Secondary battery, electric equipment and preparation method of secondary battery

Abstract

The embodiment of the invention provides a secondary battery, electric equipment and a preparation method of the secondary battery, the secondary battery comprises an electrode assembly, the electrode assembly comprises a first pole piece located on the outermost layer of the electrode assembly, the first pole piece comprises a first current collector, a first active material layer and a first insulating layer, the first current collector is provided with a first surface and a second surface which are oppositely arranged, the first active material layer is arranged on the first surface, and the first insulating layer is arranged on the second surface. The secondary battery further comprises a first bonding piece, the first bonding piece comprises a first part and a second part, the first part is bonded to the partial surface, not covered by the first insulating layer, of the second surface, or the first part is bonded to the area, of which the thickness is reduced after partial material is removed, of the first insulating layer; the second portion is bonded to the surface of the electrode assembly on one side in the second direction. In the secondary battery, the energy density of the secondary battery can be improved while the curling degree and possibility of the outermost layer pole piece of the electrode assembly can be reduced.

Description

Technical Field

[0001] The present application belongs to the field of energy storage technology, and in particular relates to a secondary battery, an electrical device, and a method for preparing the secondary battery. Background Art

[0002] The outermost pole piece of a laminated secondary battery is usually coated with an active material layer only on one side of the current collector facing the middle of the electrode assembly to increase the energy density of the secondary battery and reduce costs. However, after cold pressing, the active material particles of the pole piece coated on one side are embedded in the surface of the current collector, causing lateral stress between the active material layer and the current collector. After die-cutting, the pole piece is prone to curling, resulting in low yield or even inability to perform subsequent processing steps; the aforementioned lateral stress may also cause the pole piece to warp and separate from the isolation membrane, leading to lithium precipitation.

[0003] In order to improve the anti-curling ability of the electrode sheet, there is a solution in the prior art to increase the thickness of the current collector. However, this solution will increase the thickness of the electrode assembly and cause a loss in the energy density of the secondary battery. Summary of the invention

[0004] To address the above problems, a solution has been developed to provide a coating on the surface of the current collector that is not coated with the active material layer. Compared with the solution of thickening the current collector, this solution can produce a thinner electrode, which can improve the energy density of the secondary battery.

[0005] During the research process of the present invention, the inventors found that stacked electrode assemblies often require adhesive tape to be set on the two end faces and sides of the electrode assembly along the thickness direction to clamp the electrode sheets to maintain the structure of the electrode assembly. However, the stacking of adhesive tape and coating is not conducive to improving the energy density of the secondary battery.

[0006] In view of the above situation, the embodiments of the present application provide a first secondary battery, an electrical device and a method for preparing a secondary battery, which can improve the energy density of the secondary battery while reducing the degree and possibility of curling of the outermost electrode sheet of the electrode assembly.

[0007] The first aspect of the embodiment of the present application provides a secondary battery, which includes an electrode assembly, which is a laminated structure, and the electrode assembly includes a first pole piece located at its outermost layer, the first pole piece includes a first current collector and a first active material layer, the first current collector has a first surface and a second surface arranged opposite to each other along a first direction, the first surface faces the inner side of the electrode assembly, and the first active material layer is arranged on the first surface; the first pole piece also includes a first insulating layer, the first insulating layer is arranged on the second surface, and the first insulating layer is used to resist the curling tendency of the first current collector, and the first direction is the thickness direction of the first pole piece. The secondary battery also includes a first adhesive, the first adhesive includes a first part and a second part of an integrated structure, the first part is bonded to the surface of the electrode assembly on the same side as the first insulating layer; the second part is bonded to the surface of the electrode assembly on the second direction side, and the second direction is perpendicular to the first direction.

[0008] In this secondary battery, by providing the first insulating layer, it is helpful to reduce the degree and possibility of curling of the first pole piece due to coating the first active material layer only on one side of the first current collector. In this way, in the production process of the secondary battery, it is helpful to improve the production yield of the processing process after cold pressing; in the use of the secondary battery, it is helpful to reduce the possibility of separation of the first pole piece and the isolation membrane. The first adhesive can provide a binding force to the pole piece in the electrode assembly to maintain the stacking state of the pole piece and the isolation membrane in the electrode assembly.

[0009] In an optional embodiment of the present application, the first insulating layer is disposed on a portion of the surface of the second surface, and the first portion is bonded to a portion of the surface of the second surface that is not covered by the first insulating layer. In this way, the first insulating layer and the first adhesive member do not overlap in the first direction, which is beneficial to reducing the effect of the first insulating layer on the thickness of the secondary battery, so as to improve the energy density of the secondary battery.

[0010] In an optional embodiment of the present application, the thickness of the first insulating layer along the first direction is T1, 10μm≤T1≤20μm. When T1≥10μm is set, the thickness of the first insulating layer is not too small, which is conducive to improving the effect of the first insulating layer in resisting the curling tendency of the first pole piece; when T1≤20μm is set, the thickness of the first insulating layer is not too thick, which is conducive to reducing the influence of the setting of the first insulating layer on the thickness of the electrode assembly.

[0011] In an optional embodiment of the present application, the first insulating layer is provided on at least part of the surface of the second surface, the first insulating layer includes a main body portion and a thinning portion of an integrated structure, the thickness of the main body portion along the first direction is greater than the thickness of the thinning portion along the first direction; the first portion is bonded to the surface of the thinning portion along the first direction facing away from the first current collector. The first portion is provided on the thinning portion, which is conducive to reducing the influence of the superposition of the thickness of the first adhesive and the first insulating layer on the thickness of the secondary battery; and the provision of the thinning portion can reduce the degree and possibility of curling of the first pole piece at the position where the first portion is bonded.

[0012] In an optional embodiment of the present application, the thickness of the first part along the first direction is T2, the thickness of the main body along the first direction is T2, 10μm≤T2≤20μm. When T2≥10μm, the thickness of the main body is not too small, which is conducive to improving the ability of the main body to resist the curling of the first pole piece; when T2≤20μm, the thickness of the main body is not too large, which is conducive to reducing the influence of the main body on the thickness of the electrode assembly.

[0013] In an optional embodiment of the present application, the thickness of the thinned portion along the first direction is T3, 2μm≤T3≤4μm. When T3≥2μm is set, the thickness of the thinned portion is not too small, which is conducive to improving the ability of the thinned portion to resist the curling of the first pole piece; when T3≤4μm is set, the thickness of the thinned portion is not too large, which is conducive to reducing the influence of the sum of the thickness of the thinned portion and the first part on the thickness of the secondary battery.

[0014] In an optional embodiment of the present application, the distance between the main body and the first part along the second direction is W1, 0mm≤W1≤2mm. When W1≤2mm is set, the distance between the first part and the main body is not too large, which is conducive to increasing the projection area of ​​the main body along the first direction, thereby reducing the degree and possibility of curling of the first pole piece.

[0015] In an optional embodiment of the present application, the first insulating layer is provided on at least part of the surface of the second surface, and the thickness of the first insulating layer along the first direction is T4, 2μm≤T4≤4μm. The thickness of the first insulating layer is obtained by removing part of the material of the first insulating layer after coating. The first part is bonded to the surface of the first insulating layer along the first direction facing away from the first current collector. Thinning the first insulating layer and then bonding the first adhesive is beneficial to reducing the influence of the sum of the thickness of the first part and the first insulating layer along the first direction on the energy density of the secondary battery; in addition, setting T4≥2μm, the thickness of the first insulating layer is not too small, which is beneficial to improve the ability of the first insulating layer to resist the curling of the first pole piece; setting T4≤4μm, the thickness of the first insulating layer is not too large, which is beneficial to reduce the influence of the sum of the thickness of the first insulating layer and the first part on the thickness of the secondary battery.

[0016] In an optional embodiment of the present application, the thickness of the first part along the first direction is T5, 8μm≤T5≤12μm. When T5≥8μm is set, the thickness of the first part is not too small, which is conducive to reducing the difficulty of producing the first part on the one hand, and is conducive to improving the strength of the first part and reducing the possibility of the first part being broken due to the stress in the first pole piece 30 on the other hand; when T5≤12μm is set, the thickness of the first part is not too large, which is conducive to reducing the influence of the thickness of the first part on the thickness of the electrode assembly.

[0017] In an optional embodiment of the present application, the second surface is a polygon, and the first insulating layer contacts any vertex of the second surface. The first insulating layer's effect of resisting the curling of the first pole piece involves any corner of the first pole piece, which is conducive to reducing the possibility of curling of the first pole piece.

[0018] In an optional embodiment of the present application, the second surface is a polygon, and the first insulating layer contacts any vertex of the second surface and any edge of the second surface. The effect of the first insulating layer on resisting the curling of the first pole piece involves any corner and any edge of the first pole piece, which is conducive to further reducing the possibility of curling of the first pole piece.

[0019] In an optional embodiment of the present application, the material of the first insulating layer includes a main material and an adhesive. The main material includes at least one of aluminum oxide, boehmite, zirconium oxide or titanium oxide, and the mass percentage of the main material is 80% to 99% based on the mass of the first insulating layer; the adhesive includes at least one of styrene-butadiene rubber, polyvinylidene fluoride or polyacrylate, and the mass percentage of the adhesive is 0.3% to 20% based on the mass of the first insulating layer.

[0020] In an optional embodiment of the present application, the thickness of the first current collector along the first direction is T6, 8μm≤T6≤12μm. When T6≥8μm, the thickness of the first current collector is not too thin, which is conducive to reducing the difficulty of preparing the first current collector, improving the current carrying capacity and mechanical strength of the first current collector, and reducing the possibility of curling of the first pole piece; when T6≤12μm, the thickness of the first current collector is not too thick, which is conducive to improving the energy density of the secondary battery.

[0021] In an optional embodiment of the present application, the width of the first part along the second direction is W2, 4mm≤W2≤12mm. When W2≥4mm, the width of the first part along the second direction Y is not too small, which is conducive to improving the binding ability of the first adhesive to the electrode assembly to maintain the structure of the electrode assembly; when W2≤12mm, the width of the first adhesive along the second direction is not too large, which is conducive to saving materials.

[0022] A second aspect of the embodiments of the present application provides an electrical device, which includes a secondary battery as described in any of the above embodiments.

[0023] A third aspect of an embodiment of the present application provides a method for preparing a secondary battery, the method for preparing a secondary battery comprising the following steps: Take a first pole piece, the first pole piece includes a first current collector and a first active material layer, the first current collector has a first surface and a second surface arranged opposite to each other along a first direction, and the first active material layer is arranged on the first surface; the first direction is a thickness direction of the first pole piece; A first insulating layer is disposed on the second surface, wherein the first insulating layer covers a portion of the surface of the second surface; Arranging the first pole piece on the outermost layer of the laminated electrode assembly; Take a first adhesive and adhere the first adhesive to the partial surface of the second surface not covered by the first insulating layer and the surface of the electrode assembly located on the second direction side, where the second direction is perpendicular to the first direction.

[0024] In an optional embodiment of the present application, the method for preparing the secondary battery comprises the following steps: Before providing the first insulating layer on the second surface, adhesive tape is bonded to a portion of the surface of the second surface; After the first insulating layer is disposed on the second surface, a portion of the first insulating layer is covered with adhesive tape; After the first electrode sheet is arranged on the outermost layer of the laminated electrode assembly, the adhesive tape is removed so that a portion of the surface of the second surface is exposed to the first insulating layer.

[0025] A fourth aspect of an embodiment of the present application provides another method for preparing a secondary battery, the method for preparing a secondary battery comprising the following steps: Take a first pole piece, the first pole piece includes a first current collector and a first active material layer, the first current collector has a first surface and a second surface arranged opposite to each other along a first direction, and the first active material layer is arranged on the first surface; the first direction is a thickness direction of the first pole piece; A first insulating layer is disposed on the second surface, wherein the first insulating layer covers a portion of the surface of the second surface; Arranging the first pole piece on the outermost layer of the laminated electrode assembly; Removing part of the material of the first insulating layer to reduce the thickness of at least part of the first insulating layer along the first direction; Take a first adhesive, adhere part of the first adhesive to the surface of the first insulating layer thinning area facing away from the first current collector along the first direction, and adhere part of the first adhesive to the surface of the electrode assembly on the second direction side, the second direction is perpendicular to the first direction.

[0026] In an optional embodiment of the present application, the material of the portion of the first insulating layer is removed by laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of a secondary battery in one embodiment of the present application.

[0028] Figure 2 yes Figure 1 Schematic diagram of the cross-sectional structure at II-II.

[0029] Figure 3 It is a schematic structural diagram of an electrode assembly and a first adhesive member in one embodiment of the present application.

[0030] Figure 4 yes Figure 3 Schematic diagram of the cross-sectional structure at IV-IV in the figure.

[0031] Figure 5 It is a schematic structural diagram of an electrode assembly and a first adhesive member in one embodiment of the present application.

[0032] Figure 6 yes Figure 5 Schematic diagram of the cross-sectional structure at VI-VI in the figure.

[0033] Figure 7 It is a schematic structural diagram of an electrode assembly and a first adhesive member in one embodiment of the present application.

[0034] Figure 8 yes Figure 7 Schematic diagram of the cross-sectional structure at VIII-VIII.

[0035] Fig. 9 It is a schematic diagram of the structure of an electrical device in an embodiment of the present application.

[0036] Main component symbols 1000, secondary battery; 100, electrode assembly; 10, positive electrode sheet; 11, positive electrode collector; 12, positive electrode active material layer; 20, negative electrode sheet; 21, negative electrode collector; 22, negative electrode active material layer; 30, first electrode sheet; 31, first current collector; 311, first surface; 312, second surface; 32, first active material layer; 33, first insulating layer; 331, main body; 332, thinning portion; 40, isolation film; 50, positive electrode ear; 60, negative electrode ear; 200, shell; 300, first adhesive; 310, first part; 320, second part; 330, third part; 10000, electrical equipment; X, first direction; Y, second direction. DETAILED DESCRIPTION

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

[0038] It should be noted that when an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a centrally disposed element at the same time. When an element is considered to be "disposed on" another element, it may be directly disposed on the other element or there may be a centrally disposed element at the same time.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0040] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0041] In the description of the embodiments of the present application, the term "perpendicular" is used to describe an ideal state between two components. In actual production or use, there may be a state that is approximately perpendicular between the two components. The two components described as "perpendicular" may not be absolutely straight lines or planes, but may be roughly straight lines or planes. From a macroscopic point of view, if the overall extension direction is a straight line or a plane, the components can be considered to be "straight lines" or "planes".

[0042] The term "parallel" is used to describe the ideal state between two parts. In actual production or use, two parts may be approximately parallel. The two parts described as "parallel" may not be absolutely straight lines or planes, but may be roughly straight lines or planes. From a macroscopic point of view, if the overall extension direction is a straight line or a plane, the parts can be considered "straight" or "plane".

[0043] Reference to "embodiment" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. The various embodiments in the present application may be combined with each other in the absence of conflict.

[0044] The embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0045] like Figure 1 and Figure 2 As shown, an embodiment of the present application provides a secondary battery 1000 , which includes a housing 200 and an electrode assembly 100 , wherein the electrode assembly 100 is accommodated in the housing 200 .

[0046] In some embodiments, the housing 200 is a flexible packaging bag, such as an aluminum-plastic film. In other embodiments, the housing 200 is a hard shell, such as a plastic shell, or a metal shell including at least one of steel alloy, aluminum alloy, and copper alloy.

[0047] In some embodiments, Figure 2 As shown, the electrode assembly 100 includes a positive electrode sheet 10, a negative electrode sheet 20 and a separator 40. A plurality of positive electrode sheets 10, a plurality of separators 40 and a plurality of negative electrode sheets 20 are alternately stacked along a first direction X to form a laminated structure. For any adjacent positive electrode sheet 10 and negative electrode sheet 20, a separator 40 is disposed between the two. The first direction X is the thickness direction of the positive electrode sheet 10.

[0048] In some embodiments, Figure 2 As shown, the positive electrode sheet 10 includes a positive electrode collector 11 and a positive electrode active material layer 12. For the positive electrode sheet 10 located at the non-outermost layer of the electrode assembly 100, two positive electrode active material layers 12 are respectively disposed on two surfaces of the positive electrode collector 11 along the first direction X.

[0049] In some embodiments, Figure 2 As shown, the negative electrode sheet 20 includes a negative electrode collector 21 and a negative electrode active material layer 22. For the negative electrode sheet 20 located at the non-outermost layer of the electrode assembly 100, two negative electrode active material layers 22 are respectively disposed on two surfaces of the negative electrode collector 21 along the first direction X.

[0050] In some embodiments, Figure 2 and Figure 4 As shown, a positive electrode sheet 10 or a negative electrode sheet 20 located at the outermost layer of the electrode assembly 100 is defined as a first electrode sheet 30. The first electrode sheet 30 includes a first current collector 31 and a first active material layer 32. The first current collector 31 has a first surface 311 and a second surface 312 arranged opposite to each other along a first direction X. The first surface 311 faces the inner side of the electrode assembly 100, and the first active material layer 32 is arranged on the first surface 311. When the first electrode sheet 30 is a positive electrode sheet 10, the first current collector 31 is a positive electrode current collector 11, and the first active material layer 32 is a positive electrode active material layer 12; when the first electrode sheet 30 is a negative electrode sheet 20, the first current collector 31 is a negative electrode current collector 21, and the first active material layer 32 is a negative electrode active material layer 22.

[0051] In some embodiments, both the positive electrode current collector 11 and the negative electrode current collector 21 are metal layers. As an illustrative example, the positive electrode current collector 11 may be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil. The negative electrode current collector 21 may be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as copper foil.

[0052] In some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.

[0053] In some embodiments, the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen material, and silicon-carbon material.

[0054] In some embodiments, Figure 1 and Figure 2 As shown, the positive electrode sheet 10 further includes a positive electrode ear 50 , which is connected to the positive electrode collector 11 and extends out of the shell 200 ; the negative electrode sheet 20 further includes a negative electrode ear 60 , which is connected to the negative electrode collector 21 and extends out of the shell 200 .

[0055] In some embodiments, the isolation film 40 is made of insulating film materials such as polyethylene film, polypropylene film, polyester film or polyimide film.

[0056] In some embodiments, the secondary battery 1000 further includes an electrolyte, which is contained in the housing 200 .

[0057] 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.

[0058] In some embodiments, the electrolyte salt includes but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4) or lithium trifluoromethanesulfonate (LiCF3SO3).

[0059] In some embodiments, Figure 3 and Figure 4As shown, the first pole piece 30 further includes a first insulating layer 33, which is disposed on the second surface 312, and is used to resist the curling tendency of the first current collector 31. The first insulating layer 33 is provided to reduce the degree and possibility of curling of the first pole piece 30 due to coating the first active material layer 32 only on one side of the first current collector 31. In this way, in the production process of the secondary battery 1000, it is helpful to improve the production yield of the processing process after cold pressing; in the use process of the secondary battery 1000, it is helpful to reduce the possibility of separation of the first pole piece 30 and the isolation film 40.

[0060] In some embodiments, Figure 3 and Figure 4 As shown, the secondary battery 1000 includes a first adhesive member 300, the first adhesive member 300 includes a first portion 310 and a second portion 320 of an integrated structure, the first portion 310 is bonded to the surface of the electrode assembly 100 on the same side as the first insulating layer 33 along the first direction X, and the second portion 320 is bonded to the surface of the electrode assembly 100 on the side of the second direction Y, and the second direction Y is perpendicular to the first direction X. The first adhesive member 300 can provide a binding force to the pole piece in the electrode assembly 100 to maintain the stacked state of the pole piece and the isolation film 40 in the electrode assembly 100.

[0061] In some embodiments, the second direction Y is the direction in which the positive electrode tab 50 and the negative electrode tab 60 extend out of the housing 200. In other embodiments, the second direction Y is perpendicular to the direction in which the positive electrode tab 50 and the negative electrode tab 60 extend out of the housing 200.

[0062] In some embodiments, Figure 3 and Figure 4 As shown, the first insulating layer 33 is disposed on a portion of the surface of the second surface 312, and the first portion 310 is bonded to the portion of the surface of the second surface 312 that is not covered by the first insulating layer 33. In this way, the first insulating layer 33 and the first adhesive member 300 do not overlap in the first direction X, which is beneficial to reduce the effect of the first insulating layer 33 on the thickness of the secondary battery 1000, so as to improve the energy density of the secondary battery 1000.

[0063] In some embodiments, Figure 4 As shown, the thickness of the first insulating layer 33 along the first direction X is T1, 10μm≤T1≤20μm. When T1≥10μm is set, the thickness of the first insulating layer 33 is not too small, which is conducive to improving the effect of the first insulating layer 33 in resisting the curling tendency of the first pole piece 30; when T1≤20μm is set, the thickness of the first insulating layer 33 is not too thick, which is conducive to reducing the influence of the setting of the first insulating layer 33 on the thickness of the electrode assembly 100.

[0064] In some embodiments, Figure 5 and Figure 6 As shown, the first insulating layer 33 is provided on at least part of the surface of the second surface 312. The first insulating layer 33 includes a main body 331 and a thinning portion 332 of an integrated structure, and the thickness of the main body 331 along the first direction X is greater than the thickness of the thinning portion 332 along the first direction X; the first portion 310 of the first adhesive 300 is bonded to the surface of the thinning portion 332 facing away from the first current collector 31 along the first direction X, and the second portion 320 is bonded to the surface of the electrode assembly 100 located on one side of the second direction Y. The first portion 310 is provided on the thinning portion 332, which is conducive to reducing the influence of the superposition of the thickness of the first adhesive 300 and the first insulating layer 33 on the thickness of the electrode assembly 100; and the provision of the thinning portion 332 can reduce the degree and possibility of curling of the first electrode sheet 30 at the position where the first portion 310 is bonded.

[0065] In some embodiments, the thinned portion 332 is formed by removing part of the material of the first insulating layer 33 by laser. Removing material from only a part of the first insulating layer 33 is beneficial to improving processing efficiency. Retaining the thinned portion 332 is beneficial to reducing the possibility of laser damage to the first current collector 31.

[0066] In some embodiments, Figure 6 As shown, the thickness of the main body 331 along the first direction X is T2, 10μm≤T2≤20μm. When T2≥10μm, the thickness of the main body 331 is not too small, which is beneficial to improve the ability of the main body 331 to resist the curling of the first pole piece 30; when T2≤20μm, the thickness of the main body 331 is not too large, which is beneficial to reduce the influence of the main body 331 on the thickness of the electrode assembly 100.

[0067] As an illustrative example, the value of T2 is one of 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm or 19 μm.

[0068] In some embodiments, Figure 5 and Figure 6 As shown, the thickness of the thinned portion 332 along the first direction X is T3, 2μm≤T3≤4μm. When T3≥2μm, the thickness of the thinned portion 332 is not too small, which is beneficial to improve the ability of the thinned portion 332 to resist the curling of the first pole piece 30; when T3≤4μm, the thickness of the thinned portion 332 is not too large, which is beneficial to reduce the influence of the sum of the thickness of the thinned portion 332 and the first portion 310 on the thickness of the secondary battery 1000.

[0069] As an illustrative example, the value of T3 is one of 2.2 μm, 2.5 μm, 2.7 μm, 3 μm, 3.2 μm, 3.5 μm or 3.7 μm.

[0070] In some embodiments, Figure 5 and Figure 6 As shown, the distance between the main body 331 and the first part 310 along the second direction Y is W1, 0mm≤W1≤2mm. When W1≤2mm, the distance between the first part 310 and the main body 331 is not too large, which is conducive to increasing the projection area of ​​the main body 331 along the first direction X, thereby reducing the degree and possibility of curling of the first pole piece 30. The value of W1 can be measured with a ruler.

[0071] In some embodiments, Figure 7 and Figure 8 As shown, the first insulating layer 33 is provided on at least part of the surface of the second surface 312, and the thickness of the first insulating layer 33 along the first direction X is T4, 2μm≤T4≤4μm. The first part 310 of the first adhesive 300 is bonded to the surface of the first insulating layer 33 along the first direction X that is opposite to the first current collector 31. In this embodiment, the thickness of the first insulating layer 33 is obtained by removing part of the material of the first insulating layer 33 after coating. In other words, the first insulating layer 33 is obtained by the following steps: coating the first insulating layer 33 on the first current collector 31 using a coating device, and the thickness of the first insulating layer 33 obtained in this step is greater than 4μm. After the first electrode sheet 30 is stacked with the remaining positive electrode sheets 10 and negative electrode sheets 20 in the electrode assembly 100, the first insulating layer 33 is thinned to 2μm to 4μm. The first insulating layer 33 is thinned before bonding the first adhesive 300, which is beneficial to reduce the influence of the sum of the thickness of the first part 310 and the first insulating layer 33 along the first direction X on the thickness of the secondary battery 1000. In addition, when T4 is set to ≥ 2 μm, the thickness of the first insulating layer 33 is not too small, which is beneficial to improve the ability of the first insulating layer 33 to resist the curling of the first pole piece 30; when T4 is set to ≤ 4 μm, the thickness of the first insulating layer 33 is not too large, which is beneficial to reduce the influence of the sum of the thickness of the first insulating layer 33 and the first part 310 on the thickness of the secondary battery 1000.

[0072] In the embodiment of the present application, the values ​​of T1, T2, T3 and T4 can be measured in the following direction: a slice of the first pole piece 30 is placed under a scanning electron microscope (SEM) for observation and measurement. During observation, the viewing angle is perpendicular to the section of the slice parallel to the first direction X.

[0073] In some embodiments, Figure 4 , Figure 6 or Figure 8As shown, the thickness of the first part 310 along the first direction X is T5, 8μm≤T5≤12μm. When T5≥8μm is set, the thickness of the first part 310 is not too small, which is conducive to reducing the difficulty of producing the first part 310 on the one hand, and is conducive to improving the strength of the first part 310 on the other hand, and reducing the possibility of the first part 310 being broken due to the stress in the first pole piece 30; when T5≤12μm is set, the thickness of the first part 310 is not too large, which is conducive to reducing the influence of the thickness of the first part 310 on the thickness of the electrode assembly 100.

[0074] As an illustrative example, the value of T5 is one of 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm or 11.5 μm.

[0075] The value of T5 can be measured in the following direction: take a slice of at least part of the first pole piece 30 connected to the first portion 310 and place it under SEM for observation and measurement. When observing, the viewing angle is facing the section of the slice parallel to the first direction X.

[0076] In some embodiments, Figure 4 , Figure 6 or Figure 8 As shown, the first adhesive member 300 further includes a third portion 330 , and the third portion 330 and the first portion 310 are respectively disposed on two opposite surfaces of the electrode assembly 100 along the first direction X to further enhance the effect of the first adhesive member 300 on maintaining the shape of the electrode assembly 100 .

[0077] In some embodiments, Figure 3 , Figure 5 or Figure 7 As shown, the second surface 312 is a polygon, and the first insulating layer 33 contacts any vertex of the second surface 312. In this way, the first insulating layer 33 resists the curling of the first pole piece 30. The influence area involves any corner of the first pole piece 30, which is conducive to reducing the possibility of curling of the first pole piece 30.

[0078] In some embodiments, Figure 3 , Figure 5 or Figure 7 As shown, the first insulating layer 33 contacts any vertex and any edge of the second surface 312. In this way, the first insulating layer 33 resists the curling of the first pole piece 30. The influence area involves any corner and any edge of the first pole piece 30, which is conducive to further reducing the possibility of curling of the first pole piece 30.

[0079] In some embodiments, the material of the first insulating layer 33 includes a main material and an adhesive. The main material includes at least one of aluminum oxide, boehmite, zirconium oxide, or titanium oxide, and the mass percentage of the main material is 80% to 99% based on the mass of the first insulating layer 33; the adhesive includes at least one of styrene-butadiene rubber, polyvinylidene fluoride, or polyacrylate, and the mass percentage of the adhesive is 0.3% to 20% based on the mass of the first insulating layer 33.

[0080] In some embodiments, the first adhesive member 300 includes a substrate layer and an adhesive layer. In some embodiments, the substrate layer can be selected from one of polyethylene terephthalate, co-extruded polypropylene, oriented polystyrene, thermoplastic polyurethane, polylactic acid, polyolefin, and polyimide.

[0081] In some embodiments, the rubber layer is made of one or a combination of natural rubber, styrene-butadiene rubber, isoprene rubber, styrene-polybutadiene-styrene block copolymer, hydrogenated styrene-polybutadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated styrene-polyisoprene-styrene block copolymer, polyisobutylene, amorphous α-olefin copolymer, petroleum resin, terpene resin, and rosin resin.

[0082] In some embodiments, the thickness of the first current collector 31 along the first direction X is T6, 8μm≤T6≤12μm. When T6≥8μm, the thickness of the first current collector 31 is not too thin, which is conducive to reducing the difficulty of preparing the first current collector 31, improving the current carrying capacity and mechanical strength of the first current collector 31, and reducing the possibility of curling of the first pole piece 30; when T6≤12μm, the thickness of the first current collector 31 is not too thick, which is conducive to improving the energy density of the secondary battery 1000.

[0083] In some embodiments, the width of the first portion 310 along the second direction Y is W2, 4mm≤W2≤12mm. When W2≥4mm, the width of the first portion 310 along the second direction Y is not too small, which is conducive to improving the binding ability of the first adhesive 300 on the electrode assembly 100 to maintain the structure of the electrode assembly 100; when W2≤12mm, the width of the first adhesive 300 along the second direction Y is not too large, which is conducive to saving materials. The value of W2 can be measured with a ruler.

[0084] like Fig. 9 As shown, an embodiment of the present application further provides an electric device 1000, comprising the secondary battery 1000 involved in any of the aforementioned embodiments.

[0085] The embodiment of the present application also provides a method for preparing a secondary battery 1000, and the method for preparing the secondary battery 1000 comprises the following steps: Take a first pole piece 30, the first pole piece 30 includes a first current collector 31 and a first active material layer 32, the first current collector 31 has a first surface 311 and a second surface 312 arranged opposite to each other along a first direction X, and the first active material layer 32 is arranged on the first surface 311; A first insulating layer 33 is disposed on the second surface 312 , and the first insulating layer 33 covers a portion of the surface of the second surface 312 ; The first electrode sheet 30 is arranged at the outermost layer of the laminated electrode assembly 100; Take a first adhesive 300 and adhere the first adhesive 300 to the portion of the second surface 312 that is not covered by the first insulating layer 33 and the surface of the electrode assembly 100 located on one side of the second direction Y.

[0086] In some embodiments, the method for preparing the secondary battery 1000 further includes the following steps: Before the first insulating layer 33 is provided on the second surface 312 , adhesive tape is adhered to a part of the surface of the second surface 312 ; After the first insulating layer 33 is disposed on the second surface 312 , a portion of the first insulating layer 33 is covered with adhesive tape; After the first electrode sheet 30 is disposed on the outermost layer of the laminated electrode assembly 100 , the adhesive tape is torn off so that a portion of the surface of the second surface 312 is exposed to the first insulating layer 33 .

[0087] In some other embodiments, the first insulating layer 33 may be removed by laser cleaning.

[0088] The embodiment of the present application also provides another method for preparing a secondary battery 1000, and the method for preparing the secondary battery 1000 includes the following steps: Take a first pole piece 30, the first pole piece 30 includes a first current collector 31 and a first active material layer 32, the first current collector 31 has a first surface 311 and a second surface 312 arranged opposite to each other along a first direction X, and the first active material layer 32 is arranged on the first surface 311; A first insulating layer 33 is disposed on the second surface 312 , and the first insulating layer 33 covers a portion of the surface of the second surface 312 ; The first electrode sheet 30 is arranged at the outermost layer of the laminated electrode assembly 100; Removing part of the material of the first insulating layer 33 so as to reduce the thickness of at least part of the first insulating layer 33 along the first direction X; Take a first adhesive 300, adhere part of the first adhesive 300 to the surface of the thinned area of ​​the first insulating layer 33 facing away from the first current collector 31 along the first direction X, and adhere part of the first adhesive 300 to the surface of the electrode assembly 100 on the second direction Y side.

[0089] In some embodiments, the method for preparing the secondary battery 1000 further includes the following steps: The material of part of the first insulating layer 33 is removed by laser.

[0090] In some embodiments, the method for preparing the secondary battery 1000 further includes the following steps: using a negative pressure device to absorb dust generated when the laser removes part of the material of the first insulating layer 33 .

[0091] In order to verify the influence of the solution in the embodiment of the present application on the performance of the secondary battery 1000 , the inventors conducted the following experiment.

[0092] The experiment includes a group of comparative examples and 28 groups of examples, and each experimental group prepares 32 secondary batteries 1000. In Examples 1-8, the first insulating layer 33 of the secondary battery 1000 covers part of the surface of the second surface 312, and the first part 310 of the first adhesive 300 is bonded to the part of the surface of the second surface 312 that is not covered by the first insulating layer 33; in Examples 9-20, the first insulating layer 33 includes a main body 331 and a thinning portion 332, and the first part 310 is bonded to the surface of the thinning portion 332 that is opposite to the first current collector 31 along the first direction X; in Examples 21-28, the first insulating layer 33 covers the entire surface of the second surface 312, and the first part 310 is bonded to the surface of the first insulating layer 33 that is opposite to the first current collector 31 along the first direction X. In Examples 1-30, the first electrode sheet 30 is a positive electrode sheet 10.

[0093] The method for preparing the secondary battery 1000 in Example 1 includes the following steps: (1) Preparation of positive electrode sheet 10: Active materials lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNT (carbon nanotube), polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:0.5:0.5:1.5, N-methylpyrrolidone (NMP) is added as a solvent, and a positive electrode active material with a solid content of 75wt% is prepared, and stirred evenly for use. Aluminum foil is used as the positive electrode current collector 11, and the thickness of the aluminum foil used in each embodiment is recorded in Table 1. The above-mentioned active material material is uniformly coated on the surface of the positive electrode current collector 11 along the first direction X, and then dried at 90°C to obtain a positive electrode sheet 10 coated with a positive electrode active material layer 12 on one side. At this time, the thickness of the positive electrode active material layer 12 along the first direction X is 50μm. Afterwards, for the positive electrode sheet 10 disposed in the non-outermost layer of the electrode assembly 100, the above coating steps are repeated on the surface of the positive electrode collector 11 on the other side along the first direction X to obtain a positive electrode sheet 10 coated with a positive electrode active material layer 12 on both sides; for the positive electrode sheet 10 (first electrode sheet 30) disposed in the outermost layer of the electrode assembly 100, the material of the first insulating layer 33 is coated on the surface of the positive electrode collector 11 on the other side along the first direction X (i.e., the second surface 312 mentioned above), and the first insulating layer 33 covers part of the surface of the second surface 312. Then, the coated positive electrode sheet 10 is cold pressed. After cold pressing, the thickness of the positive electrode active material layer 12 is 35 μm. The thickness of the first insulating layer 33 in each embodiment is recorded in Table 1. The area of ​​the positive electrode collector 11 that is not covered when the positive electrode active material layer 12 and the first insulating layer 33 are coated is an empty foil area, and the empty foil area is cut to obtain the positive electrode ear 50.

[0094] (2) Preparation of negative electrode sheet 20: Active materials artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) are mixed in a weight ratio of 97:0.5:1.3:1.2, and deionized water is added as a solvent to prepare a negative electrode active material material with a weight percentage of 50wt%, and stirred evenly for use. A copper foil with a thickness of 10μm is used as the negative electrode current collector 21. The above negative electrode active material is evenly coated on the surface of the negative electrode current collector 21 along the first direction X using a slit coater, and then dried at 110°C to obtain a negative electrode sheet 20 coated with a negative electrode active material layer 22 on one side. Then, the above steps are repeated on the other side of the negative electrode current collector 21 along the first direction X to obtain a negative electrode sheet 20 coated with a negative electrode active material layer 22 on both sides. At this time, the thickness of the negative electrode active material layer 22 along the first direction X is 55μm. The coated negative electrode sheet 20 is then cold pressed, and the thickness of the negative electrode active material layer 22 along the first direction X is 45 μm after cold pressing. The negative electrode tab 60 is then welded to the portion of the negative electrode current collector 21 that is not covered by the negative electrode active material layer 22. The area of ​​the negative electrode current collector 21 that is not covered when the negative electrode active material layer 22 is coated is an empty foil area, and the empty foil area is cut to obtain the negative electrode tab 60.

[0095] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) was added to the basic organic solvent to dissolve and mix well to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0096] (4) Preparation of the isolation membrane 40 : A 7 μm thick polyethylene porous polymer film was used as the isolation membrane 40 .

[0097] (5) Preparation of electrode assembly 100: The positive electrode sheet 10, the separator 40 and the negative electrode sheet 20 are stacked in the thickness direction of the negative electrode sheet 20 to obtain the electrode assembly 100, and the first adhesive 300 is bonded to the electrode assembly 100 to maintain the structure of the electrode assembly 100. The thickness of the first portion 310 of the first adhesive 300 is 12 μm, and the first portion 310 is bonded to the surface of the second surface 312 that is not covered by the first insulating layer 310. During the preparation of the electrode assembly 100, the separation of the first electrode sheet 30 and the separator 40 is monitored. If the separator 40 is separated from the first electrode sheet 30, the electrode assembly 100 is no longer assembled with the housing 200, and the secondary battery 1000 is recorded as failed.

[0098] (6) Assembly of secondary battery 1000: Place the aluminum-plastic film with a hole formed in the assembly fixture, with the hole facing upward, place the electrode assembly 100 in the hole, and apply external force to press it. Then, cover the electrode assembly 100 with another aluminum-plastic film with a hole formed in the hole facing downward, and heat-seal the three edges of the two aluminum-plastic films by hot pressing. The unsealed edge is the side where the negative electrode ear 60 and the positive electrode ear 50 extend out of the shell 200. Then, inject the electrolyte through the unsealed edge, and after vacuum packaging, static, hot pressing, shaping and other processes, the secondary battery 1000 is manufactured.

[0099] The preparation steps of the secondary battery 1000 in Comparative Example 1 are substantially the same as those in Example 1, except that the first insulating layer 33 in Comparative Example 1 covers the entire surface of the second surface 312 , and the first portion of the first adhesive 300 is bonded to the first insulating layer 33 .

[0100] The preparation steps of the secondary battery 1000 in Examples 2-8 are substantially the same as those in Example 1, except that the data listed in Table 1 are different.

[0101] The preparation steps of the secondary battery 1000 in Examples 9-20 are basically the same as those in Example 1, with the difference that, after the electrode assembly 100 is stacked, if the first electrode sheet 30 and the isolation membrane 40 are not separated, part of the material in a partial area of ​​the first insulating layer 33 is removed to form the thinning portion 332 mentioned above, and the portion where the material is not removed is the main body 331 mentioned above, and the first portion 310 is bonded to the thinning portion 332.

[0102] The preparation steps of the secondary battery 100 in Examples 21-28 are basically the same as those in Example 1, with the difference that, after the electrode assembly 100 is stacked, if the first electrode sheet 30 and the isolation membrane 40 are not separated, part of the material is removed from the entire area of ​​the first insulating layer 33 to reduce the thickness of the first insulating layer 33 along the first direction, and the first portion 310 is bonded to the thinned first insulating layer 33.

[0103] After the secondary battery 1000 in each embodiment is prepared, a long cycle test is performed on each secondary battery 1000. The test process is as follows: 1) Maintain the test temperature at 25°C; 2) Let the secondary battery 1000 stand for 30 minutes; 3) 5C constant current charging to 4.25V, then constant voltage charging to 3C; 4) 3C constant current charging to 4.35V, then constant voltage charging to 1.5C; 5) 1.5C constant current charge to 4.45V, then constant voltage charge to 0.05C; 6) Let stand for 5 minutes; 7) 0.7C constant current discharge to 3V, record the first discharge cycle capacity; 8) Let stand for 5 minutes; 9) Repeat steps 3 to 8 800 times.

[0104] The volume energy density of the secondary battery 1000 is calculated, and the volume energy density=the first discharge cycle capacity / (the length of the secondary battery×the width of the secondary battery×the thickness). The volume energy density of the 32 secondary batteries 1000 in the same group is averaged and recorded in Table 1.

[0105] The secondary battery 1000 is disassembled to observe the separation of the first pole piece 30 and the separator 40. If the first pole piece 30 is separated from the separator 40, the secondary battery 1000 is recorded as failed. For each group of embodiments, the number of failed secondary batteries 1000 recorded in Table 1 is the sum of the number of failed secondary batteries 1000 during the preparation process and the number of failed secondary batteries 1000 after long cycles.

[0106] The experimental results are shown in Table 1 below.

[0107] Table 1 Note: In the table, “ / ” means no such data.

[0108] As can be seen from Table 1, in Examples 1-28, the average values ​​of the volume energy density of the secondary battery 1000 are higher than that of Comparative Example 1, and the number of failed secondary batteries 1000 is not significantly different from that of Comparative Example 1. It can be seen that for the secondary batteries 1000 in Examples 1-8, the first insulating layer 33 and the first adhesive 300 do not overlap in the first direction X, which is conducive to reducing the influence of the setting of the first insulating layer 33 on the thickness of the secondary battery 1000, so as to improve the energy density of the secondary battery 1000; for the secondary batteries 1000 in Examples 9-20, the first part 310 is arranged in the thinning part 332, which is conducive to reducing the influence of the superposition of the thickness of the first adhesive 300 and the first insulating layer 33 on the thickness of the secondary battery 1000; for the secondary batteries 1000 in Examples 21-28, the first insulating layer 33 is thinned before bonding the first adhesive 300, which is conducive to reducing the influence of the sum of the thickness of the first part 310 and the first insulating layer 33 along the first direction X on the energy density of the secondary battery. On this basis, the anti-curling ability of the first pole piece 30 of the secondary battery 1000 in Examples 1-28 did not show a significant decrease compared with Comparative Example 1. Therefore, the secondary battery 1000 provided in the embodiments of the present application can improve the energy density while taking into account the anti-curling ability of the first pole piece 30.

[0109] In Examples 2-4, the thickness T1 of the first insulating layer 33 satisfies 10μm≤T1≤20μm. Compared with Example 1, the number of failures of the secondary battery 1000 in Examples 2-4 is less, and as the thickness of the first insulating layer 33 increases, the volume energy density of the secondary battery 1000 shows a downward trend. It can be seen that when T1≥10μm is set, the thickness of the first insulating layer 33 is not too small, which is conducive to improving the effect of the first insulating layer 33 in resisting the curling tendency of the first pole piece 30; when T1≤20μm is set, the thickness of the first insulating layer 33 is not too thick, which is conducive to reducing the influence of the setting of the first insulating layer 33 on the thickness of the electrode assembly 100.

[0110] In Examples 10-12, the thickness T2 of the main body 331 satisfies 10μm≤T2≤20μm. Compared with Example 9, as the thickness of the main body 331 increases, the number of failures of the secondary battery 1000 in Examples 10-12 tends to decrease, and as the thickness of the main body 331 increases, the volume energy density of the secondary battery 1000 tends to decrease. It can be seen that when T2≥10μm is set, the thickness of the main body 331 is not too small, which is conducive to improving the effect of the main body 331 in resisting the curling tendency of the first pole piece 30; when T2≤20μm is set, the thickness of the main body 331 is not too thick, which is conducive to reducing the influence of the setting of the main body 331 on the thickness of the electrode assembly 100.

[0111] In Examples 13-16, as the thickness T3 of the thinned portion 332 increases, the energy density of the secondary battery 1000 tends to decrease. It can be seen that setting T3≤4μm is conducive to reducing the effect of the sum of the thickness of the thinned portion 332 and the first portion 310 on the energy density of the secondary battery 1000. Considering that a laser is used to remove part of the material of the first insulating layer 33, setting T3≥2μm is conducive to reducing the effect of the laser energy on the first current collector 31.

[0112] In Examples 21-24, as the thickness T4 of the first insulating layer 33 increases, the energy density of the secondary battery 1000 tends to decrease. It can be seen that setting T4≤4μm is conducive to reducing the influence of the sum of the thickness of the first insulating layer 33 and the first portion 310 on the energy density of the secondary battery 1000. Considering that a laser is used to remove part of the material of the first insulating layer 33, setting T4≥2μm is conducive to reducing the influence of the laser energy on the first current collector 31.

[0113] The thickness of the first current collector 31 of the secondary battery 1000 in Examples 6-7, the secondary battery 1000 in Examples 18-19, and the secondary battery 1000 in Examples 26-27 satisfies 8μm≤T6≤12μm, the number of failures of the secondary battery 1000 in Examples 6-7 is less than that of Example 5, and the volume energy density is not less than that of Example 8, the number of failures of the secondary battery 1000 in Examples 18-19 is less than that of Example 17, and the volume energy density is not less than that of Example 20, and the number of failures of the secondary battery 1000 in Examples 26-27 is less than that of Example 25, and the volume energy density is not less than that of Example 28. It can be seen that when T6≥8μm is set, the thickness of the first current collector 31 is not too thin, which is conducive to reducing the possibility of curling of the first pole piece 30; when T6≤12μm is set, the thickness of the first current collector 31 is not too thick, which is conducive to improving the energy density of the secondary battery 1000.

[0114] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, wherein the electrode assembly is a laminated structure, characterized in that: The electrode assembly includes a first pole piece located at the outermost layer thereof, the first pole piece includes a first current collector and a first active material layer, the first current collector has a first surface and a second surface arranged opposite to each other along a first direction, the first surface faces the inner side of the electrode assembly, and the first active material layer is arranged on the first surface; the first pole piece also includes a first insulating layer, the first insulating layer is arranged on a part of the surface of the second surface, and the first direction is the thickness direction of the first pole piece; The secondary battery further includes a first adhesive member, the first adhesive member includes a first part and a second part of an integrated structure, the first part is bonded to a surface portion of the second surface that is not covered by the first insulating layer; The second portion is bonded to a surface of the electrode assembly located on a side of a second direction, and the second direction is perpendicular to the first direction.

2. The secondary battery according to claim 1, wherein: The thickness of the first insulating layer along the first direction is T1, and 10 μm≤T1≤20 μm.

3. A secondary battery, comprising an electrode assembly, wherein the electrode assembly is a laminated structure, characterized in that: The electrode assembly includes a first pole piece located at the outermost layer thereof, the first pole piece includes a first current collector and a first active material layer, the first current collector has a first surface and a second surface arranged opposite to each other along a first direction, the first surface faces the inner side of the electrode assembly, and the first active material layer is arranged on the first surface; the first pole piece also includes a first insulating layer, the first insulating layer is arranged on at least a part of the surface of the second surface, and the first direction is the thickness direction of the first pole piece; The secondary battery also includes a first adhesive, the first adhesive includes a first part and a second part of an integrated structure, the first insulating layer includes a main body and a thinned portion of an integrated structure, the thickness of the main body along the first direction is greater than the thickness of the thinned portion along the first direction; the first part is bonded to the surface of the thinned portion along the first direction facing away from the first current collector, and the second part is bonded to the surface of the electrode assembly located on the second direction side, and the second direction is perpendicular to the first direction.

4. The secondary battery according to claim 3, characterized in that: The thickness of the main body along the first direction is T2, 10 μm≤T2≤20 μm; and / or The thickness of the thinned portion along the first direction is T3, 2 μm≤T3≤4 μm.

5. The secondary battery according to claim 3, characterized in that: A distance between the main body and the first portion along the second direction is W1, 0mm≤W1≤2mm.

6. A secondary battery, comprising an electrode assembly, wherein the electrode assembly is a laminated structure, characterized in that: The electrode assembly includes a first pole piece located at the outermost layer thereof, the first pole piece includes a first current collector and a first active material layer, the first current collector has a first surface and a second surface arranged opposite to each other along a first direction, the first surface faces the inner side of the electrode assembly, and the first active material layer is arranged on the first surface; the first pole piece also includes a first insulating layer, the first insulating layer is arranged on at least a part of the surface of the second surface, and the first direction is the thickness direction of the first pole piece; The thickness of the first insulating layer along the first direction is T4, 2 μm≤T4≤4 μm; The secondary battery also includes a first adhesive, which includes a first part and a second part of an integrated structure, the first part is bonded to the surface of the first insulating layer along the first direction facing away from the first current collector, and the second part is bonded to the surface of the electrode assembly located on one side of a second direction, and the second direction is perpendicular to the first direction.

7. The secondary battery according to claim 1, 3 or 6, characterized in that: A thickness of the first portion along the first direction is T5, and 8 μm≤T5≤12 μm.

8. The secondary battery according to claim 1, 3 or 6, characterized in that: The second surface is a polygon, and the first insulating layer contacts any vertex of the second surface.

9. The secondary battery according to claim 8, characterized in that The first insulating layer contacts any edge of the second surface.

10. The secondary battery according to claim 1, 3 or 6, characterized in that: The material of the first insulating layer includes a main material and an adhesive; The main material includes at least one of aluminum oxide, boehmite, zirconium oxide or titanium oxide, and the mass percentage of the main material is 80% to 99% based on the mass of the first insulating layer; The adhesive includes at least one of styrene-butadiene rubber, polyvinylidene fluoride or polyacrylate, and based on the mass of the first insulating layer, the mass percentage of the adhesive is 0.3% to 20%.

11. The secondary battery according to claim 1, 3 or 6, characterized in that: The thickness of the first current collector along the first direction is T6, and 8 μm≤T6≤12 μm.

12. The secondary battery according to claim 1, 3 or 6, characterized in that: A width of the first portion along the second direction is W2, 4 mm ≤ W2 ≤ 12 mm.

13. An electrical equipment, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 12.

14. A method for preparing a secondary battery, characterized in that: The following steps are involved: Take a first pole piece, the first pole piece includes a first current collector and a first active material layer, the first current collector has a first surface and a second surface arranged opposite to each other along a first direction, the first active material layer is arranged on the first surface; the first direction is a thickness direction of the first pole piece; Disposing a first insulating layer on the second surface, wherein the first insulating layer covers a portion of the surface of the second surface; The first electrode sheet is arranged on the outermost layer of the laminated electrode assembly; Take a first adhesive and adhere the first adhesive to the partial surface of the second surface not covered by the first insulating layer and the surface of the electrode assembly located on the second direction side, where the second direction is perpendicular to the first direction.

15. The method for preparing a secondary battery according to claim 14, characterized in that: The following steps are involved: Before providing the first insulating layer on the second surface, bonding adhesive tape on a portion of the surface of the second surface; After the first insulating layer is disposed on the second surface, a portion of the first insulating layer is covered by the adhesive tape; After the first pole piece is disposed on the outermost layer of the laminated electrode assembly, the adhesive tape is removed so that a portion of the second surface is exposed to the first insulating layer.

16. A method for preparing a secondary battery, characterized in that: The following steps are involved: Take a first pole piece, the first pole piece includes a first current collector and a first active material layer, the first current collector has a first surface and a second surface arranged opposite to each other along a first direction, the first active material layer is arranged on the first surface; the first direction is a thickness direction of the first pole piece; A first insulating layer is disposed on the second surface, wherein the first insulating layer covers a portion of the surface of the second surface; Arranging the first pole piece on the outermost layer of the laminated electrode assembly; Removing part of the material of the first insulating layer to reduce the thickness of at least part of the first insulating layer along the first direction; Take a first adhesive, adhere part of the first adhesive to the surface of the first insulating layer thinning area along the first direction facing away from the first current collector, and adhere part of the first adhesive to the surface of the electrode assembly on the second direction side, the second direction is perpendicular to the first direction.

17. The method for preparing a secondary battery according to claim 16, characterized in that: The material of a portion of the first insulating layer is removed by using a laser.

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