Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and an electronic device. The secondary battery comprises a packaging bag, an electrode assembly and a tab, the electrode assembly comprises first pole pieces, second pole pieces and isolating membranes which are opposite in polarity, the multiple first pole pieces, the multiple isolating membranes and the multiple second pole pieces are alternately stacked in the first direction, and the first direction is the thickness direction of the electrode assembly; the electrode assembly is provided with a first corner position, a second corner position, a third corner position and a fourth corner position when being observed in the first direction, the first corner position is provided with a first notch part, the second corner position is provided with a second notch part, the third corner position is provided with a third notch part, and the fourth corner position is provided with a fourth notch part. The number of the tabs is four, the four tabs correspond to the first notch part, the second notch part, the third notch part and the fourth notch part in a one-to-one mode, one end of each tab is connected with the pole piece, the other end of each tab extends out of the packaging bag from the corresponding notch part in the second direction, and the second direction is perpendicular to the first direction. The possibility that the isolating membrane shrinks inwards can be reduced.

Description

Technical Field

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

[0002] At present, the separator in a secondary battery is usually in a stretched state and has a tendency to shrink, and the adhesion between the separator and the electrode plate is weak. When the secondary battery is impacted, the separator may overcome the adhesion with the electrode plate and shrink inward. The inward shrinkage of the separator may cause the positive electrode plate and the negative electrode plate to short-circuit, resulting in the failure of the secondary battery and triggering safety risks. 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 separator shrinking inward.

[0004] A first aspect of an embodiment of this application provides a secondary battery, which includes a packaging bag, an electrode assembly, and electrode tabs. The electrode assembly is received in the packaging bag. The electrode assembly includes electrode plates and a separator. The electrode plates include a first electrode plate and a second electrode plate with opposite polarities. A plurality of first electrode plates, the separator, and a plurality of second electrode plates are alternately stacked along a first direction, and the first direction is the thickness direction of the electrode assembly; when observing along the first direction, the electrode assembly has a first angular position, a second angular position, a third angular position, and a fourth angular position. The electrode assembly further includes notch portions, and the notch portions include a first notch portion, a second notch portion, a third notch portion, and a fourth notch portion. The first notch portion is provided at the first angular position, the second notch portion is provided at the second angular position, the third notch portion is provided at the third angular position, and the fourth notch portion is provided at the fourth angular position. There are four electrode tabs, and the four electrode tabs are arranged in one-to-one correspondence with the first notch portion, the second notch portion, the third notch portion, and the fourth notch portion. One end of the electrode tab is connected to the electrode plate, and the other end of the electrode tab extends out of the packaging bag from the notch portion along a second direction, and the second direction is perpendicular to the first direction.

[0005] In this secondary battery, the electrode assembly is connected with four electrode tabs, and all four electrode tabs are connected to the packaging bag, which is beneficial to making the stress on the electrode assembly uniform. When the secondary battery is impacted (such as dropped), the degree of stress concentration generated by the electrode assembly can be reduced, thereby reducing the possibility of the separator overcoming the adhesion between it and the electrode plate and shrinking inward.

[0006] In one or more embodiments of the present application, the first electrode tab includes a first current collector and a first active material layer stacked along a first direction. The first current collector includes a first coating portion, a first connection portion, and a second connection portion, and the first active material layer is disposed on the first coating portion. The second electrode tab includes a second current collector and a second active material layer stacked along the first direction. The second current collector includes a second coating portion, a third connection portion, and a fourth connection portion, and the second active material layer is disposed on the second coating portion. When observed along the first direction, a first notch is provided at a corner position of the second current collector, and a plurality of first notches at least partially overlap in the first direction. The plurality of first notches together form a first notch portion. The first connection portion extends beyond the second current collector and is exposed from the first notch portion. A part of the separator is sandwiched between the plurality of first connection portions. When observed along the first direction, a second notch is provided at another corner position of the second current collector, and a plurality of second notches at least partially overlap in the first direction. The plurality of second notches together form a second notch portion. The second connection portion extends beyond the second current collector and is exposed from the second notch portion. A part of the separator is sandwiched between the plurality of second connection portions. When observed along the first direction, a third notch is provided at a corner position of the first current collector, and a plurality of third notches at least partially overlap in the first direction. The plurality of third notches together form a third notch portion. The third connection portion extends beyond the first current collector and is exposed from the third notch portion. A part of the separator is sandwiched between the plurality of third connection portions. When observed along the first direction, a fourth notch is provided at another corner position of the first current collector, and a plurality of fourth notches at least partially overlap in the first direction. The plurality of fourth notches together form a fourth notch portion. The fourth connection portion extends beyond the first current collector and is exposed from the fourth notch portion. A part of the separator is sandwiched between the plurality of fourth connection portions. The plurality of first connection portions converge into a first connection bundle along the first direction, the plurality of second connection portions converge into a second connection bundle along the first direction, the plurality of third connection portions converge into a third connection bundle along the first direction, and the fourth connection portion converges into a fourth connection bundle along the first direction. The electrode tabs include a first electrode tab, a second electrode tab, a third electrode tab, and a fourth electrode tab. One end of the first electrode tab is connected to the first connection bundle, one end of the second electrode tab is connected to the second connection bundle, one end of the third electrode tab is connected to the third connection bundle, and one end of the fourth electrode tab is connected to the fourth connection bundle.

[0007] In one or more embodiments of the present application, the separator includes an extension portion, and the extension portion is the part of the separator sandwiched between the first connection portions, the second connection portions, the third connection portions, and the fourth connection portions. The extension portion includes a first extension portion and a second extension portion. At the first notch portion and the second notch portion, the first extension portion is the part extending beyond the second current collector along a second direction, and the second extension portion is the part extending beyond the second current collector along a third direction. At the third notch portion and the fourth notch portion, the first extension portion is the part extending beyond the first current collector along the second direction, and the second extension portion is the part extending beyond the first current collector along the third direction. The third direction is perpendicular to the first direction and the second direction pairwise.

[0008] In one or more embodiments of the present application, along the second direction, the width of the first extension portion is W 1 , 0.5 mm ≤ W 1 ≤ 1 mm. By setting W 1 ≥ 0.5 mm, the width of the first extension portion is not too small, which is conducive to leaving a margin for the inward contraction of the separator, so that the first electrode tab and the second electrode tab remain insulated; by setting W 1 ≤ 1 mm, the width of the first extension portion is not too large, which is conducive to reducing the possibility that the separator interferes with the connection between the electrode tabs and the connection between the electrode tab and the tab.

[0009] In one or more embodiments of the present application, 0.5 mm ≤ W 1 ≤ 0.7 mm. By setting W 1 ≤ 0.7 mm, it is conducive to further reducing the possibility that the separator interferes with the connection between the electrode tabs and the connection between the electrode tab and the tab.

[0010] In one or more embodiments of the present application, along the third direction, the width of the second extension portion is W 2 , 0.5 mm ≤ W 2 ≤ 1 mm. By setting W 2 ≥ 0.5 mm, the width of the second extension portion is not too small, which is conducive to leaving a margin for the inward contraction of the separator, so that the first electrode tab and the second electrode tab remain insulated; by setting W 2 ≤ 1 mm, the width of the second extension portion is not too large, which is conducive to reducing the possibility that the separator interferes with the connection between the electrode tabs and the connection between the electrode tab and the tab.

[0011] In one or more embodiments of the present application, 0.5 mm ≤ W 2 ≤ 0.7 mm. By setting W 2 ≤ 0.7 mm, it is conducive to further reducing the possibility that the separator interferes with the connection between the electrode tabs and the connection between the electrode tab and the tab.

[0012] In one or more embodiments of the present application, one of the first electrode tabs is an outer electrode tab, the outer electrode tab is located at the outermost layer of the electrode assembly, the first current collector of the outer electrode tab includes a first surface and a second surface oppositely arranged along the first direction, the first surface is the surface facing the inside of the electrode assembly, and the first active material layer of the outer electrode tab is provided on the first surface. The outer electrode tab further includes a strengthening layer, the strengthening layer is provided on the second surface, and when observed along the first direction, the first current collector has a plurality of vertices, and the strengthening layer covers at least one vertex. By providing the strengthening layer, it is conducive to reducing the possibility of the current collector warping, so as to maintain the connection between the separator and the electrode tab.

[0013] In one or more embodiments of the present application, the reinforcing layer comprises a ceramic material, and the ceramic material comprises at least one of alumina, zirconia, titanium oxide, silicon oxide, and boehmite.

[0014] In one or more embodiments of the present application, the thickness of the reinforcing layer is T 1 , 5μm ≤ T 1 ≤ 10μm. Setting T 1 ≥ 5μm, the thickness of the reinforcing layer is not too small, which is beneficial to improving its effect of suppressing the warping of the current collector; setting T 1 ≤ 10μm, the thickness of the reinforcing layer is not too large, which is beneficial to reducing the influence of its setting on the energy density of the secondary battery.

[0015] In one or more embodiments of the present application, when observed along the first direction, the first tab and the second tab are diagonally arranged, and the third tab and the fourth tab are diagonally arranged. Diagonally arranging the tabs with the same polarity is beneficial to improving the uniformity of the current density of the electrode sheet, thereby improving the uniformity of the temperature distribution at different positions of the electrode sheet and reducing the possibility of the shrinkage of the separator due to temperature concentration.

[0016] In one or more embodiments of the present application, the first electrode sheet is a positive electrode sheet, the second electrode sheet is a negative electrode sheet, and the material of the first tab and / or the second tab comprises aluminum; the material of the third tab and / or the fourth tab comprises nickel-plated copper.

[0017] In one or more embodiments of the present application, when observed along the first direction, the electrode assembly comprises a first edge and a second edge that are oppositely arranged along the second direction, and a third edge and a fourth edge that are oppositely arranged along the third direction, and the third direction is perpendicular to the first direction and the second direction pairwise. The packaging bag has a receiving space, the electrode assembly is arranged in the receiving space, and the packaging bag comprises a packaging wall that encloses the receiving space; the packaging wall comprises a first packaging wall and a second packaging wall that are oppositely arranged along the second direction, and the first packaging wall is closer to the first edge than the second packaging wall; and a third packaging wall and a fourth packaging wall that are oppositely arranged along the third direction, and the third packaging wall is closer to the third edge than the fourth packaging wall. Thus, the outer shape of the packaging bag is adapted to the outer shape of the electrode assembly, which is beneficial to improving the energy density of the secondary battery.

[0018] In one or more embodiments of the present application, along the second direction, the distance between the first packaging wall and the first edge, and the distance between the second packaging wall and the second edge are W 3 , 0.3mm ≤ W 3 ≤ 0.8mm. Setting W 3≥0.3 mm. The distances between the first encapsulation wall and the first edge and between the second encapsulation wall and the second edge are not too small. On the one hand, it is convenient to load the electrode assembly into the packaging bag. On the other hand, it reduces the possibility of interference between the electrode assembly and the packaging bag, so as to reduce the risk of the packaging bag being damaged and leaking liquid and the deformation of the electrode assembly; set W 3 ≤0.8 mm. The distances between the first encapsulation wall and the first edge and between the second encapsulation wall and the second edge are not too large, which is beneficial to improving the heat transfer efficiency, reducing the accumulation of heat generated by the electrode assembly in the packaging bag, and further reducing the possibility of the separator film undergoing thermal shrinkage.

[0019] In one or more embodiments of the present application, 0.3 mm ≤ W 3 ≤0.5 mm. Setting W 3 ≤0.5 mm is beneficial to further improving the heat transfer efficiency to further reduce the possibility of the separator film undergoing thermal shrinkage.

[0020] In one or more embodiments of the present application, along the third direction, the distances between the third encapsulation wall and the third edge and between the fourth encapsulation wall and the fourth edge are W 4 ,0.3 mm ≤ W 4 ≤0.8 mm. Setting W 4 ≥0.3 mm. The distances between the third encapsulation wall and the third edge and between the fourth encapsulation wall and the fourth edge are not too small. On the one hand, it is convenient to load the electrode assembly into the packaging bag. On the other hand, it reduces the possibility of interference between the electrode assembly and the packaging bag, so as to reduce the risk of the packaging bag being damaged and leaking liquid and the deformation of the electrode assembly; set W 4 ≤0.8 mm. The distances between the third encapsulation wall and the third edge and between the fourth encapsulation wall and the fourth edge are not too large, which is beneficial to improving the heat transfer efficiency, reducing the accumulation of heat generated by the electrode assembly in the packaging bag, and further reducing the possibility of the separator film undergoing thermal shrinkage.

[0021] In one or more embodiments of the present application, 0.3 mm ≤ W 4 ≤0.5 mm. Setting W 4 ≤0.5 mm is beneficial to further improving the heat transfer efficiency to further reduce the possibility of the separator film undergoing thermal shrinkage.

[0022] In one or more embodiments of the present application, the separator membrane includes a substrate layer, a ceramic layer, and an adhesive layer. The material of the substrate layer includes at least one of polyethylene, polypropylene, polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, polyparaphenylene terephthalamide, polyarylethersulfoneketone, aramid, or arsulfonamide. The material of the ceramic layer includes at least one of alumina, silica, titanium dioxide, zirconia, barium titanate, and boehmite. The material of the adhesive layer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer, polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, or acrylate. The setting of the ceramic layer is beneficial to improving the thermal stability of the separator membrane and reducing the risk of shrinkage of the separator membrane; the setting of the adhesive layer is beneficial to improving the adhesion between the separator membrane and the electrode tab and reducing the risk of shrinkage of the separator membrane.

[0023] In one or more embodiments of the present application, the thickness of the ceramic layer is T 2 , 1.5μm ≤ T 2 ≤ 3μm. Setting T 2 ≥ 1.5μm, the thickness of the ceramic layer is not too small, which is beneficial to improving the thermal stability of the separator membrane; setting T 2 ≤ 3μm, the thickness of the ceramic layer is not too thick, which is beneficial to improving the energy density of the secondary battery.

[0024] In one or more embodiments of the present application, the thickness of the adhesive layer is T 3 , 0.5μm ≤ T 3 ≤ 3μm. Setting T 3 ≥ 0.5μm, the thickness of the adhesive layer is not too small, which is beneficial to improving the adhesion between the separator membrane and the electrode tab; setting T 3 ≤ 3μm, the thickness of the adhesive layer is not too thick, which is beneficial to improving the energy density of the secondary battery.

[0025] The second aspect of the embodiments of the present application provides an electronic device, which includes a secondary battery as described in any one of the foregoing embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the overall structure of a secondary battery in an embodiment of the present application.

[0027] Figure 2 is a schematic diagram of a partial structure of a secondary battery in an embodiment of the present application.

[0028] Figure 3 is a schematic diagram of the connection structure between an electrode assembly and an electrode tab in an embodiment of the present application.

[0029] Figure 4 is Figure 3Schematic diagram of the sectional structure at IV-IV

[0030] Figure 5 It is a schematic diagram of the structure of the outer electrode tab in an embodiment of the present application.

[0031] Figure 6 It is a schematic diagram of the structure of the first electrode tab in an embodiment of the present application.

[0032] Figure 7 It is a schematic diagram of the structure of the second electrode tab in an embodiment of the present application.

[0033] Figure 8 It is a schematic diagram of the structure of the first electrode tab and the second electrode tab in a stacked state in an embodiment of the present application.

[0034] Figure 9 It is Figure 2 Schematic diagram of the structure at VIII

[0035] Figure 10 It is a schematic diagram of the structure of the separator in an embodiment of the present application.

[0036] Figure 11 It is a schematic diagram of the structure of the separator and the first electrode tab in a stacked state in an embodiment of the present application.

[0037] Figure 12 It is a schematic diagram of the structure of the separator and the second electrode tab in a stacked state in an embodiment of the present application.

[0038] Figure 13 It is a schematic diagram of a partial structure of a secondary battery in an embodiment of the present application.

[0039] Figure 14 It is Figure 10 Schematic diagram of the sectional structure at XIV-XIV

[0040] Figure 15 It is a schematic diagram of the structure of an electronic device in an embodiment of the present application.

[0041] Description of main element symbols

[0042] Secondary battery 100

[0043] Packaging bag 10

[0044] First housing 11

[0045] Second housing 12

[0046] Sealing edge part 13

[0047] First encapsulation wall 10a

[0048] The second encapsulation wall 10b

[0049] The third encapsulation wall 10c

[0050] The fourth encapsulation wall 10d

[0051] The electrode assembly 20

[0052] The first pole piece 21

[0053] The first current collector 211

[0054] The first surface 211a

[0055] The second surface 211b

[0056] The first coating part 2111

[0057] The first connection part 2112

[0058] The first connection bundle 21121

[0059] The second connection part 2113

[0060] The second connection bundle 21131

[0061] The third notch 2114

[0062] The fourth notch 2115

[0063] The first active material layer 212

[0064] The outer pole piece 213

[0065] The strengthening layer 2131

[0066] The second pole piece 22

[0067] The second current collector 221

[0068] The second coating part 2211

[0069] The third connection part 2212

[0070] The third connection bundle 22121

[0071] The fourth connection part 2213

[0072] The fourth connection bundle 22131

[0073] The first notch 2214

[0074] The second notch 2215

[0075] The second active material layer 222

[0076] The separator 23

[0077] Extension part 231

[0078] First extension part 2311

[0079] Second extension part 2312

[0080] Boundary line 231a

[0081] Base material layer 231

[0082] Ceramic layer 232

[0083] Adhesive layer 233

[0084] Notch part 24

[0085] First notch part 241

[0086] Second notch part 242

[0087] Third notch part 243

[0088] Fourth notch part 244

[0089] First edge 20a

[0090] Second edge 20b

[0091] Third edge 20c

[0092] Fourth edge 20d

[0093] Tab 30

[0094] Tab body 31

[0095] Tab adhesive 32

[0096] First tab 301

[0097] Second tab 302

[0098] Third tab 303

[0099] Fourth tab 304

[0100] Electronic device 200

[0101] First direction X

[0102] Second direction Y

[0103] Third direction Z

[0104] The following specific embodiments will further illustrate the present application in conjunction with the above drawings. Specific embodiments

[0105] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0106] 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. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0107] 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 this application in this specification are only for the purpose of describing specific embodiments, and are not intended to limit this application.

[0108] 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, the meaning of "a plurality of" is more than two, unless otherwise specifically defined.

[0109] 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 two components. The two components described as "vertical" may not be absolutely 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 as "straight lines" or "planes".

[0110] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears 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.

[0111] A first aspect of an embodiment of the present application provides a secondary battery, which includes a packaging bag, an electrode assembly, and a tab. The electrode assembly is received in the packaging bag. The electrode assembly includes electrode plates and a separator. The electrode plates include a first electrode plate and a second electrode plate with opposite polarities. A plurality of first electrode plates, the separator, and a plurality of second electrode plates are alternately stacked in a first direction, and the first direction is the thickness direction of the electrode assembly. When observing in the first direction, the electrode assembly has four corner positions, and notch portions are provided at all four corner positions. The tabs are connected to the packaging bag. There are four tabs, and the tabs are arranged corresponding to the notch portions. One end of the tab is connected to the electrode plate, and the other end of the tab extends out of the packaging bag from the notch portion in a second direction, and the second direction is perpendicular to the first direction.

[0112] In this secondary battery, four tabs are connected to the electrode assembly, and all four tabs are connected to the packaging bag, which is beneficial to making the stress on the electrode assembly uniform. When the secondary battery is impacted (such as dropping), the degree of stress concentration generated in the electrode assembly can be reduced, thereby reducing the possibility that the separator shrinks inward by overcoming the adhesion force between it and the electrode plate.

[0113] The following further describes the embodiments of the present application with reference to the drawings. In the drawings, a spatial rectangular coordinate system is established with the thickness direction of the secondary battery as the first direction, the direction in which the tab extends out of the packaging bag as the second direction, and the direction perpendicular to the first direction and the second direction as the third direction.

[0114] As Figures 1 to 3 shown, an embodiment of the present application provides a secondary battery 100, which includes a packaging bag 10, an electrode assembly 20, an electrolyte, and tabs 30. The electrode assembly 20 and the electrolyte are both received in the packaging bag 10. The electrode assembly 20 is used to store or release electrical energy, and the electrolyte is used to conduct ions. The tabs 30 are connected to the electrode assembly 20, and part of the tabs 30 extends out of the packaging bag 10 to facilitate connecting the electrode assembly 20 to an external device. The tabs 30 are also connected to the packaging bag 10. In some embodiments, the packaging bag 10 is an aluminum-plastic film.

[0115] In some embodiments, the packaging bag 10 includes a first housing 11 and a second housing 12. The first housing 11 and the second housing 12 are oppositely arranged in the first direction X. The first housing 11 is heat-sealed to the second housing 12 to form a sealing edge portion 13. The middle of the tab 30 is connected to the packaging bag 10 at the sealing edge portion 13.

[0116] In some embodiments, as Figure 2 shown, the sealing edge portion 13 is bent toward the direction close to the electrode assembly 20 to reduce the volume occupied by the packaging bag and improve the energy density.

[0117] In some embodiments, as Figure 2As shown, the tab 30 includes a tab body 31 and a tab adhesive 32. The tab body 31 is made of a metal material to function as a conductor, and the tab adhesive 32 is made of a polymer material for hermetically connecting the tab body 31 to the packaging bag 10.

[0118] In some embodiments, as Figure 3 and Figure 4 shown, the electrode plate includes a first electrode plate 21 and a second electrode plate 22 with opposite polarities. In other words, one of the first electrode plate 21 and the second electrode plate 22 is a positive electrode plate and the other is a negative electrode plate. A plurality of first electrode plates 21, a separator 23, and a plurality of second electrode plates 22 are alternately stacked along a first direction X, and the first direction X is the thickness direction of the electrode assembly 20. Specifically, a layer of separator 23 is provided between adjacent first electrode plates 21 and second electrode plates 22 to insulate the first electrode plate 21 and the second electrode plate 22.

[0119] In some embodiments, the positive electrode plate includes a positive current collector and a positive active material layer, and the positive active material layer is provided on one or both sides of the positive current collector along its thickness direction.

[0120] In some embodiments, when the outermost electrode plate of the electrode assembly 20 is a positive electrode plate, the outermost positive electrode plate is provided with a positive active material layer only on the surface of the positive current collector facing the inside of the electrode assembly 20. Here, the "outermost layer" refers to the outermost layer considering only the relative positional relationship between the electrode plates.

[0121] In some embodiments, the positive current collector is a metal layer. As an exemplary example, the positive current collector can be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil.

[0122] In some embodiments, the positive active material layer includes a positive active material, and 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.

[0123] In some embodiments, the negative electrode plate includes a negative current collector and a negative active material layer, and the negative active material layer is provided on one or both sides of the negative current collector along its thickness direction.

[0124] In some embodiments, when the outermost electrode plate of the electrode assembly 20 is a negative electrode plate, the outermost negative electrode plate is provided with a negative active material layer only on the surface of the negative current collector facing the inside of the electrode assembly 20. Here, the "outermost layer" refers to the outermost layer considering only the relative positional relationship between the electrode plates.

[0125] In some embodiments, the negative current collector is a metal layer. As an exemplary example, the negative current collector can be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as copper foil.

[0126] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon oxide material, and silicon carbon material.

[0127] In some embodiments, the material of the separator 23 is one of a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0128] In some embodiments, the electrolyte includes an electrolyte salt. The electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0129] In some embodiments, the electrolyte salt includes, but is not limited to, lithium hexafluorophosphate (LiPF 6 ), lithium bis(trifluoromethanesulfonyl)imide LiN(CF 3 SO 2 )(LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO 2 F) 2 )(LiFSI), lithium hexafluorocesate (LiCsF 2 ), lithium perchlorate (LiClO 6 ), or lithium trifluoromethanesulfonate (LiCF3SO3). 4 Specifically, at least one of the four tabs 30 extends in a direction opposite to that of the other two tabs 30 along the second direction Y.

[0130] In some embodiments, as Figure 1 and Figure 2 shown, when observed along the first direction X, the electrode assembly 20 has four corner positions, and notches 24 are provided at all four corner positions. Four tabs 30 are provided, and the tabs 30 are correspondingly arranged with the notches 24. One end of each tab 30 is connected to the electrode plate, and the other end of each tab 30 extends out of the packaging bag 10 from the notch 24 along the second direction Y, and the second direction Y is perpendicular to the first direction X.

[0131] In this secondary battery 100, the electrode assembly 20 is connected with four tabs 30, and all four tabs 30 are connected to the packaging bag 10, which is beneficial to making the stress on the electrode assembly 20 uniform. When the secondary battery 100 is impacted (such as dropped), the degree of stress concentration generated in the electrode assembly 20 can be reduced, thereby reducing the possibility that the separator 23 shrinks inward by overcoming the adhesion force between it and the electrode plate.

[0132] In some embodiments, as Figure 4 shown, the first electrode plate 21 includes a first current collector 211 and a first active material layer 212 that are stacked along the first direction X. The first current collector 211 is the aforementioned positive electrode current collector or negative electrode current collector, and the first active material layer 212 is the aforementioned positive electrode active material layer or negative electrode active material layer, which is specifically determined according to the polarity of the first electrode plate 21. As Figure 6As shown, the first current collector 211 includes a first coating portion 2111, a first connection portion 2112, and a second connection portion 2113. The first active material layer 212 is disposed on the first coating portion 2111. The first connection portion 2112 and the second connection portion 2113 are respectively connected to a tab 30. As Figure 4 As shown, the second electrode plate 22 includes a second current collector 221 and a second active material layer 222 that are stacked along the first direction X. The second current collector 221 is the aforementioned positive current collector or negative current collector, and the second active material layer 222 is the aforementioned positive active material layer or negative active material layer, which specifically depends on the polarity of the second electrode plate 22. As Figure 7 As shown, the second current collector 221 includes a second coating portion 2211, a third connection portion 2212, and a fourth connection portion 2213. The second active material layer 222 is disposed on the second coating portion 2211. The third connection portion 2212 and the fourth connection portion 2213 are respectively used to connect a tab 30.

[0133] In some embodiments, as Figure 1 As shown, the notch portion 24 includes a first notch portion 241, a second notch portion 242, a third notch portion 243, and a fourth notch portion 244. As Figure 7 As shown, when observed along the first direction X, a first notch 2214 is provided at a corner position of the second current collector 221. A plurality of first notches 2214 at least partially overlap in the first direction X. The plurality of first notches 2214 together form the first notch portion 241. The first connection portion 2112 extends beyond the second current collector 221 and is exposed from the first notch portion 241 (as Figure 8 shown) to facilitate connection with the tab 30. A part of the separator 23 is clamped between the plurality of first connection portions 2112 (as Figure 3 shown), so that the first connection portion 2112 applies a clamping force to the separator 23 to reduce the possibility of the separator 23 shrinking inwards. As Figure 7 As shown, a second notch 2215 is provided at another corner position of the second current collector 221. A plurality of second notches 2215 at least partially overlap in the first direction X. The plurality of second notches 2215 together form the second notch portion 242. The second connection portion 2113 extends beyond the second current collector 221 and is exposed from the second notch portion 242 (as Figure 8 shown) to facilitate connection with the tab 30. A part of the separator 23 is clamped between the plurality of second connection portions 2113 (as Figure 3 shown), so that the first connection portion 2112 applies a clamping force to the separator 23 to reduce the possibility of the separator 23 shrinking inwards. Specifically, as Figure 2 and Figure 9As shown, a plurality of first connecting portions 2112 converge along the first direction X to form a first connecting bundle 21121, and a plurality of second connecting portions 2113 converge along the first direction X to form a second connecting bundle 21131. The tab 30 includes a first tab 301 and a second tab 302. One end of the first tab 301 is connected to the first connecting bundle 21121, and one end of the second tab 302 is connected to the second connecting bundle 21131.

[0134] As Figure 6 shown, when observed along the first direction X, a third notch 2114 is provided at a corner position of the first current collector 211. A plurality of third notches 2114 at least partially overlap in the first direction X, and the plurality of third notches 2114 together form a third notch portion 243. The third connecting portion 2212 extends beyond the first current collector 211 and is exposed from the third notch portion 243 (as Figure 8 shown), so as to be connected to the tab 30. A part of the separator 23 is clamped between the plurality of third connecting portions 2212 (as Figure 3 shown), so that the first connecting portion 2112 applies a clamping force to the separator 23 to reduce the possibility of the separator 23 shrinking inwards. As Figure 6 shown, a fourth notch 2115 is provided at another corner position of the first current collector 211. A plurality of fourth notches 2115 at least partially overlap in the first direction X, and the plurality of fourth notches 2115 together form a fourth notch portion 244. The fourth connecting portion 2213 extends beyond the first current collector 211 and is exposed from the fourth notch portion 244 (as Figure 8 shown), so as to be connected to the tab 30. A part of the separator 23 is clamped between the plurality of fourth connecting portions 2213 (as Figure 3 shown), so that the first connecting portion 2112 applies a clamping force to the separator 23 to reduce the possibility of the separator 23 shrinking inwards. Specifically, as Figure 2 and Figure 9 shown, a plurality of third connecting portions 2212 converge along the first direction X to form a third connecting bundle 22121, and the fourth connecting portion 2213 converges along the first direction X to form a fourth connecting bundle 22131. The tab 30 further includes a third tab 303 and a fourth tab 304. One end of the third tab 303 is connected to the third connecting bundle 22121, and one end of the fourth tab 304 is connected to the fourth connecting bundle 22131.

[0135] In some embodiments, as Figure 7 shown, the first notch 2214 includes two edges extending linearly and forming an included angle, and the two edges intersect to form a vertex.

[0136] In some other embodiments, the first notch 2214 includes two edges that extend linearly and form an included angle, and the two edges are smoothly connected by an arc line; or the edges of the first notch 2214 are arc lines. In this way, it is beneficial to reduce the phenomenon of current concentration on the second pole piece 22, and it is also beneficial to reduce the possibility of the separator 23 being punctured.

[0137] In some embodiments, as Figure 9 shown, one ends of the first connection bundle 21121, the second connection bundle 21131, the third connection bundle 22121, and the fourth connection bundle 22131 are bent towards the electrode assembly 20 to reduce the occupation of the internal space of the packaging bag 10 by the first connection bundle 21121, the second connection bundle 21131, the third connection bundle 22121, and the fourth connection bundle 22131, and improve the energy density of the secondary battery 100.

[0138] Please refer to Figures 10 to 12 , Figure 10 which shows a schematic structural diagram of the separator 23 in an embodiment of the present application, Figure 11 which shows a schematic structural diagram of the separator 23 and the first pole piece 21 in an overlapping state in an embodiment of the present application, Figure 12 which shows a schematic structural diagram of the separator 23 and the second pole piece 22 in an overlapping state in the first embodiment of the present application. In some embodiments, the separator 23 includes an extension portion 231. The extension portion 231 is the part of the separator 23 sandwiched between the first connection portion 2112, the second connection portion 2113, the third connection portion 2212, and the fourth connection portion 2213. The extension portion 231 includes a first extension portion 2311 and a second extension portion 2312. At the first notch portion 241 and the second notch portion 242, the first extension portion 2311 is the part that extends beyond the second current collector 221 along the second direction Y, and the second extension portion 2312 is the part that extends beyond the second current collector 221 along the third direction Z; at the third notch portion 243 and the fourth notch portion 244, the first extension portion 2311 is the part that extends beyond the first current collector 211 along the second direction Y, and the second extension portion 2312 is the part that extends beyond the first current collector 211 along the third direction Z.

[0139] In some embodiments, the demarcation line 231a between the first extension portion 2311 and the second extension portion 2312 is the connection line between the vertex of the notch edge on the separator 23 and the vertex of the notch edge on the pole piece. Figure 11 and Figure 12 show 231a with a dotted line in

[0140] In some embodiments, the notch on the separator 23 is an arc line, and the edge of the notch on the pole piece is also an arc line. At this time, the demarcation line 231a can be the connection line between the midpoints of the two arc lines.

[0141] It should be noted that the first extension portion 2311 and the second extension portion 2312 are generally of an integral structure. In the present application, the extension portion 231 is divided into the first extension portion 2311 and the second extension portion 2312 for the purpose of clearly describing the positional relationship of the extension portion 231 relative to the pole piece. Generally, it is sufficient to recognize the first extension portion 2311 and the second extension portion 2312 as the whole of the extension portion 231. Moreover, the demarcation line 231a is only an artificial division made for the convenience of distinguishing the first extension portion 2311 and the second extension portion 2312 and measuring the dimensions based on this.

[0142] In some embodiments, along the second direction Y, the width of the first extension portion 2311 is W 1 , 0.5 mm ≤ W 1 ≤ 1 mm. Setting W 1 ≥ 0.5 mm, the width of the first extension portion 2311 is not too small, which is beneficial for leaving a margin for the shrinkage of the separator 23 and keeping the first pole piece 21 and the second pole piece 22 insulated; setting W 1 ≤ 1 mm, the width of the first extension portion 2311 is not too large, which is beneficial for reducing the possibility that the separator 23 interferes with the connection between the pole pieces and the connection between the pole piece and the tab 30.

[0143] In some embodiments, 0.5 mm ≤ W 1 ≤ 0.7 mm. Setting W 1 ≤ 0.7 mm is beneficial for further reducing the possibility that the separator 23 interferes with the connection between the pole pieces and the connection between the pole piece and the tab 30.

[0144] In some embodiments, along the third direction Z, the width of the second extension portion 2312 is W 2 , 0.5 mm ≤ W 2 ≤ 1 mm. Setting W 2 ≥ 0.5 mm, the width of the second extension portion 2312 is not too small, which is beneficial for leaving a margin for the shrinkage of the separator 23 and keeping the first pole piece 21 and the second pole piece 22 insulated; setting W 2 ≤ 1 mm, the width of the second extension portion 2312 is not too large, which is beneficial for reducing the possibility that the separator 23 interferes with the connection between the pole pieces and the connection between the pole piece and the tab 30.

[0145] In some embodiments, 0.5 mm ≤ W 2 ≤ 0.7 mm. Setting W 2 ≤ 0.7 mm is beneficial for further reducing the possibility that the separator 23 interferes with the connection between the pole pieces and the connection between the pole piece and the tab 30.

[0146] In some embodiments, such as Figure 2 ,Figure 4 and Figure 5 As shown in Figure 5 , one of the first electrode plates 21 is an outer electrode plate 213. The outer electrode plate 213 is located at the outermost layer of the electrode assembly 20. The first current collector 211 of the outer electrode plate 213 includes a first surface 211a and a second surface 211b that are oppositely arranged along the first direction X. The first surface 211a is the surface facing the inside of the electrode assembly 20. The first active material layer 212 of the outer electrode plate 213 is provided on the first surface 211a. The outer electrode plate 213 further includes a reinforcing layer 2131. The reinforcing layer 2131 is provided on the second surface 214b. When observed along the first direction X, the first current collector 211 has a plurality of vertices, and the reinforcing layer 2131 covers at least one vertex. In the prior art, only an active material layer is provided on one surface of the current collector of the outer electrode plate 213, resulting in uneven forces on the two surfaces of the current collector along the thickness direction. The current collector is prone to warping, causing it to disconnect from the separator membrane, and triggering the inward contraction of the separator membrane 23. By providing the reinforcing layer 2131, it is beneficial to reduce the possibility of the current collector warping to maintain the contact between the separator membrane 23 and the electrode plate.

[0147] In some embodiments, as Figure 4 shown, the reinforcing layer 2131 covers the entire second surface 214b.

[0148] In some embodiments, as Figure 5 shown, the reinforcing layer 2131 covers the vertex positions of the second surface 214b. For the outer electrode plate 213, the stress is more concentrated at the vertex positions and is more prone to warping. By providing the reinforcing layer 2131 at the vertex positions of the second surface 214b, the warping at the vertex positions can be reduced to maintain the contact between the separator membrane 23 and the electrode plate.

[0149] In some embodiments, the reinforcing layer 2131 includes a ceramic material. The ceramic material includes at least one of, but is not limited to, alumina, zirconia, titanium oxide, silicon oxide, and boehmite.

[0150] In some embodiments, as Figure 4 shown, the thickness of the reinforcing layer 2131 is T 1 , 5 μm ≤ T 1 ≤ 10 μm. By setting T 1 ≥ 5 μm, the thickness of the reinforcing layer 2131 is not too small, which is beneficial to improving its effect of suppressing the warping of the current collector; by setting T 1 ≤ 10 μm, the thickness of the reinforcing layer 2131 is not too large, which is beneficial to reducing the impact of its setting on the energy density of the secondary battery 100.

[0151] In some embodiments, as Figure 1As shown, when observed along the first direction X, the first tab 301 and the second tab 302 are diagonally arranged, and the third tab 303 and the fourth tab 304 are diagonally arranged. The first tab 301 and the second tab 302 have the same polarity, and the third tab 303 and the fourth tab 304 have the same polarity. Diagonally arranging the tabs 30 with the same polarity is beneficial to improving the uniformity of the current density of the electrode sheet, thereby improving the uniformity of the temperature distribution at different positions of the electrode sheet and reducing the possibility of the shrinkage of the separator 23 due to temperature concentration.

[0152] In some embodiments, the first electrode sheet 21 is a positive electrode sheet, and the material of the first tab 301 and / or the second tab 302 includes aluminum.

[0153] In some embodiments, the second electrode sheet 22 is a negative electrode sheet, and the material of the third tab 303 and / or the fourth tab 304 includes nickel-plated copper.

[0154] In some embodiments, as Figure 13 shown, the packaging bag 10 has a receiving space, and the electrode assembly 20 is received and arranged in the receiving space. When observed along the first direction X, the electrode assembly 20 includes a first edge 20a and a second edge 20b that are oppositely arranged along the second direction Y, and a third edge 20c and a fourth edge 20d that are oppositely arranged along the third direction Z. The packaging bag 10 includes a packaging wall for enclosing the receiving space; the packaging wall includes a first packaging wall 10a and a second packaging wall 10b that are oppositely arranged along the second direction Y, and the first packaging wall 10a is closer to the first edge 20a than the second packaging wall 10b; and a third packaging wall 10c and a fourth packaging wall 10d that are oppositely arranged along the third direction Z, and the third packaging wall 10c is closer to the third edge 20c than the fourth packaging wall 10d. In this way, the outer shape of the packaging bag 10 is adapted to the outer shape of the electrode assembly 20, which is beneficial to improving the energy density of the secondary battery 100.

[0155] In some embodiments, along the second direction Y, the distance between the first packaging wall 10a and the first edge 20a, and the distance between the second packaging wall 10b and the second edge 20b are W 3 , 0.3 mm ≤ W 3 ≤ 0.8 mm. Setting W 3 ≥ 0.3 mm, the distance between the first packaging wall 10a and the first edge 20a and the distance between the second packaging wall 10b and the second edge 20b are not too small. On the one hand, it is convenient to install the electrode assembly 20 into the packaging bag 10, and on the other hand, it reduces the possibility of interference between the electrode assembly 20 and the packaging bag 10, so as to reduce the risk of the packaging bag 10 being damaged and leaking liquid and the deformation of the electrode assembly 20; setting W 3≤0.8 mm. The distances between the first encapsulation wall 10a and the first edge 20a, and between the second encapsulation wall 10b and the second edge 20b are not too large, which is beneficial to improving the heat transfer efficiency, reducing the accumulation of heat generated by the electrode assembly 20 in the packaging bag 10, and further reducing the possibility of thermal shrinkage of the separator film 23.

[0156] In some embodiments, 0.3 mm ≤ W 3 ≤ 0.5 mm. Setting W 3 ≤ 0.5 mm is beneficial to further improving the heat transfer efficiency to further reduce the possibility of thermal shrinkage of the separator film 23.

[0157] It should be noted that in the embodiments of the present application, W 3 = (the width of the packaging bag 10 along the second direction Y - the width of the electrode assembly 20 along the second direction Y) / 2.

[0158] In some embodiments, along the third direction Z, the distances between the third encapsulation wall 10c and the third edge 20c, and between the fourth encapsulation wall 10d and the fourth edge 20d are W 4 , 0.3 mm ≤ W 4 ≤ 0.8 mm. Setting W 4 ≥ 0.3 mm, the distances between the third encapsulation wall 10c and the third edge 20c, and between the fourth encapsulation wall 10d and the fourth edge 20d are not too small. On the one hand, it is convenient to install the electrode assembly 20 into the packaging bag 10, and on the other hand, it reduces the possibility of interference between the electrode assembly 20 and the packaging bag 10 to reduce the risks of liquid leakage due to damage of the packaging bag 10 and deformation of the electrode assembly 20; setting W 4 ≤ 0.8 mm, the distances between the third encapsulation wall 10c and the third edge 20c, and between the fourth encapsulation wall 10d and the fourth edge 20d are not too large, which is beneficial to improving the heat transfer efficiency, reducing the accumulation of heat generated by the electrode assembly 20 in the packaging bag 10, and further reducing the possibility of thermal shrinkage of the separator film 23.

[0159] In some embodiments, 0.3 mm ≤ W 4 ≤ 0.5 mm. Setting W 4 ≤ 0.5 mm is beneficial to further improving the heat transfer efficiency to further reduce the possibility of thermal shrinkage of the separator film 23.

[0160] It should be noted that in the embodiments of the present application, W 3 = (the width of the packaging bag 10 along the third direction Z - the width of the electrode assembly 20 along the third direction Z) / 2.

[0161] In some embodiments, such as Figure 14As shown, the separator 23 includes a base material layer 231, a ceramic layer 232, and an adhesive layer 233. The material of the base material layer 231 includes, but is not limited to, at least one of polyethylene, polypropylene, polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyether ether ketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, polyparaphenylene terephthalamide, polyarylether sulfone ketone, aramid, or arsulfonamide; the material of the ceramic layer 232 includes, but is not limited to, at least one of alumina, silica, titanium dioxide, zirconia, barium titanate, and boehmite; the material of the adhesive layer 233 includes, but is not limited to, at least one of polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer, polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, or acrylate. The setting of the ceramic layer 232 is beneficial to improving the thermal stability of the separator 23 and reducing the risk of shrinkage of the separator 23; the setting of the adhesive layer 233 is beneficial to improving the adhesion between the separator 23 and the electrode sheet and reducing the risk of shrinkage of the separator 23.

[0162] In some embodiments, the separator 23 only includes the base material layer 231. In other embodiments, the separator 23 is composed of the base material layer 231 and one of the ceramic layer 232 and the adhesive layer 233.

[0163] In some embodiments, the thickness of the ceramic layer 232 is T 2 , 1.5 μm ≤ T 2 ≤ 3 μm. Setting T2 ≥ 1.5 μm, the thickness of the ceramic layer 232 is not too small, which is beneficial to improving the thermal stability of the separator 23; setting T 2 ≤ 3 μm, the thickness of the ceramic layer 232 is not too thick, which is beneficial to improving the energy density of the secondary battery 100.

[0164] In some embodiments, the thickness of the adhesive layer 233 is T 3 , 0.5 μm ≤ T 3 ≤ 3 μm. Setting T3 ≥ 0.5 μm, the thickness of the adhesive layer 233 is not too small, which is beneficial to improving the adhesion between the separator 23 and the electrode sheet; setting T 3 ≤ 3 μm, the thickness of the adhesive layer 233 is not too thick, which is beneficial to improving the energy density of the secondary battery 100.

[0165] As Figure 15 shown, an embodiment of the present application also provides an electronic device 200, which includes the secondary battery 100 involved in any of the foregoing embodiments.

[0166] In some embodiments, the electronic device 200 includes, but is not limited to, a mobile phone, a laptop computer, an electric toy, an electric tool, and an electronic cigarette.

[0167] To verify the effects of the technical solutions in the present application, the inventors conducted the following experiments.

[0168] The experiment included a total of 26 experimental groups, namely one comparative example group and 25 example groups.

[0169] The preparation process of the secondary battery 100 in Example 1 includes the following steps:

[0170] (1) Preparation of the positive electrode sheet: The active material lithium cobalt oxide (LiCoO 2 )), conductive carbon black (Super P), CNT (carbon nanotube), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:0.5:0.5:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode active material with a solid content of 75 wt%, and it was stirred evenly for standby. Aluminum foil with a thickness of 10 μm was used as the positive electrode current collector. The above active material was evenly coated on one side of the positive electrode current collector along its thickness direction using a slot coater, and then dried at 90 °C to obtain a positive electrode sheet with a single-sided coating of the positive electrode active material. At this time, the thickness of the positive electrode active material layer was 50 μm. Then, the above coating steps were repeated on the other side of the positive electrode current collector 221 along its thickness direction. Then, the coated positive electrode sheet was cold-pressed. After cold pressing, the thickness of the positive electrode active material layer was 35 μm. It should be noted that the outermost electrode sheet 213 of the secondary battery 100 prepared in the experiment was the positive electrode sheet, and the outermost electrode sheet 213 was coated with the positive electrode active material layer only on one side. The positive electrode current collector included a first coating portion 2111, a first connection portion 2112, and a second connection portion 2113. The positive electrode active material layer was disposed on the first coating portion 2111, and the positive electrode current collector was also provided with a third notch 2114 and a fourth notch 2115;

[0171] (2) Preparation of the negative electrode sheet: Artificial graphite as the active material, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) are mixed according to a weight ratio of 97:0.5:1.3:1.2. Deionized water is added as a solvent to prepare a negative electrode active material with a weight percentage of 50 wt%, and it is stirred evenly for standby. A copper foil with a thickness of 10 μm is used as the negative electrode current collector. The above-mentioned negative electrode active material is evenly coated on one side of the negative electrode current collector along its thickness direction using a slot coater, and then dried at 110 °C to obtain a negative electrode sheet with a negative electrode active material layer coated on one side. Then, the above steps are repeated on the other side of the negative electrode current collector along its thickness direction to obtain a negative electrode sheet with negative electrode active material layers coated on both sides. At this time, the thickness of the negative electrode active material layer is 55 μm. Then, the coated negative electrode sheet is cold-pressed, and the thickness of the negative electrode active material layer after cold pressing is 45 μm. The negative electrode current collector includes a second coating portion 2211, a third connecting portion 2212, and a fourth connecting portion 2213. The negative electrode active material layer is provided on the second coating portion 2211, and the negative electrode current collector is also provided with a first notch 2214 and a second notch 2215;

[0172] (3) Preparation of the electrolyte: In a dry argon atmosphere, first, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF 6 ) is added to the basic organic solvent and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L;

[0173] (4) Preparation of the separator 23: A 7-μm-thick polyethylene porous polymer film is used as the separator 23. The separator 23 is provided with an extension portion 231. The specific setting method of the extension portion 231 can refer to the previous text and will not be elaborated here. In the experiment, W 1 = W 2 ;

[0174] (5) Preparation of the electrode assembly 20: The positive electrode sheets, the isolation membrane 23 and the negative electrode sheets are alternately stacked along the first direction X. After stacking, the first notches 2214 together form a first notch portion 241, and the first connecting portion 2112 is exposed from the first notch portion 241. The second notches 2215 together form a second notch portion 242, and the second connecting portion 2113 is exposed from the second notch portion 242. The third notches 2114 together form a third notch portion 243, and the third connecting portion 2212 is exposed from the third notch portion 243. The fourth notches 2115 together form a fourth notch portion 244, and the fourth connecting portion 2213 is exposed from the fourth notch portion 244. The first connection portion 2112 of each layer of positive electrode sheets is gathered along the first direction X to form a first connection bundle 21121, the second connection portion 2113 of each layer of positive electrode sheets is gathered along the first direction X to form a second connection bundle 21131, the third connection portion 2212 of each layer of negative electrode sheets is gathered along the first direction X to form a third connection bundle 22121, and the fourth connection portion 2213 of each layer of negative electrode sheets is gathered along the first direction X to form a fourth connection bundle 22131; four pole tabs 30 are taken, namely a first pole tab 301, a second pole tab 302, a third pole tab 303 and a fourth pole tab 304, the first pole tab 301 is welded to the first connection bundle 21121, the second pole tab 302 is welded to the second connection bundle 21131, the third pole tab 303 is welded to the third connection bundle 22121, and the fourth pole tab 304 is welded to the fourth connection bundle 22131. The first pole tab 301 and the second pole tab 302 are arranged diagonally, the third pole tab 303 and the fourth pole tab 304 are arranged diagonally, the first pole tab 301 and the second pole tab 302 extend in one direction of the second direction Y, and the third pole tab 303 and the fourth pole tab 304 extend in another direction of the second direction Y;

[0175] (6) Assembly of secondary battery 100: Place the aluminum-plastic film with holes punched and shaped in an assembly fixture, with the holes facing upward, place the electrode assembly 20 in the holes, and apply external force to press it. Then, cover the electrode assembly 20 with another aluminum-plastic film with holes punched and shaped with the holes facing downward. Then, heat-seal the aluminum-plastic film, inject electrolyte, vacuum package, stand, hot press, and shape the film to obtain the secondary battery 100. In the obtained secondary battery 100, W 3 =W 4 .

[0176] The preparation process of the secondary battery 100 in comparative example 1 is basically the same as that in embodiment 1, except that the secondary battery 100 in comparative example 1 is connected with only two pole tabs 30 , which are located on one side of the electrode assembly 20 along the second direction Y and extend along the second direction Y.

[0177] The preparation process of the secondary battery 100 in Examples 2 to 25 is basically the same as that in Example 1. The difference is that for the secondary battery 100 in Examples 2 to 9 and Examples 16 to 25, some parameters are different from those in Example 1; for the secondary battery 100 in Examples 10 to 14, some parameters are different from those in Example 1, and a reinforcing layer 2131 is also provided; for the secondary battery 100 in Example 15, some parameters are different from those in Example 1, and the tabs 30 of the same polarity in the secondary battery 100 in Example 15 are arranged non - diagonally. It should be added that in Example 16, the thickness T 2 of the ceramic layer 232 of the separator 23 being equal to 0 means that the ceramic layer 232 is not provided, and in Example 21, the thickness T 3 of the adhesive layer 233 of the separator 23 being equal to 0 means that the adhesive layer 233 is not provided. The specific parameters related to the experiments in each example are recorded in Table 1.

[0178] Among them, the measurement methods of W 1 / W 2 、W 3 / W 4 、T 1 、T 2 and T 3 are as follows:

[0179] 1. Measurement method of W 1 / W 2 :

[0180] Use a scanning electron microscope to measure at the first notch 241 and the second notch 242, the width by which the first extension 2311 extends beyond the second current collector 221 in the second direction Y, and at the third notch 243 and the fourth notch 244, the width by which the first extension 2311 extends beyond the first current collector 211 in the second direction Y. Take the average of the above four measured values as W 1 ;

[0181] Similarly, use a scanning electron microscope to measure at the first notch 241 and the second notch 242, the width by which the second extension 2312 extends beyond the second current collector 221 in the third direction Z, and at the third notch 243 and the fourth notch 244, the width by which the second extension 2312 extends beyond the first current collector 211 in the third direction Z. Take the average of the above four measured values as W 2 .

[0182] 2. Measurement method of W 3 / W 4 :

[0183] Discharge the secondary battery 100 to 0V, use a wire cutting machine to cut a part of the secondary battery 100 along the second direction Y. At this time, the cut surface is rough (because there is active layer material falling off). Place the secondary battery 100 on an abrasive disc to polish the cut surface until it is smooth. Observe and measure the distance from the hot melt layer in the packaging bag to the edge of the electrode assembly on the cut surface under a metallurgical microscope, which is W 3 ;

[0184] Similarly, discharge the secondary battery 100 to 0V, use a wire cutting machine to cut a part of the secondary battery 100 along the third direction Z. At this time, the cut surface is rough (because there is active layer material falling off). Place the secondary battery 100 on an abrasive disc to polish the cut surface until it is smooth. Observe and measure the distance from the hot melt layer in the packaging bag to the edge of the electrode assembly on the cut surface under a metallurgical microscope, which is W 4 。

[0185] 3.Measurement of T 1 :

[0186] Discharge the secondary battery 100 to 0V, disassemble the outermost pole piece, and cut the part of the outermost pole piece where the reinforcing layer 2131 is provided. Observe the cross-section of the pole piece using a scanning electron microscope, measure the thickness of any three points in the reinforcing layer, and take the average value as T 1 。

[0187] 4.Measurement of T 2 and T 3 :

[0188] Discharge the secondary battery 100 to 0V, and disassemble the separator 23. Immerse the separator 23 in dimethyl carbonate (DMC) for 20 minutes to remove the electrolyte residue. Then place the separator 23 in an oven and dry it at 60°C for 12 hours. Then cut the separator 23 into a size of 5 cm × 5 cm to obtain a test sample of the separator 23. Observe the cross-section of the above test sample using a scanning electron microscope, and measure the thickness T 2 of the ceramic layer 232 3 and the thickness T

[0189] After preparing the secondary battery 100 participating in the experiment according to the above content, the secondary battery 100 in each experimental group is respectively tested as follows.

[0190] 1.Hipot test after dropping

[0191] For each experimental group participating in this test, 10 secondary batteries 100 need to be randomly selected for the test, and the selected secondary batteries 100 have not been subjected to other tests listed in this article.

[0192] This test includes two parts: a drop test and a Hipot test. The secondary battery 100 selected is first subjected to the drop test and then the Hipot test.

[0193] The specific process of the drop test is as follows:

[0194] Fix the secondary battery 100 in the drop test fixture with double-sided tape. Number the six faces of the fixture as 1, 2, 3, 4, 5, and 6 in sequence, and number the four corners of the fixture as C 1 、C 2 、C 3 、C 4 ;

[0195] At 25°C, place the fixture on a test bench 1.5 m high. Drop the lithium-ion secondary battery 100 in sequence according to the numbers 1 - 6, and then drop the lithium-ion secondary battery 100 in sequence according to the numbers C 1 -C 4 . After completing the drop step, let it stand for 1 h.

[0196] The specific process of the Hipot test is as follows:

[0197] Connect the secondary battery 100 to a high-voltage machine, detect the leakage current generated by the electrode assembly 20 under the test voltage output by the high-voltage machine, and then calculate the resistance value = test voltage / leakage current. Compare the calculated resistance value with the set judgment resistance. If the detected resistance value is greater than or equal to the preset value, it is determined that the product under test passes the test (OK); if the detected resistance value is less than the preset value, the test voltage is instantly cut off and the product under test is determined to fail the test (NG). In this test, the preset value of the judgment resistance is 5 mΩ. When the measured resistance value is lower than 5 mΩ, it means that it can conduct but the resistance value is too small, there is a short circuit point, and it is determined as NG. The existence of the short circuit point can reflect the situation where the separator 23 shrinks and causes the positive and negative electrodes to short-circuit; when the resistance value is greater than or equal to 5 mΩ, it is determined as OK. Record the number a of the secondary batteries 100 that pass the test, and the test pass rate Q 1 Record it as a / 10.

[0198] 2. Volume energy density test

[0199] Each experimental group participating in this test needs to randomly select 10 secondary batteries 100 for the test, and the selected secondary batteries 100 have not been subjected to other tests listed in this article. The specific process of the test is as follows:

[0200] 1) Use a PPG battery thickness measuring instrument to measure the length, width, and thickness of the secondary battery 100 at 25°C;

[0201] 2) Keep the test temperature at 25°C and let the secondary battery 100 stand for 30 min;

[0202] 3) Charge at a constant current of 5C until 4.25V, then charge at a constant voltage until 3C;

[0203] 4) Charge at a constant current of 3C until 4.35V, then charge at a constant voltage until 1.5C;

[0204] 5) Charge at a constant current of 1.5C until 4.45V, then charge at a constant voltage until 0.05C;

[0205] 6) Stand still for 5 min;

[0206] 7) Discharge at a constant current of 0.7C until 3V;

[0207] 8) Stand still for 5 min;

[0208] Record the energy of the first discharge cycle, and calculate the volume energy density of the secondary battery 100 using the discharge energy = (discharge energy) / (length × width × thickness of the secondary battery 100);

[0209] After the tests of the 10 batteries in each group are completed, calculate the average value of the volume energy density. The final result is represented by E, with the unit of Wh / L.

[0210] 3. Long cycle test

[0211] Repeat steps 2) to 8) 999 times for the secondary battery 100 that has completed the above volume energy density test.

[0212] After the above long cycle test, disassemble the secondary battery 100 and visually observe whether the hot melt layer of the packaging bag 10 is damaged. Those without damage are considered to pass the test; record the number b of the secondary batteries 100 that pass the test and the long cycle test pass rate Q 2 Record as b / 10.

[0213] 3.1 130°C hot box test

[0214] For the experimental group participating in this test, 10 secondary batteries 100 need to be randomly selected for the test, and the selected secondary batteries 100 have not undergone other tests listed in this article.

[0215] The specific process of the experiment is as follows:

[0216] Under the condition of 25°C, charge the secondary battery 100 at a constant current of 2C until 4.5V, then charge at a constant voltage of 4.5V until the current is 0.02C, and then put it into a test chamber with circulating air convection, a temperature of 25°C, and a humidity of 80%. After standing still for 5 min, heat the test chamber to 130°C at a rate of 5°C / min, keep it at 130°C unchanged, and stop the test after 10 min. Check whether the lithium-ion battery catches fire or explodes. Those without catching fire or exploding are considered to pass. Record the number c of the secondary batteries 100 that pass the test and the hot box test pass rate Q at 130°C3 Denoted as c / 10.

[0217] 4.135°C Hot Box Test

[0218] For the experimental group participating in this test, 10 secondary batteries 100 need to be randomly selected for the test, and the selected secondary batteries 100 have not undergone other tests listed in this article.

[0219] The specific process of the experiment is as follows:

[0220] Under the condition of 25°C, the secondary battery 100 that has been charged at a constant current of 2C to 4.5V and then at a constant voltage of 4.5V until the current reaches 0.02C is placed in a test chamber with circulating air convection, a temperature of 25°C, and a humidity of 80%. After standing for 5 minutes, the test chamber is heated to 135°C at a rate of 5°C / min, and the temperature of 135°C is maintained. After 10 minutes, the test is stopped, and it is checked whether the lithium-ion battery catches fire or explodes. Record the number d of secondary batteries 100 that pass the test, and the passing rate Q of the hot box test at 135°C 4 Denoted as d / 10.

[0221] It should be added that the principle of the hot box test is as follows: Under the condition of thermal abuse, the secondary battery 100 will gradually develop towards thermal runaway. The main process is: as the temperature of the secondary battery 100 gradually rises, the electrode assembly 20 is heated and begins to undergo a thermal chemical reaction. The SEI film on the surface of the positive and negative active material layers will be thermally decomposed at high temperature, resulting in the direct exposure of the internal active materials to the electrolyte. The anode with a large amount of active lithium and the cathode in a high valence state further undergo redox reactions with the electrolyte, releasing heat. The self-heat generation of the electrode assembly 20 further raises the overall temperature of the battery cell. At this time, a large amount of redox gases are generated, and significant heat accumulation occurs inside the secondary battery 100. The packaging bag 10 begins to bulge and deform significantly. At this time, there may be a risk of internal short circuit caused by the swelling of the battery cell. At the same time, a large amount of gas generated accumulates between the electrode assembly 20 and the packaging bag 10, forming a relatively thick gas film, which inhibits the heat exchange between the bare battery cell and the outside world, further deteriorating the internal heat accumulation of the secondary battery 100 and causing thermal runaway combustion or even explosion. Therefore, by observing the thermal runaway of the secondary battery 100 caused by the hot box test, the temperature distribution inside the secondary battery 100 and its heat exchange with the outside world (i.e., heat dissipation efficiency) can be inferred.

[0222] 5. Tensile Test

[0223] For the experimental group participating in this test, 10 secondary batteries 100 need to be randomly selected for the test, and the selected secondary batteries 100 have not undergone other tests listed in this article.

[0224] The test process is as follows:

[0225] Discharge the secondary battery 100 to 3.0V, then disassemble the secondary battery 100, remove the first tab 301 and the first connection bundle 21121 welded thereto as a whole, and wipe the electrolyte on the surface with lint-free paper. Then cut out strip-shaped specimens. Along the length direction of the specimen, adhere the first connection bundle 21121 in the specimen to the steel plate through double-sided tape (Nitto 5000NS), where the adhesion length is not less than 15mm. Fix the steel plate at the corresponding position of the high-speed tensile machine, pull up one end of the first tab 301, and place it in the chuck and clamp it. The angle between the pulled part of the first tab 301 and the steel plate in space is 180°. The chuck pulls the specimen at a speed of 5±0.2mm / s, and the average value of the tensile force in the stable region finally measured is recorded as the peel strength between the first tab 301 and the first connection bundle 21121, with the unit of N / mm. Among them, the stable region refers to the part where the tensile force does not change significantly with time in the line graph made by the change of the tensile force of the chuck pulling the first bonding member 30 with time. Subsequently, test the tensile forces between the second tab 302 and the second connection bundle 21131, the third tab 303 and the third connection bundle 22121, and the fourth tab 304 and the fourth connection bundle 22131, and take the average value of the four measured tensile force values. After 10 secondary batteries 100 have all been tested, take the average value of each measured tensile force value again, and the final result is represented by F.

[0226] After the experiment, record the experimental results in Table 1, and " / " represents no such data.

[0227] Table 1

[0228]

[0229]

[0230]

[0231] Note: In Table 1, " / " represents no such data

[0232] As can be seen from Table 1, the secondary batteries 100 in Examples 1 to 25 are provided with four tabs 30. Compared with Comparative Example 1, the passing rate of the secondary batteries 100 in Examples 1 to 25 in the Hipot test after dropping is higher than that of Comparative Example 1. It can be seen that in the embodiments of the present application, the four tabs 30 of the secondary battery 100 are all connected to the packaging bag 10, which is beneficial to making the stress on the electrode assembly 20 uniform. When the secondary battery 100 is impacted (such as dropping), the degree of stress concentration generated in the electrode assembly 20 can be reduced, thereby reducing the possibility that the separator 23 shrinks inward by overcoming the adhesion force between it and the electrode sheet.

[0233] In Examples 2 to 4, the secondary battery 100 satisfies 0.5mm≤W1 ≤1 mm and 0.5 mm ≤ W 2 ≤1 mm. Compared with Example 1, the pass rate of the secondary battery 100 in the Hipot test after dropping is higher in Examples 2 to 4. It can be seen that setting W 1 ≥0.5 mm, the width of the first extension part 2311 is not too small, which is beneficial to leaving a margin for the shrinkage of the separator 23, keeping the first electrode 21 and the second electrode 22 insulated. Setting W 2 ≥0.5 mm, the width of the second extension part 2312 is not too small, which is beneficial to leaving a margin for the shrinkage of the separator 23, keeping the first electrode 21 and the second electrode 22 insulated; compared with Example 5, the average value of the tensile force measured in the tensile test of the secondary battery 100 in Examples 2 to 4 is higher. It can be seen that setting W 1 ≤1 mm, the width of the first extension part 2311 is not too large, which is beneficial to reducing the possibility that the separator 23 interferes with the connection between the electrodes and the connection between the electrode and the tab 30. Setting W 2 ≤1 mm, the width of the second extension part 2312 is not too large, which is beneficial to reducing the possibility that the separator 23 interferes with the connection between the electrodes and the connection between the electrode and the tab 30.

[0234] In Examples 2 and 3, the secondary battery 100 satisfies W 1 ≤0.7 mm and W 2 ≤0.7 mm. Compared with Examples 4 and 5, the average value of the tensile force measured in the tensile test of the secondary battery 100 in Examples 2 and 3 is higher. It can be seen that setting W 1 ≤0.7 mm is beneficial to further reducing the possibility that the separator 23 interferes with the connection between the electrodes and the connection between the electrode and the tab 30. Setting W 2 ≤0.7 mm is beneficial to further reducing the possibility that the separator 23 interferes with the connection between the electrodes and the connection between the electrode and the tab 30.

[0235] In Examples 3, 7 and 8, the secondary battery 100 satisfies 0.3 mm ≤ W 3 ≤0.8 mm and 0.3 mm ≤ W 4 ≤0.8 mm. Compared with Example 6, the pass rate of the secondary battery 100 in Examples 3, 7 and 8 is higher in the long cycle test. It can be seen that setting W 3≥0.3 mm, the distances between the first encapsulation wall 10a and the first edge 20a and between the second encapsulation wall 10b and the second edge 20b are not too small, which is beneficial to reducing the possibility of interference between the electrode assembly 20 and the packaging bag 10, so as to reduce the risks of the packaging bag 10 being damaged and leaking liquid and the electrode assembly 20 being deformed. Set W 4 ≥0.3 mm, the distances between the third encapsulation wall 10c and the third edge 20c and between the fourth encapsulation wall 10d and the fourth edge 20d are not too small, which is beneficial to reducing the possibility of interference between the electrode assembly 20 and the packaging bag 10, so as to reduce the risks of the packaging bag 10 being damaged and leaking liquid and the electrode assembly 20 being deformed; compared with Example 9, the passing rates of the secondary batteries 100 in the 130 °C hot box test and the 135 °C hot box test in Examples 3, 7 and 8 are higher. It can be seen that setting W 3 ≤0.8 mm, the distances between the first encapsulation wall 10a and the first edge 20a and between the second encapsulation wall 10b and the second edge 20b are not too large, which is beneficial to improving the heat transfer efficiency, reducing the accumulation of heat generated by the electrode assembly 20 in the packaging bag 10, and further reducing the possibility of the separator 23 undergoing thermal shrinkage. Set W 4 ≤0.8 mm, the distances between the third encapsulation wall 10c and the third edge 20c and between the fourth encapsulation wall 10d and the fourth edge 20d are not too large, which is beneficial to improving the heat transfer efficiency, reducing the accumulation of heat generated by the electrode assembly 20 in the packaging bag 10, and further reducing the possibility of the separator 23 undergoing thermal shrinkage. At the same time, limit W 3 and W 4 The upper limit value of can reduce the loss of the volumetric energy density of the secondary battery 100.

[0236] In Examples 10 to 14, the outer pole piece 213 of the secondary battery 100 is provided with a reinforcing layer 2131. Compared with Example 3, the passing rates of the secondary batteries 100 in the Hipot test after dropping in Examples 10 to 14 are higher. It can be seen that by setting the reinforcing layer 2131, it is beneficial to reduce the possibility of the current collector warping, so as to maintain the contact between the separator 23 and the pole piece, reduce the possibility of the separator 23 shrinking inwards, and thus reduce the possibility of the secondary battery 100 generating an internal short circuit.

[0237] In Examples 11 to 14, the secondary battery 100 satisfies T 1 ≥5 μm. Compared with Example 10, the passing rates of the secondary batteries 100 in the Hipot test after dropping and the passing rates of the hot box test in Examples 11 to 14 are higher. It can be seen that setting T 1≥5 μm, the thickness of the reinforcing layer 2131 is not too small, which is beneficial to improving its effect of suppressing the warping of the current collector; in Examples 10 to 13, the secondary battery 100 satisfies T 1 ≤10 μm. Compared with Example 14, the secondary battery 100 in Examples 10 to 13 has a higher volumetric energy density. It can be seen that setting T 1 ≤10 μm, the thickness of the reinforcing layer 2131 is not too large, which is beneficial to reducing the impact of its setting on the energy density of the secondary battery 100.

[0238] In Example 3, the ears 30 of the same polarity of the secondary battery 100 are diagonally arranged. In Example 15, the ears 30 of the same polarity of the secondary battery 100 are not diagonally arranged. Compared with Example 15, the passing rates of the secondary battery 100 in Example 3 in the 130 °C hot box test and the 135 °C hot box test are both higher. It can be seen that arranging the ears 30 of the same polarity diagonally is beneficial to improving the uniformity of the current density of the electrode sheet, thereby improving the uniformity of the temperature distribution at different positions of the electrode sheet and reducing the possibility of the shrinkage of the separator 23 due to temperature concentration.

[0239] In Example 3 and Examples 17 to 20, the separator 23 of the secondary battery 100 is provided with a ceramic layer 232. Compared with Example 16, the passing rates of the secondary battery 100 in Example 3 and Examples 17 to 20 in the Hipot test after dropping are higher, and the passing rate of the hot box test is higher. It can be seen that setting the ceramic layer 232 is beneficial to improving the thermal stability of the separator 23 and reducing the risk of shrinkage of the separator 23.

[0240] In Example 3 and Examples 18 to 20, the secondary battery 100 satisfies T 2 ≥1.5 μm. Compared with Example 17, the passing rates of the secondary battery 100 in Example 3 and Examples 18 to 20 in the Hipot test after dropping are higher. It can be seen that setting T 2 ≥1.5 μm, the thickness of the ceramic layer 232 is not too small, which is beneficial to improving the thermal stability of the separator 23 and reducing the risk of shrinkage of the separator 23; in Example 3 and Examples 17 to 19, the secondary battery 100 satisfies T 2 ≤3 μm. Compared with Example 20, the secondary battery 100 in Example 3 and Examples 17 to 19 has a higher volumetric energy density. It can be seen that T 2 ≤3 μm, the thickness of the ceramic layer 232 is not too thick, which is beneficial to improving the volumetric energy density of the secondary battery 100.

[0241] In Embodiment 3 and Embodiments 22 to 25, the separator 23 of the secondary battery 100 is provided with an adhesive layer 233. Compared with Embodiment 21, the passing rate of the secondary battery 100 in the Hipot test after dropping is higher in Embodiment 3 and Embodiments 22 to 25. It can be seen that setting the adhesive layer 233 is beneficial to improving the adhesion between the separator 23 and the electrode sheet and reducing the risk of inward shrinkage of the separator 23.

[0242] In Embodiment 3 and Embodiments 23 to 25, the secondary battery 100 satisfies T 3 ≥ 0.5 μm. Compared with Embodiment 22, the passing rate of the secondary battery 100 in the Hipot test after dropping is higher in Embodiment 3 and Embodiments 23 to 25. It can be seen that setting T 3 ≥ 0.5 μm, the thickness of the adhesive layer 233 is not too small, which is beneficial to improving the adhesion between the separator 23 and the electrode sheet; in Embodiment 3 and Embodiments 22 to 24, the secondary battery 100 satisfies T 3 ≤ 3 μm. Compared with Embodiment 25, the volumetric energy density of the secondary battery 100 is higher in Embodiment 3 and Embodiments 22 to 24. It can be seen that setting T 3 ≤ 3 μm, the thickness of the adhesive layer 233 is not too thick, which is beneficial to improving the energy density of the secondary battery 100.

[0243] 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 intended 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: Packaging bags; An electrode assembly, contained in the packaging bag, comprising an electrode sheet and a separator, wherein the electrode sheet comprises a first electrode sheet and a second electrode sheet with opposite polarities, wherein a plurality of the first electrode sheets, the separator and a plurality of the second electrode sheets are alternately stacked along a first direction, wherein the first direction is a thickness direction of the electrode assembly; when viewed along the first direction, the electrode assembly has a first angle position, a second angle position, a third angle position and a fourth angle position; the electrode assembly further comprises a notch portion, wherein the notch portion comprises a first notch portion, a second notch portion, a third notch portion and a fourth notch portion; the first notch portion is provided at the first angle position, the second notch portion is provided at the second angle position, the third notch portion is provided at the third angle position, and the fourth notch portion is provided at the fourth angle position; A pole lug, wherein four pole lugs are provided, and the four pole lugs are arranged in one-to-one correspondence with the first notch portion, the second notch portion, the third notch portion and the fourth notch portion, one end of the pole lug is connected to the pole piece, and the other end of the pole lug extends out of the packaging bag from the notch portion along a second direction, and the second direction is perpendicular to the first direction.

2. The secondary battery according to claim 1, wherein: The first pole piece includes a first current collector and a first active material layer stacked along the first direction, the first current collector includes a first coating portion, a first connecting portion and a second connecting portion, and the first active material layer is disposed on the first coating portion; The second pole piece includes a second current collector and a second active material layer stacked along the first direction, the second current collector includes a second coating portion, a third connecting portion and a fourth connecting portion, and the second active material layer is provided on the second coating portion; when viewed along the first direction, a first notch is provided at a corner of the second current collector, a plurality of the first notches at least partially overlap in the first direction, and the plurality of the first notches together form the first notch portion, the first connecting portion exceeds the second current collector and is exposed from the first notch portion, and a portion of the isolation film is sandwiched between the plurality of the first connecting portions; When viewed along the first direction, the second current collector is provided with a second notch at another corner thereof, a plurality of the second notches at least partially overlap in the first direction, the plurality of the second notches together form a second notch portion, the second connecting portion exceeds the second current collector and is exposed from the second notch portion, and a portion of the isolation film is sandwiched between the plurality of the second connecting portions; When viewed along the first direction, a third notch is provided at a corner of the first current collector, a plurality of the third notches at least partially overlap in the first direction, the plurality of the third notches together form the third notch portion, the third connecting portion exceeds the first current collector and is exposed from the third notch portion, and a portion of the isolation film is sandwiched between the plurality of the third connecting portions; When viewed along the first direction, a fourth notch is provided at another corner of the first current collector, a plurality of the fourth notches at least partially overlap in the first direction, the plurality of the fourth notches together form the fourth notch portion, the fourth connecting portion exceeds the first current collector and is exposed from the fourth notch portion, and a portion of the isolation film is sandwiched between the plurality of the fourth connecting portions; The plurality of first connection parts are gathered into a first connection bundle along the first direction, the plurality of second connection parts are gathered into a second connection bundle along the first direction, the plurality of third connection parts are gathered into a third connection bundle along the first direction, and the fourth connection parts are gathered into a fourth connection bundle along the first direction; The pole lugs include a first pole lug, a second pole lug, a third pole lug and a fourth pole lug, wherein one end of the first pole lug is connected to the first connecting bundle, one end of the second pole lug is connected to the second connecting bundle, one end of the third pole lug is connected to the third connecting bundle, and one end of the fourth pole lug is connected to the fourth connecting bundle.

3. The secondary battery according to claim 2, characterized in that: The isolation film includes an extension portion, which is a portion of the isolation film sandwiched between the first connection portions, between the second connection portions, between the third connection portions, and between the fourth connection portions; The extension portion includes a first extension portion and a second extension portion, wherein in the first notch portion and the second notch portion, the first extension portion is a portion extending beyond the second current collector along the second direction, and the second extension portion is a portion extending beyond the second current collector along the third direction; In the third notch portion and the fourth notch portion, the first extension portion is a portion extending beyond the first current collector along the second direction, and the second extension portion is a portion extending beyond the first current collector along the third direction, and the third direction is perpendicular to the first direction and the second direction in pairs; Along the second direction, the width of the first extension portion is W1, 0.5 mm ≤ W1 ≤ 1 mm; and / or Along the third direction, the width of the second extending portion is W2, 0.5 mm≤W2≤1 mm.

4. The secondary battery according to claim 3, characterized in that: 0.5mm≤W1≤0.7mm; and / or 0.5mm≤W2≤0.7mm.

5. The secondary battery according to claim 2, characterized in that: One of the first electrode sheets is an outer electrode sheet, the outer electrode sheet is located at the outermost layer of the electrode assembly, the first current collector of the outer electrode sheet comprises a first surface and a second surface arranged opposite to each other along the first direction, the first surface is a surface facing the inside of the electrode assembly, and the first active material layer of the outer electrode sheet is arranged on the first surface; The outer pole piece further includes a reinforcement layer, and the reinforcement layer is disposed on the second surface. When viewed along the first direction, the first current collector has a plurality of vertices, and the reinforcement layer covers at least one of the vertices.

6. The secondary battery according to claim 5, characterized in that: The reinforcement layer includes a ceramic material, and the ceramic material includes at least one of aluminum oxide, zirconium oxide, titanium oxide, silicon oxide or boehmite.

7. The secondary battery according to claim 5, characterized in that: The thickness of the reinforcement layer is T1, 5 μm≤T1≤10 μm.

8. The secondary battery according to claim 2, wherein: When viewed along the first direction, the first pole tab and the second pole tab are arranged diagonally, and the third pole tab and the fourth pole tab are arranged diagonally.

9. The secondary battery according to claim 8, characterized in that The first pole piece is a positive pole piece, the second pole piece is a negative pole piece, the material of the first pole tab and / or the second pole tab includes aluminum; the material of the third pole tab and / or the fourth pole tab includes copper-plated nickel.

10. The secondary battery according to any one of claims 1 to 9, characterized in that: When viewed along the first direction, the electrode assembly includes a first edge and a second edge disposed opposite to each other along the second direction, and a third edge and a fourth edge disposed opposite to each other along a third direction, wherein the third direction is perpendicular to the first direction and the second direction in pairs; The packaging bag has a receiving space, the electrode assembly is arranged in the receiving space, the packaging bag includes a packaging wall, the packaging wall encloses the receiving space; the packaging wall includes a first packaging wall and a second packaging wall arranged opposite to each other along the second direction, the first packaging wall is closer to the first edge than the second packaging wall; and a third packaging wall and a fourth packaging wall arranged opposite to each other along the third direction, wherein the third packaging wall is closer to the third edge than the fourth packaging wall; Along the second direction, the spacing between the first packaging wall and the first edge, and the spacing between the second packaging wall and the second edge is W3; along the third direction, the spacing between the third packaging wall and the third edge, and the spacing between the fourth packaging wall and the fourth edge is W4; 0.3mm≤W3≤0.8mm, and / or, 0.3mm≤W4≤0.8mm.

11. The secondary battery according to claim 10, characterized in that: 0.3mm≤W3≤0.5mm, and / or, 0.3mm≤W4≤0.5mm.

12. The secondary battery according to claim 1, wherein: The isolation film comprises a substrate layer, a ceramic layer and an adhesive layer; The material of the substrate layer includes at least one of polyethylene, polypropylene, polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, polyphenylamide, polyarylethersulfoneketone, aramid or aromatic sulfone; The material of the ceramic layer includes at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, barium titanate or boehmite; The material of the adhesive layer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose or acrylate.

13. The secondary battery according to claim 12, characterized in that: The thickness of the ceramic layer is T2, 1.5 μm≤T2≤3 μm; and / or The thickness of the adhesive layer is T3, 0.5 μm≤T3≤3 μm.

14. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 13.

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