Secondary battery and electronic device

Abstract

The invention relates to the technical field of energy storage, and particularly discloses a secondary battery and an electronic device. A secondary battery includes an electrode assembly. The electrode assembly comprises a plurality of first pole pieces, a plurality of second pole pieces and a plurality of isolating membranes which are arranged in a stacked mode, and the isolating membranes are arranged between the first pole pieces and the second pole pieces. The first pole piece comprises a first sub-pole piece which is located on the outermost side in the thickness direction of the electrode assembly. The isolating membrane comprises a first sub-isolating membrane, and the first sub-isolating membrane is arranged between the first sub-pole piece and the second pole piece. The electrode assembly further comprises a bonding piece, the bonding piece is bonded to the first sub-pole piece from the edge of the first sub-pole piece, and the bonding piece is bonded between the first sub-isolating membrane and the first sub-pole piece. The edge of the first sub-pole piece surrounds the outer side of the first main body part of the first sub-pole piece, and the first main body part is not provided with a bonding piece. The first sub-pole piece and the first sub-isolating membrane can be fixed through the bonding piece, the warping problem of the first sub-pole piece is reduced, and the safe and reliable performance of the electrode assembly is improved.

Description

Technical Field

[0001] This application relates to the technical field of energy storage, and particularly relates to a secondary battery and an electronic device. Background Art

[0002] As consumers' pursuit of faster mobile phone charging speeds increases, the traditional soft-pack wound structure battery cannot meet the usage requirements, which leads to the need to adopt a soft-pack battery with a stacked structure to meet consumers' needs. In a soft-pack stacked battery, one side of the outermost electrode sheet has active material, which causes the edge of the outermost electrode sheet to easily warp towards the side without active material, thus easily causing interface problems at the outermost layer, and ultimately leading to problems such as lithium deposition at the outermost layer of the battery cell, affecting the safety and reliability of the battery cell. Summary of the Invention

[0003] In view of this, it is necessary to provide a secondary battery that can improve the warping problem of the outermost electrode sheet of the electrode assembly and enhance the safety and reliability of the electrode assembly.

[0004] An embodiment of the first aspect of this application provides a secondary battery, including an electrode assembly. Along the thickness direction of the electrode assembly, the electrode assembly includes a plurality of first electrode sheets, a plurality of second electrode sheets, and a plurality of separator films stacked. The separator films are disposed between the first electrode sheets and the second electrode sheets. The first electrode sheet includes a first sub-electrode sheet, and the first sub-electrode sheet is located on the outermost side in the thickness direction of the electrode assembly. The separator film includes a first sub-separator film, and the first sub-separator film is disposed between the first sub-electrode sheet and the second electrode sheet. The electrode assembly further includes an adhesive, and the adhesive adheres to the first sub-electrode sheet from the edge of the first sub-electrode sheet, and the adhesive adheres between the first sub-separator film and the first sub-electrode sheet. The first sub-electrode sheet includes a first main body portion, and the region of the first sub-electrode sheet where the adhesive is not provided is the first main body portion.

[0005] Through the adhesive effect of the adhesive, the first sub-electrode sheet can be fixed to the first sub-separator film, so that the first sub-electrode sheet is subjected to a force towards the direction where the adhesive is located. When the edge of the second electrode sheet has a tendency to warp, the first sub-electrode sheet can be restricted, reducing the warping problem of the outermost first sub-electrode sheet of the electrode assembly and enhancing the safety and reliability of the electrode assembly.

[0006] In at least one embodiment, the first sub-electrode sheet includes a first edge portion connected to the first main body portion, and the first sub-electrode sheet includes a plurality of edges. The region of the first sub-electrode sheet where the adhesive is provided is the first edge portion, and the first edge portion includes the edge of the first sub-electrode sheet. Define the width of the first sub-electrode sheet as W, and define the sum of the distances between each edge of the first sub-electrode sheet and the edge of the first main body portion as the width of the first edge portion, and the width of the first edge portion is W1, 1.8%W ≤ W1 ≤ 18%W.

[0007] The region on the first sub - electrode tab where the bonding member is disposed is the first edge portion, which means that on the first sub - electrode tab, the bonding member starts bonding from the edge of the first sub - electrode tab. When observed along the thickness direction of the electrode assembly, the region where the first sub - electrode tab overlaps with the bonding member is the first edge portion.

[0008] The sum of the distances between the edges of each first sub - electrode tab and the edge of the first main body portion is the width of the first edge portion, which means that the width of the first edge portion is jointly determined by the positions of the edges of multiple first sub - electrode tabs to the edge of the first main body portion. Along the length or width direction of the battery assembly, the edge of one first sub - electrode tab corresponds to the edge of one first main body portion, and the width of the first edge portion is the sum of the distances from the edges of multiple first sub - electrode tabs to the edge of the first main body portion.

[0009] The width W1 of the first edge portion satisfies W1 ≤ 18%W, so that the first edge portion is not too large, making it difficult for the bonding member to cover too much of the first sub - electrode tab and reducing the impact on the battery capacity; W1 ≥ 1.8%W, so that the first sub - electrode tab has sufficient width for the bonding member to bond, improving the bonding stability between the bonding member, the first sub - electrode tab, and the first sub - separator film.

[0010] When 1.8%W ≤ W1 ≤ 2.3%W for the width of the first edge portion, the battery capacity can be further stabilized without increasing the thickness of the electrode assembly.

[0011] In at least one embodiment, the first sub - separator film has adhesiveness, and the peel strength between the bonding member and the first sub - electrode tab is greater than the peel strength between the first sub - separator film and the first sub - electrode tab. One side of the first sub - separator film is fixed to the second electrode tab through its own adhesiveness, and the other side is bonded to the bonding member through its own adhesiveness, so that the edge of the first sub - electrode tab is restricted by the first sub - separator film and is not easily warped.

[0012] In at least one embodiment, the bonding member is a polymer adhesive layer, and the polymer adhesive layer includes polyolefin. The bonding member is formed by curing the polymer adhesive layer. By coating the polymer adhesive layer to connect the first edge portion and the first sub - separator film, using the fluidity of the polymer adhesive layer before curing, the polymer adhesive layer can fully contact the first sub - electrode tab and the first sub - separator film, thus ensuring the peel strength of the bonding member between the first sub - electrode tab and the first sub - separator film.

[0013] In at least one embodiment, the polyolefin includes at least one of isotactic polypropylene (iPP), syndiotactic polypropylene (sPP), and atactic polypropylene (aPP).

[0014] In at least one embodiment, the secondary battery further includes a tab, which is disposed on one side of the electrode assembly. The first edge portion includes a first part, a second part, a third part, and a fourth part. The edge of the first sub-electrode plate on the same side as the tab is defined as the first edge, the second edge is away from the tab and is disposed opposite to the first edge. The first sub-electrode plate further includes a third edge and a fourth edge, the third edge and the fourth edge are disposed opposite to each other and both are connected to the first edge and the second edge. The first part and the tab are on the same side of the electrode assembly, the second part is away from the tab, the second part is disposed opposite to the first part, the third part and the fourth part are disposed opposite to each other, the third part and the fourth part are connected to the first part and the second part, and the first part, the second part, the third part, and the fourth part surround the outside of the first main body part. The width directions of the first part and the second part are the same as the direction in which the tab extends out of the electrode assembly, the width directions of the third part and the fourth part are perpendicular to the direction in which the tab extends out of the electrode assembly. The first part includes the first edge, the first part extends along the direction perpendicular to the extension direction of the tab to the third edge and the fourth edge, the second part includes the second edge, the second part extends along the direction perpendicular to the extension direction of the tab to the third edge and the fourth edge, the third part includes the third edge, the fourth part includes the fourth edge, and the width of the first part is S 11 The width ranges of the second part, the third part, and the fourth part are all S 12 , 0.42 mm ≤ S 11 ≤ 0.77 mm, 0.16 mm ≤ S 12 ≤ 0.3 mm.

[0015] By setting the first part to be relatively wide, the bonding area between the first part and the first sub-separator is increased, which is beneficial to improving the fixing effect on the first part, thereby reducing the degree of lithium deposition of the whole first sub-electrode plate.

[0016] In at least one embodiment, the first sub-electrode plate includes a first current collector and a first active material layer. Along the thickness direction of the first current collector, the first current collector has opposite first and second surfaces, the first surface is an empty foil surface, the first active material layer is disposed in a partial area of the second surface, and the second surface faces the first sub-separator. A part of the bonding member is bonded to the area of the second surface where the first active material layer is not disposed, and a part of the bonding member is bonded to the first active material layer of the first sub-electrode plate.

[0017] Compared with the second surface, the empty foil surface does not have the first active material layer, and the edge of the first sub-electrode plate is more likely to warp towards the empty foil surface direction. By disposing a part of the bonding member in the area where the first active material layer is not disposed and another part in the first active material layer, it is possible to ensure that the bonding member has a sufficient bonding area with the first sub-electrode plate, and it is not easy to cover too much first active material and not easy to have too much influence on the capacity of the secondary battery.

[0018] In at least one embodiment, the bonding member is adhesive tape. Compared with the bonding method of the polymer adhesive layer, bonding the first edge portion and the first sub-isolation film with adhesive tape eliminates the need to wait for the curing time, allowing for immediate use upon pasting, which is beneficial for improving the production efficiency of the electrode assembly.

[0019] In at least one embodiment, the adhesive tape includes a base material layer and a hot melt adhesive layer arranged in a stacked manner. The hot melt adhesive layers are provided on the opposite two surfaces of the base material layer, and the hot melt adhesive layer is bonded to the first sub-pole piece and the first sub-isolation film. The material of the base material layer includes polyethylene terephthalate, and the material of the hot melt adhesive layer includes at least one of styrene, isoprene, and styrene block copolymer.

[0020] During bonding, the adhesive tape can first be bonded to the first sub-pole piece and the first sub-isolation film through the hot melt adhesive layer, and then the bonding property of the hot melt adhesive layer can be improved by high-temperature formation to achieve the bonding of the bonding member and the first sub-isolation film. The hot melt adhesive layer is not easily bonded to the first sub-isolation film when not activated, reducing the phenomenon of accidental contact with the first sub-isolation film and causing wrinkles in the first sub-isolation film.

[0021] In at least one embodiment, the width of the bonding member is S1, where 2 mm ≤ S1 ≤ 5 mm. Within this range, the width of the adhesive tape can adapt to electrode assemblies of different sizes, facilitating the setting of adhesive tapes with different widths according to different electrode assemblies, and making the adhesive tape not too wide, reducing the coverage of the first active material layer, which is beneficial for reducing the loss of battery capacity; making the adhesive tape not too narrow, so that the adhesive tape can be stably bonded to the first sub-pole piece and the first sub-isolation film.

[0022] In some embodiments, the first pole piece is a positive electrode pole piece.

[0023] In at least one embodiment, the edge of the first sub-pole piece is set to be aligned with the edge of the second pole piece. The part of the first current collector that extends beyond the edge of the first active material layer forms a first edge portion, and the part of the first current collector that overlaps with the first active material layer forms a first main body portion. The bonding member is bonded to the first edge portion. The first edge portion is not provided with the first active material layer, so that compared with the first main body portion, the thickness of the first edge portion is smaller. After the bonding member is bonded to the first edge portion, not only does it increase the overall thickness of the electrode assembly less, which is beneficial for reducing the energy density loss of the secondary battery, but also the bonding member does not cover the first active material, thereby reducing the impact on the insertion of lithium ions and the impact on the battery capacity. Here, "aligned" includes the case where the error in the alignment of the edge on one side of the head of the first sub-pole piece with the edge of the second pole piece is within 0.2 mm, the error in the alignment of the edge on one side of the tail of the first sub-pole piece with the edge of the second pole piece is within 0.075 mm, and the error in the alignment of the edges on both sides in the width direction of the first sub-pole piece with the edge of the second pole piece is within 0.075 mm.

[0024] An embodiment of the second aspect of the present application provides an electronic device, including a secondary battery in any of the embodiments. Description of the Drawings

[0025] Figure 1 is a schematic diagram of a secondary battery in an embodiment of the present application.

[0026] Figure 2 is an exploded view of a secondary battery in an embodiment of the present application.

[0027] Figure 3 is a partial cross-sectional view of an electrode assembly in an embodiment of the present application.

[0028] Figure 4 is a cross-sectional view of an electrode assembly in an embodiment of the present application.

[0029] Figure 5 is a schematic diagram of a first sub-electrode tab in an embodiment of the present application.

[0030] Figure 6 is a schematic diagram of a second electrode tab in an embodiment of the present application.

[0031] Figure 7 is a cross-sectional view of an electrode assembly in an embodiment of the present application.

[0032] Figure 8 is a schematic diagram of a first sub-electrode tab and an adhesive in an embodiment of the present application.

[0033] Figure 9 is a schematic diagram of an electronic device in an embodiment of the present application.

[0034] Description of the Main Element Symbols

[0035] 100. Secondary battery; 10. Electrode assembly; 11. First electrode plate; 11a. First sub-electrode plate; 11b. Second sub-electrode plate; 111. First current collector; 1111. First surface; 1112. Second surface; 112. First active material layer; 113. First tab; 114. First edge portion; 1141. First part; 1141a. First edge; 1142. Second part; 1142a. Second edge; 1143. Third part; 1143a. Third edge; 1144. Fourth part; 1144a. Fourth edge; 115. First main body portion; 12. Second electrode plate; 121. Second current collector; 122. Second active material layer; 123. Second tab; 124. Second edge portion; 125. Second main body portion; 13. Separator; 131. First sub-separator; 14. Adhesive; 141. First section; 142. Second section; 143. Third section; 144. Fourth section; 20. Housing; 200. Electronic device; 201. Device main body; Z. First direction; X. Second direction; Y. Third direction.

[0036] The following specific embodiments will further illustrate the present application in conjunction with the above-mentioned drawings. Specific embodiments

[0037] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0038] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity, specific order or primary-secondary relationship of the indicated technical features.

[0039] As consumers' pursuit of faster mobile phone charging speeds increases, the traditional soft-pack wound structure battery cannot meet the usage requirements, which leads to the need to adopt a stacked structure soft-pack battery to meet consumer demands. In a soft-pack stacked battery, one side of the outermost electrode plate has active material, which causes the edge of the outermost electrode plate to easily warp towards the side without active material, thereby easily causing interface problems at the outermost layer, and ultimately leading to problems such as lithium deposition at the outermost layer of the battery cell, affecting the safety and reliability performance of the battery cell.

[0040] Embodiments of the present application provide a secondary battery, including an electrode assembly. Along the thickness direction of the electrode assembly, the electrode assembly includes a plurality of first pole pieces, a plurality of second pole pieces, and a plurality of separator films stacked. The separator films are disposed between the first pole pieces and the second pole pieces; the first pole piece includes a first sub-pole piece, and the first sub-pole piece is located on the outermost side in the thickness direction of the electrode assembly; the separator film includes a first sub-separator film, and the first sub-separator film is disposed between the first sub-pole piece and the second pole piece; the electrode assembly further includes an adhesive, and the adhesive is bonded to the first sub-pole piece from the edge portion of the first sub-pole piece, and the adhesive is bonded between the first sub-separator film and the first sub-pole piece. The first sub-pole piece includes a first main body portion and a first edge portion connected to each other. The area where the adhesive is provided on the first sub-pole piece is the first edge portion, and the first edge portion includes the edge of the first sub-pole piece. The area where the adhesive is not provided on the first sub-pole piece is the first main body portion.

[0041] Due to the bonding effect of the adhesive, the first sub-pole piece can be fixed to the first sub-separator film, so that the first sub-pole piece is subjected to a force towards the direction where the adhesive is located. When the edge of the second pole piece has a tendency to warp, the first sub-pole piece can be restricted, reducing the warping problem of the first sub-pole piece on the outermost layer of the electrode assembly, and improving the safety and reliability performance of the electrode assembly.

[0042] The following will further illustrate the embodiments of the present application with reference to the accompanying drawings.

[0043] As Figure 1 shown, embodiments of the present application provide a secondary battery 100. The secondary battery 100 includes an electrode assembly 10 and a housing 20, and the electrode assembly 10 is accommodated in the housing 20. The electrode assembly 10 includes a first pole piece 11, a second pole piece 12, and a separator film 13. The separator film 13 is disposed between the first pole piece 11 and the second pole piece 12, and the separator film 13 is used to isolate the first pole piece 11 and the second pole piece 12.

[0044] Please refer to Figure 3 , it can be understood that in some embodiments, there are multiple first pole pieces 11, separator films 13, and second pole pieces 12 respectively. The first pole pieces 11, separator films 13, and second pole pieces 12 are stacked in sequence to form a stacked structure, and a separator film 13 is disposed between each first pole piece 11 and each second pole piece 12.

[0045] In some embodiments, the housing 20 is a flexible packaging bag, such as an aluminum-plastic film. In some other embodiments, the housing 20 is a rigid outer shell, such as a plastic outer shell, or a metal outer shell including at least one of steel alloy, aluminum alloy, and copper alloy. Whether it can be applied to this solution.

[0046] In some embodiments, an electrolyte (not shown in the figure) is injected into the housing 20, and the electrolyte composition includes a solvent, an electrolyte salt, and an additive.

[0047] In some embodiments, the electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0048] In some embodiments, the electrolyte salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium hexafluorocaesium (LiCsF6), lithium perchlorate (LiClO4), or lithium trifluoromethanesulfonate (LiCF3SO3).

[0049] In some embodiments, the polarities of the first electrode tab 11 and the second electrode tab 12 are different. For example, the first electrode tab 11 is an anode electrode tab and the second electrode tab 12 is a cathode electrode tab. Alternatively, the first electrode tab 11 is a cathode electrode tab and the second electrode tab 12 is an anode electrode tab.

[0050] In some embodiments, the first electrode tab 11 is a positive electrode tab and the second electrode tab 12 is a negative electrode tab.

[0051] Please refer to Figure 3 , in some embodiments, the first electrode tab 11 includes a first current collector 111 and a first active material layer 112. The first active material layer 112 is disposed on at least one surface of the first current collector 111 along the thickness direction of the first current collector 111. The separator 13 is disposed between the first active material layer 112 and the second electrode tab 12. The thickness direction of the first current collector 111 is the first direction Z.

[0052] Please refer to Figure 3 , in some embodiments, the second electrode tab 12 includes a second current collector 121 and a second active material layer 122. Along the thickness direction of the second electrode tab 12, the second current collector 121 has two relatively disposed surfaces, and the thickness direction of the second electrode tab 12 is consistent with the thickness direction of the second current collector 121. At least one of the second current collectors 121 is provided with the second active material layer 122.

[0053] Please refer to Figure 2 , the first electrode tab 11 further includes a first tab 113, and the first tab 113 is welded to the first current collector 111; the second electrode tab 12 further includes a second tab 123, and the second tab 123 is welded to the second current collector 121.

[0054] In some embodiments, the secondary battery 100 includes tabs, and the tabs include a first tab 113 and a second tab 123. The first tab 113 is formed by die-cutting on the first current collector 111, and the second tab 123 is formed by die-cutting on the second current collector 121.

[0055] In some embodiments, the first tab 113 and the second tab 123 are disposed on the same side or different sides of the electrode assembly 10.

[0056] Taking the first electrode tab 11 as the cathode electrode tab and the second electrode tab 12 as the anode electrode tab as an example, the first current collector 111 and the second current collector 121 can be metal layers. The second current collector 121 can be a metal layer including at least one of copper, nickel, tantalum, titanium, etc., such as copper foil. The first current collector 111 can be a metal layer including at least one of aluminum, nickel, tantalum, titanium, etc., such as aluminum foil.

[0057] Taking the first electrode tab 11 as the cathode electrode tab and the second electrode tab 12 as the anode electrode tab as an example, the polarity of the first active material layer 112 is cathode, and the first active material layer 112 includes cathode active materials, which can include at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganate, etc. The polarity of the second active material layer 122 is anode, and the second active material layer 122 includes anode active materials, which can include at least one of graphite, hard carbon, soft carbon, silicon, silicon oxide material, silicon carbon material, etc.

[0058] In the related art, during the manufacturing process of the stacked electrode assembly 10, it is usually required that the outermost electrode tab of the electrode assembly 10 remains flat to prevent curling of the outermost electrode tab. However, since only one side of the outermost electrode tab is provided with active materials, the forces on both sides of the current collector are unbalanced, and the electrode tab is prone to curling towards the side without active materials, and the warping degree of the area of the electrode tab closer to the edge is greater, resulting in various interface problems, which will further affect the safety and reliability performance of the battery cell. Interface problems refer to problems such as black spots and lithium deposition on the surface of the electrode tab. After the electrode tab warps, the electrode tab separates from the separator 13 and the adjacent electrode tab, and there is a lack of electrolyte between the electrode tabs, blocking the lithium ion transmission path, and thus generating interface problems.

[0059] Please refer to Figure 3 , in some embodiments, the first electrode tab 11 includes a first sub - electrode tab 11a, and the first sub - electrode tab 11a is located on the outermost side in the thickness direction of the electrode assembly 10. The thickness direction of the electrode assembly 10 is the first direction Z. Along the thickness direction of the first current collector 111, the first current collector 111 of the first sub - electrode tab 11a has opposite first surface 1111 and second surface 1112, the first surface 1111 is an empty foil surface, and the first active material layer 112 is disposed on the second surface 1112, and no first active material layer 112 is provided on the empty foil surface.

[0060] Please refer to Figure 3 , in some embodiments, the first electrode tab 11 includes a second sub - electrode tab 11b, the second sub - electrode tab 11b is located between two separators 13, and both sides of the second sub - electrode tab 11b are provided with the first active material layer 112.

[0061] In some embodiments, the first electrode tab 11, the second electrode tab 12, and the separator 13 are arranged in a rectangle.

[0062] Refer to Figure 4 Figure 4 , in some embodiments, the separator 13 includes a first sub-separator 131 disposed between the first sub-electrode 11a and the second electrode 12. The electrode assembly 10 further includes an adhesive member 14 that is adhered to the edge of the first sub-electrode 11a and is adhered between the first sub-separator 131 and the first sub-electrode 11a. The first sub-electrode 11a includes a first main body 115, and the area of the first sub-electrode 11a where the adhesive member 14 is not disposed is the first main body 115.

[0063] Due to the adhesion of the adhesive member 14, the first sub-electrode 11a can be fixed to the first sub-separator 131. Thus, when the first sub-electrode 11a is subjected to a force in the direction where the adhesive member 14 is located and has a tendency to warp, the first sub-electrode 11a can be restricted, reducing the edge warping problem of the outermost first sub-electrode 11a of the electrode assembly 10 and improving the safety and reliability of the electrode assembly 10.

[0064] Refer to Figure 4 And Figure 5 Figure 4 , in some embodiments, the first sub-electrode 11a includes a first edge portion 114 connected to the first main body 115, and the first edge portion 114 includes the edge of the first sub-electrode 11a. The area of the first sub-electrode 11a where the adhesive member 14 is disposed is the first edge portion 114. The adhesive member 14 can adhere the first edge portion 114 to the first sub-separator 131 and restrict the first edge portion 114 from warping.

[0065] Refer to Figure 6 Figure 6 , in some embodiments, the second electrode 12 includes a second main body 125 and a second edge portion 124 surrounding the second main body 125 on all sides. The second active material layer 122 is disposed on opposite sides of the second main body 125, and the second active material layer 122 is not disposed on opposite sides of the second edge portion 124.

[0066] Refer to Figure 4 Figure 4 , in some embodiments, the size of the first sub-electrode 11a is the same as that of the second sub-electrode 11b and smaller than the size of the second electrode 12. Specifically, the second electrode 12 includes a second main body 125 and a second edge portion 124 surrounding the second main body 125 on all sides. When observed in the thickness direction of the electrode assembly 10, the edge of the first sub-electrode 11a projects onto the edge of the second main body 125, that is, the outer edge of the first edge portion 114 is aligned with the edge of the second electrode 12.

[0067] Refer to Figure 7, in some embodiments, the size of the first sub-electrode tab 11a is equal to the size of the second electrode tab 12. Along the length direction of the electrode assembly 10, the length of the first main body portion 115 is equal to the length of the second main body portion 125; along the width direction of the electrode assembly 10, the width of the first main body portion 115 is equal to the width of the second main body portion 125, the length direction is the second direction X, and the width direction is the third direction Y. The edges of the first sub-electrode tab 11a are aligned with the edges of the second electrode tab 12. That is, the sizes of the first edge portion 114 and the second edge portion 124 are also the same, and along the thickness direction of the electrode assembly 10, the first main body portion 115 and the second main body portion 125 overlap, and the first edge portion 114 and the second edge portion 124 overlap. It can be understood that the "alignment" here includes the case where the alignment error between the edge on the head side of the first sub-electrode tab 11a and the edge of the second electrode tab 12 is within 0.2 mm, the alignment error between the edge on the tail side of the first sub-electrode tab 11a and the edge of the second electrode tab 12 is within 0.075 mm, and the alignment error between the edges on both sides in the width direction of the first sub-electrode tab 11a and the edge of the second electrode tab 12 is within 0.075 mm. The head and tail of the first sub-electrode tab 11a are the two sides in the length direction of the first sub-electrode tab 11a, the head of the first sub-electrode tab 11a is the side where the tab is located, and the tail is the side opposite to the side where the tab is located.

[0068] The first active material layer 112 is disposed in a partial area of the second surface 1112. When observing along the thickness direction of the first sub-electrode tab 11a, the first current collector 111 of the first sub-electrode tab 11a extends beyond the edge of the first active material layer 112 to form the first edge portion 114, and the overlapping portion of the first current collector 111 and the first active material layer 112 forms the first main body portion 115, and the bonding member 14 is bonded to the first edge portion 114.

[0069] The first edge portion 114 is not provided with the first active material layer 112, so that the thickness of the first edge portion 114 is smaller than that of the first main body portion 115. After the bonding member 14 is bonded to the first edge portion 114, not only the overall thickness increase of the electrode assembly 10 is small, which is beneficial to reducing the energy density loss of the secondary battery 100, but also the bonding member 14 does not cover the first active material layer 112, thereby reducing the influence on the lithium ion insertion and reducing the influence on the battery capacity.

[0070] In some embodiments, the first active material layer 112 is disposed in a partial area of the second surface 1112, and the second surface 1112 faces the first sub-separator 131. A part of the bonding member 14 is bonded to the area of the second surface 1112 where the first active material layer 112 is not provided, and another part of the bonding member 14 is bonded to the first active material layer 112 of the first sub-electrode tab 11a.

[0071] Compared with the second surface 1112, the empty foil surface is not provided with the first active material layer 112, and the edge portion of the first sub-electrode sheet 11a is more likely to warp toward the empty foil surface direction. By disposing a part of the bonding member 14 in the region where the first active material layer 112 is not provided and another part in the first active material layer 112, it is possible to ensure that the bonding member 14 has a sufficient bonding area with the first sub-electrode sheet 11a, and it is not easy to cover too much of the first active material, and it is not easy to cause too much influence on the capacity of the secondary battery 100.

[0072] Refer to Figure 5 , in some embodiments, the first sub-electrode sheet 11a includes a plurality of edges. Define the width of the first sub-electrode sheet 11a as W, and define the sum of the distances between each edge of the first sub-electrode sheet 11a and the edge of the first main body portion 115 as the width of the first edge portion 114, and the width of the first edge portion 114 is W1, 1.8%W ≤ W1 ≤ 18%W.

[0073] The width W1 of the first edge portion 114 ≤ 18%W, so that the first edge portion 114 is not too large, making it not easy for the bonding member 14 to cover too much of the first active material layer 112 on the first sub-electrode sheet 11a, reducing the influence on the battery capacity; W1 ≥ 1.8%W, so that the first sub-electrode sheet 11a has a sufficient width for the bonding member 14 to bond, improving the bonding stability between the bonding member 14, the first sub-electrode sheet 11a, and the first sub-separator film 131.

[0074] The width of the first edge portion 114 is 1.8%W ≤ W1 ≤ 2.3%W, which can further maintain the capacity stability of the secondary battery 100 on the basis of not increasing the thickness of the electrode assembly 10.

[0075] In some embodiments, the first sub-separator film 131 has adhesiveness, and the peel strength between the bonding member 14 and the first sub-electrode sheet 11a is greater than the peel strength between the first sub-separator film 131 and the first sub-electrode sheet 11a. One side of the first sub-separator film 131 is fixed to the second electrode sheet 12 through its own adhesiveness, and the other side is bonded to the bonding member 14 through its own adhesiveness. The bonding member 14 is bonded to the first edge portion 114 through its own adhesiveness, so that the edge of the first sub-electrode sheet 11a is restricted by the first sub-separator film 131 and is not easy to warp.

[0076] In some embodiments, through a glue applicator, glue is dot-applied on the first edge portion 114 of the first sub-electrode sheet 11a, so that after the first sub-electrode sheet 11a, the first sub-separator film 131, and the second electrode sheet 12 are laminated, the first edge portion 114 can be bonded to the first sub-separator film 131, restricting the outermost first sub-separator film 131 from warping toward the empty foil surface.

[0077] In some embodiments, the temperature of the dot - applied glue is set to 160 °C, the unit glue application amount is 0.2 mg / mm, and the distance between the glue - applying needle tip and the separator is 0.08 mm, reducing the risk of glue overflow caused by excessive glue application.

[0078] In some embodiments, high - temperature - resistant and low - solubility PP (Polypropylene) - based glues are used. Such glues have high strength and durability, and can reduce the situation where the glue dissolves into the electrolyte after being exposed to high temperature and long - term immersion, resulting in weakened glue viscosity and affecting the peel strength between the first sub - electrode sheet 11a and the first sub - separator film 131.

[0079] In some embodiments, the bonding member 14 is a polymer glue layer, and the polymer glue layer includes polyolefin. The bonding member 14 is formed by curing the polymer glue layer. By coating the polymer glue layer to connect the first edge portion 114 and the first sub - separator film 131, the polymer glue layer can be in full contact with the first sub - electrode sheet 11a and the first sub - separator film 131 by utilizing the fluidity of the polymer glue layer before curing, thereby ensuring the peel strength of the bonding member 14 between the first sub - electrode sheet 11a and the first sub - separator film 131.

[0080] In some embodiments, the glue is composed of 50% - 80% of the main resin, 5% - 20% of the tackifying resin, 5% - 20% of the high - toughness resin, 5% - 10% of the rubber, and 1% - 5% of the surfactant. The main resin is polyolefin - based polypropylene or modified polypropylene (modified by copolymerizing a part of ethylene), and the main chain is a saturated resin structure. Isotactic polypropylene iPP, syndiotactic polypropylene sPP, and atactic polypropylene aPP are selected, and by adjusting the ratio of the three, the viscosity, flexibility, and surface - drying speed of the glue are regulated.

[0081] In some embodiments, the bonding member 14 is a sticker. Compared with the bonding method of the polymer glue layer, by using the sticker to bond the first edge portion 114 and the first sub - separator film 131, there is no need to wait for the curing time, and it can be used immediately after pasting, which is beneficial to improving the production efficiency of the electrode assembly 10.

[0082] In some embodiments, the sticker includes a hot - melt adhesive layer and a substrate layer arranged in a laminated manner. The hot - melt adhesive layer is provided on the opposite two surfaces of the substrate layer, and the hot - melt adhesive layer is bonded to the first sub - electrode sheet and the first sub - separator film. The material of the substrate layer includes polyethylene terephthalate, and the material of the hot - melt adhesive layer includes at least one of styrene, isoprene, and styrene block copolymer.

[0083] During bonding, the adhesive tape can be first bonded to the first sub-electrode sheet 11a and the first sub-separator 131 through the hot melt adhesive layer, and then the bonding property of the hot melt adhesive layer can be improved through high-temperature formation to realize the bonding of the bonding member 14 to the first sub-separator 131. When the hot melt adhesive layer is not activated, it is not easy to bond to the first sub-separator 131, reducing the phenomenon of accidental contact with the first sub-separator 131 and causing wrinkles in the first sub-separator 131.

[0084] In some embodiments, the material of the adhesive tape is a styrene-isoprene mixture, which has good stability and is not easy to chemically react with the electrolyte, making the adhesive tape not easy to fall off and ensuring the bonding stability.

[0085] Refer to Figure 8 , in some embodiments, the width of the bonding member 14 is S1, and 2 mm ≤ S1 ≤ 5 mm. Within this range, the width of the adhesive tape can adapt to electrode assemblies 10 of different sizes, facilitating the setting of adhesive tapes with different widths according to different electrode assemblies 10, and making the adhesive tape not too wide, reducing the coverage of the first active material layer 112, which is beneficial to reducing the loss of battery capacity; making the adhesive tape not too narrow, so that the adhesive tape can be stably bonded to the first sub-electrode sheet 11a and the first sub-separator 131, and also facilitating the bonding of the adhesive tape to the first electrode sheet 11a. If the adhesive tape is too narrow, it is not convenient for the bonding operation.

[0086] In the related art, to prevent burrs from penetrating the separator 13 and causing a short circuit, compared with other sides of the first current collector 111, the regions on the opposite two sides of the first current collector 111 where the ear is located and where the first active material layer 112 is not provided are wider. Understandably, the thickness of the first current collector 111 at the positions where the first active material layer 112 is not provided on both sides is smaller.

[0087] In some embodiments, both the first surface 1111 and the second surface 1112 of the first current collector 111 of the first edge portion 114 are empty foil regions.

[0088] Refer to Figure 5, the tab is disposed on one side in the length direction of the electrode assembly 10. The first edge portion 114 includes a first part 1141, a second part 1142, a third part 1143 and a fourth part 1144 connected end to end. The first part 1141 and the tab are on the same side of the electrode assembly 10, and the second part 1142 is away from the tab. The second part 1142 is disposed opposite to the first part 1141, the third part 1143 is disposed opposite to the fourth part 1144, the third part 1143 and the fourth part 1144 are connected to the first part 1141 and the second part 1142, and the first part 1141, the second part 1142, the third part 1143 and the fourth part 1144 surround the outside of the first main body portion 115. The width directions of the first part 1141 and the second part 1142 are the same as the direction in which the tab extends out of the electrode assembly 10, and the width directions of the third part 1143 and the fourth part 1144 are perpendicular to the direction in which the tab extends out of the electrode assembly 10. For example, the direction in which the tab extends out of the electrode assembly 10 is the length direction of the electrode assembly 10.

[0089] Define the edge on the same side as the tab in the first sub-electrode tab 11a as the first edge 1141a, the second edge 1142a is away from the tab and is disposed opposite to the first edge 1141a. The first sub-electrode tab 11a further includes a third edge 1143a and a fourth edge 1144a. The third edge 1143a and the fourth edge 1144a are disposed opposite to each other and both are connected to the first edge 1141a and the second edge 1142a. The first part 1141 includes the first edge 1141a, the first part 1141 extends along the direction perpendicular to the tab extension direction to the third edge 1143a and the fourth edge 1144a, the second part 1142 includes the second edge 1142a, the second part 1142 extends along the direction perpendicular to the tab extension direction to the third edge 1143a and the fourth edge 1144a, the third part 1143 includes the third edge 1143a, and the fourth part 1144 includes the fourth edge 1144a.

[0090] The width directions of the first part 1141 and the second part 1142 are the same as the length direction of the electrode assembly 10, the width directions of the third part 1143 and the fourth part 1144 are the same as the width direction of the electrode assembly 10, and the width of the first part 1141 is greater than the widths of the second part 1142, the third part 1143 and the fourth part 1144 respectively.

[0091] Setting the first part 1141 to be relatively wide can set a bonding member 14 with a larger size on the tab side. While improving the fixing effect on the first sub-electrode tab 11a, it makes the bonding member 14 not easily overlap with the thickness of the first active material layer 112 of the first sub-electrode tab 11a, reducing the loss of volume energy density.

[0092] Refer to Figure 5, in some embodiments, the tab is disposed on one side in the length direction of the electrode assembly 10. The bonding member 14 includes a first section 141, a second section 142, a third section 143, and a fourth section 144. The first section 141 and the second section 142 are disposed opposite to each other in the length direction of the electrode assembly 10, the third section 143 and the fourth section 144 are disposed opposite to each other in the width direction of the electrode assembly 10, and the first section 141 and the tab are on the same side of the electrode assembly 10. It can be understood that the width of the first edge portion 114 is equal to the width of the bonding member 14.

[0093] The width direction of the first section 141 and the second section 142 is the same as the length direction of the electrode assembly 10, the width direction of the third section 143 and the fourth section 144 is the same as the width direction of the electrode assembly 10, and the width of the first section 141 is S 11 , the width ranges of the second section 142, the third section 143, and the fourth section 144 are all S 12 , 0.42 mm ≤ S 11 ≤ 0.77 mm, 0.16 mm ≤ S 12 ≤ 0.3 mm.

[0094] The first section 141 is set to be relatively wide, increasing the bonding area between the first section 141 and the first sub-isolation film 131, which is beneficial to improving the fixing effect on the first section 141, thereby reducing the degree of lithium plating of the entire first sub-electrode 11a.

[0095] Refer to Figure 5 , in some embodiments, the first section 141, the third section 143, the second section 142, and the fourth section 144 are connected end to end in sequence. The first section 141 is disposed on the first part 1141, the second section 142 is disposed on the second part 1142, the third section 143 is disposed on the third part 1143, and the fourth section 144 is disposed on the fourth part 1144, so that each position in the circumferential direction of the first sub-electrode 11a is fixed to the first sub-isolation film 131 by the bonding member 14, thereby reducing the warping risk of the first edge portion 114.

[0096] Refer to Figure 9 , an embodiment of the present application further provides an electronic device 200, and the electronic device 200 includes the secondary battery 100 in any of the above embodiments.

[0097] In some embodiments, the electronic device 200 may be a mobile phone, a laptop computer, a tablet computer, a drone, a power tool, an electric toy, a game console, a video recorder, a portable recorder, a radio, or a smart watch, etc., which will not be listed one by one here.

[0098] In some embodiments, the electronic device 200 further includes a device body 201, and the secondary battery 100 is installed in the device body 201. Since the electronic device 200 adopts the technical solution of the secondary battery 100 in any of the above embodiments, it has at least the beneficial effects brought by the technical solution of any of the above embodiments of the secondary battery 100, which will not be elaborated here one by one.

[0099] To verify the influence of the setting of the first edge portion 114 and the setting of the bonding member 14 on the performance of the secondary battery 100, the inventor conducted the following experiments:

[0100] The experiment includes 1 comparative example and 24 examples. The settings of the first edge portion 114 and the bonding member 14 in each comparative example and example are shown in Table 1 below.

[0101] The following describes the specific implementation manners of the secondary battery 100 in the examples and comparative examples.

[0102] The assembly process of the secondary battery 100 in the comparative example and the example is as follows:

[0103] (1) Preparation of the cathode electrode sheet: Mix the active material lithium cobaltate (LiCoO2), conductive carbon black (Super P), CNT (carbon nanotube), and polyvinylidene fluoride (PVDF) according to a weight ratio of 97.5:0.5:0.5:1.5, add N-methylpyrrolidone (NMP) as a solvent, and formulate a cathode active material with a solid content of 75 wt%, and stir evenly for standby. Use an aluminum foil with a thickness of 10 μm as the cathode current collector. Use a slot coater to evenly coat the above active material on one side of the cathode current collector, and then dry it at 90 °C to obtain a cathode electrode sheet with the cathode active material coated on one side. At this time, the thickness of the cathode active material layer in the thickness direction of the cathode current collector is 90 μm. Then repeat the above coating steps on the other side of the cathode current collector. Then cold press the coated cathode electrode sheet. After cold pressing, the thickness of the cathode active material layer on one side is 80 μm. Then die-cut the cathode tab on the part of the cathode current collector not covered by the cathode active material layer. The cathode electrode sheet is the second electrode sheet 12. It should be noted that there are multiple cathode electrode sheets prepared in this step, and two of the cathode electrode sheets are only coated with the cathode active material layer on one side of the cathode current collector to serve as the two outermost first sub-electrode sheets 11a of the electrode assembly 10;

[0104] (2) Preparation of the anode electrode sheet: The active material artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) are mixed in a weight ratio of 97:0.5:1.3:1.2, and deionized water is added as a solvent to formulate an anode active material with a weight percentage of 50 wt%. After stirring evenly, it is set aside. A copper foil with a thickness of 10 μm is used as the anode current collector. The above-mentioned anode active material is evenly coated on one side of the anode current collector using a slot coater, and then dried at 110 °C to obtain an anode electrode sheet with an anode active material layer coated on one side. Then, the above steps are repeated on the other side of the anode current collector to obtain an anode electrode sheet with anode active material layers coated on both sides. At this time, the thickness of the anode active material layers on both sides in the thickness direction of the anode current collector is 90 μm. Then, the coated anode electrode sheet is cold-pressed, and the thickness of the anode active material layer on one side after cold pressing is 80 μm. After that, anode tabs are die-cut from the part of the anode current collector not covered by the anode active material layer.

[0105] (3) Preparation of the electrolyte: In a dry argon atmosphere, first, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0106] (4) Preparation of the separator: A 7-μm-thick polyethylene porous polymer film is used as the separator.

[0107] (5) Preparation of the electrode assembly 10: The adhesive 14 is composed of 50% - 80% of the main resin, 5% - 20% of the tackifying resin, 5% - 20% of the high-toughness resin, 5% - 10% of the rubber, and 1% - 5% of the surfactant. The main resin is polyolefin polypropylene or modified polypropylene, and the main chain is a saturated resin structure. Isotactic polypropylene iPP, syndiotactic polypropylene sPP, and atactic polypropylene aPP are selected.

[0108] The adhesive 14 is bonded to the first edge portion 114. The cathode electrode sheet, the separator, and the anode electrode sheet are stacked along the thickness direction of the anode electrode sheet. The first edge portion 114 is bonded to the first sub-separator 131 through the adhesive 14 to obtain the electrode assembly 10. Among them, the electrode sheet with a cathode active material layer coated on one side is located on the outermost side in the thickness direction of the electrode sheet.

[0109] (6) Assembly of the secondary battery 100: Place the formed aluminum-plastic film with indentations in the assembly fixture with the indented surface facing up, place the electrode assembly 10 in the indentation, and apply an external force to press it firmly. Then cover the electrode assembly 10 with another formed aluminum-plastic film with the indented surface facing down, and heat-seal three edges of the two aluminum-plastic films by hot pressing. The un-sealed edge is the side where the tab protrudes from the housing 20. Then inject electrolyte through the un-sealed edge, and after processes such as vacuum packaging, standing, hot pressing formation, and shaping, the secondary battery 100 is obtained.

[0110] The difference between the secondary battery 100 in Comparative Example 1 and each of the Examples is that the bonding member 14 is not provided in the secondary battery 100 of Comparative Example 1. The width W1 of the first edge portion 114 of the secondary battery 100 in Comparative Example 1 and each of the Examples is 6 mm.

[0111] In the secondary battery 100 of Comparative Example 1 and each of the Examples, the size of the first sub-electrode sheet 11a is the same as that of the second electrode sheet 12. The length of the first sub-electrode sheet 11a is 60 mm and the width is 55 mm. The thickness of the electrode assembly 10 (except for the bonding member 14) is 7.4 mm. In the electrode assembly 10, the total number of layers of the cathode electrode sheet, the anode electrode sheet, and the separator 13 is 27 layers.

[0112] The following tests are performed on the secondary battery 100 in each of the Examples and Comparative Example 1:

[0113] 1. Test for the proportion of the lithium deposition area:

[0114] Disassemble the first sub-electrode sheet 11a from the secondary battery 100;

[0115] Clean the residual electrolyte on the surface of the first sub-electrode sheet 11a;

[0116] Lay the first sub-electrode sheet 11a flat on the stage, avoiding wrinkles or warping that may affect imaging;

[0117] Use a high-resolution CCD camera to collect the surface image of the first sub-electrode sheet 11a;

[0118] Identify the lithium deposition area through an image processing algorithm and calculate the lithium deposition area.

[0119] When calculating the lithium deposition area, first take a photo of the entire first sub-electrode sheet 11a, identify the lithium deposition area through color difference, and then divide the entire first sub-electrode sheet 11a into multiple squares of equal area. Calculate the lithium deposition area by multiplying the number of squares occupied by the lithium deposition area by the area of a single square. The color of the lithium deposition area appears black, and the non-lithium deposition area appears silver-white.

[0120] After calculating the lithium deposition area of the first sub-electrode sheet 11a, divide the lithium deposition area by the area of the first sub-electrode sheet 11a to obtain the proportion of the lithium deposition area.

[0121] 2. Battery capacity test:

[0122] Charging: At 25 °C, charge at 0.2C CC (constant current) until the full charge voltage (4.5V), then CV (constant voltage) with a cut-off current of 0.02C, and let it stand for 3 minutes;

[0123] Discharging (actual capacity): DC (constant current discharge), discharge at 0.2C until 3.0V, then calculate the current discharged during this period, and the battery capacity = I·T.

[0124] The experimental results are shown in Table 1 below:

[0125] Table 1

[0126]

[0127]

[0128] Note: In Table 1, " / " indicates no such data.

[0129] From Table 1, by comparing Comparative Example 1 with Examples 1 to 24, it can be concluded that the setting of the bonding member 14 can improve the degree of warping of the first sub-electrode plate 11a, thereby reducing the proportion of the lithium deposition area of the first sub-electrode plate.

[0130] From Examples 1 to 5, it can be seen that when the width of the first edge portion 114 is small, the width of the bonding member 14 bonding the first sub-electrode plate 11a is small, making it difficult for the coated polymer adhesive layer to flow to the first active material layer 112, reducing the risk of the polymer adhesive layer being coated on the first active material layer 112. For example, in Examples 1 to 2, when the width of the first edge portion is within 1.8%W ≤ W1 ≤ 2.3%W, the thickness of the electrode assembly is not likely to increase, and the battery capacity remains stable; and there is sufficient bonding width between the bonding member 14 and the first sub-electrode plate 11a to ensure bonding stability and effectively reduce the proportion of the lithium deposition area of the first sub-electrode plate 11a. From Examples 3 to 5, it can be seen that when the width of the first edge portion 114 is large, it is easy for the polymer adhesive layer to be coated on the first active material layer 112, resulting in an increase in the thickness of the electrode assembly and a loss of the capacity of the secondary battery 100.

[0131] From Examples 6 to 12, it can be seen that when the width of the first part 1141 is 0.42mm ≤ S 11Within ≤ 0.77 mm, compared with the second part 1142, the third part 1143 and the fourth part 1144, the first part 1141 is set to be relatively wider, increasing the bonding area between the first part 1141 and the first sub-isolation film 131, which is beneficial to improving the fixing effect on the first part 1141, thereby reducing the degree of lithium deposition of the whole first sub-electrode 11a, and not easily affecting the battery capacity and the thickness of the electrode assembly.

[0132] It can be seen from Examples 13 to 18 that when the width of the first part 1141 remains unchanged, the larger the widths of the second part 1142, the third part 1143 and the fourth part 1144 are, the smaller the proportion of the lithium deposition area of the first sub-electrode is, and within the range of 0.16 mm ≤ S 12 ≤ 0.3 mm, it is not easy to affect the battery capacity and the thickness of the electrode assembly.

[0133] It can be seen from Examples 19 to 24 that when the bonding member 14 is set as adhesive tape, within the range of 2 mm ≤ S1 ≤ 5 mm, it makes the adhesive tape not too wide and not easy to cover the first active material layer 112, which is beneficial to reducing the loss of battery capacity; it makes the adhesive tape not too narrow, so that the adhesive tape can be stably bonded with the first sub-electrode 11a and the first sub-isolation film 131, reducing the proportion of the lithium deposition area of the first sub-electrode 11a. However, when the adhesive tape is pasted, it is easy to cause an error in the bonding position, resulting in the overlap of the adhesive tape and the first active material layer 112, causing a certain loss of battery capacity and an increase in the thickness of the electrode assembly.

[0134] In addition, those of ordinary skill in the art of the present technology should recognize that the above embodiments are only used to illustrate the present application, rather than to limit the present application. As long as it is within the scope of the substantial spirit of the present application, appropriate changes and variations made to the above embodiments fall within the scope of the disclosure of the present application.

Claims

1. A secondary battery, characterized in that, Comprising: An electrode assembly, along the thickness direction of the electrode assembly, the electrode assembly includes a plurality of first pole pieces, a plurality of second pole pieces and a plurality of separator films stacked, and the separator film is disposed between the first pole piece and the second pole piece; The first pole piece includes a first sub-pole piece, and the first sub-pole piece is located on the outermost side in the thickness direction of the electrode assembly; the separator film includes a first sub-separator film, and the first sub-separator film is disposed between the first sub-pole piece and the second pole piece; The electrode assembly further includes an adhesive, and the adhesive is adhered to the first sub-pole piece from the edge of the first sub-pole piece, and the adhesive is adhered between the first sub-separator film and the first sub-pole piece; The first sub-pole piece includes a first main body portion and a first edge portion connected to each other. The area of the first sub-pole piece where the adhesive is provided is the first edge portion, and the first edge portion includes the edge of the first sub-pole piece. The area of the first sub-pole piece where the adhesive is not provided is the first main body portion.

2. The secondary battery according to claim 1, characterized in that, The first sub-pole piece includes a plurality of edges, the width of the first sub-pole piece is W, and the sum of the distances between each edge of the first sub-pole piece and the edge of the first main body portion is the width W1 of the first edge portion, and 1.8%W ≤ W1 ≤ 18%W.

3. The secondary battery according to claim 1, wherein 1.8%W ≤ W1 ≤ 2.3%W.

4. The secondary battery according to claim 1, wherein The adhesive is a polymer adhesive layer, and the polymer adhesive layer includes polyolefin.

5. The secondary battery according to claim 4, wherein The polyolefin includes at least one of isotactic polypropylene iPP, syndiotactic polypropylene sPP, and atactic polypropylene aPP.

6. The secondary battery according to claim 3, wherein The secondary battery further includes a tab, and the tab is disposed on one side of the electrode assembly; The first edge portion includes a first part, a second part, a third part and a fourth part. The first part and the tab are on the same side of the electrode assembly. The second part is far from the tab, and the second part is disposed opposite to the first part. The third part and the fourth part are disposed opposite to each other. The third part and the fourth part are connected to the first part and the second part. The first part, the second part, the third part and the fourth part surround the outside of the first main body portion; The width directions of the first part and the second part are consistent with the direction in which the tab extends out of the electrode assembly, the width directions of the third part and the fourth part are perpendicular to the direction in which the tab extends out of the electrode assembly, and the width of the first part is S 11 , and the width ranges of the second part, the third part, and the fourth part are all S 12 , 0.42 mm ≤ S 11 ≤ 0.77 mm, 0.16 mm ≤ S 12 ≤ 0.3 mm.

7. The secondary battery according to claim 1, wherein The first sub-pole piece includes a first current collector and a first active material layer. Along the thickness direction of the first current collector, the first current collector has a first surface and a second surface opposite to each other. The first surface is an empty foil surface, and the first active material layer is disposed in a partial area of the second surface, and the second surface faces the first sub-separator film; A part of the adhesive is adhered to the area of the second surface where the first active material layer is not provided, and a part of the adhesive is adhered to the surface of the first active material layer of the first sub-pole piece.

8. The secondary battery according to claim 7, characterized in that, The adhesive is adhesive tape.

9. The secondary battery according to claim 8, wherein, The adhesive tape includes a substrate layer and a hot melt adhesive layer stacked. The hot melt adhesive layer is disposed on opposite two surfaces of the substrate layer, and the hot melt adhesive layer is adhered to the first sub-pole piece and the first sub-separator film.

10. The secondary battery according to claim 8 or 9, characterized in that, The width of the adhesive is S1, and 2mm ≤ S1 ≤ 5mm.

11. The secondary battery according to claim 1, characterized in that, Along the thickness direction of the electrode assembly, the edge of the first sub-pole piece is aligned with the edge of the second pole piece; The first sub-electrode includes a first current collector and a first active material layer which are stacked. When observed in the thickness direction of the first sub-electrode, an edge portion of the first current collector extends beyond the edge of the first active material layer to form a first edge portion, and a portion where the first current collector overlaps with the first active material layer forms a first main portion. The bonding member is bonded to the first edge portion.

12. The secondary battery according to claim 1, wherein The first electrode is a positive electrode.

13. An electronic device, characterized in that, A secondary battery includes the secondary battery according to any one of claims 1 to 12.

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