduce the direct transmission of lithium ions into the first groove and reduce the direct bypass of the first region into the first groove or the vicinity of the first groove, thereby reducing the occurrence of lithium plating. On the other hand, it helps to make the lithium ion transmission path smoother and reduce lithium ion aggregation and transmission barriers caused by structural mutations.

[0092] For the entire second adhesive layer, the length of the second adhesive layer can be selected as L m , that is, L m =L m1 +L1+L m2 , select 12mm≤L m1 +L1+L m2 ≤35mm; Select the width of the second adhesive layer to be 17mm≤W m ≤30mm.

[0093] In Examples 1-5 to 1-6, the risk of lithium plating is low and the impact on the energy density of the secondary battery is small; similarly, in Examples 1-10 to 1-12 and Example 1-4, the risk of lithium plating is low and the impact on the energy density of the secondary battery is small. Considering the reduction of the occurrence of lithium plating and the reduction of the impact on the energy density of the secondary battery, in the embodiments of the present application, it is preferred that 6mm≤L m1 ≤9mm, and preferably 4.5mm≤W m3 ≤12mm.

[0094] For the entire second adhesive layer, its length is preferably 22mm≤L m1 +L1+L m2 ≤28mm, its width is preferably 19.5mm≤W m ≤27mm.

[0095] In combination with Examples 1-14 to 1-22, in Example 1-22, the average porosity G2 of the second region is large, which will result in a high lithium ion passage rate, and a large number of lithium ions will flow into the vicinity of the first groove, which can easily cause the local lithium ion concentration to be too high, increasing the risk of lithium plating. In Example 1-14, the average porosity G2 of the second region is small, which may seriously hinder the passage of lithium ions through the second region, resulting in insufficient number of lithium ions reaching the vicinity of the first groove, making it difficult to fully utilize the negative electrode active material layer, and the capacity of the secondary battery is difficult to be effectively utilized, resulting in energy density loss. In addition, the lithium plating rate of Example 1-14 is similar to that of Example 1-15, while in Example 1-15, the porosity is greater than that of Example 1-14, and the effect on energy density is small. Therefore, in the embodiments of the present application, in combination with Examples 1-15 to 1-21, 20%≤G2≤60% can be selected.

[0096] Combined with Examples 1-23 to 1-26 and Example 1-18, in Example 1-23, the average porosity of the second section is G m22 Large, may cause too many lithium ions to pass through, may cause lithium ion aggregation, there is a certain risk of lithium precipitation. In Example 1-26, the average porosity of the first section is greater than the average porosity of the second section, the risk of lithium precipitation is greater. Combined with Examples 1-24 to 1-25 and Example 1-18, the risk of lithium precipitation is low. Therefore, in this application, 20%≤G m21 ≤40%, and 40%≤G m22 ≤60%.

[0097] In Examples 1-24 to 1-25, the risk of lithium deposition is further reduced, preferably G m21 <G m22 Since the current density is greater closer to the first groove, the first section is closer to the first groove, and a relatively small porosity is set in the first section, which can appropriately limit the transmission speed and number of lithium ions, and reduce problems such as lithium plating caused by excessive lithium ions in high current density areas.

[0098] Different from Example 1-1, the relevant parameters in Examples 2-1 to 2-8 are shown in Table 3 below, wherein the length of the first adhesive layer is L2, and the length of the first groove is L1.

[0099] Table 2

[0100] In combination with Example 1-1 and Examples 2-1 to 2-8, in Example 2-1, the length L2 of the first adhesive layer is relatively small, and the current density near the first groove is relatively large, which may make it difficult for the first adhesive layer to effectively cover this part, and the lithium ion deintercalation reaction is still intense, and the risk of lithium plating is still high. In Example 2-8, the length L2 of the first adhesive layer is relatively large, which affects the energy density of the secondary battery, and the lithium plating rate of Example 2-8 is similar to that of Example 2-7. However, in Example 2-7, the length of the first adhesive layer is smaller, and the impact on the energy density of the secondary battery is smaller. Therefore, in the embodiments of the present application, in combination with Examples 2-2 to 2-7, 1mm≤L2-L1≤10mm can be selected.

[0101] In Examples 1-1 and 2-2 to 2-5, the lithium plating rates are all relatively low, and the length of the first glue layer is smaller, so that part of the active material layer near the negative electrode of the first groove can still participate in the electrochemical reaction, which can further improve the energy density of the secondary battery. Therefore, in the embodiments of the present application, 1mm≤L2-L1≤6mm can be preferably used.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Based on the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes in different aspects of the present application as described above. For the sake of simplicity, they are not provided in detail. Although the present application has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary battery, comprising a positive electrode sheet, a separator, a negative electrode sheet and a negative electrode tab, wherein the separator is stacked between the positive electrode sheet and the negative electrode sheet; the negative electrode sheet comprises a negative electrode active material layer facing the positive electrode sheet, and the negative electrode active material layer is provided with a first groove; the negative electrode tab is partially provided in the first groove, and the other part of the negative electrode tab extends out of the negative electrode sheet, and the direction of the negative electrode sheet pointing to the protruding part of the negative electrode tab is a first direction; the separator is provided on the side of the first groove facing the positive electrode sheet, the positive electrode sheet comprises a positive electrode active material layer facing the negative electrode active material layer, and a first glue layer is provided on the surface of the positive active material layer facing the negative active material layer, and along a third direction, the first glue layer covers the first groove, characterized in that ； The secondary battery further includes a second adhesive layer, the second adhesive layer being bonded to the isolation film, the second adhesive layer including a first region and a second region disposed around the first region; along the third direction, the first region coincides with the first groove; The second region includes a first portion and a third portion; Along the first direction, the first portion has a width equal to that of the first region; Along the second direction, the first portion is connected to the first region, and the length of the first portion is L m1 , 1 mm≤L m1 ≤10mm; Along the first direction, the third portion is connected to the first region, and the width of the third portion is W. m3 , 2mm≤W m3 ≤15mm; The third direction is the thickness direction of the positive electrode sheet, and the first direction, the second direction and the third direction are perpendicular to each other.

2. The secondary battery according to claim 1, wherein The second region further includes a second portion, and along the second direction, the first region is connected between the first portion and the second portion; along the first direction, the width of the second portion is equal to the width of the first region; Along the second direction, the length of the first groove is L1, and the length of the second portion is L m2 , 12mm≤L m1 +L1+L m2 ≤35mm.

3. The secondary battery according to claim 2, wherein 22mm≤L m1 +L1+L m2 ≤28mm。 4. The secondary battery according to claim 1, wherein 6mm≤L m1 ≤9mm。 5. The secondary battery according to claim 1, wherein A plurality of through holes are provided in the second region along the third direction, and an average porosity of the second region is G2, where 20%≤G2≤60%.

6. The secondary battery according to claim 1, wherein Along the second direction, the first portion is divided into a first segment and a second segment of equal length, and the first segment is located between the second segment and the first portion; Along the third direction, the first portion is provided with a plurality of through holes, and the average porosity of the first section is G m21 The average porosity of the second section is G m22 , G m21 <G m22 .

7. The secondary battery according to claim 6, characterized in that 20%≤G m21 ≤40%,40%≤G m22 ≤60%。 8. The secondary battery according to claim 6, wherein The porosity of the first portion gradually increases along a direction from the first section to the second section.

9. The secondary battery according to claim 1, wherein Along the first direction, the width of the second adhesive layer is W m , 17mm≤W m ≤30mm.

10. The secondary battery according to claim 9, wherein 19.5mm≤W m ≤27mm。 11. The secondary battery according to claim 1, wherein 4.5mm≤W m3 ≤12mm。 12. The secondary battery according to claim 1, wherein Along the first direction, the third portion is divided into a third segment and a fourth segment with equal widths, and the third segment is located between the fourth segment and the first region; Along the third direction, the third portion is provided with a plurality of through holes; the average porosity of the third section is G m31 The average porosity of the fourth section is G m32 , G m31 <G m32 .

13. The secondary battery according to any one of claims 1 to 12, characterized in that: Along the third direction, the second adhesive layer covers the first adhesive layer.

14. The secondary battery according to any one of claims 1 to 12, characterized in that: Along the second direction, the length of the first groove is L1, the length of the first adhesive layer is L2, and 1mm≤L2-L1≤10mm.

15. The secondary battery according to claim 14, characterized in that 1mm≤L2-L1≤6mm.

16. The secondary battery according to any one of claims 1 to 12, characterized in that: Along the second direction, the second adhesive layer further includes a second portion, and the first region is connected between the first portion and the second portion; Along the second direction, the negative electrode active material layer includes a first end portion and a second end portion that are opposite to each other; along the third direction, a projection of the first portion on the negative electrode active material layer is located between the first groove and the first end portion, and a projection of the second portion on the negative electrode active material layer is located between the first groove and the second end portion; Along the second direction, the distance from the first groove to the first end is L3, and the distance from the first groove to the second end is L4; Along the second direction, the length of the first portion is L m1 , the length of the second part is L m2 ; L3>L4, L m1 >L m2 ; or, L3 <L4,L m1 <L m2 .

17. An electronic device, characterized in that: The secondary battery according to any one of claims 1 to 16 is included.

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