Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and electronic equipment, an electrode assembly comprises a first inner-layer pole piece, an isolating membrane and a second inner-layer pole piece, and the isolating membrane is stacked between the first inner-layer pole piece and the second inner-layer pole piece. The first single-sided pole piece is the outermost pole piece of the electrode assembly and comprises a first current collector and a first active material layer; the first current collector comprises a first surface and a second surface which are oppositely arranged, the second surface faces the first inner-layer pole piece, and the first active material layer is arranged on the second surface. The first surface is provided with a first groove, the first bonding piece is arranged in the first groove, and the first bonding piece is bonded with the first groove. Therefore, the energy density of the secondary battery can be improved, wrinkles or falling of the first bonding piece caused by collision of the secondary battery or expansion of the pole piece can be reduced, and the structural stability of the electrode assembly can be effectively improved.

Description

Technical Field

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

[0002] With the rapid development of modern technology, the demand for high-performance energy storage devices is growing in areas such as portable electronic devices and electric vehicles. As a highly efficient and environmentally friendly energy storage device, lithium-ion secondary batteries have found widespread application in numerous fields. To improve the battery life of portable electronic devices and electric vehicles, the energy density requirements for lithium-ion batteries are also increasing. Summary of the Invention

[0003] The present application aims to provide a secondary battery and an electronic device, aiming to improve the energy density of the secondary battery.

[0004] In a first aspect, the present application proposes a secondary battery comprising a housing and an electrode assembly disposed within the housing, the electrode assembly comprising a first inner electrode sheet, an isolation membrane, and a second inner electrode sheet, with an isolation membrane stacked between the first inner electrode sheet and the second inner electrode sheet. The secondary battery further comprises a first single-sided electrode sheet and a first adhesive for fixing the electrode assembly. The first single-sided electrode sheet is the outermost electrode sheet of the electrode assembly, and the first single-sided electrode sheet comprises a first current collector and a first active material layer. The first current collector comprises a first surface and a second surface disposed opposite to each other, the second surface facing the first inner electrode sheet, and the first active material layer is disposed on the second surface. A first groove is disposed on the first surface, a first adhesive is disposed in the first groove, and the first adhesive is bonded to the first groove.

[0005] In the above technical solution, a first groove is provided on the first surface of the first single-sided electrode sheet, where no active material layer is provided. This groove accommodates the first adhesive, effectively reducing the space occupied by the first adhesive, facilitating the ultra-thin design of the secondary battery and contributing to increased energy density. Furthermore, the sidewalls of the first groove physically constrain the first adhesive, forming a mechanically interlocking structure between the first adhesive and the first current collector. This reduces displacement of the first adhesive, such as wrinkling or shedding of the first adhesive due to secondary battery collisions or electrode sheet expansion, and effectively improves the structural stability of the electrode assembly.

[0006] In some embodiments, the first single-sided electrode sheet is a negative electrode sheet, the thickness of the first current collector is T1, the depth of the first groove is D1, and 20%≤D1 / T1≤67%. This can reduce the wrinkling or falling off of the first adhesive, reduce the space occupied by the first adhesive, increase the energy density of the secondary battery, and ensure that the first current collector still has better mechanical strength.

[0007] In some embodiments, 1.2 μm ≤ D1 ≤ 4 μm, which is beneficial to endowing the first current collector with relatively high mechanical strength and enabling the first bonding member to be fully accommodated in the first groove, thereby improving the energy density of the secondary battery.

[0008] In some embodiments, the first single-sided electrode is a positive electrode, the thickness of the first current collector is T1, the depth of the first groove is D1, and 20% ≤ D1 / T1 ≤ 50%. The strength of aluminum foil is weaker than that of copper foil, and retaining more matrix materials is beneficial to maintaining structural stability.

[0009] In some embodiments, 2.4 μm ≤ D1 ≤ 6 μm, which is beneficial to endowing the first current collector with relatively high mechanical strength and enabling the first bonding member to be fully accommodated in the first groove, thereby improving the energy density of the secondary battery.

[0010] In some embodiments, the first inner electrode has the same polarity as the first single-sided electrode. The first inner electrode includes a first inner current collector, the thickness of the first inner current collector is T2, the thickness of the first current collector is T1, and T1 > T2. The depth of the first groove is D1, and 100% ≤ (T1 - D1) / T2 ≤ 200%. T1 - D1 ≥ T2 ensures that the remaining thickness of the first current collector at the bottom of the first groove is not less than the thickness of the first inner current collector, reducing the insufficient mechanical strength of the first current collector caused by the first groove being too deep and reducing the deformation or curling of the first current collector. (T1 - D1) / T2 ≤ 200% limits the remaining thickness at the bottom of the first groove not to exceed twice the thickness of the first inner current collector, reducing the large thickness occupied by the first current collector and reducing the loss of energy density.

[0011] In some embodiments, the first inner electrode has the same polarity as the first single-sided electrode. The first inner electrode includes a first inner current collector, the thickness of the first inner current collector is T2, the thickness of the first current collector is T1, and T1 < T2. The depth of the first groove is D1, and 60% ≤ (T1 - D1) / T2 ≤ 73%. This endows the first current collector with better mechanical strength, facilitates the accommodation of the first bonding member, and reduces the loss of energy density.

[0012] In some embodiments, the first bonding member includes a first adhesive layer, a substrate layer, and a second adhesive layer which are stacked. The first adhesive layer and the second adhesive layer are respectively disposed on two opposite surfaces of the substrate layer. The first adhesive layer is bonded to the first groove, and the second adhesive layer is bonded to the housing.

[0013] In some embodiments, at least a part of the second adhesive layer protrudes from the first surface. During hot pressing, the second adhesive layer can be subjected to a relatively large pressure, so as to be fully bonded to the housing and improve the bonding strength with the housing.

[0014] In some embodiments, the thickness of the first adhesive layer is T a1 and the thickness of the second adhesive layer is Ta2 , the thickness of the substrate layer is T a3 117%≤T a1 / T a2 ≤163%, which is conducive to the first adhesive layer fully bonding the bottom wall and side wall of the first groove, and improving the bonding strength between the first adhesive and the first current collector. 117%≤T a3 / T a2 ≤150%, the substrate layer has a high structural strength, which can make up for the loss of strength of the first current collector caused by the provision of the first groove, so that the first current collector still has a high mechanical strength and reduces the curling or damage and tearing of the first current collector.

[0015] In some embodiments, along the first direction, a plurality of first inner pole pieces and a plurality of second inner pole pieces are alternately stacked, and an isolation film is provided between adjacent first inner pole pieces and second inner pole pieces. The electrode assembly also includes a second single-sided pole piece, and along the first direction, the outermost pole pieces on both sides of the electrode assembly are respectively the first single-sided pole piece and the second single-sided pole piece. The second single-sided pole piece includes a second current collector and a second active material layer, and the second current collector includes a third surface and a fourth surface arranged opposite to each other, the fourth surface faces the first inner pole piece, the fourth surface is provided with a second active material layer, and the third surface is provided with a second groove. The secondary battery also includes a second adhesive, the first adhesive is provided in the second groove, and the second adhesive is bonded to the second groove. Grooves are provided on the single-sided pole pieces on both sides of the outermost layer of the electrode assembly to accommodate the adhesive, which can further improve the energy density of the secondary battery.

[0016] In some embodiments, along the second direction, the first current collector includes a first edge and a second edge disposed opposite each other, and the second current collector includes a fifth edge and a sixth edge disposed opposite each other; the second direction is perpendicular to the first direction. Along the first direction, the first edge is disposed opposite the fifth edge, and the second edge is disposed opposite the sixth edge; the first groove extends to the first edge, and the second groove extends to the fifth edge. The secondary battery also includes a third adhesive, one end of which extends to the first edge, one end of which is connected to the first adhesive, the other end of which extends to the fifth edge, and the other end of which is connected to the second adhesive. This allows the first, second, and third adhesives to form a single unit, tightening the electrode assembly and reducing loosening of the electrode assembly. At the same time, the third adhesive can limit the extension of the separator, thereby reducing the effect of the separator on the welding of the housing and the welding of the tabs.

[0017] In some embodiments, the first adhesive, the second adhesive, and the third adhesive are integrally arranged, which can eliminate the multi-component splicing process and reduce positional deviation during assembly of sub-components. A wrapping structure is formed from the upper and lower surfaces to the sides of the electrode assembly, and the binding force has no breakpoints, which can reduce local stress concentration during bonding of sub-components, and is beneficial for making the forces on various parts of the electrode assembly more balanced, reducing the risk of local deformation of the electrode assembly.

[0018] In some embodiments, the thickness of the first adhesive member is T a , the thickness of the second adhesive is T b , the thickness of the third adhesive is T c . T a <T c and / or, T b <T c By thinning the first adhesive member and / or the second adhesive member, the energy density of the secondary battery can be further improved.

[0019] In some embodiments, 2 μm ≤ T c -T a ≤20μm, which is beneficial for improving the energy density while making the connection strength between the first adhesive and the first current collector higher. 2μm≤T c -T b ≤20μm. This is beneficial for improving the energy density while ensuring a higher connection strength between the second adhesive and the second current collector.

[0020] In some embodiments, along the second direction, a plurality of first grooves are provided on the first surface, and the plurality of first grooves are sequentially provided along the third direction, and the plurality of first grooves extend to the first edge. The secondary battery further includes a pole tab, which is connected to the electrode assembly, and the pole tab is connected to the third edge. The thickness of the first current collector is T1, and the thickness of the first inner current collector is T2, and T1≤T2. Along the third direction, the distance between the first groove and the third edge is L1, and the distance between the first groove and the fourth edge is L2. 8mm≤L1≤25mm; and / or, 5mm≤L2≤20mm. It can effectively reduce the curling of the first single-sided pole piece and improve the restrictive effect on the isolation membrane.

[0021] In some embodiments, a plurality of first grooves are provided on the first surface, the plurality of first grooves are arranged in sequence along the third direction, and the plurality of first grooves extend to the first edge. The secondary battery further includes a pole tab, which is connected to the electrode assembly, and the pole tab is connected to the third edge. The thickness of the first current collector is T1, the thickness of the first inner current collector is T2, and T1>T2. Along the third direction, the distance between the first groove and the third edge is L1, and the distance between the first groove and the fourth edge is L2. 5mm≤L1≤25mm; and / or, 3mm≤L2≤20mm. It can effectively reduce the curling of the first single-sided pole piece and improve the restrictive effect on the isolation membrane.

[0022] In some embodiments, along the third direction, the distance between two adjacent first grooves is L3, 4mm≤L3≤50mm, which is conducive to the first adhesive in each first groove forming a continuous binding network, improving the overall deformation resistance of the electrode assembly, and reducing the serious structural damage of the first single-sided electrode sheet caused by excessive density of the first grooves.

[0023] 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.

[0024] 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

[0025] One or more embodiments are exemplarily described by the figures in the accompanying drawings, which are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0026] Figure 1 This is a schematic structural diagram of a secondary battery in some embodiments of the present application; Figure 2 Schematic diagram of the stacked structure of the electrode assembly of some embodiments of the present application; Figure 3 This is a schematic structural diagram of a first single-sided pole piece in some embodiments of the present application; Figure 4 This is a schematic structural diagram of the first current collector in some embodiments of the present application; Figure 5 This is a schematic structural diagram of the first current collector in some embodiments of the present application; Figure 6 This is a schematic structural diagram of the first current collector in some embodiments of the present application; Figure 7 Schematic diagram of the stacked structure of the electrode assembly of some embodiments of the present application; Figure 8Schematic diagram of the bonding between the first bonding member and the first current collector in some embodiments of the present application; Figure 9 This is a schematic structural diagram of a first adhesive member in some embodiments of the present application; Figure 10 Schematic diagram of the stacked structure of the electrode assembly of some embodiments of the present application; Figure 11 A top view of a first single-sided pole piece according to some embodiments of the present application; Figure 12 A top view of a second single-sided pole piece according to some embodiments of the present application; Figure 13 Schematic diagram of the connection of the first adhesive member, the second adhesive member, and the third adhesive member in some embodiments of the present application; Figure 14 This is a top view of the first single-sided pole piece in some embodiments of the present application.

[0027] Description of reference numerals: 100. Secondary battery; 10. Housing; 11. First portion; 12. Second portion; 13. Accommodating chamber; 20. Electrode assembly; 201. First edge; 202. Second edge; 203. Third edge; 204. Fourth edge; 205. Fifth edge; 206. Sixth edge; 21. First inner layer pole piece; 211. First inner layer current collector; 22. The second inner pole piece; 23. Isolation film; 20a, first single-sided pole piece; 20a1, first current collector; 20a2, first active material layer; 20a3, first surface; 20a4, second surface; 20a5, first groove; 20b, second single-sided pole piece; 20b1, second current collector; 20b2, second active material layer; 20b3, third surface; 20b4, fourth surface; 20b5, second groove; 30. First adhesive member; 31. First adhesive layer; 32. Second adhesive layer; 33. Base material layer; 40. second adhesive member; 50. a third adhesive member; 60. Extreme ears; X, third direction; Y, second direction; Z, first direction. DETAILED DESCRIPTION

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] In the first aspect, the present application proposes a secondary battery 100, please refer to Figure 1 The secondary battery 100 includes a shell 10 and an electrode assembly 20. The shell 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte infiltrates the electrode assembly 20 in the shell 10, thereby generating an electrochemical reaction.

[0034] For the above-mentioned housing 10, please refer to Figure 1, the shell 10 encloses a accommodating cavity 13, and the electrode assembly 20 is arranged in the accommodating cavity 13. In an embodiment of the present application, the shell 10 can be formed by punching out a metal sheet, and the thickness of the metal sheet can be set to 0.1mm to 0.4mm, so that the shell 10 has a high punching strength. Among them, the metal sheet can be made of metal materials such as aluminum, aluminum alloy, steel, stainless steel, nickel, copper or magnesium alloy, which is beneficial to improve the strength of the shell 10, and thus protect the electrode assembly 20 inside the secondary battery 100. In addition, each material of the above-mentioned shell 10 has good thermal conductivity, which is beneficial to improve the heat dissipation performance of the secondary battery 100. At the same time, each metal material has good electrical conductivity, so that the shell 10 can lead to a certain polarity of the secondary battery 100, for example, the shell 10 itself is used as the positive electrode or negative electrode of the secondary battery 100. In some other embodiments, the shell 10 may also use soft packaging materials, such as aluminum plastic film or copper plastic film, which has a smaller mass, is conducive to achieving a lightweight setting of the secondary battery 100, and can make the shell 10 have better ductility, thereby improving the design flexibility of the shell 10.

[0035] The housing 10 includes a first portion 11 and a second portion 12. The first portion 11 is provided with a first cavity, in which the electrode assembly 20 can be disposed (not shown). The second portion 12 can be provided with a second cavity (not shown), or it can be provided without a cavity. By covering the first cavity with the second portion 12 and connecting the second portion 12 to the first portion 11, the first and second portions 11, 12, together, form a complete housing 10. The connection between the second portion 12 and the first portion 11 includes, but is not limited to, welding or bonding.

[0036] For the electrode assembly 20, please refer to Figure 1 and Figure 2 The electrode assembly 20 is disposed in the housing cavity 13 of the housing 10. The shape of the electrode assembly 20 can be configured to match the housing 10 to fully utilize the space of the housing cavity 13 of the housing 10, which is beneficial for improving the energy density of the secondary battery 100. The electrode assembly 20 includes a first inner electrode sheet 21, a second inner electrode sheet 22, and a separator 23. The polarity of the first inner electrode sheet 21 and the second inner electrode sheet 22 are opposite. For example, the first inner electrode sheet 21 is a positive electrode sheet and the second inner electrode sheet 22 is a negative electrode sheet, or the first inner electrode sheet 21 is a negative electrode sheet and the second inner electrode sheet 22 is a positive electrode sheet. A plurality of first inner electrode sheets 21 and a plurality of second inner electrode sheets 22 are alternately stacked, and a separator 23 is provided between adjacent first inner electrode sheets 21 and second inner electrode sheets 22 to form a stacked electrode assembly 20.

[0037] In some other embodiments, the electrode assembly 20 includes a first electrode sheet (not shown), a separator 23, and a second electrode sheet (not shown). The first electrode sheet, separator 23, and second electrode sheet are stacked and wound to form a wound electrode assembly 20. In this case, the inner portion of the first electrode sheet is referred to as the first inner electrode sheet 21, and the inner portion of the second electrode sheet is referred to as the second inner electrode sheet 22.

[0038] In some embodiments, please refer to Figures 1 to 3 The electrode assembly 20 includes a first single-sided electrode sheet 20a, which is the outermost electrode sheet of the electrode assembly 20. The first single-sided electrode sheet 20a includes a first current collector 20a1 and a first active material layer 20a2. Along the thickness direction of the first current collector 20a1, the first current collector 20a1 includes a first surface 20a3 and a second surface 20a4 that are arranged opposite each other. The second surface 20a4 is arranged facing the inner layer, for example, facing the first inner layer electrode sheet 21. The first single-sided electrode sheet 20a can serve as either a positive electrode sheet or a negative electrode sheet. For example, when the housing 10 is a conductive housing, the first single-sided electrode sheet 20a can serve as the negative electrode sheet. When the housing 10 is a soft-package housing (such as an aluminum-plastic film), the first single-sided electrode sheet 20a can serve as the positive electrode sheet.

[0039] Taking the first single-sided electrode sheet 20a as an example, the first current collector 20a1 can be made of aluminum foil. Aluminum foil has good conductivity and good ductility. In addition, aluminum foil forms an aluminum oxide passivation film in an electrolyte environment, which improves the corrosion resistance of the first current collector 20a1. The first active material layer 20a2 includes a positive electrode active material, a conductive agent, and a binder. These components are mixed, stirred, and evenly applied to the second surface 20a4 of the first current collector 20a1 to form the first active material layer 20a2. 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.

[0040] In other embodiments, the first single-sided electrode sheet 20a can also serve as the negative electrode sheet, and the first current collector 20a1 can be made of copper foil. Copper foil has good conductivity, relatively good mechanical strength, and excellent tolerance to electrolyte environments, which helps extend the service life of the negative electrode sheet. In this case, the first active material layer 20a2 includes a negative electrode active material, a conductive agent, and a binder. These materials are mixed, stirred, and evenly coated on the second surface 20a4 of the first current collector 20a1 to form the first active material layer 20a2. The negative electrode active material includes one or more of graphite, soft carbon, hard carbon, elemental silicon, silicon-carbon compounds, silicon-oxygen compounds, and silicon alloys.

[0041] In the embodiment of the present application, the outermost electrode sheet of the electrode assembly 20 is a first single-sided electrode sheet 20a having an active material layer provided on a single side. The outer side (first surface 20a3) of the first single-sided electrode sheet 20a does not directly participate in the electrochemical reaction. Single-sided coating can optimize the space utilization of the shell 10, which is beneficial to improving the energy density of the secondary battery 100.

[0042] The secondary battery 100 typically also includes an adhesive for securing the electrode assembly 20. For example, the adhesive bonds the electrode sheets to the outer surface of the electrode assembly 20 to tighten the electrode assembly 20, and / or bonds the electrode assembly 20 to the housing 10 to reduce relative movement between the two. However, the inventors of this application have discovered that the adhesive should have a certain thickness, typically 10 μm to 100 μm, to provide good adhesion and high mechanical strength. The total thickness of the adhesive on the upper and lower surfaces of the electrode assembly 20 (e.g., 30 μm for a single-sided adhesive and 60 μm for both sides) directly increases the thickness of the electrode assembly 20, which can result in a loss of energy density in the secondary battery 100. Reducing the adhesive thickness results in insufficient bonding strength, potentially leading to failure in securing the electrode assembly 20. Furthermore, thinner adhesives lack sufficient adhesion, which can easily lead to wrinkling or even loosening of the adhesive, resulting in poor performance.

[0043] To reduce the above problems, in the embodiments of this application, please refer to Figure 2 and Figure 3 The secondary battery 100 also includes a first adhesive 30. The inventors of this application discovered that there is usable space on the inactive surface of the outermost first single-sided electrode sheet 20a (the surface of the single-sided electrode sheet not coated with active material), and proposed a solution of "machining grooves on the surface of the current collector and embedding the adhesive within the grooves." For example, the first surface 20a3 of the first current collector 20a1 is provided with a first groove 20a5. The first groove 20a5 can be formed on the first surface 20a3 of the first current collector 20a1 through processes such as laser cleaning, mechanical stamping, and chemical etching. The first adhesive 30 is disposed within the first groove 20a5 and adheres to the first current collector 20a1 to securely bond the electrode assembly 20.

[0044] In the embodiment of the present application, a first groove 20a5 is provided on the first surface 20a3 of the first single-sided electrode sheet 20a, where no active material layer is provided. The first groove 20a5 accommodates the first adhesive 30, effectively reducing the space occupied by the first adhesive 30, facilitating the ultra-thin design of the secondary battery 100 and improving the energy density of the secondary battery 100. Furthermore, the sidewalls of the first groove 20a5 physically constrain the first adhesive 30, forming a mechanically interlocking structure between the first adhesive 30 and the first current collector 20a1. This reduces displacement of the first adhesive 30, such as wrinkling or shedding of the first adhesive 30 due to collisions with the secondary battery 100 or expansion of the electrode sheet, thereby effectively improving the structural stability of the electrode assembly 20.

[0045] For the first groove 20a5, the first groove 20a5 may be extended to three edges of the first current collector 20a1, such as Figure 4 As shown, the first groove 20a5 only includes one side wall, which can be used to limit the first adhesive 30. The first groove 20a5 can also extend to the two edges of the first current collector 20a1, as shown in FIG. Figure 5 As shown, the first groove 20a5 includes two side walls, which can be used to limit the first adhesive 30. The first groove 20a5 can also extend to one side edge of the first current collector 20a1, as shown in FIG. Figure 6 As shown, the first groove 20a5 includes three sidewalls, which can be used to limit the first adhesive member 30. The first groove 20a5 can have various shapes, such as arc, trapezoidal or square, as long as it can limit the first adhesive member 30.

[0046] In some other embodiments, when the electrode assembly 20 has a stepped structure and the first adhesive 30 is used to restrain and tighten the electrode assembly 20, the first adhesive 30 can also be set at the step, so that the first adhesive 30 can utilize the space at the step, and the energy density of the secondary battery 100 can be improved without setting the first groove 20a5.

[0047] In some embodiments, please refer to Figure 3 Taking the first single-sided electrode sheet 20a as the negative electrode sheet as an example, the first current collector 20a1 is made of copper foil. The thickness of the first current collector 20a1 is T1, the depth of the first groove 20a5 is D1, and 20%≤D1 / T1≤67%. Any value between 20% and 67% can be selected, such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 67%. Copper foil has high mechanical strength, and the limit of 20%≤D1 / T1≤67% can reduce wrinkling or shedding of the first adhesive 30, reduce the space occupied by the first adhesive 30, improve the energy density of the secondary battery 100, and ensure that the first current collector 20a1 still has good mechanical strength.

[0048] The depth D1 of the first groove 20a5 can be selected to be 1 μm ≤ D1 ≤ 20 μm, and can be any value between 1 μm and 20 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, or 20 μm. Furthermore, 1.2 μm ≤ D1 ≤ 4 μm can be selected, which helps to increase the mechanical strength of the first current collector 20a1, reduce irregular deformation of the first current collector 20a1, and allow the first adhesive member 30 to be fully accommodated in the first groove 20a5, thereby improving the energy density of the secondary battery 100.

[0049] In some embodiments, please refer to Figure 3 The first single-sided electrode sheet 20a can also serve as the positive electrode sheet, that is, the first current collector 20a1 is made of aluminum foil. The thickness of the first current collector 20a1 is T1, and the depth of the first groove 20a5 is D1, with 20%≤D1 / T1≤50%. Any value between 20% and 50% can be selected, such as 20%, 22%, 24%, 26%, 28%, 30%, 35%, 40%, 45%, or 50%. The upper limit of the first groove 20a5 depth ratio of the positive electrode aluminum foil (20% to 50%) is lower than that of the negative electrode copper foil (20% to 67%). Aluminum foil is weaker than copper foil, and more matrix material must be retained to maintain structural and electrochemical stability.

[0050] The depth D1 of the first groove 20a5 can be selected to be 2 μm ≤ D1 ≤ 10 μm, and can be any value between 2 μm and 10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. Furthermore, 2.4 μm ≤ D1 ≤ 6 μm can be selected, which helps to increase the mechanical strength of the first current collector 20a1 and allows the first adhesive member 30 to be fully accommodated in the first groove 20a5, thereby improving the energy density of the secondary battery 100.

[0051] In some embodiments, please refer to Figure 7, the first inner layer pole piece 21 has the same polarity as the first single-sided pole piece 20a, for example, the first inner layer pole piece 21 and the first single-sided pole piece 20a are both positive pole pieces or both negative pole pieces. The first inner layer pole piece 21 includes a first inner layer current collector 211, the thickness of the first inner layer current collector 211 is T2, the thickness of the first current collector 20a1 is T1, and T1>T2. The inventors of the present application have found that the first single-sided pole piece 20a is subject to fewer restrictions and cannot be squeezed on both sides like the first inner layer pole piece 21, so the first single-sided pole piece 20a is prone to curling. In addition, the active material layer is only provided on one side of the first single-sided pole piece 20a, and the stress on both sides in the thickness direction is uneven, which further increases the risk of curling. In the embodiment of the present application, by increasing the thickness of the first current collector 20a1, that is, T1>T2, the first current collector 20a1 can have higher mechanical strength, which can reduce the risk of curling of the first single-sided pole piece 20a.

[0052] Based on the assumption that T1 > T2, in some embodiments, the depth of the first groove 20a5 is D1, and 100% ≤ (T1-D1)T2 ≤ 200%. Any value between 100% and 200% can be selected, such as 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, or 200%. (T1-D1)T2 ≥ 100%, ensuring that the remaining thickness (T1-D1) of the first current collector 20a1 at the bottom of the first groove 20a5 is no less than the thickness T2 of the first inner current collector 211. This reduces the mechanical strength of the first current collector 20a1 due to the excessive depth of the first groove 20a5, and reduces deformation or curling of the first current collector 20a1. (T1-D1)T2≤200%, limiting the remaining thickness at the bottom of the first groove 20a5 to no more than twice the thickness of the first inner current collector 211, reducing the thickness occupied by the first current collector 20a1 and reducing energy density loss.

[0053] In some other embodiments, the first inner-layer electrode sheet 21 includes a first inner-layer current collector 211 with a thickness of T2, and the thickness of the outer first current collector 20a1 is T1, where T1 < T2. The inventors of the present application have found that since the first single-sided electrode sheet 20a has an active material layer disposed only on one side, while the first inner-layer electrode sheet 21 has active material layers disposed on both sides, the lithium-ion insertion and extraction reaction of the first inner-layer electrode sheet 21 is more intense than that of the outer layer. And the lithium-ion insertion and extraction reaction is usually related to the current density. In the embodiments of the present application, by defining T1 < T2, that is, the thickness of the first current collector 20a1 is less than the thickness of the first inner-layer current collector 211, the resistance of the first current collector 20a1 can be increased, its current-carrying capacity can be weakened, and further the current density of the first single-sided electrode sheet 20a can be reduced, and the occurrence of lithium deposition can be reduced. For reducing the curling of the first current collector 20a1, the strength can be increased on the first current collector 20a1, or a reinforcing member can be adhesively attached to improve the strength of the first current collector 20a1.

[0054] Based on T1 < T2, in some embodiments, the depth of the first groove 20a5 is D1, and 60% ≤ (T1 - D1) / T2 ≤ 73%. Any value between 60% and 73% can be selected, for example, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72% or 73%. This enables the first current collector 20a1 to have better mechanical strength and facilitates accommodating the first bonding member 30, reducing the loss of energy density.

[0055] In some embodiments, please refer to Figure 8 , the first bonding member 30 includes a first adhesive layer 31, a substrate layer 33, and a second adhesive layer 32 which are stacked. The first adhesive layer 31 and the second adhesive layer 32 are respectively disposed on opposite surfaces of the substrate layer 33. Both the first adhesive layer 31 and the second adhesive layer 32 can be made of at least one of ethylene, polypropylene, polyurethane, epoxy resin, styrene-butadiene rubber, polyvinylidene fluoride or polyacrylic acid. The substrate layer 33 can be made of at least one of polyethylene terephthalate or polyimide. The first adhesive layer 31 is bonded to the first current collector 20a1, and the second adhesive layer 32 can be bonded to the housing 10. During assembly, the first bonding member 30 can be first bonded to the electrode assembly 20 in the first groove 20a5. After the electrode assembly 20 is placed in the housing 10, the first bonding member 30 is bonded to the inner wall of the housing 10 by pressing. The first groove 20a5 and the first bonding member 30 form a mechanical fit, and the first bonding member is bonded to the housing 10, which can reduce the relative movement between the electrode assembly 20 and the housing 10 and improve the stability of the internal structure of the secondary battery 100.

[0056] Both the first adhesive layer 31 and the second adhesive layer 32 may be made of hot melt adhesive and / or pressure sensitive adhesive. Hot pressing can be used to bond the first adhesive member 30 to the first current collector 20a1 and the housing 10. The second adhesive layer 32 at least partially protrudes from the first surface 20a3. During hot pressing, the second adhesive layer 32 is subjected to greater pressure, thereby fully bonding to the housing 10 and improving the bonding strength.

[0057] In some embodiments, the thickness of the first adhesive layer 31 is T a1 The thickness of the second adhesive layer 32 is T a2 , the thickness of the base material layer 33 is T a3 The thickness of the first adhesive layer 31 can be set to be slightly larger than that of the second adhesive layer 32, which is conducive to the first adhesive layer 31 fully adhering to the bottom wall and side wall of the first groove 20a5, improving the bonding strength between the first adhesive 30 and the first current collector 20a1, and to a certain extent compensating for the strength loss of the first current collector 20a1 caused by the provision of the first groove 20a5, thereby reducing the curling or damage and tearing of the first current collector 20a1. In the embodiment of the present application, 117%≤T a1 / T a2 ≤163%, any value between 117% and 160% can be selected, for example, 117%, 118%, 119%, 120%, 122%, 124%, 126%, 128%, 130%, 140%, 150%, 160%, 163%, etc.

[0058] For the substrate layer 33, in the embodiment of the present application, 117%≤T a3 / T a2 ≤150%. Any value between 117% and 150% can be selected, for example, 117%, 118%, 119%, 120%, 122%, 124%, 126%, 128%, 130%, 140%, or 150%. The substrate layer 33 has a high structural strength, which helps improve the overall mechanical strength of the first adhesive member 30. When the first adhesive member 30 is bonded to the first current collector 20a1 within the first groove 20a5, the thicker substrate layer 33 helps compensate for the loss in strength of the first current collector 20a1 caused by the provision of the first groove 20a5, ensuring that the first current collector 20a1 maintains a high mechanical strength and reduces the risk of curling, deformation, or damage or tearing of the first current collector 20a1.

[0059] In some embodiments, please refer to Figure 10Along the first direction Z, a plurality of first inner electrode sheets 21 and a plurality of second inner electrode sheets 22 are alternately stacked, and an isolation film 23 is provided between adjacent first inner electrode sheets 21 and second inner electrode sheets 22, thereby forming a stacked electrode assembly 20. The electrode assembly 20 also includes a second single-sided electrode sheet 20b. Along the first direction Z, the outermost electrode sheets on both sides of the electrode assembly 20 are respectively a first single-sided electrode sheet 20a and a second single-sided electrode sheet 20b. The second single-sided electrode sheet 20b includes a second current collector 20b1 and a second active material layer 20b2. The second current collector 20b1 includes a third surface 20b3 and a fourth surface 20b4 arranged opposite each other. The fourth surface 20b4 faces the first inner electrode sheet 21. The fourth surface 20b4 is provided with a second active material layer 20b2. The third surface 20b3 is provided with a second groove 20b5. Secondary battery 100 also includes a second adhesive member 40. First adhesive member 30 is disposed in second groove 20b5 and bonded to second current collector 20b1. Grooves (first groove 20a5 and second groove 20b5) are provided on both sides of the outermost single-sided electrode sheets of electrode assembly 20 to accommodate these adhesive members (first adhesive member 30 and second adhesive member 40), further increasing the energy density of secondary battery 100.

[0060] Among them, the structure of the second single-sided pole piece 20b is similar to that of the first single-sided pole piece 20a. For details, please refer to the relevant description of the first single-sided pole piece 20a above, and this application will not go into details one by one.

[0061] The separator 23 is a key component that isolates the positive and negative electrodes inside the secondary battery 100 and prevents short circuits. At the same time, the separator 23 allows lithium ions to pass through, thereby allowing the positive and negative electrodes to undergo lithium ion deintercalation reactions. The inventors of this application have found that during the stacking or winding process of the electrode assembly 20, the pole pieces and the separator 23 are alternately stacked, which can easily cause the structure of the electrode assembly 20 to be loose. The separator 23 is easily displaced or wrinkled due to external forces, which may cause the positive and negative electrodes to directly contact, posing the risk of short circuits. In addition, when welding the first part 11 and the second part 12 of the shell 10, or when welding the electrode assembly 20 to the tab 60, the high welding temperature may cause the separator 23 to melt or cause the separator 23 to be drawn into the welding area, affecting the welding quality.

[0062] To reduce the above problems, please refer to Figures 10 to 12, the secondary battery 100 further includes a third adhesive member 50. Along the second direction Y, the first current collector 20a1 includes a first edge 201 and a second edge 202 disposed opposite each other, and the second current collector 20b1 includes a fifth edge 205 and a sixth edge 206 disposed opposite each other. The second direction Y is perpendicular to the first direction Z. Along the first direction Z, the first edge 201 and the fifth edge 205 are disposed opposite each other, and the second edge 202 and the sixth edge 206 are disposed opposite each other. The first groove 20a5 extends to the first edge 201, and the second groove 20b5 extends to the fifth edge 205. One end of the third adhesive member 50 extends to the first edge 201, one end of the third adhesive member 50 is connected to the first adhesive member 30, the other end of the third adhesive member 50 extends to the fifth edge 205, and the other end of the third adhesive member 50 is connected to the second adhesive member 40. The third adhesive 50 is bonded to the first adhesive 30 and the second adhesive 40 on both sides of the electrode assembly 20, respectively, so that the first adhesive 30, the second adhesive 40, and the third adhesive 50 form a whole, and tighten the electrode assembly 20 to prevent the electrode assembly 20 from loosening. At the same time, the third adhesive 50 can limit the extension of the separator 23, thereby reducing the impact of the separator 23 on the welding of the housing 10 and the welding of the tab 60.

[0063] In some embodiments, the first adhesive 30, the second adhesive 40 and the third adhesive 50 are integrally arranged, which can eliminate the multi-component splicing process and reduce the position deviation during assembly of the components. A wrapping structure is formed from the upper and lower surfaces to the sides of the electrode assembly 20, and the binding force has no breakpoints, which can reduce the local stress concentration during the bonding of the components, and is beneficial for making the forces on various parts of the electrode assembly 20 more balanced, reducing the risk of local deformation of the electrode assembly 20.

[0064] In the embodiment of the present application, the provision of the first groove 20a5 allows the sidewalls of the first groove 20a5 to physically constrain the first adhesive member 30, forming a mechanically interlocking structure between the first adhesive member 30 and the first current collector 20a1. This reduces displacement of the first adhesive member 30, for example, reducing wrinkling or shedding of the first adhesive member 30 due to collisions with the secondary battery 100 or expansion of the electrode sheet, thereby effectively improving the structural stability of the electrode assembly 20. Therefore, the thickness of the first adhesive member 30 can be appropriately reduced, with minimal impact on the bonding strength between the first adhesive member 30 and the first current collector 20a1.

[0065] Please refer to further Figure 13 , the thickness of the first adhesive member 30 is T a , the thickness of the second adhesive member 40 is T b , the thickness of the third adhesive member 50 is T c . T a <T c and / or, T b <Tc Typically, there is a gap between the electrode assembly 20 and the housing 10 in the length or width direction of the secondary battery 100 (the side direction of the electrode assembly 20, such as the second direction Y or the third direction X). Figure 1 ), so that the electrolyte can enter the interior of the electrode assembly 20. The third adhesive 50 is on the side of the electrode assembly 20 and has little effect on the energy density of the secondary battery 100. However, the space in the thickness direction of the electrode assembly 20 is small, so the first welding member and the second adhesive 40 have a greater impact on the energy density of the secondary battery 100. In the embodiment of the present application, it is defined as T a <T c and / or, T b <T c By thinning the first adhesive 30 and / or the second adhesive 40, the energy density of the secondary battery 100 is improved. A thicker third adhesive 50 is used to strengthen the structure in the lateral direction to support the binding structure and reduce the loosening of the electrode assembly 20. Furthermore, due to the provision of the first groove 20a5, the risk of wrinkling or falling off of the first adhesive 30 and the second adhesive 40 is reduced. The thinning of the first adhesive 30 and the second adhesive 40 also has a smaller impact on their bonding strength. Therefore, by limiting T a <T c and / or, T b <T c , which is beneficial to further improve the energy density of the secondary battery 100 without affecting the bonding strength (or having a smaller impact).

[0066] In some embodiments, 2 μm ≤ T c -T a ≤20 μm, and any value between 2 μm and 20 μm can be selected, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm, etc. This is beneficial for improving the energy density while ensuring a higher connection strength between the first adhesive member 30 and the first current collector 20 a 1 .

[0067] Based on the same inventive concept, 2μm≤T c -T b≤20 μm, and any value between 2 μm and 20 μm can be selected, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm, etc. This is beneficial for improving the energy density while ensuring a higher connection strength between the second adhesive member 40 and the second current collector 20 b 1 .

[0068] When the first adhesive member 30 is used to tighten the electrode assembly 20, the first adhesive member 30 may be similar to Figure 11 In this case, the thickness of the first adhesive 30 can even be less than the depth of the first groove 20b5, which fully reduces the influence of the first adhesive 30 on the thickness. When the first adhesive 30 is used to bond the electrode assembly 20 and the housing 10, the first adhesive 30 can be similar to Figure 11 or Figure 14 In this case, the thickness of the first adhesive member 30 may be greater than or equal to the depth of the first groove 20b5 to facilitate bonding with the housing 10.

[0069] In some embodiments, please refer to Figure 7 and Figure 11 Along the second direction Y, the first surface 20a3 is provided with a plurality of first grooves 20a5 (each of which contains a first adhesive 30). These first grooves 20a5 are sequentially arranged along the third direction X and extend to the first edge 201. The secondary battery 100 also includes a tab 60, which is connected to the electrode assembly 20. For example, the tab 60 is connected to the first single-sided electrode sheet 20a of the electrode assembly 20 and is also connected to the third edge 203. The first current collector 20a1 has a thickness of T1, and the first inner current collector 211 has a thickness of T2, where T1 ≤ T2. Along the third direction X, the distance between the first groove 20a5 and the third edge 203 is L1, 8mm≤L1≤25mm, and any value between 8mm and 25mm can be selected, for example, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm, 23mm, 24mm or 25mm, etc.

[0070] Normally, the overhang area (the portion where the negative electrode active material layer extends beyond the positive electrode active material layer) of the head of the electrode assembly 20 (the end close to the extension direction of the tab 60 is usually regarded as the head) is usually larger than the overhang area of ​​the non-head. A thinning area will be set at the head of the electrode assembly 20 (near the extension direction of the tab 60). The head thinning area is limited to 8mm≤L1≤25mm due to the thinning of the material thickness, which is beneficial for the head thinning area to maintain a certain strength and can effectively restrain the isolation membrane 23, reducing the influence of the isolation membrane on welding.

[0071] Based on T1≤T2, for the tail region, the distance between the first groove 20a5 and the fourth edge 204 is L2, 5mm≤L2≤20mm, and any value between 5mm and 20mm can be selected, such as 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm. This facilitates the first groove 20a5 to avoid the electrolyte channel at the tail corner, while providing a mechanical locking structure for the first adhesive member 30 within a range of 20mm, reducing displacement of the separator 23 during welding, and facilitating a balanced balance between electrode sheet electrolyte infiltration and structural reliability of the electrode assembly 20.

[0072] In other embodiments, T1 > T2, meaning the thickness of the first current collector 20a1 is greater than the thickness of the first inner current collector 211. In this case, the first current collector 20a1 itself has relatively high strength, and L1 can be limited to 5 mm ≤ L1 ≤ 25 mm. Any value between 5 mm and 25 mm can be selected, such as 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, 22 mm, 23 mm, 24 mm, or 25 mm. This facilitates avoiding areas with sudden changes in thickness (such as the thinned head region), reducing warping of the head of the first current collector 20a1 due to thickness differences. It also helps prevent misalignment between the separator 23 and the pole pieces, reducing the effect of the separator 23 on the welding of the tab 60 or the housing 10.

[0073] Based on T1>T2, 3mm≤L2≤20mm, any value between 3mm and 20mm can be selected, for example, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm. This facilitates the first groove 20a5 to avoid the electrolyte channel at the tail corner, while providing a mechanical locking structure for the first adhesive member 30 within a range of 20mm, reducing displacement of the separator 23 during welding, and facilitating a balanced balance between electrode sheet electrolyte infiltration and structural reliability of the electrode assembly 20.

[0074] In some embodiments, along the third direction X, the distance between two adjacent first grooves 20a5 is L3, where 4 mm ≤ L3 ≤ 50 mm. Any value between 4 mm and 50 mm can be selected, such as 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 30 mm, 40 mm, or 50 mm. This facilitates forming a continuous binding network among the adhesive components, reduces the effect of the separator 23 on welding, and reduces the effect on electrolyte infiltration. It also reduces the serious structural damage to the first single-sided electrode sheet 20a caused by overcrowding of the first grooves 20a5.

[0075] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, electronic devices include but are not limited to Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0076] Example 1-1 <Preparation of the first single-sided pole piece>: The first single-sided electrode sheet is the negative electrode sheet. The negative electrode active materials (graphite powder, silicon powder, conductive carbon black (Super P), and binder (SD-3)) are mixed in a mass ratio of 87.5:10:1:1.5. Deionized water is then added as a solvent to create a negative electrode slurry with a solids content of 70wt%, which is then stirred evenly. A copper foil with a thickness T1 of 6μm, a length of 70mm, and a width of 50mm is used as the first current collector. The negative electrode slurry is evenly coated on one surface of the first current collector and dried at 90°C to obtain the first single-sided electrode sheet coated with the negative electrode active material layer on one side. The other surface coated with the negative electrode active material layer is the first surface.

[0077] <Preparation of the first inner layer pole piece>: The first inner electrode sheet has the same polarity as the first single-sided electrode sheet. A copper foil with a thickness T2 of 6 μm, a length of 70 mm, and a width of 50 mm is selected as the first inner current collector. According to the above-mentioned preparation plan of the first single-sided electrode sheet, the negative electrode slurry is coated on both surfaces of the first inner current collector in the thickness direction and dried at 90°C to obtain the first inner electrode sheet with a negative electrode active material layer coated on both sides.

[0078] <Preparation of the second inner layer pole piece>: The second inner electrode is the positive electrode. The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10 5 ) were mixed in a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 75wt%. This was then stirred evenly in a vacuum mixer. Aluminum foil with a thickness of 12μm, a length of 70mm, and a width of 50mm was used as the positive electrode current collector. The positive electrode slurry was evenly coated on one surface of the aluminum foil and dried at 110°C. The positive electrode slurry was then evenly coated on the other surface of the aluminum foil. After drying, the second inner layer positive electrode sheet, coated on both sides with a positive electrode active material layer, was obtained.

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

[0080] <Preparation of Electrolyte> 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 solution, and then lithium hexafluorophosphate was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0081] <Preparation of Adhesive> Select thickness T a3 The polyethylene terephthalate layer is 5 μm thick and is used as the substrate layer. The first adhesive layer and the second adhesive layer of epoxy resin are respectively compounded on the two surfaces in the thickness direction of the substrate layer. The thickness of the first adhesive layer is T a1 is 5μm, and the thickness of the second adhesive layer is T a2 5μm.

[0082] <Preparation of Lithium Ion Secondary Battery> By laser cleaning, a first groove with a depth D1 of 1 μm is cleaned on the surface of the empty foil in the thickness direction of the first current collector, and the first groove extends to an edge in the width direction of the first current collector. After the pole pieces are welded to the pole ears, the first single-sided pole piece, the first inner pole piece and the second inner pole piece prepared above are stacked, and an isolation film is set between adjacent pole pieces to form a stacked electrode assembly. The first single-sided pole piece is the outermost pole piece, and the positive and negative pole pieces of the electrode assembly are 20 layers in total. The adhesive is bonded to the electrode assembly to form a similar Figure 1 In the illustrated bonding structure, the first adhesive members on the first current collector are each provided with a corresponding first groove to accommodate the first adhesive. The distance L1 from the leading edge of the first groove to the trailing edge is 15 mm, and the distance L2 from the trailing edge is 10 mm. The distance L3 between two adjacent first grooves along the length of the first current collector is 10 mm. The punched steel shell is placed in an assembly fixture with the pits facing upward. The electrode assembly is placed in the pits, and the shell is welded. After packaging, liquid injection, hot pressing, and shaping, a lithium-ion secondary battery is produced.

[0083] Energy density (VED) test: Charge the secondary battery at a constant current of 1C to the cutoff voltage, then charge it to 0.05C at the cutoff voltage constant voltage. Then discharge it at a constant current of 0.2C to the discharge cutoff voltage, recording the discharge energy E. Measure the external dimensions of the secondary battery and calculate its volume, which is V. Energy density W = E / V. It should be understood that 1C, 0.05C, and 0.2C are calculated based on the capacity specified on the battery's factory packaging.

[0084] Pole curl degree (mechanical strength) test: After laser cleaning, the pole piece is placed horizontally for 1 hour at room temperature (25°C), and then the pole piece is photographed using the OMM (optical microscopy test system). The pole piece is then picked up and the curl vertex of the pole piece edge is tangent at this point to obtain the tangent line of the pole piece curl edge. The angle between this line and the horizontal line is used as the overall curl angle of the pole piece. When measuring the head curl test, the pole piece needs to be cut along the vertical center line of the head, and the two parts are tested separately to obtain the average curl angle of the two parts. When measuring the tail curl, the pole piece needs to be cut along the vertical center line of the tail, and the two parts are tested separately to obtain the average curl angle of the two parts. When measuring the middle curl, the pole piece needs to be cut along the horizontal center line of the middle, and the two parts are tested separately to obtain the average curl angle of the two parts. A curling angle of ≥90° is severe curling, indicating that the electrode is prone to deformation when the secondary battery is used. An angle of 20°≤<90° is moderate curling, an angle of <20° is mild curling, and ≤5° is no curling.

[0085] Depth measurement of the first groove: Use a laser rangefinder to measure. The first laser rangefinder measures the distance from the cleaning area at the bottom of the current collector (d1), and the second laser rangefinder measures the distance from the bottom of the current collector to the surface of the current collector (d2). The depth of the first groove = d1-d2.

[0086] Interface black spot test: The battery is cycled 200 times, disassembled, and the area of ​​black spots in the center of the electrode is identified using an optical microscope. The total area of ​​the electrode is calculated, and the ratio of the black spot area to the total area of ​​the electrode is obtained. If the black spot area ratio is ≥50%, severe black spots appear, indicating severe poor infiltration; if the black spot area ratio is 10% ≤ <50%, moderate black spots appear, indicating moderate poor infiltration; if the black spot area ratio is 5% ≤ <10%, mild black spots appear, indicating mild poor infiltration; if the black spot area ratio is <5%, it is considered to be no black spots and no poor infiltration. The cycle process is as follows: 1C charge to 4.4V, constant voltage charge to 0.025C, then stand for 5 minutes, start discharge, 0.5C discharge to 3V, and then stand for 10 minutes.

[0087] Unlike Example 1-1, the relevant parameters in Examples 1-2 to 1-14 and Comparative Examples 1-1 to 1-2 are shown in Table 1 below. In Comparative Examples 1-1 to 1-2, the first single-sided pole piece is not provided with a first groove. In Comparative Example 1-2 and Examples 1-8 to 1-14, the first single-sided pole piece is positive polarity.

[0088] Table 1

[0089] According to Table 1 above, in combination with Examples 1-1 to 1-14 and Comparative Examples 1-1 to 1-2, when a first groove is provided on the first surface of the first single-sided electrode where no active material layer is provided, and the first adhesive is accommodated by the first groove, the energy density of the secondary battery can be effectively improved.

[0090] In Examples 1-1 to 1-7, the first single-sided electrode sheet is a negative electrode sheet. In Examples 1-2 to 1-6, the energy density is higher than that of Example 1-1, and the degree of winding of the electrode sheet is better than that of Example 1-7. In combination with Examples 1-2 to 1-6, when the first single-sided electrode sheet is a negative electrode sheet, 20%≤D1 / T1≤67% can be selected, which can reduce the space occupied by the first adhesive, increase the energy density of the secondary battery, and ensure that the first current collector still has good mechanical strength. Among them, the depth D1 of the first groove can be selected as 1.2μm≤D1≤4μm.

[0091] In Examples 1-8 to 1-14, the first single-sided electrode sheet is a positive electrode sheet. In Examples 1-9 to 1-13, the energy density is higher than that of Example 1-8, and the degree of curling of the electrode sheet is better than that of Example 1-14. In combination with Examples 1-9 to 1-13, when the first single-sided electrode sheet is a positive electrode sheet, 20% ≤ D1 / T1 ≤ 50% can be selected, which is beneficial for improving the energy density of the secondary battery while giving the first current collector better mechanical strength. Among them, the depth of the first groove D1 can be selected as 2.4μm ≤ D1 ≤ 6μm.

[0092] Different from Example 1, the relevant parameters in Examples 2-1 to 2-22 are shown in Table 2 below. In Examples 2-1 to 2-5 and Examples 2-11 to 2-16, T1>T2 is adopted. In Examples 2-6 to 2-10 and Examples 2-17 to 2-22, T1 is adopted. <T2。

[0093] Table 2

[0094] According to Table 2 above, in Examples 2-1 to 2-5, the first single-sided electrode sheets are all negative electrode sheets, and all employ a first current collector having a thickness T1 greater than the first inner current collector having a thickness T2. The energy density in Examples 2-2 to 2-4 is higher than that in Example 2-5, and the degree of electrode curling is better than that in Example 2-1. Based on the fact that T1 > T2, in combination with Examples 2-2 to 2-4, 100% ≤ (T1 - D1) T2 ≤ 200% can be selected, which is beneficial for increasing energy density while reducing curling of the first current collector.

[0095] In Examples 2-6 to 2-10, the first single-sided electrode is a negative electrode, and the thickness T1 of the first current collector is less than the thickness T2 of the first inner current collector. In Examples 2-7 to 2-9, the energy density is higher than that in Example 2-10, and the degree of electrode curling is better than that in Example 2-7. Based on T1 < T2 and combining Examples 2-7 to 2-9, it can be selected that 60% ≤ (T1 - D1) / T2 ≤ 73%, so that the first current collector has better mechanical strength, reduces the curling of the first current collector, and is convenient for accommodating the first bonding member, reducing the loss of energy density.

[0096] In Examples 2-11 to 2-16, the first single-sided electrode is a positive electrode, and the thickness T1 of the first current collector is greater than the thickness T2 of the first inner current collector. In Examples 2-12 to 2-15, the energy density is higher than that in Example 2-16, and the degree of electrode curling is better than that in Example 2-12. Based on T1 > T2 and combining Examples 2-12 to 2-15, it can be selected that 100% ≤ (T1 - D1) / T2 ≤ 200%, which is beneficial to reducing the curling of the first current collector while increasing the energy density.

[0097] In Examples 2-17 to 2-22, the first single-sided electrode is a positive electrode, and the thickness T1 of the first current collector is less than the thickness T2 of the first inner current collector. In Examples 2-18 to 2-21, the energy density is higher than that in Example 2-22, and the degree of electrode curling is better than that in Example 2-17. Based on T1 < T2 and combining Examples 2-18 to 2-21, it can be selected that 60% ≤ (T1 - D1) / T2 ≤ 73%, so that the first current collector has better mechanical strength, reduces the curling of the first current collector, and is convenient for accommodating the first bonding member, reducing the loss of energy density.

[0098] Different from Example 1-4, the relevant parameters in Examples 3-1 to 3-11 are shown in Table 3 below.

[0099] Table 3

[0100] According to Table 3 above and combining Examples 3-1 to 3-6, in Example 3-1, the ratio of the thickness T of the first adhesive layer a1 to the thickness T of the second adhesive layer 32 a2 is relatively small, which may be unfavorable for the adhesion force between the first groove and the first current collector, and the formed mechanical interlocking structure has limited improvement on the mechanical strength of the first current collector. In Example 3-6, T a1 / T a2If the thickness of the second adhesive layer is larger, the second adhesive layer will be thinner, which is not conducive to improving the bonding strength between the second adhesive layer and the shell. If the thickness of the second adhesive layer remains unchanged and the thickness of the first adhesive layer is increased, the first adhesive member will be thicker, and the energy density will not be significantly improved. a1 / T a2 ≤163%. Similarly, in combination with Examples 3-7 to 3-11, 117%≤T a3 / T a2 ≤150%, which can facilitate the bonding of the first adhesive member to the first current collector and to the shell, and can improve the mechanical strength of the first current collector and reduce the curling of the first current collector.

[0101] Different from Example 1-2, the relevant parameters in Examples 4-1 to 4-6 are shown in Table 4 below.

[0102] Table 4

[0103] According to Table 4 above, combined with Examples 4-1 to 4-6, the energy density in Examples 4-2 to 4-5 is higher than that in Example 4-6, and the degree of curling of the pole piece is better than that in Example 4-1. Combined with Examples 4-2 to 4-5, 2μm≤T c -T a ≤20μm, which is beneficial to improve the energy density while making the first adhesive and the first current collector have a higher connection strength. c The thickness of the second adhesive member is T b , 2μm≤T can be selected c -T b ≤20 μm, which is beneficial for improving the energy density while ensuring a higher connection strength between the second adhesive and the second current collector.

[0104] Different from Example 2-9, the relevant parameters in Examples 5-1 to 5-17 are shown in Table 5 below. Different from Example 2-2, the relevant parameters in Examples 5-18 to 5-37 are shown in Table 5 below.

[0105] Table 5

[0106] According to Table 5 above, Examples 5-1 to 5-5 all adopted T1 ≤ T2. Examples 5-2 to 5-4 achieved better curling of the electrode head than Example 5-1, and reduced the risk of black spots on the interface. In Example 5-5, L1 was relatively large, which had little effect on strengthening the separator. For the head region, combined with Examples 5-2 to 5-4, a value of 8mm ≤ L1 ≤ 25mm can be selected. This helps reduce the impact on the strength of the first current collector head, reduces curling of the head, and reduces the impact on electrolyte infiltration. It also facilitates the separator at the head, reducing the separator's impact on welding.

[0107] In Examples 5-6 to 5-10, T1 ≤ T2 was used. In Examples 5-7 to 5-9, the degree of electrode curl was superior to that of Example 5-6. In Example 5-10, L2 was relatively large, which did not significantly improve the barrier film's restraint. For the tail region, in combination with Examples 5-7 to 5-9, a value of 5mm ≤ L2 ≤ 20mm was chosen. This helped avoid the electrolyte channels at the tail corners, reduced curling, and facilitated the restraint of the tail barrier film, reducing its impact on welding.

[0108] In Examples 5-11 to 5-17, T1≤T2 is used. In Examples 5-12 to 5-16, the degree of curling of the pole piece is better than that of Example 5-11. In Example 17, L3 is relatively large, and the effect of improving the binding isolation membrane is not obvious. For the distance L3 between two adjacent first grooves, combined with Examples 5-12 to 5-16, 4mm≤L3≤50mm can be selected, which is conducive to forming a continuous binding network for each adhesive, reducing the influence of the isolation membrane on welding, and reducing the serious structural damage of the first single-sided pole piece caused by the over-density of the first grooves, thereby reducing the curling of the first current collector.

[0109] In Examples 5-18 to 5-23, T1>T2 is used. Similar to Examples 5-1 to 5-5 above, for the head region, in combination with Examples 5-19 to 5-22, a value of 5mm≤L1≤25mm can be selected. This helps reduce the impact on the strength of the first current collector head, reduces head curling, and reduces the impact on electrolyte infiltration. It also facilitates the restraint of the separator at the head, reducing the separator's impact on welding.

[0110] In conjunction with Examples 5-24 to 5-30, Examples 5-18 to 5-23 all employ T1 > T2. Similar to Examples 5-6 to 5-10, for the tail region, in conjunction with Examples 5-25 to 5-29, a value of 3mm ≤ L2 ≤ 20mm can be selected. This helps to avoid the electrolyte channel at the corner of the tail, reduces curling of the tail, and facilitates the restraint of the tail separator, reducing the effect of the separator on welding.

[0111] In conjunction with Examples 5-31 to 5-37, T1>T2 is adopted in all of Examples 5-31 to 5-37. Similar to the above-mentioned Examples 5-11 to 5-17, for the distance L3 between two adjacent first grooves, in conjunction with Examples 5-32 to 5-36, 4mm≤L3≤50mm can be selected. This is conducive to forming a continuous binding network for each adhesive member, reducing the impact of the isolation film on welding, and can also reduce the serious structural damage of the first single-sided electrode sheet caused by the overcrowding of the first grooves, thereby reducing the curling of the first current collector.

[0112] 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 housing and an electrode assembly disposed within the housing, the electrode assembly comprising a first inner electrode sheet, a separator, and a second inner electrode sheet, wherein the separator is stacked between the first inner electrode sheet and the second inner electrode sheet, wherein: The secondary battery further includes a first single-sided electrode sheet and a first adhesive member for fixing the electrode assembly; The first single-sided pole piece is the outermost pole piece of the electrode assembly, and the first single-sided pole piece includes a first current collector and a first active material layer; The first current collector includes a first surface and a second surface arranged opposite to each other, the second surface faces the first inner pole piece, and the first active material layer is arranged on the second surface; the first surface is provided with a first groove, the first adhesive is provided in the first groove, and the first adhesive is bonded to the first groove.

2. The secondary battery according to claim 1, wherein The first single-sided pole piece is a negative pole piece, the thickness of the first current collector is T1, the depth of the first groove is D1, and 20%≤D1 / T1≤67%.

3. The secondary battery according to claim 2, wherein 1.2μm≤D1≤4μm.

4. The secondary battery according to claim 1, wherein The first single-sided pole piece is a positive pole piece, the thickness of the first current collector is T1, the depth of the first groove is D1, and 20%≤D1 / T1≤50%.

5. The secondary battery according to claim 4, wherein 2.4μm≤D1≤6μm.

6. The secondary battery according to claim 1, wherein The first inner pole piece has the same polarity as the first single-sided pole piece, and the first inner pole piece includes a first inner current collector. The thickness of the first inner current collector is T2, and the thickness of the first current collector is T1, where T1>T2; The depth of the first groove is D1, 100%≤(T1-D1)T2≤200%.

7. The secondary battery according to claim 1, wherein The first inner electrode piece has the same polarity as the first single-sided electrode piece. The first inner electrode piece includes a first inner current collector. The thickness of the first inner current collector is T2. The thickness of the first current collector is T1. <T2; The depth of the first groove is D1, 60%≤(T1-D1)T2≤73%.

8. The secondary battery according to claim 1, wherein The first adhesive component includes a first adhesive layer, a base material layer and a second adhesive layer which are stacked together. The first adhesive layer and the second adhesive layer are respectively arranged on two opposite surfaces of the base material layer. The first adhesive layer is bonded to the first groove, and the second adhesive layer is bonded to the shell.

9. The secondary battery according to claim 8, wherein The second adhesive layer at least partially protrudes from the first surface.

10. The secondary battery according to claim 8, wherein The thickness of the first adhesive layer is T a1 , the thickness of the second adhesive layer is T a2 , the thickness of the substrate layer is T a3 ; 117%≤T a1 / T a2 ≤163%; and / or, 117%≤T a3 / T a2 ≤150%.

11. The secondary battery according to claim 1, wherein Along the first direction, a plurality of the first inner electrode sheets and a plurality of the second inner electrode sheets are alternately stacked, and the isolation film is provided between adjacent first inner electrode sheets and second inner electrode sheets; The electrode assembly further includes a second single-sided electrode sheet. Along the first direction, the outermost electrode sheets on both sides of the electrode assembly are the first single-sided electrode sheet and the second single-sided electrode sheet respectively. The second single-sided pole piece includes a second current collector and a second active material layer. The second current collector includes a third surface and a fourth surface that are oppositely disposed. The fourth surface faces the first inner pole piece. The second active material layer is disposed on the fourth surface. The third surface is provided with a second groove. The secondary battery further includes a second adhesive member, the first adhesive member is disposed in the second groove, and the second adhesive member is adhered to the second groove.

12. The secondary battery according to claim 11, wherein Along a second direction, the first current collector includes a first edge and a second edge that are oppositely disposed, and the second current collector includes a fifth edge and a sixth edge that are oppositely disposed; the second direction is perpendicular to the first direction; Along the first direction, the first edge is arranged opposite to the fifth edge, and the second edge is arranged opposite to the sixth edge; the first groove extends to the first edge, and the second groove extends to the fifth edge; The secondary battery further includes a third adhesive member, one end of which extends to the first edge and is connected to the first adhesive member, the other end of which extends to the fifth edge and is connected to the second adhesive member.

13. The secondary battery according to claim 12, characterized in that The first adhesive component, the second adhesive component and the third adhesive component are integrally provided.

14. The secondary battery according to claim 12, wherein: The thickness of the first adhesive is T a , the thickness of the second adhesive member is T b , the thickness of the third adhesive is T c ; T a <T c and / or, T b <T c .

15. The secondary battery according to claim 14, characterized in that 2μm≤T c -T a ≤20μm; and / or, 2μm≤T c -T b ≤20μm.

16. The secondary battery according to claim 12, wherein: Along the second direction, the first surface is provided with a plurality of the first grooves, the plurality of the first grooves are sequentially arranged along the third direction, and the plurality of the first grooves all extend to the first edge; The secondary battery further includes a tab connected to the electrode assembly and connected to the third edge; The thickness of the first current collector is T1, the thickness of the first inner current collector is T2, and T1≤T2; Along the third direction, the distance between the first groove and the third edge is L1, and the distance between the first groove and the fourth edge is L2; 8mm≤L1≤25mm; and / or, 5mm≤L2≤20mm.

17. The secondary battery according to claim 12, wherein: The first surface is provided with a plurality of first grooves, the plurality of first grooves are sequentially arranged along the third direction, and the plurality of first grooves all extend to the first edge; The secondary battery further includes a tab connected to the electrode assembly and connected to the third edge; The thickness of the first current collector is T1, the thickness of the first inner current collector is T2, and T1>T2; Along the third direction, the distance between the first groove and the third edge is L1, and the distance between the first groove and the fourth edge is L2; 5mm≤L1≤25mm; and / or, 3mm≤L2≤20mm.

18. The secondary battery according to claim 16 or 17, characterized in that: Along the third direction, a distance between two adjacent first grooves is L3, 4mm≤L3≤50mm.

19. An electronic device, characterized in that: The secondary battery according to any one of claims 1 to 18 is included.

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