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, one part of a negative tab is arranged in the first groove, and the other part of the negative tab extends out of the negative active material layer along a first direction. The secondary battery further comprises a first adhesive layer, the first adhesive layer is arranged on the surface, facing the negative pole piece, of the positive active material layer, and the first groove is covered with the first adhesive layer in the third direction. In the first direction, the width of the first adhesive layer in the second direction is increased. In the second direction, the maximum length of the first adhesive layer is L, the length of the first groove is L1, and L / L1 is larger than or equal to 1.3 and smaller than or equal to 3.5. The length of the first adhesive layer is set according to the current density of the negative electrode active material layer at the first groove, so that lithium precipitation can be reduced, and the influence of the first adhesive layer on the energy density of the secondary battery can be 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. Positive and negative electrodes are usually required to lead out the positive and negative electrodes of the lithium-ion battery. For example, a groove is provided on the active material layer of the negative electrode to connect the negative electrode tab and lead out the negative electrode. However, the lithium ions released from the active material layer of the positive electrode corresponding to the groove of the negative electrode tab may be difficult to embed into the negative electrode active material layer, which can easily lead to lithium deposition at the groove of the negative electrode tab. Summary of the Invention

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

[0004] In order to solve the technical problems, the embodiments of the present application adopt the following technical solutions:

[0005] In a first aspect, the present application provides a secondary battery comprising a stacked or stacked and wound positive electrode sheet, a separator, and a negative electrode sheet. The negative electrode sheet includes a negative active material layer facing the positive electrode sheet, and the positive electrode sheet includes a positive active material layer facing the negative active material layer. The secondary battery also includes a negative electrode tab. The negative electrode active material layer is provided with a first groove, with a portion of the negative electrode tab disposed in the first groove and another portion of the negative electrode tab extending out of the negative electrode sheet in a first direction. The secondary battery also includes a first adhesive layer disposed on a surface of the positive electrode active material layer facing the negative electrode sheet. Along a third direction, the projection of the first adhesive layer covers the first groove. Along the first direction, the width of the first adhesive layer increases in a second direction. Along the second direction, the maximum length of the first adhesive layer is L, and the length of the first groove is L1, where 1.3 ≤ L / L1 ≤ 3.5. The third direction is the thickness direction of the positive and / or negative electrode sheet, and the first, second, and third directions are mutually perpendicular.

[0006] In the above technical solution, the length of the first adhesive layer is set according to the current density of the negative electrode active material layer at the first groove. In the edge region in the first direction, the current density is relatively high. The higher the current density in this edge region, the higher the risk of lithium plating. The first adhesive layer is set to have a larger width in the second direction. This can isolate the portion of the negative electrode active material layer with a higher current density in the edge region, thereby reducing the accumulation of lithium ions in the edge region and thus reducing the occurrence of lithium plating. Setting the length gradient of the first adhesive layer according to the above current density can optimize the distribution of the reaction zones between the positive and negative electrode active material layers, thereby reducing lithium plating while improving the utilization rate of the positive and negative electrode active material layers, thereby increasing the energy density of the secondary battery.

[0007] And by limiting 1.3≤L / L1≤3.5, the part with higher current density can be isolated by the first glue layer, reducing the aggregation of lithium ions near the first groove, thereby reducing the occurrence of lithium plating. In addition, the loss of energy density of the secondary battery can be reduced, which can facilitate achieving a balance between reducing energy density loss and reducing the occurrence of lithium plating. At the same time, by limiting 1.3≤L / L1≤3.5, the local polarization of the negative electrode active material layer is reduced, which can reduce the decomposition of the electrolyte, thereby reducing the generation of the solid electrolyte interface (SEI) film, and further reducing lithium plating. In addition, the heat concentration at the first groove can be alleviated, the occurrence of side reactions can be reduced, and the performance of the secondary battery can be improved.

[0008] In some embodiments, along the first direction, the maximum width of the first adhesive layer is W, the width of the first groove is W1, and 1.1≤W / W1≤2. This can reduce energy density loss while reducing lithium plating.

[0009] In some embodiments, 2≤L / L1≤2.8; and / or 1.33≤W / W1≤1.87, which can further reduce lithium plating while reducing the impact of the first adhesive layer on the energy density of the secondary battery.

[0010] In some embodiments, along the second direction, the first adhesive layer includes a first part and a second part arranged in sequence, and the second part is connected to the first part. Along the first direction, the width of the second part is equal to the width of the first part. Along the third direction, the first part coincides with the first groove. Along the second direction, the maximum length of the second part is L2, 0.15≤L2 / L1≤1.25. Setting the length of the second part according to the above-mentioned current density can reduce the occurrence of lithium plating on one side of the length direction of the first groove and reduce the loss of energy density of the secondary battery. Optionally, 1.5mm≤L2≤12.5mm.

[0011] In some embodiments, 0.6≤L2 / L1≤0.9, optionally, 6mm≤L2≤9mm, which can reduce the impact on energy density while reducing lithium plating.

[0012] In some embodiments, 8 mm ≤ L1 ≤ 20 mm.

[0013] In some embodiments, a first through hole is formed in the second portion along the third direction. The first through hole exposes a portion of the positive electrode active material layer. This exposed portion of the positive electrode active material layer can undergo a lithium ion deintercalation reaction with the portion of the negative electrode active material layer that can exert its capacity, thereby improving the utilization rate of the positive and negative electrode active material layers and thereby increasing the energy density of the secondary battery.

[0014] In some embodiments, when viewed along the third direction, the area of ​​the second portion is S1, the area occupied by all the first through holes on the second portion is S2, and 40%≤S2 / S1≤60%. This can reduce the risk of lithium plating while improving the utilization rate of the negative electrode active material layer and the positive electrode active material layer, thereby improving the energy density of the secondary battery.

[0015] In some embodiments, the radius of the first through hole is R1, 0.1 mm ≤ R1 ≤ 1 mm, which can reduce the risk of lithium plating while improving the utilization rate of the negative electrode active material layer, thereby improving the energy density of the secondary battery.

[0016] In some embodiments, the second portion includes a first region and a second region, and along the second direction, the first region is located between the first portion and the second region. Along the first direction, the maximum width of the first region is W2, and the maximum width of the second region is W3, W3 < W2. In the second portion, the closer to the first groove, the greater the current density. The closer the second region is to the first groove, by limiting W3 < W2, the occurrence of lithium plating can be further reduced, and the impact of the first glue layer on the energy density of the secondary battery can be reduced.

[0017] In some embodiments, along the second direction, a width of the first region is equal to a width of the second region.

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

[0019] The negative electrode active material layer corresponding to the first region has a higher current density, a higher risk of lithium plating, and less negative electrode active material that can exert its capacity. By setting the pore density of the first region to be smaller, the amount of lithium desorption in the first region can be reduced, thereby reducing the occurrence of lithium plating in the negative electrode active material layer. The negative electrode active material layer corresponding to the second region has a lower current density, a lower risk of lithium plating, and more negative electrode active material that can exert its capacity. By setting the pore density of the second region to be larger, the amount of lithium desorption in the second region can be increased, which can facilitate more negative electrode active material to participate in the electrochemical reaction and improve the energy density of the secondary battery. By reasonably setting the distribution of the first through holes in the second part, the energy density of the secondary battery can be improved while reducing lithium plating.

[0020] In some embodiments, the positive electrode active material layer has an edge region on the side where the negative electrode tab extends, and the first adhesive layer covers a portion of the edge region. This can reduce the accumulation of lithium ions at the edge of the negative electrode active material layer, reduce the occurrence of lithium plating, and reduce the occurrence of side reactions.

[0021] In some embodiments, the width of the second portion in the first direction gradually decreases from the first portion to the second portion, which is closer to the gradient design of current density, can further reduce the occurrence of lithium plating, and can further reduce the impact of the first glue layer on the energy density of the secondary battery.

[0022] In some embodiments, the first adhesive layer further includes a third part, and along the second direction, the third part, the first part and the second part are arranged in sequence, and the third part is connected to the first part. Along the first direction, the width of the third part is equal to the width of the first part. Along the second direction, the maximum length of the third part is L3, 0.15≤L3 / L1≤1.25. According to the current density, the maximum length of the second part can be set close to the above-mentioned edge area, that is, in the second section, which can reduce the occurrence of lithium plating on the other side of the length direction of the first groove and reduce the loss of energy density of the secondary battery. Optionally, 1.5mm≤L3≤12.5mm.

[0023] In some embodiments, 0.6≤L3 / L1≤0.9, optionally, 6mm≤L3≤9mm, which can reduce the impact on energy density while reducing lithium plating.

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

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

[0026] The negative electrode active material layer corresponding to the fourth region has a higher current density, a higher risk of lithium plating, and less negative electrode active material that can exert its capacity. By setting the pore density of the first region to be smaller, the amount of lithium desorption in the fourth region can be reduced, thereby reducing the occurrence of lithium plating in the negative electrode active material layer. The negative electrode active material layer corresponding to the third region has a lower current density, a lower risk of lithium plating, and more negative electrode active material that can exert its capacity. By setting the pore density of the third region to be larger, the amount of lithium desorption in the third region can be increased, which can facilitate more negative electrode active material to participate in the electrochemical reaction and improve the energy density of the secondary battery. By reasonably setting the distribution of the first through holes in the second part, the energy density of the secondary battery can be improved while reducing lithium plating.

[0027] In some embodiments, the first adhesive layer further includes a fourth portion, which is disposed sequentially with the first portion along the first direction and is connected to the first portion. Along the third direction, the first portion overlaps with the first groove, and the fourth portion is disposed within the positive electrode active material layer. Along the first direction, the maximum width of the fourth portion is W4, with a range of 1.5 mm ≤ W4 ≤ 15 mm. This can reduce energy density loss while also minimizing lithium plating. Furthermore, 5 mm ≤ W4 ≤ 13 mm.

[0028] In some embodiments, the fourth portion includes a fifth region and a sixth region arranged in sequence, and along the first direction, the sixth region is located between the first portion and the fifth region. Along the second direction, the maximum length of the fifth region is L 51 , the maximum length of the sixth region is L 61 , L 51 <L 61 On the side of the first groove away from the edge of the negative electrode active material layer, the closer to the first groove, the greater the current density. Similarly, the length gradient of the fourth part can be set according to the current density to optimize the distribution of the fourth part, thereby reducing the loss of energy density and the occurrence of lithium plating.

[0029] In some embodiments, along the first direction, a width of the fifth region is equal to a width of the sixth region.

[0030] In some embodiments, a third through hole is provided in the fourth portion along the third direction, so that part of the positive electrode active material layer is exposed. The exposed part of the positive electrode active material layer can undergo lithium ion deintercalation reaction with the part of the negative electrode active material layer that can exert the capacity, thereby improving the utilization rate of the positive electrode active material layer and the negative electrode active material layer, thereby improving the energy density of the secondary battery.

[0031] In some embodiments, the fourth portion includes a fifth region and a sixth region. Along the first direction, the sixth region is located between the first portion and the fifth region. When viewed along the third direction, the area of ​​the fifth region is S 51 The sum of the areas of all third through holes in the fifth region is S 61 Observing along the third direction, the area of ​​the sixth region is S 52 The sum of the areas of all third through holes in the sixth region is S 62 , S 61 / S 51 >S 62 / S 52 .

[0032] The negative electrode active material layer corresponding to the sixth region has a higher current density, a higher risk of lithium plating, and less negative electrode active material that can fully utilize its capacity. By setting the pore density of the sixth region to a lower value, the amount of lithium desorption in the sixth region can be reduced, thereby reducing the occurrence of lithium plating in the negative electrode active material layer. The negative electrode active material layer corresponding to the fifth region has a lower current density, a lower risk of lithium plating, and more negative electrode active material that can fully utilize its capacity. By setting the pore density of the fifth region 1 to a higher value, the amount of lithium desorption in the fifth region can be increased, allowing more negative electrode active material to participate in the electrochemical reaction and improving the energy density of the secondary battery. By reasonably setting the distribution of the third through holes in the fourth portion, the energy density of the secondary battery can be increased while reducing lithium plating.

[0033] In some embodiments, along the second direction, the first adhesive layer includes a third portion, a first portion, and a second portion arranged in sequence, the third portion being connected to the first portion, and the second portion being connected to the first portion. Along the second direction, the negative electrode active material layer includes a first end portion and a second end portion arranged opposite each other, the second portion being located between the first groove and the first end portion, and the third portion being located between the first groove and the second end portion. Along the second direction, the length from the first groove to the first end portion is L4, and the length from the negative electrode tab to the second end portion is L5. Along the second direction, the length of the second portion is L2, and the length of the third portion is L3. L4>L5, L2>L3; or, L4<L5, L2<L3. By reasonably setting the lengths of the second and third portions, the size of the first adhesive layer can be reduced while reducing the risk of lithium plating, thereby increasing the energy density of the secondary battery.

[0034] In some embodiments, along the third direction, the thickness of the positive electrode active material layer covered by the first glue layer is H1, and the thickness of the positive electrode active material layer not covered by the first glue layer is H2, H1<H2, so that the amount of the positive electrode active material layer covered by the first glue layer is reduced, which can reduce the impact of the first glue layer on the energy density of the secondary battery.

[0035] In some embodiments, along the third direction, the thickness of the first glue layer is H3, H1+H3≤H2, so that the first glue layer does not occupy the thickness of the positive electrode active material layer, fully improving the energy density of the secondary battery and reducing the occurrence of lithium plating.

[0036] In some embodiments, the first adhesive layer includes a substrate layer and an adhesive layer, and the adhesive layer is disposed on the surface of the substrate layer facing the positive electrode active material layer. The material of the substrate layer includes at least one of polyethylene terephthalate or polyimide, so that the substrate layer has good insulation properties, mechanical strength and high temperature resistance, and can provide structural support for the adhesive layer, so that the entire first adhesive layer can maintain a stable shape inside the secondary battery. The material of the adhesive layer includes at least one of polyethylene, polypropylene, polyurethane, epoxy resin, styrene-butadiene rubber, polyvinylidene fluoride or polyacrylic acid. The adhesive layer has good initial adhesion and persistent adhesion and can be tightly bonded to the positive electrode active material layer.

[0037] 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.

[0038] 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

[0039] One or more embodiments are exemplarily illustrated by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, and unless otherwise stated, the figures in the drawings do not constitute proportional limitations.

[0040] Figure 1 This is a schematic structural diagram of a secondary battery in some embodiments of the present application;

[0041] Figure 2 Schematic diagram of the winding structure of the electrode assembly in some embodiments of the present application;

[0042] Figure 3 Schematic diagram of the stacked structure of the electrode assembly in some embodiments of the present application;

[0043] Figure 4 Schematic diagram of the stacked structure of the positive electrode sheet and the negative electrode sheet in some embodiments of the present application;

[0044] Figure 5 A schematic cross-sectional view of the first adhesive layer in some embodiments of the present application;

[0045] Figure 6 A schematic diagram of the current density of a portion of the negative electrode active material layer at the first groove in some embodiments of the present application;

[0046] Figure 7 Schematic diagram of the structure of part of the negative electrode active material layer (including the first groove) and the first glue layer in some embodiments of the present application;

[0047] Figure 8 Schematic diagram of the structure of part of the negative electrode active material layer (including the first groove) and part of the positive electrode active material layer (including the first glue layer) in some embodiments of the present application;

[0048] Figure 9 Schematic diagram of the structure of part of the negative electrode active material layer (including the first groove) and part of the positive electrode active material layer (including the first glue layer) in some embodiments of the present application;

[0049] Figure 10 Schematic diagram of the structure of part of the negative electrode active material layer (including the first groove) and part of the positive electrode active material layer (including the first glue layer) in some embodiments of the present application;

[0050] Figure 11 Schematic diagram of the structure of the first adhesive layer according to one embodiment of the present application (top view);

[0051] Figure 12 This is a schematic structural diagram of the negative electrode sheet and the first adhesive layer in some embodiments of the present application;

[0052] Figure 13 This is a schematic structural diagram of the positive electrode sheet of some embodiments of the present application.

[0053] Description of reference numerals:

[0054] 1000. Secondary battery;

[0055] 100. Electrode assembly;

[0056] 10. Positive electrode sheet; 11. Positive electrode current collector; 111. First surface; 112. Second surface; 12. Positive electrode active material layer; 121. Edge region;

[0057] 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, edge;

[0058] 30. Isolation film;

[0059] 40. Negative electrode tab;

[0060] 50, first adhesive layer; 50a, substrate layer; 50b, adhesive layer; 501, first section; 502, second section; 51, first portion; 52, second portion; 521, first region; 522, second region; 523, first through-hole; 53, third portion; 531, third region; 532, fourth region; 533, second through-hole;

[0061] 60, second adhesive layer; 54, fourth portion; 541, fifth region; 542, sixth region; 543, third through hole;

[0062] 200, housing;

[0063] X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] In the first aspect, the present application proposes a secondary battery 1000, please refer to Figure 1The 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 .

[0070] For the electrode assembly 100, please refer to Figure 2 and Figure 3 The electrode assembly 100 includes a positive electrode sheet 10, a negative electrode sheet 20 and a separator 30. The positive electrode sheet 10, the separator 30 and the negative electrode sheet 20 are stacked and wound, wherein Figure 2 The winding structure of the electrode assembly 100 is shown, for example, the positive electrode sheet 10 and / or the negative electrode sheet 20 are stacked in the thickness direction and wound 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.

[0071] 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 a laminated electrode assembly, 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.

[0072] 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 serves as the conductive substrate of the positive electrode sheet 10 and can be made of an overall flat aluminum foil. Aluminum foil has high electrical conductivity and low resistance, which can improve the charge and discharge rate of the secondary battery 1000. In addition, aluminum foil has certain strength and ductility. During the production process such as winding or lamination, the aluminum foil is not easy to break or deform, thereby ensuring the structural integrity of the positive electrode sheet 10. At the same time, the positive electrode of the secondary battery 1000 is at a relatively high potential during the charge and discharge process. The aluminum foil is relatively stable at this potential and is not prone to chemical reactions, thereby improving the charge and discharge stability of the secondary battery 1000. In some other embodiments, the positive electrode current collector 11 can also be made of titanium foil, nickel foil or stainless steel foil.

[0073] The positive electrode active material layer 12 can be disposed on at least one surface in the thickness direction of the positive electrode current collector 11. For example, along the third direction Z, the positive electrode current collector 11 includes 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, and evenly 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.

[0074] Please refer to Figure 4 The negative electrode sheet 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 serves as the conductive substrate of the negative electrode sheet 20 and can be made of a flat copper foil. Copper foil has high electrical conductivity and low resistance, which can improve the charge and discharge rate of the secondary battery 1000. In addition, copper foil has certain strength and ductility. During the production process such as winding or lamination, the copper foil is not easy to break or deform, thereby ensuring the structural integrity of the negative electrode sheet 20. At the same time, the negative electrode of the secondary battery 1000 is at a low potential during the charge and discharge process. The copper foil is relatively stable at this potential and is not prone to chemical reactions, thereby improving the charge and discharge stability of the secondary battery 1000. In some other embodiments, the negative electrode current collector 21 can also be made of titanium foil, nickel foil, stainless steel foil or silver foil.

[0075] The negative electrode active material layer 22 can be disposed on at least one surface along the thickness direction of the negative electrode current collector 21. For example, along the third direction Z, the negative electrode current collector 21 includes a third surface 211 and a fourth surface 212 disposed opposite each other. The negative electrode active material layer 22 can be disposed on the third surface 211 and / or the fourth surface 212. The negative electrode active material layer 22 includes a negative electrode active material, a conductive agent, and a binder. These materials are mixed, stirred, and evenly coated on the third surface 211 and / or the fourth surface 212 to form the negative electrode active material layer 22. The negative electrode active material includes one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxides, and silicon alloys.

[0076] 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, so that the negative electrode current collector 21 is exposed from the first groove 221. A portion of the negative electrode tab 40 is disposed in the first groove 221 and connected to the negative electrode current collector 21, using methods including but 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 along the first direction X.

[0077] During the charging process, the external power supply transmits current to the electrode assembly 100 through the tabs, causing lithium ions to escape from the positive electrode sheet 10 and embed into the negative electrode sheet 20. The inventors of the present application have discovered that because the negative electrode active material layer 22 is provided with the first groove 221, the remaining amount of the negative electrode active material layer 22 is reduced. In the portion of the positive electrode active material layer 12 facing the first groove 221, the escaped lithium ions are difficult to embed into the negative electrode active material layer 22, which can easily lead to lithium plating. Lithium plating will form lithium metal dendrites, which may pierce the diaphragm, causing a short circuit between the positive and negative electrodes, causing safety problems, and also reducing the capacity and cycle life of the secondary battery 1000.

[0078] To reduce the above problems, in the embodiments of this application, please refer to Figure 4 The secondary battery 1000 further includes a first adhesive layer 50, which is disposed on the surface of the positive electrode active material layer 12 facing the negative electrode plate 20. Along the third direction Z, the projection of the first adhesive layer 50 covers the first groove 221. This allows the portion of the positive electrode active material layer 12 corresponding to the first groove 221 to be covered by the first adhesive layer 50, thereby reducing or preventing the release of lithium ions from this portion. This, in turn, allows the negative electrode active material layer 22 to have sufficient residual lithium ions to be embedded, thereby reducing the risk of lithium plating.

[0079] In other embodiments, a second adhesive layer 60 may be used when welding the negative electrode tab 40 to the negative electrode current collector 21. The second adhesive layer 60 may be disposed on the negative electrode active material layer 22 and cover the first groove 221. This can reduce the risk of welding burrs piercing the separator 30, thereby reducing the occurrence of short circuits. When the second adhesive layer 60 is provided, the length of the first adhesive layer 50 may be set to be greater than the length of the second adhesive layer 60, and the width of the first adhesive layer 50 may be set to be greater than the width of the second adhesive layer 60. This allows the negative electrode active material layer 22 to have sufficient margin to embed lithium ions released from the positive electrode active material layer 12, thereby reducing the occurrence of lithium plating. For example, along the third direction Z, the projection of the second adhesive layer 60 is located within the projection of the first adhesive layer 50.

[0080] Regarding the material of the first adhesive layer 50, in some embodiments, please refer to Figure 4 and Figure 5The first adhesive layer 50 includes a substrate layer 50a and an adhesive layer 50b, and the adhesive layer 50b is arranged on the surface of the substrate layer 50a facing the positive electrode active material layer 12. The material of the substrate layer 50a includes at least one of polyethylene terephthalate or polyimide. The substrate layer 50a has good insulation properties, mechanical strength and high temperature resistance, and can provide structural support for the adhesive layer 50b, so that the entire first adhesive layer 50 can maintain a stable shape inside the secondary battery 1000. The material of the adhesive layer 50b includes at least one of polyethylene, polypropylene, polyurethane, epoxy resin, styrene-butadiene rubber, polyvinylidene fluoride or polyacrylic acid. The adhesive layer 50b has good initial adhesion and persistent adhesion, and can be tightly combined with the positive electrode active material layer 12.

[0081] The inventors of this application have found that the negative electrode active material in the first groove 221 may form a solid electrolyte interface (SEI) film, which further hinders the insertion of lithium ions and aggravates the occurrence of lithium precipitation. The inventors of this application have concluded through analysis that there is a problem of uneven current density in the first groove 221 of the negative electrode active material layer 22. Please refer to Figure 6 , Figure 6 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 6 It can be seen that the closer to the first groove 221, the greater the current density. When the current density of the negative electrode active material layer 22 is large, a large number of lithium ions reach the surface of the negative electrode active material layer 22 per unit time, which easily causes lithium ions to accumulate on the surface of the negative electrode active material layer 22, thereby causing lithium precipitation. In addition, high current density will cause the local polarization of the negative electrode active material layer 22 to increase (the potential in the local area deviates from the equilibrium potential), which may 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 precipitation may occur.

[0082] The inventors of this application set the length of the first adhesive layer 50 based on the current density of the negative electrode active material layer 22 at the first groove 221. In the embodiment of this application, referring to the figure, along the second direction Y, the maximum length of the first adhesive layer 50 is L, and the length of the first groove 221 is L1. 1.3≤L / L1≤3.5 can isolate the portion with higher current density from the first adhesive layer 50, reducing the accumulation of lithium ions near the first groove 221 and thus reducing the occurrence of lithium plating. Furthermore, the limit of 1.3≤L / L1≤3.5 can reduce the loss of energy density of the secondary battery 1000, which can facilitate achieving a balance between reducing energy density loss and reducing the occurrence of lithium plating.

[0083] The inventors of this application have also discovered that by limiting the ratio 1.3 ≤ L / L1 ≤ 3.5, local polarization of the negative electrode active material layer 22 is reduced, which can reduce electrolyte decomposition and, in turn, the formation of a solid electrolyte interface (SEI) film, further reducing lithium plating. Furthermore, heat concentration in the first groove 221 is alleviated, reducing the occurrence of side reactions and thereby improving the performance of the secondary battery 1000.

[0084] Please refer to further Figures 6 to 8 The positive electrode active material layer 12 has an edge region 121. Near the edge 222 of the negative electrode active material layer 22, the current density is high. This increases the risk of lithium deposition at the edge 222, generates high heat, and is prone to side reactions. To mitigate this issue, in the embodiment of the present application, the first adhesive layer 50 covers a portion of the edge region 121. This reduces the accumulation of lithium ions at the edge 222 of the negative electrode active material layer 22, thereby reducing the occurrence of lithium deposition and side reactions.

[0085] The closer to the first groove 221, the greater the current density, and the closer to the edge 222 of the negative electrode active material layer 22, the greater the current density. The first adhesive layer 50 with a special-shaped structure can be set according to the current density. Please refer to Figure 7 , along the first direction X, the width of the first adhesive layer 50 in the second direction Y increases. For example, along the first direction X, the first adhesive layer 50 can be divided into a first section 501 and a second section 502 arranged in sequence. Along the second direction Y, the maximum length of the first section 501 is L a , the maximum length of the second segment 502 is L b , L a <L b .

[0086] After the positive electrode sheet 10 and the negative electrode sheet 20 are stacked, the edge region 121 overlaps or approaches overlap with the edge 222 of the negative electrode active material layer 22, or the edge 222 extends beyond the edge 222 along the first direction X. The first segment 501 is away from the edge region 121. The current density of the portion of the negative electrode active material layer 22 corresponding to the first segment 501 is low, and the risk of lithium plating is low. Accordingly, providing a shorter first segment 501 can reduce lithium plating while allowing more of the positive electrode active material layer 12 and the negative electrode active material layer 22 to participate in the electrochemical reaction, thereby improving the energy density of the secondary battery 1000.

[0087] The second segment 502 is located near the edge region 121, where the current density is higher and the risk of lithium plating is higher. Therefore, a longer second segment 502 is provided. This isolates the higher current density portion at the edge 222 of the negative electrode active material layer 22 from the second segment 502, reducing lithium ion aggregation in this portion and, consequently, reducing the occurrence of lithium plating. Setting the length gradient of the first adhesive layer 50 based on the current density optimizes the distribution of the reaction zones between the positive electrode active material layer 12 and the negative electrode active material layer 22, thereby reducing lithium plating while increasing the utilization of the positive electrode active material layer 12 and the negative electrode active material layer 22, thereby increasing the energy density of the secondary battery 1000.

[0088] Regarding the length of the first groove 221 , in some embodiments, the length of the first groove 221 can be selected to be 8 mm ≤ L1 ≤ 20 mm, which can meet the manufacturing process requirements of the negative electrode tab 40 and balance the energy density.

[0089] For the width of the first adhesive layer 50, please refer to Figure 6 and Figure 7 Along the first direction X, the current density increases as the first groove 221 moves away from the edge 222 and closer to the center of the first groove 221. The inventors set the maximum width of the first adhesive layer 50 based on the current density in the width direction. Along the first direction X, the maximum width of the first adhesive layer 50 is W, and the width of the first groove 221 is W1. 1.1 ≤ W / W1 ≤ 2. This reduces energy density loss while also minimizing lithium plating. This reduces lithium plating while minimizing the impact on energy density.

[0090] In some examples, 2≤L / L1≤2.8, which can further reduce lithium plating while reducing the impact of the first adhesive layer 50 on the energy density of the secondary battery 1000. Similarly, 1.33≤W / W1≤1.87.

[0091] In some embodiments, please refer to Figure 9 , along the second direction Y, the first adhesive layer 50 includes a first part 51 and a second part 52 arranged in sequence, and the second part 52 is connected to the first part 51. Along the third direction Z, the first part 51 coincides with the first groove 221, that is, along the second direction Y, the length of the first part 51 can be set to L1. Along the second direction Y, the maximum length of the second part 52 is L2, 0.15≤L2 / L1≤1.25. According to the above current density, the maximum length of the second part 52 can be set close to the above-mentioned edge area 121, that is, set in the second section 502, which can reduce the occurrence of lithium plating on one side of the length direction of the first groove 221 and reduce the loss of energy density of the secondary battery 1000.

[0092] In the second direction Y, the length L2 of the second portion 52 is selected to be 1.5 mm ≤ L2 ≤ 12.5 mm, and any value between 1.5 mm and 12.5 mm can be selected. For example, L2 is selected from 1.5 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, or 12.5 mm. Preferably, 6 mm ≤ L2 ≤ 9 mm can reduce lithium plating while reducing the impact on energy density.

[0093] In some embodiments, along the first direction, the width of the second portion 52 is equal to the width of the first portion 51. For example, when the size of the first groove 221 is small, please refer to Figure 10 , the width of the first portion 51 is W a , the width of the first portion 51 is consistent with the width of the first groove 221, that is, W a =W1, the width of the second portion 52 is W b , W a =W1=W b .

[0094] The inventors of this application have found that the current density of the negative electrode active material layer 22 near the first groove 221 is relatively high, and the risk of lithium plating is relatively high. However, near the first groove 221, there is still a part of the negative electrode active material layer 22 that can undergo electrochemical reactions and exert the capacity of the secondary battery 1000. Under the premise that there is no lithium plating under the same conditions, compared with the part with lower current density, the part with higher current density can receive fewer lithium ions, rather than being unable to receive them. Regardless of whether it is a part with higher current density or a part with lower current density, a certain capacity can be exerted. The inventors of this application have opened a through hole on the second part 52, for example, please refer to Figure 11 Along the third direction Z, the second portion 52 is provided with a first through hole 523, which exposes a portion of the positive electrode active material layer 12. The exposed portion of the positive electrode active material layer 12 can undergo lithium ion deintercalation reaction with the portion of the negative electrode active material layer 22 that can exert its capacity, thereby improving the utilization rate of the positive electrode active material layer 12 and the negative electrode active material layer 22, thereby improving the energy density of the secondary battery 1000.

[0095] Regarding the area ratio of the first through hole 523 on the second portion 52, the inventors of this application have found that if the area ratio of the first through hole 523 on the second portion 52 is too large, it may cause more lithium ions to be released from the positive electrode active material layer 12, which may lead to insufficient residual negative electrode active material layer 22 and thus cause lithium deposition. If the area ratio of the first through hole 523 on the second portion 52 is too small, it will be difficult for the negative electrode active material layer 22 to fully utilize its capacity, resulting in a loss of energy density in the secondary battery 1000.

[0096] In the embodiment of the present application, when observed along the third direction Z, the area of ​​the second portion 52 is S1, and the sum of the areas occupied by all the first through holes 523 on the second portion 52 is S2, 40%≤S2 / S1≤60%, which can reduce the risk of lithium plating while improving the utilization rate of the negative electrode active material layer 22 and the positive electrode active material layer 12, thereby improving the energy density of the secondary battery 1000.

[0097] To measure the area percentage of the first through-hole 523 on the second portion 52, image analysis can be used. First, isolate the second portion 52 on the first adhesive layer 50. Scan or photograph the image of the first adhesive layer 50 and import it into image analysis software such as Adobe Photoshop. Adjust the contrast and brightness of the image to clearly define the boundary between the second portion 52 and the first through-hole 523. Use the threshold adjustment tool to convert the image into a binary image, with the adhesive portion white and the through-hole portion black. Within the image analysis software, use the measurement tool to measure the total area of ​​the second portion 52 and the total area of ​​the first through-hole 523.

[0098] according to Figure 6 Since the current density increases as it approaches the first groove 221, the distribution density gradient of the first through holes 523 in the first adhesive layer 50 can be set according to the current density. Figure 11 The second portion 52 includes a first region 521 and a second region 522. Along the second direction Y, the first region 521 is located between the first portion 51 and the second region 522. When viewed along the third direction Z, the area of ​​the first region 521 is S. 11 The sum of the areas of all first through holes 523 in the first region 521 is S 21 Observed along the third direction Z, the area of ​​the second region 522 is S 12 The sum of the areas of all first through holes 523 in the second region 522 is S 22 , S 21 / S 11 <S 22 / S 12 .

[0099] The negative electrode active material layer 22 corresponding to the first region 521 has a larger current density, a higher risk of lithium plating, and less negative electrode active material that can exert its capacity. By setting the pore density of the first region 521 to be smaller, the amount of lithium desorption in the first region 521 can be reduced, thereby reducing the occurrence of lithium plating in the negative electrode active material layer 22.

[0100] The negative electrode active material layer 22 corresponding to the second region 522 has a lower current density, a lower risk of lithium plating, and more negative electrode active material available for full capacity. By increasing the pore density of the second region 522, the amount of lithium released from the second region 522 can be increased, allowing more negative electrode active material to participate in the electrochemical reaction and improving the energy density of the secondary battery 1000. By rationally arranging the distribution of the first through holes 523 in the second portion 52, the energy density of the secondary battery 1000 can be increased while reducing lithium plating.

[0101] In some embodiments, along the second direction Y, the width of the first region 521 is equal to the width of the second region 522 .

[0102] Regarding the radius of the above-mentioned first through hole 523, the inventors of the present application have found that if the radius of the first through hole 523 is too large, it may cause the positive electrode active material layer 12 to release more lithium ions per unit area, which may easily lead to insufficient margin on the single-sided area of ​​the negative electrode active material layer 22, thereby causing lithium plating problems. If the radius of the first through hole 523 is too small, the lithium ions released per unit area are relatively small, making it difficult for the negative electrode active material layer 22 that can fully exert its capacity, resulting in a loss of energy density of the secondary battery 1000. In the embodiment of the present application, the radius of the first through hole 523 is R1, 0.1mm≤R1≤1mm, which can reduce the risk of lithium plating while improving the utilization rate of the negative electrode active material layer 22, thereby improving the energy density of the secondary battery 1000. Among them, the radius of the first through hole 523 can be the radius of the first through hole 523 itself, or the radius of the fitting circle where the first through hole 523 is located.

[0103] For the width of the second portion 52, please refer to Figure 11 In some embodiments, along the first direction X, the maximum width of the first region 521 is W2, and the maximum width of the second region 522 is W3, where W3 < W2. In the second portion 52, the closer to the first groove 221, the greater the current density. The second region 522 is closer to the first groove 221. By limiting W3 < W2, lithium plating can be further reduced, and the impact of the first adhesive layer 50 on the energy density of the secondary battery 1000 can be mitigated.

[0104] In some embodiments, the width of the second portion 52 in the first direction X gradually decreases along the direction from the first portion 51 to the second portion 52. Figure 6 As can be seen from the figure, the current density gradually decreases from the first groove 221 to both sides. By limiting the width of the second portion 52 in the first direction X to gradually decrease, a gradient design closer to the current density can be achieved, which can further reduce the occurrence of lithium plating and further reduce the impact of the first adhesive layer 50 on the energy density of the secondary battery 1000.

[0105] In some embodiments, the first adhesive layer 50 further includes a third portion 53 , which can be configured similarly to the first portion 51 . Along the second direction Y, the third portion 53 has a maximum length L3 , where 0.15 ≤ L3 / L1 ≤ 1.25. Based on the current density, the maximum length of the second portion 52 can be set near the edge region 121 , i.e., within the second segment 502 . This can reduce lithium deposition on the other side of the first groove 221 along its length, thereby reducing energy density loss in the secondary battery 1000 .

[0106] The length L3 of the second portion 52 along the second direction Y can be selected to be 1.5 mm ≤ L3 ≤ 12.5 mm, and can be any value between 1.5 mm and 12.5 mm. For example, L3 is selected from 1.5 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, or 12.5 mm. Preferably, 6 mm ≤ L3 ≤ 9 mm can reduce lithium plating while reducing the impact on energy density.

[0107] In some embodiments, along the first direction X, the width of the third portion 53 is equal to the width of the first portion 51. For example, see Figure 11 , the width of the third portion 53 is W c , W c =W a =W1.

[0108] Please refer to Figure 9 and Figure 11 Along the third direction Z, the third portion 53 is provided with a second through hole 533, which exposes a portion of the positive electrode active material layer 12. The exposed portion of the positive electrode active material layer 12 can also undergo lithium ion deintercalation reaction with the portion of the negative electrode active material layer 22 that can exert its capacity, thereby further improving the utilization rate of the negative electrode active material layer 22 and the energy density of the secondary battery 1000.

[0109] Regarding the area ratio of the second through holes 533 on the third part 53, in the embodiment of the present application, when observed along the third direction Z, the area of ​​the third part 53 is S3, and the sum of the areas occupied by all the second through holes 533 on the third part 53 is S4, 40%≤S4 / S3≤60%, which can reduce the risk of lithium plating while improving the utilization rate of the negative electrode active material layer 22, thereby improving the energy density of the secondary battery 1000.

[0110] In some embodiments, please refer to Figure 11 The third portion 53 includes a third region 531 and a fourth region 532. Along the second direction Y, the fourth region 532 is located between the first portion 51 and the third region 531. When viewed along the third direction Z, the area of ​​the third region 531 is S.31 The sum of the areas of all second through holes 533 in the third region 531 is S 41 Observing along the third direction Z, the fourth area 5 32 The area is S 32 The sum of the areas of all second through holes 533 in the fourth region 532 is S 42 , S 41 / S 31 >S 42 / S 32 .

[0111] The negative electrode active material layer 22 corresponding to the fourth region 532 has a larger current density, a higher risk of lithium plating, and less negative electrode active material that can exert its capacity. By setting the pore density of the first region 521 to be smaller, the amount of lithium desorption in the fourth region 532 can be reduced, thereby reducing the occurrence of lithium plating in the negative electrode active material layer 22.

[0112] The negative electrode active material layer 22 corresponding to the third region 531 has a lower current density, a lower risk of lithium plating, and more negative electrode active material available for full capacity. By increasing the pore density of the third region 531, the amount of lithium released from the third region 531 can be increased, allowing more negative electrode active material to participate in the electrochemical reaction and improving the energy density of the secondary battery 1000. By rationally arranging the distribution of the first through holes 523 in the second portion 52, the energy density of the secondary battery 1000 can be increased while reducing lithium plating.

[0113] The radius of the second through hole 533 is similar to that of the first through hole 523 . In the embodiment of the present application, the radius of the second through hole 533 is R2, 0.1 mm ≤ R2 ≤ 1 mm, which can reduce the risk of lithium plating while improving the utilization rate of the negative electrode active material layer 22 , thereby improving the energy density of the secondary battery 1000 .

[0114] The first through holes 523 and the second through holes 533 can be formed on the first adhesive layer 50 by mechanical punching, laser drilling, or other processes. For example, by using a nail roller punching method in mechanical punching, the radii of the first through holes 523 and the second through holes 533 can be made close to the same, which facilitates the setting of the hole density according to the current density.

[0115] In some embodiments, please refer to Figure 6 , there is still a large current density on the side of the first groove 221 away from the edge 222, and there is a risk of lithium deposition in this part. To reduce this problem, in the embodiment of this application, please refer to Figure 11The first adhesive layer 50 also includes a fourth portion 54. Along the first direction X, the fourth portion 54 is disposed sequentially with the first portion 51 and is connected to the first portion 51. Along the third direction Z, the first portion 51 overlaps with the first groove 221, and the fourth portion 54 is disposed on the positive electrode active material layer 12. Along the first direction X, the maximum width of the fourth portion 54 is W4, with a range of 1.5 mm ≤ W4 ≤ 15 mm. This reduces energy density loss and lithium plating. Furthermore, 5 mm ≤ W4 ≤ 13 mm.

[0116] In some other embodiments, the fourth portion 54 includes a fifth region 541 and a sixth region 542. Along the first direction X, the sixth region 542 is located between the first portion 51 and the fifth region 541. Along the second direction Y, the maximum length of the fifth region 541 is L 51 , the maximum length of the sixth region 542 is L 61 , L 51 <L 61 On the side of the first groove 221 away from the edge 222 of the negative electrode active material layer 22, the closer to the first groove 221, the greater the current density. Similarly, the length gradient of the fourth portion 54 can be set according to the current density to optimize the distribution of the fourth portion 54, thereby reducing the loss of energy density and the occurrence of lithium plating.

[0117] In some embodiments, along the first direction X, a width of the fifth region 541 is equal to a width of the sixth region 542 .

[0118] In some embodiments, please refer to Figure 11 Along the third direction Z, the fourth portion 54 is provided with a third through hole 543, which exposes a portion of the positive electrode active material layer 12. The exposed portion of the positive electrode active material layer 12 can undergo lithium ion deintercalation reaction with the portion of the negative electrode active material layer 22 that can exert its capacity, thereby improving the utilization rate of the positive electrode active material layer 12 and the negative electrode active material layer 22, thereby improving the energy density of the secondary battery 1000.

[0119] In some other embodiments, when observed along the third direction Z, the area of ​​the fourth portion 54 is S5, the sum of the areas occupied by all the third through holes 543 on the fourth portion 54 is S6, and 40%≤S6 / S5≤60%. This can reduce the risk of lithium plating while improving the utilization rate of the negative electrode active material layer 22, thereby improving the energy density of the secondary battery 1000.

[0120] The closer to the first groove 221, the greater the current density. Similar to the distribution of the first through hole 523, the distribution density gradient of the third through hole 543 in the fourth portion 54 can be set according to the magnitude of the current density. For example, the fourth portion 54 includes a fifth region 541 and a sixth region 542. Along the first direction X, the sixth region 542 is located between the first portion 51 and the fifth region 541. When viewed along the third direction Z, the area of ​​the fifth region 541 is S 51 The sum of the areas of all third through holes 543 in the fifth region 541 is S 61 Observed along the third direction Z, the area of ​​the sixth region 542 is S 52 The sum of the areas of all third through holes 543 in the sixth region 542 is S 62 , S 61 / S 51 >S 62 / S 52 .

[0121] The negative electrode active material layer 22 corresponding to the sixth region 542 has a larger current density, a higher risk of lithium plating, and less negative electrode active material that can exert its capacity. By setting the pore density of the sixth region 542 to a smaller value, the amount of lithium desorption in the sixth region 542 can be reduced, thereby reducing the occurrence of lithium plating in the negative electrode active material layer 22.

[0122] The negative electrode active material layer 22 corresponding to the fifth region 541 has a lower current density and a lower risk of lithium plating, allowing for more negative electrode active material to fully utilize its capacity. By increasing the pore density of the fifth region 541, the amount of lithium removed from the fifth region 541 can be increased, allowing more negative electrode active material to participate in the electrochemical reaction and improving the energy density of the secondary battery 1000. By rationally arranging the distribution of the third through holes 543 in the fourth portion 54, the energy density of the secondary battery 1000 can be increased while reducing lithium plating.

[0123] The radius of the third through hole 543 is similar to that of the first through hole 523. The radius of the third through hole 543 is R3, and 0.1 mm ≤ R3 ≤ 1 mm. This can reduce the risk of lithium plating while improving the utilization rate of the negative electrode active material layer 22, thereby improving the energy density of the secondary battery 1000. The radius of the third through hole 543 can be the radius of the third through hole 543 itself, or the radius of the fitted circle in which the third through hole 543 is located.

[0124] In some embodiments, along the second direction Y, the first adhesive layer 50 includes a third portion 53, a first portion 51, and a second portion 52, which are sequentially arranged. The third portion 53 is connected to the first portion 51, and the second portion 52 is connected to the first portion 51. Figure 12Along 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. The second portion 52 is located between the first groove 221 and the first end portion 20a, and the third portion 53 is located between the first groove 221 and the second end portion 20b. Along the second direction Y, the length from the first groove 221 to the first end portion 20a is L4, and the length from the first groove 221 to the second end portion 20b is L5.

[0125] The inventors of this application have discovered that for the negative electrode sheet 20, the larger L4 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 second portion 52 and the third portion 53 based on the length L4 from the first groove 221 to the first end 20a and the length L5 from the first groove 221 to the second end 20b.

[0126] For example, along the second direction Y, the length of the second portion 52 is L2, and the length of the third portion 53 is L3. When L4>L5, it indicates that the current density between the first groove 221 and the first end 20a is relatively high, and L2>L3 can be set. When L4<L5, it indicates that the current density between the first groove 221 and the second end 20b is relatively high, and L2<L3 can be set. By reasonably setting the lengths of the second portion 52 and the third portion 53, the size of the first adhesive layer 50 can be reduced while reducing the risk of lithium plating, thereby increasing the energy density of the secondary battery 1000. When L4=L5, L3 and L2 can be set to be approximately equal, for example, |L3-L2|≤0.5mm.

[0127] In some embodiments, please refer to Figure 13 Along the third direction Z, the thickness of the positive electrode active material layer 12 covered by the first adhesive layer 50 is H1, and the thickness of the positive electrode active material layer 12 not covered by the first adhesive layer 50 is H2, where H1<H2. This reduces the amount of the positive electrode active material layer 12 covered by the first adhesive layer 50, thereby reducing the impact of the first adhesive layer 50 on the energy density of the secondary battery 1000.

[0128] When the second portion 52 is provided with the first through hole 523 , the third portion 53 is provided with the second through hole 533 , and the fourth portion 54 is provided with the third through hole 543 , the amount of the covered positive electrode active material layer 12 can be reduced, thereby reducing the escape of lithium ions and thus reducing the occurrence of lithium plating.

[0129] When the second portion 52 is not provided with the first through hole 523, the third portion 53 is provided with the second through hole 533, and the fourth portion 54 is provided with the third through hole 543, the covered positive electrode active material layer 12 is difficult or even unable to participate in the electrochemical reaction. The first glue layer 50 can be set to not exceed the above-mentioned uncovered positive electrode active material layer 12. For example, along the third direction Z, the thickness of the first glue layer 50 is H3, H1+H3≤H2, so that the first glue layer 50 does not occupy the thickness of the positive electrode active material layer 12, thereby fully improving the energy density of the secondary battery 1000 and reducing the occurrence of lithium plating.

[0130] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery 1000 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.

[0131] Experiment 1: Lithium plating test of lithium-ion batteries

[0132] Example A1:

[0133] <Preparation of positive electrode sheet>

[0134] The positive electrode active material lithium iron phosphate, 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%. The mixture was then stirred evenly in a vacuum mixer. An aluminum foil with a thickness of 8μm and a length of 1000mm was selected as the positive electrode current collector. 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.

[0135] <Preparation of negative electrode sheet>

[0136] The negative electrode active materials, graphite powder, silicon powder, conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR), are mixed in a weight ratio of 87.5:10:1:1.5. Deionized water is then added as a solvent to prepare a negative electrode slurry with a solid content of 50 wt%, which is then stirred evenly. A copper foil with a thickness of 5 μm and a length of 1050 mm is selected as the negative electrode current collector. The negative electrode slurry is evenly coated on one surface of the negative electrode current collector copper foil, and an empty foil area is reserved on the copper foil for uncoated negative electrode slurry. The copper foil is then dried at 90°C to obtain a single-sided negative electrode sheet. After completing the above steps, the negative electrode sheet is coated on one side. The above steps are then repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated on both sides with a negative electrode active material layer.

[0137] <Preparation of Separator>

[0138] A polyethylene (PE) porous film with a thickness of 7 μm was used as the separator.

[0139] <Electrolyte Preparation>

[0140] 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.

[0141] <Preparation of lithium-ion batteries>

[0142] 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, polyethylene terephthalate is selected as the base material layer, and epoxy resin is used as the adhesive layer to prepare a first adhesive layer with a maximum length L of 13mm and a maximum width W of 20mm. The first adhesive layer is set on the positive active material layer. The isolation film, positive electrode sheet, isolation film, and negative electrode sheet prepared above are stacked in order and wound to obtain an electrode assembly. The first adhesive layer corresponds to the first groove. The first adhesive layer exceeds 1.5mm on one side of the length direction of the positive electrode sheet (the second part L2) and exceeds 1.5mm on one side (the third part L3). The first adhesive layer is divided into a first section and a second section arranged in sequence in the width direction of the positive electrode sheet. The maximum length of the first section is L a The second section is close to the edge and the maximum length is L b The electrode assembly is placed in the shell, the positive and negative tabs are led out, and then the electrolyte is injected to seal the package.

[0143] Lithium deposition test

[0144] Place the secondary battery at a test temperature of 25°C for 30 minutes, and then charge it to 4.5V according to the following charging steps:

[0145] (1) 5C constant current charging to 4.23V;

[0146] (2) 4C constant current charging to 4.3V;

[0147] (3) 3C constant current charging to 4.5V;

[0148] (4) 2C constant current charging to 4.5V, constant voltage charging to 0.05C;

[0149] After standing for 10 minutes, discharge according to the following steps:

[0150] 0.2C DC discharge to 3V.

[0151] The above charge and discharge process is one cycle. After 100 cycles, when the 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 negative electrode. If the lithium deposition area on the surface of the negative electrode active material layer near the negative electrode tab is greater than or equal to 2mm, 2 , it is determined to be lithium deposition. Each group tests 20 batteries, the number of lithium deposition is X, and the lithium deposition rate is X / 20.

[0152] Different from Example A1, the relevant parameters in Examples A2 to A28 and Comparative Examples A1 to A12 are shown in Table 2 below. b It is consistent with the maximum length L of the first adhesive layer.

[0153] Table 2

[0154]

[0155]

[0156] According to Table 1 above, in Comparative Example A5, the lithium deposition rate is similar to that in Example A1. In Example A1, the L a <L b , which can expose more active material layers, that is, more active material layers participating in the electrochemical reaction, which can improve the energy density of lithium-ion batteries. Therefore, when L / L1≥1.3, L a <L b .

[0157] In Comparative Example A6, the first adhesive layer is too long, resulting in a large loss of energy density. In addition, the first adhesive layer is too long, which will cover too many active material layers, which may hinder ion transmission and affect the distribution of electrolyte. It may also cause uneven pressure distribution between the pole pieces, which may easily lead to deterioration of the pole piece interface, affecting the transmission and embedding of lithium ions, and also pose a risk of lithium plating. In Example A11, the risk of lithium plating is lower than that of Comparative Example A6, and Example A11 adopts L a <L b , the length of the first adhesive layer is smaller, and the influence on energy density is smaller. Therefore, in the embodiment of the present application, when 1.3≤L / L1≤3.5, L is selected. a <L b That is, the width of the first glue layer is increased (along the extension direction of the tab, the width is larger on the side close to the positive electrode active material layer), which can improve the energy density and has less impact on lithium plating.

[0158] Combining Examples A1 to A28 and Comparative Examples A1 to A12, it can be seen that setting the first glue layer according to the current density gradient and when 1.3≤L / L1≤3.5 can effectively reduce lithium plating. In addition, the closer the negative electrode active material layer is to the edge, the greater the current density, and the closer it is to the first groove, the greater the current density. Limit L a <L b , has little impact on the risk of lithium plating, and setting the length gradient of the first gel layer according to the current density can optimize the distribution of the reaction zones between the positive and negative active material layers, thereby reducing lithium plating while improving the utilization of the positive and negative active material layers, thereby increasing the energy density of the secondary battery. Similarly, 0.15≤L2 / L1≤1.25 and 0.15≤L3 / L1≤1.25 are optional.

[0159] In Examples A5 to A8, 2≤L / L1≤2.8 is satisfied, and in Examples A13 to A14, Examples 19 to 20, and Examples 25 to 26, 2≤L / L1≤2.8 is also approximately satisfied, and the risk of lithium plating is further reduced. In the embodiments of the present application, 2≤L / L1≤2.8 is preferably used, which can reduce the impact on energy density while reducing lithium plating. Similarly, preferably, 0.6≤L2 / L1≤0.9, and 0.6≤L3 / L1≤0.9.

[0160] Unlike Example A7, the relevant parameters in Examples B1 to B18 are shown in Table 2 below. The first adhesive layer extends beyond the first groove along the width of the positive electrode sheet, with the maximum width of the extension being W4 (the fourth portion). The parameters of W4 are as follows. Along the width of the positive electrode sheet, the fourth portion includes a fifth region and a sixth region, with the sixth region being adjacent to the first groove. The length relationship between the fifth region (L4) and the sixth region (L5) is shown in Table 2 below.

[0161] Table 2

[0162]

[0163]

[0164] According to Table 2 above, combined with Example B1 to Example B18, it can be seen that in Example B4 to Example B16, the risk of lithium plating is relatively low. In this application, 1.1≤W / W1≤2 can be selected, and the risk of lithium plating is relatively low. In addition, limiting L4<L5 has a smaller impact on the risk of lithium plating. On the side of the first groove away from the edge of the negative electrode active material layer, the closer to the first groove, the greater the current density. Similarly, the length gradient of the fourth part can be set according to the current density, and the distribution of the fourth part can be optimized to reduce the loss of energy density while reducing the occurrence of lithium plating. Combined with Example B7 to Example B14, 1.33≤W / W1≤1.87 is preferred, which can reduce the impact of the first glue layer on the energy density while reducing lithium plating.

[0165] 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, and a negative electrode sheet stacked or stacked and wound, wherein the negative electrode sheet comprises a negative electrode active material layer facing the positive electrode sheet, and the positive electrode sheet comprises a positive electrode active material layer facing the negative electrode active material layer; the secondary battery further comprises a negative electrode tab, the negative electrode active material layer being provided with a first groove, a portion of the negative electrode tab being provided in the first groove, and another portion of the negative electrode tab extending out of the negative electrode sheet along a first direction, characterized in that: The secondary battery further includes a first glue layer; The first adhesive layer is provided on the surface of the positive electrode active material layer facing the negative electrode sheet, and along the third direction, the first adhesive layer covers the first groove; Along the first direction, the first adhesive layer is arranged to increase in width in the second direction; Along the second direction, the maximum length of the first adhesive layer is L, the length of the first groove is L1, and 1.3≤L / L1≤3.5; 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 Along the first direction, the maximum width of the first adhesive layer is W, the width of the first groove is W1, and 1.1≤W / W1≤2.

3. The secondary battery according to claim 2, wherein 2≤L / L1≤2.8; and / or, 1.33≤W / W1≤1.

87.

4. The secondary battery according to claim 1 or 2, characterized in that Along the second direction, the first adhesive layer includes a first portion and a second portion, and the second portion is connected to the first portion; along the first direction, the width of the second portion is equal to the width of the first portion; Along the third direction, the first portion overlaps with the first groove; Along the second direction, the maximum length of the second portion is L2, and 0.15≤L2 / L1≤1.

25.

5. The secondary battery according to claim 4, wherein 0.6≤L2 / L1≤0.

9.

6. The secondary battery according to claim 4, characterized in that 1.5mm≤L2≤12.5mm.

7. The secondary battery according to claim 6, characterized in that 6mm≤L2≤9mm.

8. The secondary battery according to any one of claims 1 to 7, characterized in that 8mm≤L1≤20mm.

9. The secondary battery according to any one of claims 4 to 8, characterized in that: Along the third direction, the second portion defines a first through hole.

10. The secondary battery according to claim 9, wherein When viewed along the third direction, the area of ​​the second portion is S1, the area of ​​all the first through holes is S2, and 40%≤S2 / S1≤60%.

11. The secondary battery according to claim 9 or 10, characterized in that: The radius of the first through hole is R1, 0.1 mm≤R1≤1 mm.

12. The secondary battery according to any one of claims 4 to 11, characterized in that: The second portion includes a first area and a second area, and along the second direction, the first area is located between the first portion and the second area; Along the first direction, the maximum width of the first region is W2, the maximum width of the second region is W3, and W3<W2.

13. The secondary battery according to claim 12, wherein: Along the second direction, a width of the first region is equal to a width of the second region.

14. The secondary battery according to any one of claims 10 to 13, characterized in that The second portion includes a first area and a second area, and along the second direction, the first area is located between the first portion and the second area; When viewed along the third direction, the area of ​​the first region is S 11 The sum of the areas of all the first through holes in the first region is S 21 ; When viewed along the third direction, the area of ​​the second region is S 12 The sum of the areas of all the first through holes in the second region is S 22 , S 21 / S 11 <S 22 / S 12 .

15. The secondary battery according to any one of claims 1 to 14, characterized in that The positive electrode active material layer has an edge region on one side of the negative electrode tab extending direction, and the first glue layer covers a portion of the edge region.

16. The secondary battery according to any one of claims 4 to 13, characterized in that: Along the direction from the first portion to the second portion, the width of the second portion in the first direction gradually decreases.

17. The secondary battery according to any one of claims 4 to 13, characterized in that: The first adhesive layer further includes a third portion, and along the second direction, the third portion, the first portion, and the second portion are sequentially arranged, and the third portion is connected to the first portion; Along the first direction, the width of the third portion is equal to the width of the first portion; Along the second direction, the maximum length of the third portion is L3, and 0.15≤L3 / L1≤1.

25.

18. The secondary battery according to claim 17, wherein 0.6≤L3 / L1≤0.

9.

19. The secondary battery according to claim 17 or 18, characterized in that 1.5mm≤L3≤12.5mm.

20. The secondary battery according to claim 19, wherein 6mm≤L3≤9mm.

21. The secondary battery according to any one of claims 17 to 20, characterized in that A second through hole is formed in the third portion along the third direction.

22. The secondary battery according to claim 21, wherein The third portion includes a third area and a fourth area, and along the second direction, the fourth area is located between the first portion and the third area; When viewed along the third direction, the area of ​​the third region is S 31 The sum of the areas of all the second through holes in the third region is S 41 ; When viewed along the third direction, the area of ​​the fourth region is S 32 The sum of the areas of all the second through holes in the fourth region is S 42 , S 41 / S 31 >S 42 / S 32 .

23. The secondary battery according to any one of claims 1 to 22, characterized in that: The first adhesive layer further includes a fourth portion, which is arranged sequentially with the first portion along the first direction and is connected to the first portion; Along the third direction, the first portion overlaps with the first groove, and the fourth portion is provided on the positive electrode active material layer; Along the first direction, the maximum width of the fourth portion is W4, 1.5 mm ≤ W4 ≤ 15 mm.

24. The secondary battery according to claim 23, characterized in that 5mm≤W4≤13mm.

25. The secondary battery according to claim 23 or 24, characterized in that The fourth portion includes a fifth area and a sixth area arranged in sequence, and along the first direction, the sixth area is located between the first portion and the fifth area; Along the second direction, the maximum length of the fifth region is L 51 , the maximum length of the sixth region is L 61 , L 51 <L 61 .

26. The secondary battery according to claim 25, characterized in that Along the first direction, a width of the fifth region is equal to a width of the sixth region.

27. The secondary battery according to any one of claims 24 to 26, characterized in that A third through hole is formed in the fourth portion along the third direction.

28. The secondary battery according to claim 27, characterized in that The fourth portion includes a fifth area and a sixth area, and along the first direction, the sixth area is located between the first portion and the fifth area; When viewed along the third direction, the area of ​​the fifth region is S 51 The sum of the areas of all the third through holes in the fifth region is S 61 ; When viewed along the third direction, the area of ​​the sixth region is S 52 The sum of the areas of all the third through holes in the sixth region is S 62 , S 61 / S 51 >S 62 / S 52 .

29. The secondary battery according to any one of claims 1 to 28, characterized in that Along the second direction, the first adhesive layer includes a third portion, a first portion, and a second portion arranged in sequence, the third portion is connected to the first portion, and the second portion is connected to the first portion; Along the second direction, the negative electrode active material layer includes a first end portion and a second end portion opposite to each other, the second portion is located between the first groove and the first end portion, and the third portion is located between the first groove and the second end portion; Along the second direction, the length from the first groove to the first end is L4, and the length from the negative electrode tab to the second end is L5; Along the second direction, the length of the second portion is L2, and the length of the third portion is L3; L4>L5, L2>L3; or, L4<L5, L2<L3.

30. The secondary battery according to any one of claims 1 to 29, characterized in that Along the third direction, the thickness of the positive electrode active material layer covered by the first glue layer is H1, and the thickness of the positive electrode active material layer not covered by the first glue layer is H2, where H1<H2.

31. The secondary battery according to claim 30, characterized in that Along the third direction, the thickness of the first adhesive layer is H3, where H1+H3≤H2.

32. The secondary battery according to any one of claims 1 to 31, characterized in that The first glue layer includes a substrate layer and an adhesive layer, and the adhesive layer is provided on the surface of the substrate layer facing the positive electrode active material layer; The material of the substrate layer includes at least one of polyethylene terephthalate and polyimide; The material of the adhesive layer includes at least one of polyethylene, polypropylene, polyurethane, epoxy resin, styrene-butadiene rubber, polyvinylidene fluoride and polyacrylic acid.

33. An electronic device, characterized in that: A secondary battery according to any one of claims 1 to 32 is included.

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