Secondary battery and electric device

Abstract

The invention discloses a secondary battery and electric equipment. The secondary battery comprises an electrode assembly, a shell and a first adhesive layer, the electrode assembly comprises a plurality of first pole pieces, a plurality of second pole pieces and an isolating membrane; the orthographic projection of the second pole piece is located in the orthographic projection range of the first pole piece; each first pole piece comprises a first edge extending along a second direction and a second edge extending along a third direction; the intersection point of the first edge and the second edge of the same first pole piece is a first intersection point; in the first direction, the first intersection points are combined to form a first edge. The shell comprises a first protection layer and a metal layer which are stacked in the first direction, the shell comprises a first space, and the electrode assembly is contained in the first space; the first protective layer is between the metal layer and the electrode assembly. The first adhesive layer covers the first edge. In the secondary battery, the first adhesive layer is arranged to wrap the first edge, so that the possibility that the corner of the first pole piece punctures the first protective layer of the shell is reduced, and the corrosion of the shell is reduced.

Description

Technical Field

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

[0002] At present, during the charge and discharge process of a secondary battery, the electrode plates in the electrode assembly will expand, and the corners of the electrode plates may pierce the protective layer of the housing, causing corrosion of the housing and affecting the service life of the secondary battery. Summary of the Invention

[0003] In view of the above situation, it is necessary to provide a secondary battery that can reduce the possibility of the corners of the electrode plates piercing the protective layer of the housing.

[0004] An embodiment of this application provides a secondary battery, which includes an electrode assembly, a housing, and a first adhesive layer. The electrode assembly includes a plurality of first electrode plates, a plurality of second electrode plates, and a separator. The polarities of the first electrode plates and the second electrode plates are opposite, and the first electrode plates and the second electrode plates are alternately stacked. A separator is provided between adjacent first electrode plates and second electrode plates; along a first direction, the orthographic projection of the second electrode plate is within the orthographic projection range of the first electrode plate, and the first direction is the thickness direction of the electrode assembly; each first electrode plate includes a first edge extending along a second direction and a second edge extending along a third direction, and the first direction, the second direction, and the third direction are perpendicular to each other in pairs; the intersection point of the first edge and the second edge of the same first electrode plate is a first intersection point; along the first direction, a plurality of first intersection points form a first edge. The housing includes a first protective layer and a metal layer stacked along the first direction, and the housing includes a first space, and the electrode assembly is received in the first space; the first protective layer is located between the metal layer and the electrode assembly. The first adhesive layer covers the first edge.

[0005] In this secondary battery, by providing the first adhesive layer to cover the first edge, it is beneficial to reduce the possibility of the corners of the first electrode plates piercing the first protective layer of the housing, reduce housing corrosion, and thus is beneficial to improving the service life of the secondary battery.

[0006] In one or more embodiments of this application, when viewed from the first direction, the distance from the first edge to the outer edge of the part of the first adhesive layer away from the first electrode plate is the thickness of the first adhesive layer. The maximum thickness of the first adhesive layer is H1, and 0.1 mm ≤ H1 ≤ 0.6 mm. Setting H1 ≥ 0.1 mm ensures that the thickness of the first adhesive layer is not too small, which is beneficial to improving the effect of the first adhesive layer in preventing the first electrode plate from piercing the first protective layer; setting H1 ≤ 0.6 mm ensures that the thickness of the first adhesive layer is not too large, which is beneficial to reducing the difficulty of inserting the electrode assembly into the housing and is also beneficial to reducing the possibility of the housing squeezing the electrode assembly to reduce lithium plating.

[0007] In one or more embodiments of the present application, 0.2 mm ≤ H1 ≤ 0.4 mm. Setting H1 ≥ 0.2 mm ensures that the thickness of the first adhesive layer is not too small, which is beneficial to further improving the effect of the first adhesive layer in preventing the first electrode tab from piercing the first protective layer. Setting H1 ≤ 0.4 mm ensures that the thickness of the first adhesive layer is not too large, which is beneficial to further reducing the difficulty of inserting the electrode assembly into the housing and also beneficial to further reducing the possibility of the housing squeezing the electrode assembly to reduce lithium plating.

[0008] In one or more embodiments of the present application, the first adhesive layer covers a part of at least one first edge. The first adhesive layer covering a part of the first edge is beneficial to improving the bonding stability between the first adhesive layer and the first electrode tab and reducing the risk of the first adhesive layer peeling off.

[0009] In one or more embodiments of the present application, along the second direction, the length of the first adhesive layer covering the first edge is L1, and 0.1 mm ≤ L1 ≤ 2 mm. Setting L1 ≥ 0.1 mm ensures that the length of the first adhesive layer covering the first edge is not too short, which is beneficial to improving the bonding stability between the first adhesive layer and the first electrode tab and reducing the risk of the first adhesive layer peeling off. Setting L1 ≤ 2 mm ensures that the length of the first adhesive layer covering the first edge is not too long, which is beneficial to improving the wetting effect of the electrolyte on the first electrode tab and reducing the risk of lithium plating at the corner of the first electrode tab.

[0010] In one or more embodiments of the present application, 0.4 mm ≤ L1 ≤ 1.6 mm. Setting L1 ≥ 0.4 mm is beneficial to further reducing the risk of the first adhesive layer peeling off. Setting L1 ≤ 1.6 mm is beneficial to further improving the wetting effect of the electrolyte on the first electrode tab and reducing the risk of lithium plating at the corner of the first electrode tab.

[0011] In one or more embodiments of the present application, 0.6 mm ≤ L1 ≤ 1.0 mm. Setting L1 ≥ 0.6 mm is beneficial to further reducing the risk of the first adhesive layer peeling off. Setting L1 ≤ 1.0 mm is beneficial to further improving the wetting effect of the electrolyte on the first electrode tab and reducing the risk of lithium plating at the corner of the first electrode tab.

[0012] In one or more embodiments of the present application, along the third direction, the maximum thickness of the first adhesive layer is H2, and 0.1 mm ≤ H2 ≤ 0.4 mm. Setting H2 ≥ 0.1 mm ensures that the thickness of the first adhesive layer is not too small, which is beneficial to improving the effect of the first adhesive layer in preventing the first electrode tab from piercing the first protective layer. Setting H2 ≤ 0.4 mm ensures that the thickness of the first adhesive layer is not too large, which is beneficial to reducing the difficulty of inserting the electrode assembly into the housing and also beneficial to reducing the possibility of the housing squeezing the electrode assembly to reduce lithium plating.

[0013] In one or more embodiments of the present application, 0.15 mm ≤ H2 ≤ 0.3 mm. Setting H2 ≥ 0.15 mm is beneficial to further improve the effect of the first adhesive layer in preventing the first electrode tab from piercing the first protective layer; setting H2 ≤ 0.3 mm is beneficial to further reduce the difficulty of inserting the electrode assembly into the housing, and is also beneficial to further reduce the possibility of the housing squeezing the electrode assembly, so as to reduce lithium plating.

[0014] In one or more embodiments of the present application, the first adhesive layer covers a part of at least one second edge. The first adhesive layer covering a part of the second edge is beneficial to improving the bonding stability between the first adhesive layer and the first electrode tab and reducing the risk of the first adhesive layer falling off.

[0015] In one or more embodiments of the present application, an insulating film is covered between the first adhesive layer and the first edge. In this way, it is beneficial to improve the effect of the insulating film in insulating the first electrode tab and the second electrode tab; the first adhesive layer bonds the first electrode tab and the insulating film at the same time, which can fix the insulating film and is beneficial to reducing the risk of short circuit between the first electrode tab and the second electrode tab caused by the shrinkage of the insulating film.

[0016] In one or more embodiments of the present application, an insulating film is covered between the first adhesive layer and the first edge. On the one hand, it is beneficial to improve the effect of the insulating film in insulating the first electrode tab and the second electrode tab; on the other hand, it is beneficial to reduce the risk of short circuit between the first electrode tab and the second electrode tab caused by the shrinkage of the insulating film.

[0017] In one or more embodiments of the present application, each first electrode tab includes a first surface and a second surface that are oppositely arranged along the first direction. The first surface faces away from the inside of the electrode assembly, and the second surface faces the inside of the electrode assembly; the first adhesive layer includes a first overlapping portion, and the first overlapping portion is the part where the first adhesive layer overlaps with at least one first surface or at least one second surface. The first adhesive layer bonding at least one of the first surface and the second surface is beneficial to improving the bonding strength of the first adhesive layer to the first electrode tab and reducing the risk of the first adhesive layer falling off; moreover, the insulating film is fixed by the first adhesive layer, which is beneficial to reducing the possibility of the insulating film shrinking. Further, based on the fixing effect of the first adhesive layer on the insulating film, the winding adhesive provided at the periphery of the electrode assembly to fix the insulating film in the prior art can be omitted, thereby improving the volume energy density of the secondary battery.

[0018] In one or more embodiments of the present application, along the first direction, the maximum thickness of the first overlapping portion is H3, and along the third direction, the maximum length of the first overlapping portion is L2; 150 μm ≤ H3 ≤ 210 μm, 0.1 mm ≤ L2 ≤ 2 mm. Setting H3 ≥ 150 μm ensures that the thickness of the first overlapping portion along the first direction is not too small, which is beneficial to improving the bonding strength between the first adhesive layer and the first electrode tab and enhancing the fixing effect of the first adhesive layer on the separator. Setting H3 ≤ 210 μm ensures that the thickness of the first overlapping portion is not too large, which is beneficial to reducing the impact of the setting of the first overlapping portion on the thickness of the electrode assembly. Setting L2 ≥ 0.1 mm ensures that the length of the first overlapping portion is not too small, which is beneficial to improving the bonding strength between the first adhesive layer and the first electrode tab and enhancing the fixing effect of the first adhesive layer on the separator. Setting L2 ≤ 2 mm ensures that the length of the first overlapping portion is not too large, which is beneficial to reducing the possibility of the first overlapping portion overlapping with the second electrode tab, thereby reducing the impact of the setting of the first overlapping portion on the thickness of the electrode assembly.

[0019] In one or more embodiments of the present application, 0.4 mm ≤ L2 ≤ 1.6 mm. Setting L2 ≥ 0.4 mm is beneficial to further improving the bonding strength between the first adhesive layer and the first electrode tab and further enhancing the fixing effect of the first adhesive layer on the separator. Setting L2 ≤ 1.6 mm is beneficial to further reducing the possibility of the first overlapping portion overlapping with the second electrode tab, thereby reducing the impact of the setting of the first overlapping portion on the thickness of the electrode assembly.

[0020] In one or more embodiments of the present application, 0.6 mm ≤ L2 ≤ 1.0 mm. Setting L2 ≥ 0.6 mm is beneficial to further improving the bonding strength between the first adhesive layer and the first electrode tab and further enhancing the fixing effect of the first adhesive layer on the separator. Setting L2 ≤ 1.0 mm is beneficial to further reducing the possibility of the first overlapping portion overlapping with the second electrode tab, thereby reducing the impact of the setting of the first overlapping portion on the thickness of the electrode assembly.

[0021] In one or more embodiments of the present application, along the first direction, at least one end of the first adhesive layer extends beyond the first edge. In this way, it is beneficial to improve the effect of the first adhesive layer covering the first edge and reduce the possibility of the corner of the first electrode tab piercing the first protective layer.

[0022] In one or more embodiments of the present application, along the first direction, the first electrode tab located on the outermost layer of the electrode assembly is the first outer electrode tab. The first outer electrode tab includes an outer surface and an inner surface that are oppositely arranged along the first direction, and the outer surface faces away from the inside of the electrode assembly; the first adhesive layer includes a second overlapping portion, and the second overlapping portion is the part where the first adhesive layer overlaps with the outer surface. In this way, it is beneficial to improve the bonding strength between the first adhesive layer and the first electrode tab and reduce the possibility of the first adhesive layer detaching.

[0023] In one or more embodiments of the present application, the second pole piece located on the outermost layer of the electrode assembly is the second outermost layer pole piece. The second outermost layer pole piece is located on the outermost layer of the electrode assembly, and the first outermost layer pole piece is located on the second outermost layer of the electrode assembly; along the first direction, the maximum thickness of the second overlapping portion is H4, 60 μm ≤ H4 ≤ 130 μm; along the second direction, the maximum length of the second overlapping portion is L3, 0.1 mm ≤ L3 ≤ 2 mm; along the third direction, the maximum length of the second overlapping portion is L4, 0.1 mm ≤ L4 ≤ 2 mm. Setting H4 ≥ 60 μm, the thickness of the second overlapping portion is not too small, which is beneficial to improving the bonding strength between the first adhesive layer and the first pole piece and reducing the possibility of the first adhesive layer falling off; setting H4 ≤ 130 μm, the thickness of the second overlapping portion is not too large, which is beneficial to reducing the influence of the setting of the first overlapping portion on the thickness of the electrode assembly; setting L3 ≥ 0.1 mm, the maximum length of the second overlapping portion along the second direction is not too small, which is beneficial to improving the bonding strength between the first adhesive layer and the first pole piece, setting L3 ≤ 2 mm, the maximum length of the second overlapping portion along the second direction is not too large, which is beneficial to reducing the possibility that the second overlapping portion is stacked with the second pole piece and affects the thickness of the electrode assembly; setting L4 ≥ 0.1 mm, the maximum length of the second overlapping portion along the third direction is not too small, which is beneficial to improving the bonding strength between the first adhesive layer and the first pole piece, setting L4 ≤ 2 mm, the maximum length of the second overlapping portion along the third direction is not too large, which is beneficial to reducing the possibility that the second overlapping portion is stacked with the second pole piece and affects the thickness of the electrode assembly.

[0024] In one or more embodiments of the present application, 0.4 mm ≤ L3 ≤ 1.6 mm; 0.4 mm ≤ L4 ≤ 1.6 mm. Setting L3 ≥ 0.4 mm is beneficial to further improving the bonding strength between the first adhesive layer and the first pole piece, setting L3 ≤ 1.6 mm is beneficial to further reducing the possibility that the second overlapping portion is stacked with the second pole piece and affects the thickness of the electrode assembly; setting L4 ≥ 0.4 mm is beneficial to further improving the bonding strength between the first adhesive layer and the first pole piece, setting L4 ≤ 1.6 mm is beneficial to further reducing the possibility that the second overlapping portion is stacked with the second pole piece and affects the thickness of the electrode assembly.

[0025] In one or more embodiments of the present application, 0.6 mm ≤ L3 ≤ 1.0 mm; 0.6 mm ≤ L4 ≤ 1.0 mm. Setting L3 ≥ 0.6 mm is beneficial to further improving the bonding strength between the first adhesive layer and the first pole piece, setting L3 ≤ 1.0 mm is beneficial to further reducing the possibility that the second overlapping portion is stacked with the second pole piece and affects the thickness of the electrode assembly; setting L4 ≥ 0.6 mm is beneficial to further improving the bonding strength between the first adhesive layer and the first pole piece, setting L4 ≤ 1.0 mm is beneficial to further reducing the possibility that the second overlapping portion is stacked with the second pole piece and affects the thickness of the electrode assembly.

[0026] In one or more embodiments of the present application, the secondary battery further includes a tab. Along the second direction, one end of the tab is connected to the electrode assembly, and the other end of the tab extends out of the housing; each first electrode plate further includes a third edge and a fourth edge. The third edge and the first edge are oppositely arranged along the third direction, and the fourth edge and the second edge are oppositely arranged along the second direction; the intersection point of the second edge and the third edge of the same first electrode plate is the second intersection point. Along the first direction, a plurality of second intersection points are combined into a second edge; the intersection point of the first edge and the fourth edge of the same first electrode plate is the third intersection point. Along the first direction, a plurality of third intersection points are combined into a third edge; the intersection point of the third edge and the fourth edge of the same first electrode plate is the fourth intersection point. Along the first direction, a plurality of fourth intersection points are combined into a fourth edge; along the second direction, the first edge is farther from the tab than the third edge and the fourth edge. The first edge being farther from the tab than the third edge and the fourth edge is equivalent to disposing the first adhesive layer at the tail of the secondary battery. Through the buffering effect of the first adhesive layer, the possibility of the first electrode plate piercing the first protective layer is reduced. Compared with the prior art, the distance between the first electrode plate and the first protective layer can be reduced, enabling the secondary battery to obtain a gain in volume energy density.

[0027] In one or more embodiments of the present application, the first edge, the second edge, the third edge, and the fourth edge are all coated with a first adhesive layer. In this way, it is beneficial to further reduce the risk of the first electrode plate piercing the first protective layer. On this basis, using the first adhesive layer to fix the separator can eliminate the winding adhesive setting around the periphery of the electrode assembly in the prior art, improving the energy density of the secondary battery.

[0028] In one or more embodiments of the present application, the material of the first adhesive layer includes at least one of photosensitive adhesive and hot melt adhesive.

[0029] In one or more embodiments of the present application, the material of the first protective layer includes at least one of polyethylene, polypropylene, polymethyl methacrylate, polycarbonate, polyamide, polyethylene terephthalate, acrylonitrile-butadiene-styrene copolymer, polyoxymethylene, or polyphenylene ether.

[0030] In one or more embodiments of the present application, along the third direction, the distance from the surface of the first protective layer facing away from the metal layer to the first edge is 0.25 mm to 0.4 mm. By adopting the solution of the present invention, the distance between the first protective layer and the first edge can be reduced, improving the volume energy density of the secondary battery.

[0031] In one or more embodiments of the present application, along the second direction, the distance from the surface of the first protective layer facing away from the metal layer to the second edge is 0.25 mm to 0.4 mm. By adopting the solution of the present invention, the distance between the first protective layer and the second edge can be reduced, improving the volume energy density of the secondary battery.

[0032] In one or more embodiments of the present application, along the direction pointing from the first edge to the corner position of the housing, the distance from the surface of the first protective layer facing away from the metal layer to the first edge is 0.3 mm to 0.6 mm. By adopting the solution of the present invention, the distance from the first protective layer to the first edge can be reduced, and the volumetric energy density of the secondary battery can be improved.

[0033] In one or more embodiments of the present application, the first electrode sheet is a negative electrode sheet, and the first electrode sheet includes a first current collector and a first active material layer stacked thereon, and the material of the first active material layer contains silicon element.

[0034] In one or more embodiments of the present application, based on the mass of the first active material layer, the mass content of silicon element is 4% to 90%. The mass content of silicon element not less than 4% is beneficial to improving the capacity of the secondary battery; the mass content of silicon element not higher than 90% is beneficial to reducing the swelling amount of the first electrode sheet during use.

[0035] The second aspect of the embodiments of the present application provides an electrical device, and the electrical device includes the secondary battery involved in any of the foregoing embodiments. Description of the Drawings

[0036] Figure 1 is a schematic structural diagram of a secondary battery in an embodiment of the present application.

[0037] Figure 2 is Figure 1 the cross-sectional structural diagram at II-II in

[0038] Figure 3 is a schematic structural diagram of an electrode assembly in an embodiment of the present application.

[0039] Figure 4 is a schematic connection structure diagram of an electrode assembly and a first adhesive layer in an embodiment of the present application.

[0040] Figure 5 is a schematic exploded view of the structure of an electrode assembly in an embodiment of the present application.

[0041] Figure 6 is a schematic structural diagram of a first electrode sheet in an embodiment of the present application.

[0042] Figure 7 is Figure 4 the cross-sectional structural diagram at VII-VII in

[0043] Figure 8 is a schematic structural diagram of a first outer electrode sheet in an embodiment of the present application.

[0044] Figure 9 is a schematic structural diagram of an electrical device in an embodiment of the present application.

[0045] Description of Main Component Symbols

[0046] Secondary Battery 100

[0047] Housing 10

[0048] First Protective Layer 11

[0049] Metal Layer 12

[0050] Second Protective Layer 13

[0051] Electrode Assembly 20

[0052] First Edge 201

[0053] First Intersection Point 2011

[0054] Second Edge 202

[0055] Second Intersection Point 2021

[0056] Third Edge 203

[0057] Third Intersection Point 2031

[0058] Fourth Edge 204

[0059] Fourth Intersection Point 2041

[0060] First Electrode Tab 21

[0061] First Edge 211

[0062] Second Edge 212

[0063] Third Edge 213

[0064] Fourth Edge 214

[0065] First Surface 21a

[0066] Second Surface 21b

[0067] First Outer Electrode Tab 210

[0068] Outer Surface 210a

[0069] Inner Surface 210b

[0070] Second Electrode Tab 22

[0071] Second Outer Electrode Tab 220

[0072] Separator 23

[0073] Positive Electrode Tab 24

[0074] Positive current collector 241

[0075] Positive electrode active material layer 242

[0076] Negative electrode sheet 25

[0077] Negative current collector 251

[0078] Negative electrode active material layer 252

[0079] First adhesive layer 30

[0080] First overlapping portion 31

[0081] Second overlapping portion 32

[0082] Tab 40

[0083] Electrical device 1000

[0084] First direction X

[0085] Second direction Y

[0086] Third direction Z

[0087] The following specific embodiments will further illustrate the present application in conjunction with the above drawings. Specific embodiments

[0088] The technical solutions in the embodiments of the present application will be described below with reference to the 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 of the embodiments.

[0089] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element. When an element is considered to be "disposed" on another element, it can be directly disposed on the other element or there may be an intermediate element.

[0090] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of the present application herein are only for the purpose of describing specific embodiments, and are not intended to limit this application.

[0091] 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 indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, "a plurality of" means more than two, unless otherwise specifically defined.

[0092] In the description of the embodiments of the present application, the term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there may be a state approximately vertical between the two components. The two components described as "vertical" may not be absolute straight lines or planes, and may also be approximately straight lines or planes. From a macroscopic perspective, as long as the overall extension direction is a straight line or a plane, the components can be considered "straight lines" or "planes".

[0093] Mentioning "embodiment" in this article means that the specific features, structures or characteristics described in combination with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Without conflict, the various embodiments in the present application can be combined with each other.

[0094] An embodiment of the present application provides a secondary battery, which includes an electrode assembly, a housing, and a first adhesive layer. The electrode assembly includes a plurality of first electrode plates, a plurality of second electrode plates, and a separator. The polarities of the first electrode plates and the second electrode plates are opposite, and the first electrode plates and the second electrode plates are alternately stacked. A separator is provided between adjacent first electrode plates and second electrode plates; along a first direction, the orthographic projection of the second electrode plate is within the orthographic projection range of the first electrode plate, and the first direction is the thickness direction of the electrode assembly; each first electrode plate includes a first edge extending along a second direction and a second edge extending along a third direction, and the first direction, the second direction, and the third direction are perpendicular to each other in pairs; the intersection point of the first edge and the second edge of the same first electrode plate is a first intersection point; along the first direction, a plurality of first intersection points are combined into a first edge. The housing includes a first protective layer and a metal layer stacked along the first direction, and the housing includes a first space, and the electrode assembly is received in the first space; the first protective layer is located between the metal layer and the electrode assembly. The first adhesive layer covers the first edge.

[0095] In this secondary battery, by providing the first adhesive layer to cover the first edge, it is beneficial to reduce the possibility that the corner of the first electrode plate pierces the first protective layer of the housing, reduce the corrosion of the housing, and thus be beneficial to improving the service life of the secondary battery.

[0096] The following will further illustrate the embodiments of the present application with reference to the accompanying drawings.

[0097] As Figure 1 and Figure 2 shown, a first aspect of the embodiment of the present application provides a secondary battery 100, which includes a housing 10 and an electrode assembly 20. The electrode assembly 20 is received in the housing 10, and the electrode assembly 20 is used to store and release electrical energy.

[0098] In some embodiments, as Figure 2As shown, the housing 10 includes a first protective layer 11 and a metal layer 12 stacked in the first direction X. The housing 10 includes a first space, and the electrode assembly 20 is received in the first space; the first protective layer 11 is located between the metal layer 12 and the electrode assembly 20.

[0099] In some embodiments, the material of the first protective layer 11 includes, but is not limited to, at least one of polyethylene, polypropylene, polymethyl methacrylate, polycarbonate, polyamide, polyethylene terephthalate, acrylonitrile-butadiene-styrene copolymer, polyoxymethylene, or polyphenylene ether. Using the foregoing materials, the first protective layer 11 is difficult to be dissolved or swollen by the electrolyte, which is beneficial to reducing the risk of corrosion of the metal layer 12 adjacent to the first protective layer 11.

[0100] In some embodiments, the material of the metal layer 12 includes, but is not limited to, aluminum foil, austenitic-ferritic duplex stainless steel foil. Using the foregoing materials, the metal layer 12 can not only improve the structural strength of the housing 10, but also react with oxygen in the air to form a dense oxide film, thereby reducing the risk of water vapor penetrating into the accommodation cavity.

[0101] In some embodiments, the housing 10 further includes a second protective layer 13. The first protective layer 11, the metal layer 12, and the second protective layer 13 are stacked in sequence, and the first protective layer 11 and the second protective layer 13 jointly wrap the metal layer 12.

[0102] In some embodiments, the material of the second protective layer 13 includes, but is not limited to, polyamide, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, acrylonitrile-butadiene-styrene copolymer, polyoxymethylene, and polyphenylene ether. Using the foregoing materials, the second protective layer 13 can not only reduce the risk of air penetrating into the accommodation cavity, but also improve the deformation ability of the housing 10.

[0103] In some embodiments, as Figure 2 shown, the electrode assembly 20 includes a plurality of first electrode plates 21, a plurality of second electrode plates 22, and a separator 23. The polarities of the first electrode plates 21 and the second electrode plates 22 are opposite, the first electrode plates 21 and the second electrode plates 22 are alternately stacked, and a separator 23 is provided between adjacent first electrode plates 21 and second electrode plates 22; along the first direction X, the orthographic projection of the second electrode plate 22 is located within the orthographic projection of the first electrode plate 21, and the first direction X is the thickness direction of the electrode assembly 20. Among them, the polarities of the first electrode plates 21 and the second electrode plates 22 are opposite, that is, one of the first electrode plates 21 and the second electrode plates 22 is a positive electrode plate 24, and the other is a negative electrode plate 25.

[0104] In some embodiments, as Figure 2 shown, the positive electrode plate 24 includes a positive electrode current collector 241 and a positive electrode active material layer 242 stacked.

[0105] In some embodiments, the positive current collector 241 is a metal foil. As an exemplary example, the positive current collector 241 may be a metal foil including at least one of aluminum, nickel, tantalum, and titanium, such as an aluminum foil.

[0106] In some embodiments, the positive active material layer 242 includes a positive active material. As an exemplary example, the positive active material includes at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganate.

[0107] In some embodiments, as Figure 2 shown, the negative electrode sheet 25 includes a negative current collector 251 and a negative active material layer 252 that are stacked.

[0108] In some embodiments, the negative current collector 251 is a metal foil. As an exemplary example, the negative current collector 251 may be a metal foil including at least one of copper, nickel, tantalum, and titanium, such as a copper foil.

[0109] In some embodiments, the negative active material layer 252 includes a negative active material. As an exemplary example, the negative active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon oxide material, and silicon carbon material.

[0110] In some embodiments, the separator 23 is one of a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0111] In some embodiments, as Figures 3 to 5 shown, each first electrode sheet 21 includes a first edge 211 extending in the second direction Y and a second edge 212 extending in the third direction Z, and the first direction X, the second direction Y, and the third direction Z are perpendicular to each other in pairs; the intersection point of the first edge 211 and the second edge 212 of the same first electrode sheet 21 is the first intersection point 2011; along the first direction X, a plurality of first intersection points 2011 are combined into a first edge 201. It should be noted that due to the layered structure of the electrode assembly 20, the first edge 201 is not actually continuous, but a part of it is distributed on each first electrode sheet 21. Here, for the convenience of describing the structure, it is treated as a whole. The secondary battery 100 further includes a first adhesive layer 30, and the first adhesive layer 30 covers the first edge 201. It should be noted that Figure 5 the separator 23 is omitted.

[0112] In this secondary battery 100, by providing the first adhesive layer 30 to cover the first edge 201, it is beneficial to reduce the possibility that the corner of the first electrode sheet 21 pierces the first protective layer 11 of the housing 10, reduce the corrosion of the housing 10, and thus is beneficial to improving the service life of the secondary battery 100.

[0113] In some embodiments, as Figure 6As shown, when observed from the first direction X, the distance from the first edge 201 to the outer edge of the portion of the first adhesive layer 30 away from the first electrode tab 21 is the thickness of the first adhesive layer 30. The maximum thickness of the first adhesive layer 30 is H1, where 0.1 mm ≤ H1 ≤ 0.6 mm. Setting H1 ≥ 0.1 mm ensures that the thickness of the first adhesive layer 30 is not too small, which is beneficial for enhancing the effect of the first adhesive layer 30 in preventing the first electrode tab 21 from piercing the first protective layer 11. Setting H1 ≤ 0.6 mm ensures that the thickness of the first adhesive layer 30 is not too large, which is beneficial for reducing the difficulty of inserting the electrode assembly 20 into the housing and also for reducing the possibility of the housing 10 squeezing the electrode assembly 20, thereby reducing lithium plating. Here, the outer edge of the portion of the first adhesive layer 30 away from the first electrode tab 21 refers to the outer edge of the portion of the first adhesive layer 30 that does not overlap with the first electrode tab 21.

[0114] In some embodiments, 0.2 mm ≤ H1 ≤ 0.4 mm. Setting H1 ≥ 0.2 mm ensures that the thickness of the first adhesive layer 30 is not too small, which is beneficial for further enhancing the effect of the first adhesive layer 30 in preventing the first electrode tab 21 from piercing the first protective layer 11. Setting H1 ≤ 0.4 mm ensures that the thickness of the first adhesive layer 30 is not too large, which is beneficial for further reducing the difficulty of inserting the electrode assembly 20 into the housing and also for further reducing the possibility of the housing 10 squeezing the electrode assembly 20, thereby reducing lithium plating.

[0115] In some embodiments, as Figure 6 shown, the first adhesive layer 30 covers a part of at least one first edge 211. The first adhesive layer 30 covering the first edge 211 is beneficial for enhancing the bonding stability between the first adhesive layer 30 and the first electrode tab 21 and reducing the risk of the first adhesive layer 30 peeling off.

[0116] In some embodiments, as Figure 6 shown, along the second direction Y, the length of the first adhesive layer 30 covering the first edge 211 is L1, where 0.1 mm ≤ L1 ≤ 2 mm. Setting L1 ≥ 0.1 mm ensures that the length of the first adhesive layer 30 covering the first edge 211 is not too short, which is beneficial for enhancing the bonding stability between the first adhesive layer 30 and the first electrode tab 21 and reducing the risk of the first adhesive layer 30 peeling off. Setting L1 ≤ 2 mm ensures that the length of the first adhesive layer 30 covering the first edge 211 is not too long, which is beneficial for improving the wetting effect of the electrolyte on the first electrode tab 21 and reducing the risk of lithium plating at the corner of the first electrode tab 21.

[0117] In some embodiments, 0.4 mm ≤ L1 ≤ 1.6 mm. Setting L1 ≥ 0.4 mm is beneficial for further reducing the risk of the first adhesive layer 30 peeling off. Setting L1 ≤ 1.6 mm is beneficial for further improving the wetting effect of the electrolyte on the first electrode tab 21 and reducing the risk of lithium plating at the corner of the first electrode tab 21.

[0118] In some embodiments, 0.6 mm ≤ L1 ≤ 1.0 mm. Setting L1 ≥ 0.6 mm is beneficial to further reduce the risk of the first adhesive layer 30 peeling off; setting L1 ≤ 1.0 mm is beneficial to further improve the wetting effect of the electrolyte on the first electrode sheet 21 and reduce the risk of lithium plating at the corners of the first electrode sheet 21.

[0119] In some embodiments, as Figure 6 shown, along the third direction Z, the maximum thickness of the first adhesive layer 30 is H2, and 0.1 mm ≤ H2 ≤ 0.4 mm. Setting H2 ≥ 0.1 mm ensures that the thickness of the first adhesive layer 30 is not too small, which is beneficial to improving the effect of the first adhesive layer 30 in preventing the first electrode sheet 21 from piercing the first protective layer 11; setting H2 ≤ 0.4 mm ensures that the thickness of the first adhesive layer 30 is not too large, which is beneficial to reducing the difficulty of inserting the electrode assembly 20 into the housing and also beneficial to reducing the possibility of the housing 10 squeezing the electrode assembly 20 to reduce lithium plating.

[0120] In some embodiments, 0.15 mm ≤ H2 ≤ 0.3 mm. Setting H2 ≥ 0.15 mm is beneficial to further improve the effect of the first adhesive layer 30 in preventing the first electrode sheet 21 from piercing the first protective layer 11; setting H2 ≤ 0.3 mm is beneficial to further reduce the difficulty of inserting the electrode assembly 20 into the housing and also beneficial to further reducing the possibility of the housing 10 squeezing the electrode assembly 20 to reduce lithium plating.

[0121] In some embodiments, as Figure 6 shown, the first adhesive layer 30 covers a part of at least one second edge 212. The part of the first adhesive layer 30 covering the second edge 212 is beneficial to improving the bonding stability between the first adhesive layer 30 and the first electrode sheet 21 and reducing the risk of the first adhesive layer 30 peeling off.

[0122] In some embodiments, as Figure 7As shown, a separator film 23 is covered between the first adhesive layer 30 and the first edge 201. In other words, the separator film 23 extends beyond the edge of the first electrode tab 21. Thus, it is beneficial to improve the insulation effect of the separator film 23 between the first electrode tab 21 and the second electrode tab 22. It should be noted that in this embodiment, the first adhesive layer 30 penetrates through the separator film 23 and adheres to both the first electrode tab 21 and the separator film 23 simultaneously. Since the electrode assembly 20 needs to be pressed during the manufacturing process, the separator film 23 is in a stretched state, and the position of the separator film 23 relative to the electrode tab mainly depends on the adhesive force between the electrode tab and the separator film 23. When the secondary battery 100 drops, or when heat is generated during the operation of the electrode assembly 20, causing the separator film 23 to heat up and shrink thermally, it is possible for the separator film 23 to overcome the adhesive force and shrink inward, thereby causing a short circuit between the first electrode tab 21 and the second electrode tab 22. Therefore, the first adhesive layer 30 adhering to both the first electrode tab 21 and the separator film 23 can fix the separator film 23, which is beneficial to reducing the risk of short circuit between the first electrode tab 21 and the second electrode tab 22 caused by the inward shrinkage of the separator film 23.

[0123] In some embodiments, a separator film 23 is covered between the first adhesive layer 30 and the first edge 211. Thus, on the one hand, it is beneficial to improve the insulation effect of the separator film 23 between the first electrode tab 21 and the second electrode tab 22; on the other hand, it is beneficial to reduce the risk of short circuit between the first electrode tab 21 and the second electrode tab 22 caused by the inward shrinkage of the separator film 23.

[0124] In some embodiments, as Figure 7 shown, each first electrode tab 21 includes a first surface 21a and a second surface 21b that are oppositely arranged along the first direction X. The first surface 21a faces away from the inside of the electrode assembly 20, and the second surface 21b faces the inside of the electrode assembly 20; the first adhesive layer 30 includes a first overlapping portion 31, and the first overlapping portion 31 is the part where the first adhesive layer 30 overlaps with at least one first surface 21a or at least one second surface 21b. The first adhesive layer 30 adhering to at least one of the first surface 21a and the second surface 21b is beneficial to improving the bonding strength of the first adhesive layer 30 to the first electrode tab 21 and reducing the risk of the first adhesive layer 30 falling off; moreover, the separator film 23 is fixed by the first adhesive layer 30, which is beneficial to reducing the possibility of the separator film 23 shrinking inward. Further, based on the fixing effect of the first adhesive layer 30 on the separator film 23, the winding adhesive provided at the periphery of the electrode assembly 20 in the prior art to fix the separator film 23 can be omitted, thereby improving the volume energy density of the secondary battery 100.

[0125] In some embodiments, as Figure 6 and Figure 7As shown, along the first direction X, the maximum thickness of the first overlapping portion 31 is H3, and along the third direction Z, the maximum length of the first overlapping portion 31 is L2; 150 μm ≤ H3 ≤ 210 μm, 0.1 mm ≤ L2 ≤ 2 mm. Setting H3 ≥ 150 μm ensures that the thickness of the first overlapping portion 31 along the first direction X is not too small, which is beneficial to improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21 and enhancing the fixing effect of the first adhesive layer 30 on the separator 23; setting H3 ≤ 210 μm ensures that the thickness of the first overlapping portion 31 is not too large, which is beneficial to reducing the impact of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20; setting L2 ≥ 0.1 mm ensures that the length of the first overlapping portion 31 is not too small, which is beneficial to improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21 and enhancing the fixing effect of the first adhesive layer 30 on the separator 23; setting L2 ≤ 2 mm ensures that the length of the first overlapping portion 31 is not too large, which is beneficial to reducing the possibility of the first overlapping portion 31 overlapping with the second electrode tab 22, thereby reducing the impact of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20.

[0126] In some embodiments, 0.4 mm ≤ L2 ≤ 1.6 mm. Setting L2 ≥ 0.4 mm is beneficial to further improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21 and further enhancing the fixing effect of the first adhesive layer 30 on the separator 23; setting L2 ≤ 1.6 mm is beneficial to further reducing the possibility of the first overlapping portion 31 overlapping with the second electrode tab 22, thereby reducing the impact of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20.

[0127] In some embodiments, 0.6 mm ≤ L2 ≤ 1.0 mm. Setting L2 ≥ 0.6 mm is beneficial to further improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21 and further enhancing the fixing effect of the first adhesive layer 30 on the separator 23; setting L2 ≤ 1.0 mm is beneficial to further reducing the possibility of the first overlapping portion 31 overlapping with the second electrode tab 22, thereby reducing the impact of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20.

[0128] In some embodiments, as Figure 7 shown, along the first direction X, at least one end of the first adhesive layer 30 extends beyond the first edge 201. Thus, it is beneficial to improve the effect of the first adhesive layer 30 covering the first edge 201 and reduce the possibility of the corner of the first electrode tab 21 piercing the first protective layer 11.

[0129] In some embodiments, as Figure 7As shown, along the first direction X, the first pole piece 21 located at the outermost layer of the electrode assembly 20 is the first outermost pole piece 210. The first outermost pole piece 210 includes an outer surface 210a and an inner surface 210b that are oppositely arranged along the first direction X. The outer surface 210a faces away from the interior of the electrode assembly 20; the first adhesive layer 30 includes a second overlapping portion 32, and the second overlapping portion 32 is the part where the first adhesive layer 30 overlaps with the outer surface 210a. In this way, it is beneficial to improve the bonding strength between the first adhesive layer 30 and the first pole piece 21 and reduce the possibility of the first adhesive layer 30 detaching. It should be noted that the "outermost layer of the electrode assembly 20" described when identifying the first outermost pole piece 210 refers to the outermost layer between the first pole pieces 21, without considering the influence of the second pole piece 22 and the separator 23.

[0130] In some embodiments, as Figure 7 and Figure 8 shown, the second pole piece 22 located at the outermost layer of the electrode assembly 20 is the second outermost pole piece 220. The second outermost pole piece 220 is located at the outermost layer of the electrode assembly 20, and the first outermost pole piece 210 is located at the second outermost layer of the electrode assembly 20; along the first direction X, the maximum thickness of the second overlapping portion 32 is H4, and 60 μm ≤ H4 ≤ 130 μm; along the second direction Y, the maximum length of the second overlapping portion 32 is L3, and 0.1 mm ≤ L3 ≤ 2 mm; along the third direction Z, the maximum length of the second overlapping portion 32 is L4, and 0.1 mm ≤ L4 ≤ 2 mm. Setting H4 ≥ 60 μm ensures that the thickness of the second overlapping portion 32 is not too small, which is beneficial to improving the bonding strength between the first adhesive layer 30 and the first pole piece 21 and reducing the possibility of the first adhesive layer 30 peeling off; setting H4 ≤ 130 μm ensures that the thickness of the second overlapping portion 32 is not too large, which is beneficial to reducing the influence of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20; setting L3 ≥ 0.1 mm ensures that the maximum length of the second overlapping portion 32 along the second direction Y is not too small, which is beneficial to improving the bonding strength between the first adhesive layer 30 and the first pole piece 21. Setting L3 ≤ 2 mm ensures that the maximum length of the second overlapping portion 32 along the second direction Y is not too large, which is beneficial to reducing the possibility that the second overlapping portion 32 overlaps with the second pole piece 22 and affects the thickness of the electrode assembly 20; setting L4 ≥ 0.1 mm ensures that the maximum length of the second overlapping portion 32 along the third direction Z is not too small, which is beneficial to improving the bonding strength between the first adhesive layer 30 and the first pole piece 21. Setting L4 ≤ 2 mm ensures that the maximum length of the second overlapping portion 32 along the third direction Z is not too large, which is beneficial to reducing the possibility that the second overlapping portion 32 overlaps with the second pole piece 22 and affects the thickness of the electrode assembly 20.

[0131] In some embodiments, 0.4 mm ≤ L3 ≤ 1.6 mm; 0.4 mm ≤ L4 ≤ 1.6 mm. Setting L3 ≥ 0.4 mm is beneficial to further improve the bonding strength between the first adhesive layer 30 and the first electrode tab 21. Setting L3 ≤ 1.6 mm is beneficial to further reduce the possibility that the second overlapping portion 32 and the second electrode tab 22 are stacked to affect the thickness of the electrode assembly 20. Setting L4 ≥ 0.4 mm is beneficial to further improve the bonding strength between the first adhesive layer 30 and the first electrode tab 21. Setting L4 ≤ 1.6 mm is beneficial to further reduce the possibility that the second overlapping portion 32 and the second electrode tab 22 are stacked to affect the thickness of the electrode assembly 20.

[0132] In some embodiments, 0.6 mm ≤ L3 ≤ 1.0 mm; 0.6 mm ≤ L4 ≤ 1.0 mm. Setting L3 ≥ 0.6 mm is beneficial to further improve the bonding strength between the first adhesive layer 30 and the first electrode tab 21. Setting L3 ≤ 1.0 mm is beneficial to further reduce the possibility that the second overlapping portion 32 and the second electrode tab 22 are stacked to affect the thickness of the electrode assembly 20. Setting L4 ≥ 0.6 mm is beneficial to further improve the bonding strength between the first adhesive layer 30 and the first electrode tab 21. Setting L4 ≤ 1.0 mm is beneficial to further reduce the possibility that the second overlapping portion 32 and the second electrode tab 22 are stacked to affect the thickness of the electrode assembly 20.

[0133] In some embodiments, such as Figures 1 to 4As shown, the secondary battery 100 further includes a tab 40. Along the second direction Y, one end of the tab 40 is connected to the electrode assembly 20, and the other end of the tab 40 extends out of the housing 10; each first electrode plate 21 further includes a third edge 213 and a fourth edge 214. The third edge 213 and the first edge 211 are oppositely arranged along the third direction Z, and the fourth edge 214 and the second edge 212 are oppositely arranged along the second direction Y; the intersection point of the second edge 212 and the third edge 213 of the same first electrode plate 21 is the second intersection point 2021. Along the first direction X, a plurality of second intersection points 2021 are combined into a second edge 202; the intersection point of the first edge 211 and the fourth edge 214 of the same first electrode plate 21 is the third intersection point 2031. Along the first direction X, a plurality of third intersection points 2031 are combined into a third edge 203; the intersection point of the third edge 213 and the fourth edge 214 of the same first electrode plate 21 is the fourth intersection point 2041. Along the first direction X, a plurality of fourth intersection points 2041 are combined into a fourth edge 204; along the second direction Y, the first edge 201 is farther from the tab 40 than the third edge 203 and the fourth edge 204. In the prior art, in order to prevent the first electrode plate 21 from piercing the first protective layer 11, an appropriate distance needs to be left between the first electrode plate 21 and the first protective layer 11. Since the head of the secondary battery 100 needs to accommodate part of the tab 40, therefore, at the head of the secondary battery 100, the distance between the first electrode plate 21 and the first protective layer 11 is usually greater than that at other positions and also greater than the thickness of the first adhesive layer 30 usually required. Due to the existence of the tab 40, it is also difficult to reduce this distance. In this embodiment, the first edge 201 is farther from the tab 40 than the third edge 203 and the fourth edge 204, which is equivalent to arranging the first adhesive layer 30 at the tail of the secondary battery 100. Through the buffering effect of the first adhesive layer 30, the possibility of the first electrode plate 21 piercing the first protective layer 11 is reduced. Compared with the prior art, the distance between the first electrode plate 21 and the first protective layer 11 can be reduced, enabling the secondary battery 100 to obtain a gain in volume energy density.

[0134] In some embodiments, as Figure 4 shown, the first edge 201, the second edge 202, the third edge 203, and the fourth edge 204 are all coated with the first adhesive layer 30. Thus, it is beneficial to further reduce the risk of the first electrode plate 21 piercing the first protective layer 11. On this basis, using the first adhesive layer 30 to fix the separator 23, the winding adhesive setting around the periphery of the electrode assembly 20 in the prior art can be cancelled, improving the energy density of the secondary battery 100.

[0135] In some embodiments, the material of the first adhesive layer 30 includes at least one of photosensitive adhesive and hot melt adhesive.

[0136] In some embodiments, along the third direction Z, the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the first edge 211 is 0.25 mm to 0.4 mm. By adopting the solution of the present invention, the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the first edge 211 can be reduced, thereby improving the volumetric energy density of the secondary battery.

[0137] It should be noted that the test method for the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the first edge 211 is as follows: discharge the secondary battery 100 to 0 V, use a wire cutting and separating machine tool to cut a part of the secondary battery 100 along the second direction Y. At this time, the cut surface is rough (due to the shedding of the active layer). Place the secondary battery 100 on an abrasive disc and polish the cut surface until it is smooth. Observe the cut surface under a metallurgical microscope and measure the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the first edge 211.

[0138] In some embodiments, along the second direction Y, the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the second edge 212 is 0.25 mm to 0.4 mm. By adopting the solution of the present invention, the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the second edge 212 can be reduced, thereby improving the volumetric energy density of the secondary battery.

[0139] It should be noted that the test method for the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the second edge 212 is as follows: discharge the secondary battery 100 to 0 V, use a wire cutting and separating machine tool to cut a part of the secondary battery 100 along the third direction Z. At this time, the cut surface is rough (due to the shedding of the active layer). Place the secondary battery 100 on an abrasive disc and polish the cut surface until it is smooth. Observe the cut surface under a metallurgical microscope and measure the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the second edge 212.

[0140] In some embodiments, along the direction from the first edge 201 to the corner position of the housing, the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the first edge 201 is 0.3 mm to 0.6 mm. By adopting the solution of the present invention, the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the first edge 201 can be reduced, thereby improving the volumetric energy density of the secondary battery.

[0141] It should be noted that the test method for the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the first edge 201 is as follows: Discharge the secondary battery 100 to 0V, place it on the stage of an X-ray computed tomography scanner, observe and measure the distance from the metal layer of the housing to the first edge 201 (since only the metal can be observed under the X-ray computed tomography scanner and the first protective layer 11 cannot be observed), and then calculate the distance from the surface of the first protective layer 11 facing away from the metal layer 12 to the first edge 201 by subtracting the thickness of the first protective layer 11 from the distance from the metal layer to the first edge 201.

[0142] In some embodiments, the first electrode tab 21 is a negative electrode tab 25. The first electrode tab 21 includes a first current collector and a first active material layer stacked thereon, and the material of the first active material layer contains silicon element.

[0143] In some embodiments, based on the mass of the first active material layer, the mass content of silicon element is 4% to 90%. The mass content of silicon element not being less than 4% is beneficial to improving the capacity of the secondary battery 100; the mass content of silicon element not being higher than 90% is beneficial to reducing the swelling amount of the first electrode tab 21 during use.

[0144] As Figure 9 shown, the second aspect of the embodiments of the present application provides an electrical device 1000, and the electrical device 1000 includes the secondary battery 100 involved in any of the foregoing embodiments.

[0145] In some embodiments, the electrical device 1000 includes, but is not limited to, mobile phones, laptop computers, electric toys, and power tools.

[0146] To verify the technical effects of the solutions in the embodiments of the present application, the inventors of the present application conducted the following experiments. The experimental work included 48 experimental groups, one of which was a comparative example, and the remaining 47 groups were examples, marked as Example 1 to Example 47. Each experimental group included 20 secondary batteries 100. In the experiment, the negative electrode tab 25 was used as the first electrode tab 21, the positive electrode tab 24 was used as the second electrode tab 22, and the electrode tabs at both ends of the electrode assembly 20 along the first direction X were both positive electrode tabs 24.

[0147] The preparation process of the secondary battery 100 in Example 1 included the following steps:

[0148] (1) Preparation of the positive electrode sheet 24: Mix the active material lithium cobalt oxide (LiCoO₂), conductive carbon black (Super P), CNT (carbon nanotube), and polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:0.5:0.5:1.5, add N-methylpyrrolidone (NMP) as a solvent, and formulate a positive electrode 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 positive electrode current collector 241. Use a slot coater to evenly coat the above active material on one side of the positive electrode current collector 241 along its thickness direction, and then dry it at 90 °C to obtain a positive electrode sheet 24 with a positive electrode active material coated on one side. At this time, the thickness of the positive electrode active material layer 242 is 110 μm. Then repeat the above coating steps on the other side of the positive electrode current collector 241 along its thickness direction. Then cold press the coated positive electrode sheet 24. After cold pressing, the thickness of the positive electrode active material layer 242 is 95 μm. At this time, there is an empty foil area on the positive electrode current collector 241 that is not covered by the positive electrode active material layer 242, and the empty foil area is cut to obtain the positive electrode tab 40. In addition, from the perspective of improving the energy density of the secondary battery 100, the two positive electrode sheets 24 located on the outermost layer of the electrode assembly 20 are the sheets with the positive electrode active material layer 242 coated on one side. To reduce the risk of warping of the outermost single-sided coated positive electrode sheet 24, the positive electrode current collector 241 in the outermost single-sided coated positive electrode sheet 24 uses an aluminum foil with a thickness of 20 μm, and the rest of the preparation process is the same as that of the positive electrode sheet 24 located in the inner layer.

[0149] (2) Preparation of the negative electrode sheet 25: Mix the active material artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) in a weight ratio of 97:0.5:1.3:1.2, add deionized water as a solvent, and formulate a negative electrode active material with a weight percentage of 50 wt%, and stir evenly for standby. Use a copper foil with a thickness of 10 μm as the negative electrode current collector 251. Use a slot coater to evenly coat the above negative electrode active material on one side of the negative electrode current collector 251 along its thickness direction, and then dry it at 110 °C to obtain a negative electrode sheet 25 with a negative electrode active material layer 252 coated on one side. At this time, the thickness of the negative electrode active material layer 252 is 105 μm. Then repeat the above steps on the other side of the negative electrode current collector 251 along its thickness direction to obtain a negative electrode sheet 25 with the negative electrode active material layer 252 coated on both sides. Then cold press the coated negative electrode sheet 25. After cold pressing, the thickness of the negative electrode active material layer 252 is 95 μm. At this time, there is an empty foil area on the negative electrode current collector 251 that is not covered by the negative electrode active material layer 252, and the empty foil area is cut to obtain the negative electrode tab 40.

[0150] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0151] (4) Preparation of the isolation film 23: A 7 μm thick polyethylene porous polymer film was used as the substrate layer of the isolation film 23. A ceramic layer of aluminum oxide as ceramic particles and an adhesive layer of polyvinylidene fluoride as a binder were coated on the substrate layer by gravure coating. The total thickness of the isolation film 23 was 15 μm.

[0152] (5) Preparation of the electrode assembly 20: Multiple positive electrode sheets 24, multiple separators 23, and multiple negative electrode sheets 25 are alternately stacked along the first direction X to obtain the electrode assembly 20, the positive electrode tabs 40 are gathered into a positive electrode tab bundle along the first direction X, the positive electrode adapter is welded to the positive electrode tab bundle, the positive electrode tab bundle is bent into a U shape, and the positive electrode adapter is bent into an L shape; the negative electrode tabs 40 are gathered into a negative electrode tab bundle along the first direction X, the negative electrode adapter is welded to the negative electrode tab bundle, the negative electrode tab bundle is bent into a U shape, and the negative electrode adapter is bent into an L shape. The first glue layer 30 is coated on the first edge 201 of the negative electrode sheet 25. During the coating, the material of the first glue layer 30 penetrates the separator 23 and adheres to the negative electrode sheet 25. The first edge 201 is located at the tail of the secondary battery 100, and the surrounding glue is pasted on the periphery of the electrode assembly 20.

[0153] (6) Assembly of secondary battery 100: Place the aluminum-plastic film with a hole punched into an assembly fixture, with the hole facing upward, place the electrode assembly 20 in the hole, and apply external force to press it. Then, cover the electrode assembly 20 with another aluminum-plastic film with a hole punched into it, with the hole facing downward. Heat-seal the three edges of the two aluminum-plastic films by hot pressing. The unsealed edge is the side where the positive electrode adapter and the negative electrode adapter extend out of the shell 10. Then, inject electrolyte through the unsealed edge, and after vacuum packaging, standing, hot pressing, shaping and other processes, the secondary battery 100 is obtained. The side where the positive electrode adapter and the negative electrode adapter extend out of the shell 10 is the head of the secondary battery 100, and the side opposite to the head is the tail.

[0154] The preparation process of the secondary battery 100 in comparative example 1 is substantially the same as that in embodiment 1, except that the secondary battery 100 in comparative example 1 is not provided with the first adhesive layer 30 , and a wrapping adhesive is attached to the periphery of the electrode assembly 20 to fix the isolation film 23 .

[0155] The parameters of the secondary battery 100 in Comparative Example 2 are basically the same as those in Comparative Example 1, except that there is no adhesive tape wrapped around the periphery of the electrode assembly 20.

[0156] The preparation methods of the secondary batteries 100 in Examples 2 to 53 are basically the same as that in Example 1, except that some parameters of the secondary batteries 100 in Examples 2 to 52 are different from those in Example 1, and the specific differences are recorded in Table 1 below.

[0157] The preparation method of the secondary battery 100 in Example 54 is basically the same as that in Example 1, except that the first edge 201 of the secondary battery 100 in Example 53 is located at the head of the secondary battery 100.

[0158] The preparation method of the secondary battery 100 in Example 55 is basically the same as that in Example 1, except that the secondary battery 100 in Example 54 is provided with a first adhesive layer 30 on each of the first edge 201, the second edge 202, the third edge 203 and the fourth edge 204.

[0159] The preparation method of the secondary battery 100 in Example 56 is basically the same as that in Example 55, except that there is no adhesive tape wrapped around the periphery of the electrode assembly 20.

[0160] It should be noted that the size parameters in Table 1 are all measured by a scanning electron microscope (SEM).

[0161] After the secondary batteries 100 in all experimental groups are prepared, 20 secondary batteries 100 are taken from each experimental group for testing.

[0162] (1) A long cycle test is performed on each experimental group, and the test process includes the following steps:

[0163] 1) A parallel plate gauge (PPG) measures the initial thickness of the secondary battery 100 under a force of 700 g.

[0164] 2) The test temperature is maintained at 25 °C.

[0165] 3) The secondary battery 100 is left standing for 30 min.

[0166] 4) Constant current charge at 5C to 4.25V, and then constant voltage charge to 3C.

[0167] 5) Constant current charge at 3C to 4.35V, and then constant voltage charge to 1.5C.

[0168] 6) Constant current charge at 1.5C to 4.45V, and then constant voltage charge to 0.05C.

[0169] 7) Leave standing for 5 min.

[0170] 8) Discharge at a constant current of 0.7C until 3V, and record the capacity of the first discharge cycle;

[0171] 9) Stand still for 5 min;

[0172] 10) Repeat steps 3 to 8 for 1000 times;

[0173] 10) Observe whether there is liquid leakage at the corner of the housing 10 adjacent to the first edge 201. If there is liquid leakage, it means that the first protective layer 11 here is severely damaged. Record the number X1 of the secondary batteries 100 with liquid leakage, and the liquid leakage rate of the secondary battery is recorded as X1 / 20;

[0174] 11) Use a flat thickness gauge (PPG) to measure the thickness of the secondary battery 100 after cycling under the condition of a force of 700 g;

[0175] 12) Disassemble the secondary battery 100, observe the lithium deposition situation of the negative electrode sheet 25 near the first edge 201, record the number X2 of the secondary batteries 100 with lithium deposition, and the lithium deposition rate is recorded as X2 / 20; and use an optical microscope to observe whether the first protective layer 11 of the housing 10 adjacent to the first edge is damaged, record the number X3 of the damaged first protective layers 11, and the damage rate of the first protective layer is recorded as X3 / 20;

[0176] 13) Calculate the expansion rate of the secondary battery 100. The expansion rate = (thickness after cycling - initial thickness) / initial thickness × 100%; The expansion rate is used to reflect the damage situation of the first protective layer 11. When the first protective layer 11 is damaged, water vapor is likely to invade the secondary battery 100, resulting in an increase in the expansion rate of the secondary battery 100 after long cycling; The expansion rate of each experimental group takes the average value of 20 secondary batteries 100 in this group;

[0177] 14) Calculate the volume energy density of the secondary battery 100. The volume energy density = the first cycle discharge capacity × the platform voltage / (the length of the secondary battery 100 × the width of the secondary battery 100 × the thickness of the secondary battery 100); The volume energy density in each experimental group takes the average value of 20 secondary batteries 100 in this group.

[0178] (2) Perform a drop test on each experimental group. The test process is as follows: After standing still at 25 °C for 60 min, measure the voltage V1 of the secondary battery 100 before the drop test; fix the secondary battery 100 in the drop test fixture with double-sided tape, and use a dropping device to freely drop it from a position 1.5 m above the ground in the following order: head - tail - right corner of the head - right corner of the tail - left corner of the head - left corner of the tail (angle: 45° ± 15°), and repeat 6 rounds. After the drop, let it stand still at 25 °C for 24 h, measure and record the voltage V2 of the secondary battery 100, and calculate the voltage drop K = V2 - V1; Check the appearance of the secondary battery 100 and take pictures before and after the test.

[0179] The passing criteria for the drop test: no smoking, no leakage of liquid, and voltage drop < 10 mV. Record the number X4 of secondary batteries 100 that pass the drop test in each experimental group, and the passing rate of the drop test is recorded as X4 / 20.

[0180] The experimental results are recorded in Table 1.

[0181] Table 1

[0182]

[0183]

[0184]

[0185]

[0186]

[0187] Note: In Table 1, " / " indicates no such data.

[0188] As can be seen from Table 1, compared with Comparative Example 1, the breakage rate of the first protective layer 11 of the secondary batteries 100 in Examples 1 to 56 is reduced after long cycling, the probability of liquid leakage at the corner positions of the housing 10 adjacent to the first edge 201 is decreased, and the swelling rate is lower. It can be seen that by providing the first adhesive layer 30 to cover the first edge 201, it is beneficial to reduce the possibility of the corner of the first electrode sheet 21 piercing the first protective layer 11 of the housing 10, reduce the corrosion of the housing 10, and thus is beneficial to improving the service life of the secondary battery 100.

[0189] In Embodiment 1, Embodiments 3 to 6, the secondary battery 100 satisfies 0.1 mm ≤ H1 ≤ 0.6 mm. Compared with Embodiment 2, in the secondary batteries 100 of Embodiment 1, Embodiments 3 to 6, the breakage rate of the first protective layer 11 after long cycling is reduced, the number of secondary batteries 100 with liquid leakage at the corner positions of the housing 10 adjacent to the first edge 201 is smaller, the swelling rate is lower, and the passing rate of the drop test is higher. It can be seen that by setting H1 ≥ 0.1 mm, the thickness of the first adhesive layer 30 is not too small, which is beneficial to improving the effect of the first adhesive layer 30 in preventing the first electrode sheet 21 from piercing the first protective layer 11, and reducing the risk of shrinkage of the corner isolation film 23 during the drop test; compared with Embodiment 7, in the secondary batteries 100 of Embodiment 1, Embodiments 3 to 6, the number of secondary batteries 100 with lithium deposition on the negative electrode sheet 25 adjacent to the first edge 201 after long cycling is smaller. It can be seen that by setting H1 ≤ 0.6 mm, the thickness of the first adhesive layer 30 is not too large, which is beneficial to reducing the possibility of the housing 10 squeezing the electrode assembly 20, so as to reduce lithium deposition at the corresponding position.

[0190] In Embodiment 1, Embodiments 4 and 5, the secondary battery 100 satisfies 0.2 mm ≤ H1 ≤ 0.4 mm. Compared with Embodiment 3, in the secondary batteries 100 of Embodiment 1, Embodiments 4 and 5, the breakage rate of the first protective layer 11 after long cycling is further reduced, the number of secondary batteries 100 with liquid leakage at the corner positions of the housing 10 adjacent to the first edge 201 is further reduced, the swelling rate is further reduced, and the passing rate of the drop test is further increased. By setting H1 ≥ 0.2 mm, it is beneficial to further improve the effect of the first adhesive layer 30 in preventing the first electrode sheet 21 from piercing the first protective layer 11, and increasing the passing rate of the drop test; compared with Embodiment 6, the number of lithium deposition in the secondary batteries 100 of Embodiment 1, Embodiments 4 and 5 is further reduced. It can be seen that by setting H1 ≤ 0.4 mm, it is beneficial to further reduce the possibility of the housing 10 squeezing the electrode assembly 20, so as to reduce lithium deposition.

[0191] In Embodiment 1, Embodiments 9 to 14, the secondary battery 100 satisfies 0.1 mm ≤ L1 ≤ 2 mm. Compared with Embodiment 8, in the secondary batteries 100 of Embodiment 1, Embodiments 9 to 14, the breakage rate of the first protective layer 11 after long cycling decreases, the number of secondary batteries 100 with liquid leakage at the corner positions of the housing 10 adjacent to the first edge 201 is smaller, the swelling rate is lower, and the passing rate of the drop test is higher. It can be seen that by setting L1 ≥ 0.1 mm, the length of the first adhesive layer 30 covering the first edge 211 is not too short, which is beneficial to improving the bonding stability between the first adhesive layer 30 and the first electrode sheet 21, reducing the risk of the first adhesive layer 30 falling off, and at the same time being beneficial to reducing the risk of the corner separator film 23 shrinking during the drop test; compared with Embodiment 15, the number of secondary batteries 100 with lithium plating in Embodiment 1, Embodiments 9 to 14 is smaller. It can be seen that by setting L1 ≤ 2 mm, the length of the first adhesive layer 30 covering the first edge 211 is not too long, which is beneficial to improving the wetting effect of the electrolyte on the first electrode sheet 21 and reducing the risk of lithium plating at the corner positions of the first electrode sheet 21.

[0192] In Embodiment 1, Embodiments 10 to 13, the secondary battery 100 satisfies 0.4 mm ≤ L1 ≤ 1.6 mm. Compared with Embodiment 9, in the secondary batteries 100 of Embodiment 1, Embodiments 10 to 13, the breakage rate of the first protective layer 11 during long cycling decreases, the number of secondary batteries 100 with liquid leakage at the corner positions of the housing 10 adjacent to the first edge 201 further decreases, the swelling rate further decreases, and the passing rate of the drop test further increases. It can be seen that by setting L1 ≥ 0.4 mm, it is beneficial to further reduce the risk of the first adhesive layer 30 falling off and the risk of the separator film 23 at the corner position where the first edge 201 is located shrinking during the drop; compared with Embodiment 14, the number of secondary batteries 100 with lithium plating in Embodiment 1, Embodiments 10 to 13 further decreases. It can be seen that by setting L1 ≤ 1.6 mm, it is beneficial to further improve the wetting effect of the electrolyte on the first electrode sheet 21 and reduce the risk of lithium plating at the corner positions of the first electrode sheet 21.

[0193] In Embodiment 1, Embodiment 11, and Embodiment 12, the secondary battery 100 satisfies 0.6 mm ≤ L1 ≤ 1.0 mm. Compared with Embodiment 10, for the secondary batteries 100 in Embodiment 1, Embodiment 11, and Embodiment 12, the breakage rate of the first protective layer 11 after long-term cycling decreases, the number of secondary batteries 100 with liquid leakage at the corner position of the housing 10 adjacent to the first edge 201 further decreases, the swelling rate further decreases, and the passing rate of the drop test further increases. It can be seen that setting L1 ≥ 0.6 mm is beneficial to further reducing the risk of the first adhesive layer 30 peeling off and reducing the risk of the separator 23 at the corner position where the first edge 201 is located shrinking during dropping. Compared with Embodiment 13, the number of secondary batteries 100 with lithium plating in Embodiment 1, Embodiment 11, and Embodiment 12 further decreases. It can be seen that setting L1 ≤ 1.0 mm is beneficial to further improving the wetting effect of the electrolyte on the first electrode sheet 21 and reducing the risk of lithium plating at the corner position of the first electrode sheet 21.

[0194] In Embodiment 1, Embodiment 17 to Embodiment 20, the secondary battery 100 satisfies 0.1 mm ≤ H2 ≤ 0.4 mm. Compared with Embodiment 16, for the secondary batteries 100 in Embodiment 1, Embodiment 17 to Embodiment 20, the breakage rate of the first protective layer 11 after long-term cycling decreases, the number of secondary batteries 100 with liquid leakage at the corner position of the housing 10 adjacent to the first edge 201 is smaller, the swelling rate is lower, and the passing rate of the drop test is higher. It can be seen that setting H2 ≥ 0.1 mm ensures that the thickness of the first adhesive layer 30 is not too small, which is beneficial to improving the effect of the first adhesive layer 30 in preventing the first electrode sheet 21 from piercing the first protective layer 11 and reducing the risk of the separator 23 at the corner position where the first edge 201 is located shrinking during dropping. Compared with Embodiment 21, the number of secondary batteries 100 with lithium plating in Embodiment 1, Embodiment 17 to Embodiment 20 is smaller. It can be seen that setting H2 ≤ 0.4 mm ensures that the thickness of the first adhesive layer 30 is not too large, which is beneficial to reducing the possibility of the housing 10 squeezing the electrode assembly 20 and reducing the risk of lithium plating at the corner position of the first electrode sheet 21.

[0195] In Embodiment 1, Embodiment 18, and Embodiment 19, the secondary battery 100 satisfies 0.15 mm ≤ H2 ≤ 0.3 mm. Compared with Embodiment 17, the probability of the first protective layer 11 being damaged after long cycling of the secondary battery 100 in Embodiment 1, Embodiment 18, and Embodiment 19 is further reduced, the number of secondary batteries 100 with liquid leakage is further reduced, the swelling rate is further reduced, and the passing rate of the drop test is further increased. Setting H2 ≥ 0.15 mm is beneficial to further improving the effect of the first adhesive layer 30 in preventing the first electrode sheet 21 from piercing the first protective layer 11, and reducing the risk of the separator 23 at the corner where the first edge 201 is located from shrinking during the drop process. Compared with Embodiment 20, the number of lithium deposition occurrences in the secondary battery 100 in Embodiment 1, Embodiment 18, and Embodiment 19 is further reduced. It can be seen that setting H2 ≤ 0.3 mm is beneficial to further reducing the possibility of the housing 10 squeezing the electrode assembly 20, so as to reduce the risk of lithium deposition at the corner of the first electrode sheet 21.

[0196] In Embodiment 1, Embodiment 23, and Embodiment 24, the secondary battery 100 satisfies 150 μm ≤ H3 ≤ 210 μm. Compared with Embodiment 22, for the secondary batteries 100 in Embodiment 1, Embodiment 23, and Embodiment 24, the breakage rate of the first protective layer 11 after long-term cycling is reduced, the number of secondary batteries 100 with liquid leakage at the corner position of the housing 10 adjacent to the first edge 201 is smaller, the swelling rate is lower, and the passing rate of the drop test is higher. It can be seen that setting H3 ≥ 150 μm ensures that the thickness of the first overlapping portion 31 along the first direction X is not too small, which is beneficial to improving the effect of the first adhesive layer 30 in preventing the first electrode sheet 21 from piercing the first protective layer 11, and is also beneficial to improving the bonding strength between the first adhesive layer 30 and the first electrode sheet 21, reducing the risk of shrinkage of the separator 23 at the corner position where the first edge 201 is located during the drop process. Compared with Embodiment 25, the average volume energy density of the secondary batteries 100 in Embodiment 1, Embodiment 23, and Embodiment 24 is higher. The reason is that when the value of H3 increases to a certain extent, the thickness of the first overlapping portion 31 exceeds the total thickness of the two second electrode sheets 22 adjacent to the first electrode sheet 21 and the separator 23 between the first electrode sheet 21 and the second electrode sheet 22, resulting in an increase in the total thickness of the electrode assembly 20 due to the overly thick first overlapping portion 31 and causing a loss of volume energy density. In addition, as H3 increases, the lithium deposition condition at the corner of the first electrode sheet 21 corresponding to the first edge 201 gradually deteriorates. This is because the increase in the thickness of the first overlapping portion 31 makes it increasingly difficult for the electrolyte to infiltrate at the corner of the first electrode sheet 21, leading to the deterioration of the lithium deposition degree at the corner of the first electrode sheet 21 due to poor electrolyte infiltration. It can be seen that setting H3 ≤ 210 μm ensures that the thickness of the first overlapping portion 31 is not too large, which is beneficial to reducing the impact of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20 and reducing the risk of lithium deposition at the corner of the first electrode sheet 21.

[0197] In Embodiment 1, Embodiments 27 to 32, the secondary battery 100 satisfies 0.1 mm ≤ L2 ≤ 2 mm. Compared with Embodiment 26, the secondary batteries 100 in Embodiment 1, Embodiments 27 to 32 have a lower breakage rate of the first protective layer 11 after long-term cycling, a smaller number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201, a lower swelling rate, and a higher passing rate in the drop test. It can be seen that setting L2 ≥ 0.1 mm ensures that the length of the first overlapping portion 31 is not too small, which is beneficial to improving the effect of the first adhesive layer 30 in preventing the first electrode tab 21 from piercing the first protective layer 11, and is also beneficial to improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21, reducing the risk of shrinkage of the separator 23 at the corner where the first edge 201 is located during dropping. Compared with Embodiment 33, the secondary batteries 100 in Embodiment 1, Embodiments 27 to 32 have a higher average volume energy density. It can be seen that setting L2 ≤ 2 mm ensures that the length of the first overlapping portion 31 is not too large, which is beneficial to reducing the possibility of the first overlapping portion 31 overlapping with the second electrode tab 22, thereby reducing the impact of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20. At the same time, Embodiment 1, Embodiments 27 to 32 have a lower lithium plating rate compared with Embodiment 33. It can be seen that setting L2 ≤ 2 mm ensures that the length of the first overlapping portion 31 is not too large, which is beneficial to reducing the impact of the setting of the first overlapping portion 31 on electrolyte infiltration, thereby reducing the risk of lithium plating at the corner of the first electrode tab 21.

[0198] In Embodiment 1, Embodiments 28 to 31, the secondary battery 100 satisfies 0.4 mm ≤ L2 ≤ 1.6 mm. Compared with Embodiment 27, the probability of breakage of the first protective layer 11 in the secondary batteries 100 in Embodiment 1, Embodiments 28 to 31 is further reduced after long-term cycling, the number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201 is further reduced, the swelling rate is further reduced, and the passing rate in the drop test is further increased. It can be seen that setting L2 ≥ 0.4 mm is beneficial to further improving the effect of the first adhesive layer 30 in preventing the first electrode tab 21 from piercing the first protective layer 11, and is also beneficial to further improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21. Compared with Embodiment 32, the average volume energy density of the secondary batteries 100 in Embodiment 1, Embodiments 28 to 31 is further increased, and the lithium plating rate is further reduced. It can be seen that setting L2 ≤ 1.6 mm is beneficial to further reducing the possibility of the first overlapping portion 31 overlapping with the second electrode tab 22, thereby reducing the impact of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20, and further reducing the impact of the setting of the first overlapping portion 31 on electrolyte infiltration.

[0199] In Embodiment 1, Embodiment 29, and Embodiment 30, the secondary battery 100 satisfies 0.6 mm ≤ L2 ≤ 1.0 mm. Compared with Embodiment 28, the probability of the first protective layer 11 being damaged after long cycling of the secondary battery 100 in Embodiment 1, Embodiment 29, and Embodiment 30 is further reduced, the number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201 is further reduced, the swelling rate is further reduced, and the passing rate of the drop test is further increased. It can be seen that setting L2 ≥ 0.6 mm is beneficial to further improving the effect of the first adhesive layer 30 in preventing the first electrode tab 21 from piercing the first protective layer 11, and is beneficial to further improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21; compared with Embodiment 31, the average volume energy density of the secondary battery 100 in Embodiment 1, Embodiment 29, and Embodiment 30 is further increased, and the lithium plating rate is further reduced. It can be seen that setting L2 ≤ 1.0 mm is beneficial to further reducing the possibility of the first overlapping portion 31 and the second electrode tab 22 being stacked, thereby reducing the influence of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20, and further reducing the influence of the setting of the first overlapping portion 31 on the electrolyte infiltration.

[0200] In Embodiment 1, Embodiment 35, and Embodiment 36, the secondary battery 100 satisfies 60 μm ≤ H4 ≤ 130 μm. Compared with Embodiment 34, the damage rate of the first protective layer 11 of the secondary battery 100 in Embodiment 1, Embodiment 35, and Embodiment 36 after long cycling is lower, the number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201 is smaller, the swelling rate is lower, and the passing rate of the drop test is higher. It can be seen that setting H4 ≥ 60 μm, the thickness of the second overlapping portion 32 is not too small, which is beneficial to improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21 and reducing the possibility of the first adhesive layer 30 falling off; compared with Embodiment 37, the average volume energy density of the secondary battery 100 in Embodiment 1, Embodiment 35, and Embodiment 36 is higher. The reason is that when the value of H4 increases beyond the thickness of the outermost second electrode tab 22, the overall thickness of the electrode assembly 20 increases, resulting in a loss of the volume energy density of the secondary battery 100. It can be seen that setting H4 ≤ 130 μm, the thickness of the second overlapping portion 32 is not too large, which is beneficial to reducing the influence of the setting of the first overlapping portion 31 on the thickness of the electrode assembly 20.

[0201] In Embodiment 1, Embodiment 39 to Embodiment 44, the secondary battery 100 satisfies 0.1 mm ≤ L3 ≤ 2 mm. Compared with Embodiment 38, in the secondary batteries 100 of Embodiment 1, Embodiment 39 to Embodiment 44, the probability of the first protective layer 11 being damaged after long cycling is reduced, the number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201 is smaller, the swelling rate is lower, and the passing rate of the drop test is higher. It can be seen that by setting L3 ≥ 0.1 mm, the maximum length of the second overlapping portion 32 along the second direction Y is not too small, which is beneficial to improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21, reducing the risk of the first adhesive layer 30 peeling off, and at the same time reducing the risk of the separator 23 at the corner of the first electrode tab 21 shrinking during the drop process; compared with Embodiment 45, the average volume energy density of the secondary batteries 100 of Embodiment 1, Embodiment 39 to Embodiment 44 is higher, and the lithium plating rate is reduced. It can be seen that by setting L3 ≤ 2 mm, the maximum length of the second overlapping portion 32 along the second direction Y is not too large, which is beneficial to reducing the possibility of the second overlapping portion 32 overlapping with the second electrode tab 22 and affecting the thickness of the electrode assembly 20, and at the same time reducing the poor electrolyte infiltration caused by too large L3.

[0202] In Embodiment 1, Embodiment 40 to Embodiment 43, the secondary battery 100 satisfies 0.4 mm ≤ L3 ≤ 1.6 mm. Compared with Embodiment 39, in the secondary batteries 100 of Embodiment 1, Embodiment 40 to Embodiment 43, the probability of the first protective layer 11 being damaged after long cycling is further reduced, the number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201 is further reduced, the swelling rate is further reduced, and the passing rate of the drop test is further improved. It can be seen that by setting L3 ≥ 0.4 mm, it is beneficial to further improve the bonding strength between the first adhesive layer 30 and the first electrode tab 21, reducing the risk of the first adhesive layer 30 peeling off, and at the same time reducing the risk of the separator 23 at the corner of the first electrode tab 21 shrinking during the drop process; compared with Embodiment 44, the average volume energy density of the secondary batteries 100 of Embodiment 1, Embodiment 40 to Embodiment 43 is further improved, and the lithium plating rate is further reduced. It can be seen that by setting L3 ≤ 1.6 mm, it is beneficial to further reduce the possibility of the second overlapping portion 32 overlapping with the second electrode tab 22 and affecting the thickness of the electrode assembly 20, and at the same time reducing the poor electrolyte infiltration caused by too large L3.

[0203] In Embodiment 1, Embodiment 41, and Embodiment 42, the secondary battery 100 satisfies 0.6 mm ≤ L3 ≤ 1.0 mm. Compared with Embodiment 40, the probability of the first protective layer 11 being damaged after long cycling of the secondary battery 100 in Embodiment 1, Embodiment 42, and Embodiment 43 is further reduced, the number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201 is further reduced, the swelling rate is further reduced, and the passing rate of the drop test is further increased. It can be seen that setting L3 ≥ 0.6 mm is beneficial to further improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21, reducing the risk of the first adhesive layer 30 peeling off, and at the same time reducing the risk of the separator 23 at the corner of the first electrode tab 21 shrinking during the drop process. Compared with Embodiment 43, the average volume energy density of the secondary battery 100 in Embodiment 1, Embodiment 41, and Embodiment 42 is further increased, and the lithium plating rate is further reduced. It can be seen that setting L3 ≤ 1.0 mm is beneficial to further reducing the possibility that the second overlapping portion 32 and the second electrode tab 22 are stacked to affect the thickness of the electrode assembly 20, and at the same time reducing the poor electrolyte infiltration caused by too large L3.

[0204] In Embodiment 1, Embodiment 47 to Embodiment 52, the secondary battery 100 satisfies 0.1 mm ≤ L4 ≤ 2 mm. Compared with Embodiment 46, the probability of the first protective layer 11 being damaged after long cycling of the secondary battery 100 in Embodiment 1, Embodiment 47 to Embodiment 52 is reduced, the number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201 is smaller, the swelling rate is lower, and the passing rate of the drop test is higher. It can be seen that setting L4 ≥ 0.1 mm, the maximum length of the second overlapping portion 32 along the third direction Z is not too small, which is beneficial to improving the bonding strength between the first adhesive layer 30 and the first electrode tab 21, reducing the risk of the first adhesive layer 30 peeling off, and at the same time reducing the risk of the separator 23 at the corner of the first electrode tab 21 shrinking during the drop process. Compared with Embodiment 53, the average volume energy density of the secondary battery 100 in Embodiment 1, Embodiment 47 to Embodiment 52 is higher, and the lithium plating rate is lower. It can be seen that setting L4 ≤ 2 mm, the maximum length of the second overlapping portion 32 along the third direction Z is not too large, which is beneficial to reducing the possibility that the second overlapping portion 32 and the second electrode tab 22 are stacked to affect the thickness of the electrode assembly 20, and at the same time reducing the poor electrolyte infiltration caused by too large L4.

[0205] In Embodiment 1, Embodiments 48 to 51, the secondary battery 100 satisfies 0.4 mm ≤ L4 ≤ 1.6 mm. Compared with Embodiment 47, in Embodiment 1, Embodiments 48 to 51, the probability of the first protective layer 11 being damaged after long cycling of the secondary battery 100 is further reduced, the number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201 is further reduced, the swelling rate is further reduced, and the passing rate of the drop test is further increased. It can be seen that setting L4 ≥ 0.4 mm is beneficial to further improve the bonding strength between the first adhesive layer 30 and the first electrode tab 21, reduce the risk of the first adhesive layer 30 peeling off, and at the same time reduce the risk of the separator 23 at the corner of the first electrode tab 21 shrinking during dropping; compared with Embodiment 44, in Embodiments 3, 41 to 43, the average volume energy density of the secondary battery 100 is further increased, and the lithium plating rate is further reduced. It can be seen that setting L4 ≤ 1.6 mm is beneficial to further reduce the possibility that the second overlapping portion 32 and the second electrode tab 22 are stacked to affect the thickness of the electrode assembly 20, and at the same time reduce the poor electrolyte infiltration caused by too large L4.

[0206] In Embodiment 1, Embodiments 49 and 50, the secondary battery 100 satisfies 0.6 mm ≤ L4 ≤ 1.0 mm. Compared with Embodiment 48, in Embodiment 1, Embodiments 49 and 50, the probability of the first protective layer 11 being damaged after long cycling of the secondary battery 100 is further reduced, the number of secondary batteries 100 with liquid leakage at the corner of the housing 10 adjacent to the first edge 201 is further reduced, the swelling rate is further reduced, and the passing rate of the drop test is further increased. It can be seen that setting L4 ≥ 0.6 mm is beneficial to further improve the bonding strength between the first adhesive layer 30 and the first electrode tab 21, reduce the risk of the first adhesive layer 30 peeling off, and at the same time reduce the risk of the separator 23 at the corner of the first electrode tab 21 shrinking during dropping; compared with Embodiment 51, in Embodiments 1, 49 and 50, the average volume energy density of the secondary battery 100 is further increased, and the lithium plating rate is further reduced. It can be seen that setting L4 ≤ 1.0 mm is beneficial to further reduce the possibility that the second overlapping portion 32 and the second electrode tab 22 are stacked to affect the thickness of the electrode assembly 20, and at the same time reduce the poor electrolyte infiltration caused by too large L4.

[0207] In Embodiment 54, the first adhesive layer 30 is disposed at the head of the secondary battery 100. Compared with Embodiment 1, the average volume energy density of the secondary battery 100 in Embodiment 54 is lower because the distance between the first electrode tab 21 and the first protective layer 11 at the head is mainly determined by the size of the tab 40. It can be seen that by disposing the first adhesive layer 30 at the tail of the secondary battery 100, the distance between the first electrode tab 21 and the first protective layer 11 can be reduced, enabling the secondary battery 100 to obtain greater benefits in terms of volume energy density.

[0208] In Example 55, the secondary battery 100 is provided with four first adhesive layers 30. Compared with Comparative Example 1 and Example 1, the probability of the first protective layer 11 being damaged in the secondary battery 100 in Example 55 is lower, the number of leaked liquids is less, the swelling rate is lower, and the passing rate of the drop test is higher. It can be seen that setting the first adhesive layer 30 on the first edge 201, the second edge 202, the third edge 203, and the fourth edge 204 is beneficial to further reduce the risk of the first electrode sheet 21 piercing the first protective layer 11 and reduce the risk of the separator 23 shrinking during the drop process; and compared with Comparative Example 1 and Example 1, the average volume energy density of the secondary battery 100 in Example 55 is higher. It can be seen that setting the first adhesive layer 30 at the four corner positions is beneficial to reducing the distance between the first protective layer 11 and the first electrode sheet 21 and is beneficial to improving the energy density of the secondary battery 100.

[0209] In Example 56, the secondary battery 100 is provided with four first adhesive layers 30, and based on this, the winding of the adhesive is cancelled. Compared with Comparative Example 2, the probability of the first protective layer 11 being damaged in the secondary battery 100 in Example 56 is lower, the number of leaked liquids is less, the swelling rate is lower, and the passing rate of the drop test is higher. It can be seen that setting the first adhesive layer 30 on the first edge 201, the second edge 202, the third edge 203, and the fourth edge 204 is beneficial to further reduce the risk of the first electrode sheet 21 piercing the first protective layer 11 and reduce the risk of the separator 23 shrinking during the drop process; compared with Example 55, using the first adhesive layer 30 to fix the separator 23, thereby cancelling the winding of the adhesive provided on the periphery of the electrode assembly 20, is beneficial to improving the energy density of the secondary battery 100.

[0210] Those of ordinary skill in the art of this technology should recognize that the above embodiments are only used to illustrate the present application and are not used 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: include: An electrode assembly, the electrode assembly comprising a plurality of first pole pieces, a plurality of second pole pieces and a separation film, the first pole pieces and the second pole pieces have opposite polarities, the first pole pieces and the second pole pieces are alternately stacked, and the separation film is provided between adjacent first pole pieces and second pole pieces; along a first direction, the orthographic projection of the second pole piece is located within the orthographic projection range of the first pole piece, and the first direction is the thickness direction of the electrode assembly; each of the first pole pieces comprises a first edge extending along the second direction, and a second edge extending along a third direction, and the first direction, the second direction and the third direction are perpendicular to each other; the intersection point of the first edge and the second edge of the same first pole piece is a first intersection point; Along the first direction, a plurality of the first intersection points are combined into a first edge; a shell, the shell comprising a first protective layer and a metal layer stacked along the first direction, the shell comprising a first space, the electrode assembly is accommodated in the first space; the first protective layer is located between the metal layer and the electrode assembly; A first adhesive layer, wherein the first adhesive layer covers the first edge.

2. The secondary battery according to claim 1, wherein: When viewed from the first direction, the distance from the first edge to the outer edge of the first adhesive layer away from the first pole piece is the thickness of the first adhesive layer. The maximum thickness of the first adhesive layer is H1, and 0.1 mm≤H1≤0.6 mm.

3. The secondary battery according to claim 2, characterized in that: 0.2mm≤H1≤0.4mm.

4. The secondary battery according to claim 1, wherein: The first adhesive layer covers a portion of at least one of the first edges.

5. The secondary battery according to claim 4, characterized in that: Along the second direction, the length of the first adhesive layer covering the first edge is L1, 0.1 mm≤L1≤2 mm.

6. The secondary battery according to claim 5, characterized in that: 0.4mm≤L1≤1.6mm.

7. The secondary battery according to claim 6, characterized in that: 0.6mm≤L1≤1.0mm.

8. The secondary battery according to claim 4, characterized in that: Along the third direction, the maximum thickness of the first adhesive layer is H2, 0.1 mm≤H2≤0.4 mm.

9. The secondary battery according to claim 8, characterized in that 0.15mm≤H2≤0.3mm.

10. The secondary battery according to claim 1 or 4, characterized in that: The first adhesive layer covers a portion of at least one of the second edges.

11. The secondary battery according to claim 1, wherein The isolation film covers the first adhesive layer and the first edge.

12. The secondary battery according to claim 4, characterized in that: The isolation film covers between the first adhesive layer and the first edge.

13. The secondary battery according to claim 12, characterized in that: Each of the first electrode sheets includes a first surface and a second surface arranged opposite to each other along the first direction, the first surface faces away from the interior of the electrode assembly, and the second surface faces the interior of the electrode assembly; the first adhesive layer includes a first overlapping portion, which is a portion where the first adhesive layer overlaps with at least one of the first surfaces or at least one of the second surfaces.

14. The secondary battery according to claim 13, characterized in that: Along the first direction, the maximum thickness of the first overlapping portion is H3, and along the third direction, the maximum length of the first overlapping portion is L2; ​​150 μm≤H3≤210 μm, 0.1 mm≤L2≤2 mm.

15. The secondary battery according to claim 14, characterized in that: 0.4mm≤L2≤1.6mm.

16. The secondary battery according to claim 15, characterized in that: 0.6mm≤L2≤1.0mm.

17. The secondary battery according to claim 1, wherein: Along the first direction, at least one end of the first adhesive layer exceeds the first edge.

18. The secondary battery according to claim 17, wherein: Along the first direction, the first electrode piece located at the outermost layer of the electrode assembly is a first outer electrode piece, and the first outer electrode piece includes an outer surface and an inner surface arranged opposite to each other along the first direction, and the outer surface faces away from the interior of the electrode assembly; the first glue layer includes a second overlapping portion, and the second overlapping portion is the portion where the first glue layer overlaps with the outer surface.

19. The secondary battery according to claim 18, wherein: The second pole piece located at the outermost layer of the electrode assembly is a second outer pole piece, the second outer pole piece is located at the outermost layer of the electrode assembly, and the first outer pole piece is located at the second outermost layer of the electrode assembly; Along the first direction, the maximum thickness of the second overlapping portion is H4, 60 μm≤H4≤130 μm; Along the second direction, the maximum length of the second overlapping portion is L3, 0.1 mm≤L3≤2 mm; along the third direction, the maximum length of the second overlapping portion is L4, 0.1 mm≤L4≤2 mm.

20. The secondary battery according to claim 19, wherein: The 0.4mm≤L3≤1.6mm; 0.4mm≤L4≤1.6mm.

21. The secondary battery according to claim 20, characterized in that: 0.6mm≤L3≤1.0mm; 0.6mm≤L4≤1.0mm.

22. The secondary battery according to claim 1, characterized in that: The secondary battery also includes a pole ear, one end of which is connected to the electrode assembly along the second direction, and the other end of the pole ear extends from the shell; each first pole piece also includes a third edge and a fourth edge, the third edge and the first edge are arranged opposite to each other along the third direction, and the fourth edge and the second edge are arranged opposite to each other along the second direction; the intersection of the second edge and the third edge of the same first pole piece is a second intersection, and along the first direction, multiple second intersections are combined into a second edge; the intersection of the first edge and the fourth edge of the same first pole piece is a third intersection, and along the first direction, multiple third intersections are combined into a third edge; the intersection of the third edge and the fourth edge of the same first pole piece is a fourth intersection, and along the first direction, multiple fourth intersections are combined into a fourth edge; along the second direction, the first edge is farther away from the pole ear than the third edge and the fourth edge.

23. The secondary battery according to claim 22, characterized in that: The first edge, the second edge, the third edge and the fourth edge are all covered with the first adhesive layer.

24. The secondary battery according to claim 1, characterized in that: The material of the first adhesive layer includes at least one of photosensitive adhesive and hot melt adhesive.

25. The secondary battery according to claim 1, characterized in that: The material of the first protective layer includes at least one of polyethylene, polypropylene, polymethyl methacrylate, polycarbonate, polyamide, polyethylene terephthalate, acrylonitrile-butadiene-styrene copolymer, polyoxymethylene or polyphenylene ether.

26. The secondary battery according to claim 1, characterized in that: The housing satisfies at least one of the following conditions: (1) Along the third direction, the distance from the surface of the first protective layer facing away from the metal layer to the first edge is 0.25 mm to 0.4 mm; (2) Along the second direction, the distance from the surface of the first protective layer facing away from the metal layer to the second edge is 0.25 mm to 0.4 mm; (3) Along the direction of the first edge pointing to the corner of the shell, the distance from the surface of the first protective layer facing away from the metal layer to the first edge is 0.3 mm to 0.6 mm.

27. The secondary battery according to claim 1, characterized in that: The first electrode sheet is a negative electrode sheet, and the first electrode sheet includes a first current collector and a first active material layer which are stacked, and the material of the first active material layer contains silicon.

28. The secondary battery according to claim 27, characterized in that Based on the mass of the first active material layer, the mass content of the silicon element is 4% to 90%.

29. An electrical equipment, characterized in that: Includes the secondary battery according to any one of claims 1 to 28.

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