Secondary battery, electric device, and preparation method for secondary battery

Abstract

The present application discloses a secondary battery, an electric device, and a preparation method for a secondary battery. The secondary battery comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector, a first coating layer, and a second coating layer. The first coating layer is separately bonded and fixed to the negative electrode current collector and the second coating layer. The negative electrode current collector comprises a first surface and a second surface that are arranged opposite to each other. The negative electrode current collector comprises a main body portion and a bare foil portion which are integrally arranged, wherein the bare foil portion is configured to be electrically connected to an external circuit. The main body portion comprises a first portion and a second portion which are sequentially connected in a second direction, the second portion is located between the first portion and the bare foil portion, the second coating layer and the first coating layer are sequentially stacked on the first surface of the first portion, and the second coating layer is stacked on the first surface of the second portion. The dyne value of the second portion is Dyn, wherein Dyn≥30 mN / m. In the secondary battery, the dyne value Dyn of the second portion is set to be greater than or equal to 30 mN / m, thereby helping to reduce the possibility of the second coating layer peeling off, and reduce the possibility of adhesive tape residue remaining on the second portion.

Description

Secondary batteries, electrical equipment, and methods for preparing secondary batteries Technical Field

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

[0002] Currently, the negative electrode sheet of a secondary battery typically includes a negative current collector, a base coating, and a negative active material layer. The base coating is located between the negative current collector and the negative active material layer to increase the adhesion between them. For negative electrode sheets with die-cut tabs, the manufacturing process requires first attaching adhesive tape to the negative current collector, followed by applying the base coating and the negative active material layer. Then, the adhesive tape is removed to form an empty foil area, which is subsequently die-cut to obtain the tabs. Summary of the Invention

[0003] The inventors of this application discovered that, due to the thickness of the adhesive tape, during the base coating process, some surfaces of the negative electrode current collector at the edge of the adhesive tape cannot be covered by the base coating. These uncovered surfaces of the negative electrode current collector directly adhere to the negative electrode active material layer. Compared to the areas where the base coating is applied, the adhesion between the negative electrode current collector and the negative electrode active material layer is lower, and the negative electrode active material layer is prone to detachment. On the one hand, this will reduce the energy density of the secondary battery, and on the other hand, the detached negative electrode active material poses a risk of causing an internal short circuit in the secondary battery.

[0004] In view of the above situation, it is necessary to provide a secondary battery that can reduce the risk of the negative electrode active material layer peeling off.

[0005] A first aspect of this application provides a secondary battery including a negative electrode sheet. The negative electrode sheet includes a negative current collector, a first coating, and a second coating. Along a first direction, the first coating is disposed between the negative current collector and the second coating, and the first coating is bonded and fixed to both the negative current collector and the second coating. The second coating includes a negative electrode active material. The first direction is the thickness direction of the negative electrode sheet. Along the first direction, the negative current collector includes a first surface and a second surface disposed opposite to each other. The negative current collector includes an integrally formed main body portion and a hollow foil portion. The hollow foil portion is used for electrical connection with an external circuit and is located on one side of the main body portion along a second direction, which is perpendicular to the first direction. The main body portion includes a first part and a second part sequentially connected along the second direction. The second part is located between the first part and the hollow foil portion. Along the first direction, the second coating and the first coating are sequentially stacked on the first surface of the first part, and the second coating is stacked on the first surface of the second part. Along the second direction, the second coating extends beyond the first coating in a direction closer to the hollow foil portion. The dyne value of the second part is Dyn, where Dyn ≥ 30 mN / m.

[0006] In this secondary battery, by setting the dyne value of the second part to Dyn≥30mN / m, the dyne value of the area in direct contact between the negative electrode current collector and the second coating is not too small. This is beneficial to improving the adhesion between the negative electrode current collector and the second coating, and also beneficial to improving the wettability of the first coating on the negative electrode current collector, increasing the coverage area of ​​the first coating on the main body, thereby reducing the possibility of the second coating falling off.

[0007] In one or more embodiments of this application, 34mN / m≤Dyn≤60mN / m. Setting Dyn≥34mN / m helps to further improve the adhesion between the negative electrode current collector and the second coating, reducing the possibility of the second coating falling off. Setting Dyn≤60mN / m prevents the dyne value of the second part from being too high. On the one hand, this helps to reduce the difficulty of selecting materials or performing surface treatment on the negative electrode current collector. On the other hand, it helps to further reduce the possibility of adhesive residue remaining in the second part during the removal of adhesive tape, thereby reducing the risk of adhesive residue affecting the welding quality of the empty foil part.

[0008] In one or more embodiments of this application, 40mN / m≤Dyn≤50mN / m. Setting Dyn≥40mN / m helps to further improve the adhesion between the negative electrode current collector and the second coating, reducing the possibility of the second coating falling off. Setting Dyn≤50mN / m helps to further reduce the difficulty of selecting materials or performing surface treatment on the negative electrode current collector, and also helps to further reduce the possibility of adhesive residue remaining in the second part during the removal of adhesive tape, thereby further reducing the risk of adhesive residue affecting the welding quality of the empty foil part.

[0009] In one or more embodiments of this application, the dyne value of the first portion is equal to the dyne value of the second portion. When the surface of the negative electrode current collector needs to be treated to make the dyne value of the second portion meet the required range, treating both the first and second portions simultaneously helps to reduce the complexity of the process.

[0010] In one or more embodiments of this application, the thickness of the negative electrode current collector along the first direction is T, where 1 μm ≤ T ≤ 30 μm. Setting T ≥ 1 μm prevents the thickness of the negative electrode current collector from being too small, which is beneficial for improving the processing performance of the negative electrode current collector; setting T ≤ 30 μm prevents the thickness of the negative electrode current collector from being too large, which is beneficial for improving the energy density of the secondary battery.

[0011] In one or more embodiments of this application, the material of the negative electrode current collector includes one of copper, copper-nickel alloy, or copper-chromium alloy.

[0012] In one or more embodiments of this application, the first surface of the second portion is configured to undergo corona treatment, such that the first surface of the second portion has a mesh pattern.

[0013] In one or more embodiments of this application, viewed along a first direction, the second coating includes a first side and a second side disposed opposite to each other along a second direction. The first side is closer to the empty foil portion than the second side. The first side is a wavy curve. The first side has a first reference point that is closest to the empty foil portion along the second direction. The tangent line of the first side extending along the third direction from the first reference point is a first reference line, which serves as a reference line. The first coating also includes a third side and a fourth side disposed opposite to each other along the second direction. The third side is closer to the empty foil portion than the fourth side. The third side is a wavy curve. Along the second direction, the average distance from a point on the third side to the first reference line is D1, where D1 ≤ 60 μm. Setting D1 ≤ 60 μm prevents the area of ​​the first surface not covered by the first coating from becoming too large, thus reducing the risk of the second coating 13 peeling off.

[0014] In one or more embodiments of this application, D1 ≥ 1 μm. This ensures that the value of D1 is not too small, which helps reduce the complexity of the manufacturing process.

[0015] In one or more embodiments of this application, the secondary battery further includes a positive electrode and a separator. The positive electrode, separator, and negative electrode are stacked along a first direction X, with the separator located between the positive and negative electrode. Along the first direction X, the orthographic projection of the second portion lies outside the range of the orthographic projection of the positive electrode. Compared to the second coating located in the first portion, the second coating located in the second portion has a higher risk of peeling off. Setting the orthographic projection of the second portion outside the range of the orthographic projection of the positive electrode helps to reduce the impact of the second coating peeling off on the energy density of the secondary battery.

[0016] In one or more embodiments of this application, the mass percentage of the negative electrode active material is M, based on the mass of the second coating, where 92% ≤ M ≤ 99.5%. Setting M ≥ 92% ensures that the mass content of the negative electrode active material layer is not too low, which is beneficial for improving the energy density of the secondary battery; setting M ≤ 99.5% ensures that the mass content of the negative electrode active material is not too high, which ensures that the mass content of the binder in the second coating is not too low, which is beneficial for improving the adhesion between the second coating and the first coating and the negative electrode current collector.

[0017] In one or more embodiments of this application, the materials of the first coating include a conductive agent and an adhesive. The conductive agent is made of at least one of carbon nanotubes, graphene, graphene oxide, or conductive carbon black. The adhesive is made of at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyimide, polyaniline, or polyacrylonitrile.

[0018] A second aspect of the embodiments of this application provides an electrical device including a secondary battery as described in any of the foregoing embodiments.

[0019] A third aspect of the embodiments of this application provides a method for preparing a secondary battery, the method comprising the following steps:

[0020] A negative electrode current collector is selected, which includes a first surface and a second surface disposed opposite to each other along its thickness direction;

[0021] Apply adhesive tape to the first surface; the part of the negative electrode current collector not covered by the adhesive tape is the coating area.

[0022] A first coating is applied to the coating area;

[0023] A second coating is applied on the first coating and the adhesive tape;

[0024] Remove the adhesive tape. The area where the negative electrode current collector is exposed between the first coating and the second coating is the empty foil area. Cut the empty foil area to form the empty foil portion.

[0025] The portion of the negative electrode current collector having a first coating and a second coating stacked on it is the first part, and the portion of the negative electrode current collector having only a second coating stacked on it is the second part;

[0026] Before applying the adhesive tape, the first surface of the second part is subjected to corona treatment or plasma treatment. After corona treatment, the dyne value of the first surface of the second part is not less than 30 mN / m.

[0027] In one or more embodiments of this application, the first surface of the entire negative current collector is subjected to corona treatment before the adhesive tape is applied, and the dyne value of the first surface of the negative current collector after corona treatment is between 30 mN / m and 60 mN / m.

[0028] In one or more embodiments of this application, the power of the negative current collector during corona treatment is from 20W to 20000W.

[0029] In one or more embodiments of this application, the power of the negative current collector during corona treatment is from 800W to 16000W.

[0030] In one or more embodiments of this application, the corona treatment of the negative current collector is performed at a speed of 1 m / min to 200 m / min. Attached Figure Description

[0031] Figure 1 is a schematic diagram of the structure of a secondary battery in one embodiment of this application.

[0032] Figure 2 is a schematic diagram of the negative electrode structure in one embodiment of this application.

[0033] Figure 3 is a schematic diagram of the negative electrode sheet in one embodiment of this application.

[0034] Figure 4 is a schematic diagram of the negative electrode sheet in one embodiment of this application.

[0035] Figure 5 is a schematic diagram of the cross-sectional structure at point III-III in Figure 2.

[0036] Figure 6 is a schematic diagram of the negative electrode structure in one embodiment of this application.

[0037] Figure 7 is a schematic diagram of the cross-sectional structure at VI-VI in Figure 1.

[0038] Figure 8 is a schematic diagram of the cross-sectional structure at point VII-VII in Figure 1.

[0039] Figure 9 is a schematic diagram of the structure of a secondary battery in one embodiment of this application.

[0040] Figure 10 is a schematic diagram of the structure of an electrical device in one embodiment of this application.

[0041] Figure 11 is a schematic diagram of the preparation process of a secondary battery in one embodiment of this application.

[0042] Figure 12 is a schematic diagram of the preparation process of a secondary battery in one embodiment of this application.

[0043] Key Component Symbols: Secondary Battery 100; Negative Electrode 10; Negative Current Collector 11; First Surface 11a; Second Surface 11b; Main Body 111; First Part 1111; Second Part 1112; Empty Foil Part 112; Negative Electrode Bundle 1121; First Coating 12; Third Side 121; First Reference Point 1211; Fourth Side 122; Second Coating 13; First Side 131; First Reference Point 1311; Second Side 132; First Reference Line 133; Second Reference Line 134; First Region 135; First Sub-Region 1351; Second Sub-Region 1352; Casing 20; Positive Electrode30 Positive current collector; 31 Positive active material layer; 32 Positive electrode tab; 33 Positive electrode tab bundle; 331 Separator membrane; 40 Positive electrode adapter; 50 Negative electrode adapter; 60 Terminal post; 70 Electrical equipment; 1000 First direction X; Second direction Y; Third direction Z.

[0044] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0045] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0046] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also have a component that is centrally located. When a component is considered to be "set" on another component, it can be directly set on the other component or may also have a component that is centrally located.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0048] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0049] In the description of the embodiments of this application, the term "perpendicular" is used to describe the ideal state between two components. In actual production or use, two components may exist in a state that is approximately perpendicular. The two components described as "perpendicular" may not be absolutely straight lines or planes, but may be approximately straight lines or planes. From a macroscopic perspective, if the overall extension direction is a straight line or plane, the component can be considered as a "straight line" or "plane".

[0050] The term "parallel" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately parallel. The two components described as "parallel" do not have to be absolute straight lines or planes, but can be approximately straight lines or planes. From a macroscopic perspective, if the overall direction of extension is a straight line or plane, the component can be considered a "straight line" or "plane".

[0051] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. Where there is no conflict, the various embodiments in this application can be combined with each other.

[0052] It should be noted that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative examples and should not constitute any limitation on this application.

[0053] This application provides a secondary battery including a negative electrode sheet. The negative electrode sheet includes a negative current collector, a first coating, and a second coating. Along a first direction, the first coating is disposed between the negative current collector and the second coating, and the first coating is bonded and fixed to both the negative current collector and the second coating. The second coating includes a negative electrode active material. The first direction is the thickness direction of the negative electrode sheet. Along the first direction, the negative current collector includes a first surface and a second surface disposed opposite to each other. The negative current collector includes an integrally formed main body and a hollow foil portion. The hollow foil portion is used for electrical connection with an external circuit and is located on one side of the main body along a second direction, which is perpendicular to the first direction. The main body includes a first portion and a second portion sequentially connected along the second direction. The second portion is located between the first portion and the hollow foil portion. Along the first direction, the second coating and the first coating are sequentially stacked on the first surface of the first portion, and the second coating is stacked on the first surface of the second portion. Along the second direction, the second coating extends beyond the first coating towards the hollow foil portion. The dyne value of the second portion is Dyn, where Dyn ≥ 30 mN / m.

[0054] In this secondary battery, by setting the dyne value of the second part to Dyn≥30mN / m, the dyne value of the area in direct contact between the negative electrode current collector and the second coating is not too small. This is beneficial to improving the adhesion between the negative electrode current collector and the second coating, and also beneficial to improving the wettability of the first coating on the negative electrode current collector, increasing the coverage area of ​​the first coating on the main body, thereby reducing the possibility of the second coating falling off.

[0055] The embodiments of this application will be further described below with reference to the accompanying drawings.

[0056] As shown in Figures 1 and 2, a first aspect of an embodiment of this application provides a secondary battery 100, which includes a negative electrode 10. The negative electrode 10 includes a negative current collector 11, a first coating 12, and a second coating 13. In Figure 2, the edge of the first coating 12 is indicated by a dashed line. Along a first direction X, the first coating 12 is disposed between the negative current collector 11 and the second coating 13, and the first coating 12 is bonded and fixed to the negative current collector 11 and the second coating 13 respectively. The second coating 13 includes a negative electrode active material, and the first direction X is the thickness direction of the negative electrode sheet.

[0057] In some embodiments, the negative electrode current collector 11 is a metal foil. As an example, the material of the negative electrode current collector 11 includes at least one selected from copper, copper-nickel alloy, copper-chromium alloy, nickel, tantalum, and titanium.

[0058] In some embodiments, the negative electrode current collector 11 is a composite current collector.

[0059] In some embodiments, the material of the first coating 12 includes a conductive agent, an adhesive, and a solvent. The conductive agent includes, but is not limited to, at least one of carbon nanotubes, graphene, graphene oxide, or conductive carbon black. The adhesive includes, but is not limited to, at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyimide, polyaniline, or polyacrylonitrile. The solvent is water or an organic solvent.

[0060] In some embodiments, the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen materials, and silicon-carbon materials.

[0061] In some embodiments, as shown in FIG5, the negative electrode current collector 11 includes a first surface 11a and a second surface 11b disposed opposite to each other along the first direction X. The negative electrode current collector 11 includes an integrally disposed main body portion 111 and an empty foil portion 112. The empty foil portion 112 is used for electrical connection with an external circuit. The empty foil portion 112 is located on one side of the main body portion 111 along the second direction Y, which is perpendicular to the first direction X. The main body portion 111 includes a first portion 1111 and a second portion 1112 connected sequentially along the second direction Y. The second portion 1112 is located between the first portion 1111 and the empty foil portion 112. Along the first direction X, a second coating 13 and a first coating 12 are sequentially stacked on the first surface 11a of the first portion 1111, and a second coating 13 is stacked on the first surface 11a of the second portion 1112. Along the second direction Y, the second coating 13 extends beyond the first coating 12 in a direction close to the empty foil portion 112. In other words, in the second portion 1112, the second coating 13 is in direct contact with the negative electrode current collector 11. The dyne value of Part 2, 1112 is Dyn, and Dyn ≥ 30 mN / m.

[0062] In this secondary battery 100, by setting the dyne value Dyn≥30mN / m of the second part 1112, the dyne value of the area in direct contact between the negative electrode current collector 11 and the second coating 13 is not too small. This is beneficial for improving the adhesion between the negative electrode current collector 11 and the second coating 13, and also for improving the wettability of the first coating 12 on the negative electrode current collector 11 (wettability refers to the ability or tendency of a liquid to spread on a solid surface), increasing the coverage area of ​​the first coating 12 on the main body 111, thereby reducing the possibility of the second coating 13 falling off. Here, "adhesive paper" refers to the adhesive paper used to cover the surface of the negative electrode current collector 11 during the preparation of the negative electrode sheet 10. Unless otherwise specified, "adhesive paper" uses this definition in the following text.

[0063] It should be noted that the first part 1111 and the second part 1112 are defined by the relative relationship between the main body 111 and the first coating 12. The first part 1111 is the part of the main body 111 covered by the first coating 12, and the second part 1112 is the part of the main body 111 covered by the second coating 13. The empty foil part 112 is neither covered by the first coating 12 nor by the second coating 13.

[0064] It should be added that the empty foil portion 112 is not equivalent to the tab as commonly defined by those skilled in the art. As shown in FIG2, the empty foil portion 112 may include the tab, and as shown in FIG3 and FIG4, the empty foil portion 112 may also be only a part of the tab.

[0065] In some embodiments, 34mN / m ≤ Dyn ≤ 60mN / m. Setting Dyn ≥ 34mN / m helps to further improve the adhesion between the negative electrode current collector 11 and the second coating 13, reducing the possibility of the second coating 13 detaching. Setting Dyn ≤ 60mN / m prevents the dyne value of the second part 1112 from being too high. This helps to reduce the difficulty of selecting materials or performing surface treatment on the negative electrode current collector 11, and also helps to further reduce the possibility of adhesive residue remaining in the second part 1112 during the removal of adhesive tape, thereby reducing the risk of adhesive residue affecting the welding quality of the empty foil part 112. Here, the welding of the empty foil part 112 refers to the welding between the empty foil parts 112 of different negative electrode sheets 10, the welding of the empty foil part 112 to the housing 20, and the solder joint of the empty foil part 112 to the electrode post 70.

[0066] In some embodiments, 40mN / m≤Dyn≤50mN / m. Setting Dyn≥40mN / m helps to further improve the adhesion between the negative electrode current collector 11 and the second coating 13, reducing the possibility of the second coating 13 falling off. Setting Dyn≤50mN / m helps to further reduce the difficulty of material selection or surface treatment of the negative electrode current collector 11, and also helps to further reduce the possibility of adhesive residue remaining in the second part 1112 during the removal of adhesive tape, thereby further reducing the risk of adhesive residue affecting the welding quality of the empty foil part 112.

[0067] In some embodiments, the dyne value of the first portion 1111 is equal to the dyne value of the second portion 1112. In embodiments of this application, when the difference between the dyne value of the first portion 1111 and the dyne value of the second portion 1112 is less than or equal to 5% of the dyne value of the second portion 1112, they are considered equal. When the surface of the negative electrode current collector 11 needs to be treated to make the dyne value of the second portion 1112 meet the required range, simultaneously treating the first portion 1111 and the second portion 1112 helps to reduce the process difficulty.

[0068] In some embodiments, as shown in FIG5, the thickness of the negative electrode current collector 11 along the first direction X is T, where 1μm≤T≤30μm. Setting T≥1μm prevents the thickness of the negative electrode current collector 11 from being too small, which is beneficial to improving the processing performance of the negative electrode current collector 11; setting T≤30μm prevents the thickness of the negative electrode current collector 11 from being too large, which is beneficial to improving the energy density of the secondary battery 100.

[0069] In some embodiments, the first surface 11a of the second portion 1112 is configured to undergo corona treatment, such that the first surface 11a of the second portion 1112 has a grid pattern.

[0070] In the embodiments of this application, whether the first surface 11a of the second part 1112 has undergone corona treatment can be determined by the following method:

[0071] Take 100 finished secondary batteries, discharge them at 0.1C to the cutoff voltage, and disassemble 10 negative electrode plates;

[0072] Remove the first coating 12 and the second coating 13 until there is no obvious active material residue on the surface of the negative electrode current collector 11;

[0073] The negative electrode current collector 11 is used to make an observation sample. The sample size is determined according to the requirements of the instrument used, and no specific limit is made here.

[0074] With the smooth or shiny side of the negative electrode current collector 11 facing upwards, observe it under an electron microscope at a magnification of 50KX-1KX.

[0075] The negative electrode current collector 11 that has undergone corona treatment can be clearly seen to have a slight network texture on its surface. When viewed under an electron microscope, the network texture appears as connected irregular polygons.

[0076] Preferably, the distance between the farthest edges or points on the irregular polygon in the length or width direction of the observed image is 200μm to 400μm.

[0077] In some embodiments, as shown in FIG6, viewed along the first direction X, the second coating 13 includes a first side 131 and a second side 132 disposed opposite to each other along the second direction Y. Compared to the second side 132, the first side 131 is closer to the empty foil portion 112, and the first side 131 is a wavy curve. The first side 131 has a first reference point 1311 that is closest to the empty foil portion along the second direction Y. The tangent of the first side 131 extending from the first reference point 1311 along the third direction Z is the first reference line 133, which is a reference line. The first coating 12 includes a third side 121 and a fourth side 122 disposed opposite to each other along the second direction Y. Compared to the fourth side 122, the third side 121 is closer to the empty foil portion 112, and the third side 121 is a wavy curve. Along the second direction Y, the average distance from a point on the third side 121 to the first reference line 123 is D1, where D1 ≤ 60 μm. In this embodiment, D1 reflects the average distance between the edge of the first coating 12 and the empty foil portion 112, that is, it reflects the degree to which the coating of the first coating 12 is restricted by the adhesive tape. The smaller the value of D1, the less restricted the coating of the first coating 12 is by the adhesive tape, that is, the smaller the area of ​​the first surface 11a of the main body portion 111 that is not covered by the first coating 12. By increasing the dyne value of the negative electrode current collector 11, the wettability of the first coating 12 on the negative electrode current collector 11 can be improved, allowing the first coating 12 to spread towards the edge of the adhesive tape, thereby reducing the area of ​​the first surface 11a of the main body portion 111 that is not covered by the first coating 12. The first coating 12 can bond the second coating 13 and the negative electrode current collector 11. The smaller the area of ​​the first surface 11a that is not covered by the first coating 12, the greater the mass of the second coating 13 that can be fixed by the second coating 13. Therefore, setting D1 ≤ 60 μm prevents the area of ​​the first surface 11a that is not covered by the first coating 12 from being too large, which helps to reduce the risk of the second coating 13 falling off. In the embodiments of this application, the value of D1 can be determined using a scanning electron microscope (SEM). When measuring the value of D1, a first reference line 133 is first determined using the first side 131 and marked on the negative electrode. Then, the second coating 13 is removed, and the distance from a point on the third side 121 to the first reference line 133 is measured. During the measurement, 100 points can be evenly selected on the third side 121 (the number of points can be adjusted as needed). The average value of the distances is then taken to obtain the value of D1.

[0078] It should be noted that Figure 6 shows a structural schematic diagram of the negative electrode 10 under magnification. Therefore, the first side 131 and the third side 121 appear as obvious wavy curves. However, under human observation, the first side 131 and the third side 121 may appear as straight lines or wavy curves.

[0079] In some embodiments, D1 ≥ 1 μm. This ensures that the value of D1 is not too small, which helps to reduce the difficulty of the process.

[0080] The value of D1 is related to the thickness and width of the adhesive tape. During the preparation process, the value of D1 can be adjusted by adjusting the thickness and width of the adhesive tape.

[0081] In some embodiments, the secondary battery 100 further includes a positive electrode 30 and a separator 40, wherein the positive electrode 30, the separator 40, and the negative electrode 10 are stacked along a first direction X, and the separator 40 is located between the positive electrode 30 and the negative electrode 40. Along the first direction X, the orthographic projection of the second portion 1112 is outside the range of the orthographic projection of the positive electrode 30. Compared to the second coating 13 located in the first portion 1111, the second coating 13 located in the second portion 1112 has a higher risk of peeling off. Setting the orthographic projection of the second portion 1112 outside the range of the orthographic projection of the positive electrode 30 helps to reduce the impact of the peeling off of the second coating 13 on the energy density of the secondary battery 100.

[0082] The energy density of the secondary battery 100 is positively correlated with the content of the negative electrode active material in the second coating 13. However, the content of the negative electrode active material is negatively correlated with the adhesion between the second coating 13 and the negative electrode current collector 11. In other words, the higher the content of the negative electrode active material, the more likely the second coating 13 will detach. Therefore, existing solutions cannot further increase the content of the negative electrode active material in the second coating 13. The embodiments of this application improve the dyne value of the negative electrode current collector 11, thereby further increasing the content of the negative electrode active material in the second coating 13 compared to existing technologies. In some embodiments, based on the mass of the second coating 13, the mass percentage of the negative electrode active material is M, where 92% ≤ M ≤ 99.5%. Setting M≥92% ensures that the mass content of the negative electrode active material layer is not too small, which is beneficial to improving the energy density of the secondary battery 100; setting M≤99.5% ensures that the mass content of the negative electrode active material is not too large, which ensures that the mass content of the adhesive in the second coating 13 is not too small, which is beneficial to improving the adhesion between the second coating 13 and the first coating 12 and the negative electrode current collector 11.

[0083] In some embodiments, as shown in Figures 1, 7, and 8, the secondary battery 100 further includes a housing 20, a positive electrode 30, a separator 40, an electrolyte, a positive electrode adapter 50, and a negative electrode adapter 60. The first coating 12 of the negative electrode 10 is omitted in Figures 7 and 8. The positive electrode 30, the separator 40, and the negative electrode 10 are stacked and housed within the housing 20, and the electrolyte is also housed within the housing 20. The empty foil portion 112 of the negative electrode 10 is gathered to form a negative electrode bundle 1121, and the negative electrode adapter 60 connects to the negative electrode bundle 1121. The positive electrode 30 includes a positive electrode current collector 31, a positive electrode active material layer 32, and positive electrode tabs 33. The positive electrode active material layer 32 is disposed on the positive electrode current collector 31, and the positive electrode tabs 33 are integrally disposed with the positive electrode current collector 31. Multiple positive electrode tabs 33 are gathered to form a positive electrode bundle 331, and the positive electrode adapter 50 connects to the positive electrode bundle 331.

[0084] In some embodiments, as shown in FIG9, the housing 20 is made of a rigid material, for example, the housing 20 is a steel shell. The secondary battery 100 also includes a terminal post 70, one of which, a negative terminal adapter 60 and a positive terminal adapter 50, is connected to the terminal post 70 and the other is connected to the housing 20; or, there are two terminals 70, and the negative terminal adapter 60 and the positive terminal adapter 50 are each connected to one terminal post 70.

[0085] In some embodiments, as shown in FIG1, the housing 20 is a packaging bag. Part of the positive electrode adapter 50 and part of the negative electrode adapter 60 extend out of the housing 20.

[0086] In some embodiments, a plurality of positive electrode sheets 30, a multilayer separator 40, and a plurality of negative electrode sheets 10 are stacked to form a laminated structure. In this embodiment, a single negative electrode sheet 10 has one or more empty foil portions 112, and a single positive electrode sheet 30 has one or more positive electrode tabs 33.

[0087] In some embodiments, the positive electrode 30, the separator 40, and the negative electrode 10 are stacked and then wound to form a wound structure. In this embodiment, a single negative electrode 10 has a plurality of empty foil portions 112, and a single positive electrode 30 has a plurality of positive electrode tabs 33.

[0088] In some embodiments, the positive electrode 30 includes a positive current collector 31 and a positive active material layer 32 stacked together, and the portion of the positive current collector 31 not covered by the positive active material layer is the positive tab 33.

[0089] In some embodiments, the positive current collector 31 is a metal layer. As an example, the positive current collector 31 may be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil.

[0090] In some embodiments, the positive current collector 31 is a composite current collector.

[0091] In some embodiments, the positive electrode active material layer 32 includes a positive electrode active material, which 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.

[0092] In some embodiments, the separator 40 is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0093] In some embodiments, the electrolyte comprises an electrolyte salt. The electrolyte salt comprises at least one of an organic lithium salt or an inorganic lithium salt.

[0094] In some embodiments, the electrolyte salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluoromethanesulfonyl)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).

[0095] As shown in FIG10, a second aspect of the embodiments of this application provides an electrical device 1000, which includes a secondary battery 100 as described in any of the foregoing embodiments.

[0096] In some embodiments, the electrical device 1000 includes, but is not limited to, mobile phones, laptops, electric toys, and power tools.

[0097] As shown in Figures 11 and 12, a third aspect of the embodiments of this application provides a method for preparing a secondary battery 100, the method comprising the following steps:

[0098] A negative electrode current collector 11 is provided, which includes a first surface 11a and a second surface 11b disposed opposite to each other along its thickness direction.

[0099] Apply adhesive tape to the first surface; the part of the negative electrode current collector 11 not covered by the adhesive tape is the coating area.

[0100] A first coating 12 is applied to the coating area;

[0101] A second coating 13 is applied to the first coating 12 and the adhesive tape;

[0102] After removing the adhesive tape, the area of ​​the negative electrode current collector 11 exposed in the first coating 12 and the second coating 13 is the empty foil area. The empty foil area is cut to form the empty foil portion 112.

[0103] The portion of the negative electrode current collector 11 on which the first coating 12 and the second coating 13 are stacked is the first portion 1111, and the portion of the negative electrode current collector 11 on which only the second coating 13 is stacked is the second portion 1112;

[0104] Before applying the adhesive tape, the first surface 11a of the second part 1112 is subjected to corona treatment, and the dyne value of the first surface 11a of the second part 1112 after corona treatment is not less than 30mN / m.

[0105] In some embodiments, the method for preparing the secondary battery 100 includes the following steps:

[0106] Before applying the adhesive tape, the first surface 11a of the entire negative electrode current collector 11 is subjected to corona treatment or plasma treatment. After corona treatment, the dyne value of the first surface 11a of the negative electrode current collector 11 is between 30mN / m and 60mN / m.

[0107] In some embodiments, when corona treatment is performed on the negative current collector 11, the power is from 20W to 20000W.

[0108] In some embodiments, when corona treatment is applied to the negative current collector 11, the power is from 800W to 16000W.

[0109] In some embodiments, when corona treatment is performed on the negative current collector 11, the speed is from 1 m / min to 200 m / min.

[0110] To verify the effectiveness of the solutions in the embodiments of this application, the inventors conducted the following experiments.

[0111] The experiment consisted of 26 experimental groups, one of which was a comparative example and the remaining 25 were exemplary examples. Each experimental group included 100 secondary batteries.

[0112] The preparation process of the secondary battery 100 in Example 1 includes the following steps:

[0113] (1) Preparation of positive electrode sheet 30: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNT (carbon nanotubes), 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 75wt%, and stirred evenly for later use. A 10μm thick aluminum foil was used as the positive electrode current collector 31. The above active material was uniformly coated on one side of the positive electrode current collector 31 using a slit coater, and then dried at 90°C to obtain a positive electrode sheet with a single-sided coating of positive electrode active material. At this time, the thickness of the positive electrode active material layer was 65μm. The above coating steps were then repeated on the other side of the positive electrode current collector 31. The coated positive electrode sheet 30 was then cold-pressed. After cold pressing, the thickness of the single-layer positive electrode active material layer 32 was 35μm. The area of ​​the positive electrode current collector not covered by the positive electrode active material layer 32 is the positive electrode empty foil area. The positive electrode empty foil area is die-cut to obtain the positive electrode tab 33.

[0114] (2) Preparation of negative electrode 10: Active materials artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) were mixed in a weight ratio of 97:0.5:1.3:1.2. Deionized water was added as a solvent to prepare a negative electrode active material with a weight percentage of 50 wt%, and the mixture was stirred evenly for later use. An 8 μm thick copper foil was used as the negative electrode current collector 11. The negative electrode current collector 11 underwent corona treatment to achieve a dyne value of 30 mN / m. Adhesive tape was applied to the negative electrode current collector 11, and a first coating layer 12 was applied to the coating area. A slot coater was used to evenly coat the negative electrode active material onto the first coating layer 12 and the adhesive tape. The coating was then dried at 110°C to obtain a negative electrode 10 with a second coating layer 13 on one side. The adhesive tape was then removed. At this point, the thickness of the second coating layer 13 was 80 μm. Then, the above steps are repeated on the other side of the negative electrode current collector 11 to obtain a negative electrode sheet 10 coated with the second coating 13 on both sides. The coated negative electrode sheet 10 is then cold-pressed, and the thickness of the single layer of the second coating 13 after cold pressing is 45 μm. The area of ​​the negative electrode current collector 11 not covered by the second coating 13 is the negative electrode empty foil area, and the negative electrode empty foil area is die-cut to obtain the empty foil portion 112.

[0115] (3) Preparation of the isolation membrane: A 7μm thick polyethylene porous polymer film was used as the isolation membrane 40;

[0116] (4) Preparation of electrode assembly: The positive electrode 30, the separator 40 and the negative electrode 10 are stacked in sequence and wound into a winding structure; the positive electrode tab 33 is gathered and welded to form a positive electrode tab bundle 331, and a positive electrode adapter 50 is welded on the positive electrode tab bundle 331; the empty foil portion 112 is gathered and welded to form a negative electrode tab bundle 1121, and a negative electrode adapter 60 is welded on the negative electrode tab bundle 1121.

[0117] (5) Assembly of the secondary battery 100: Place the dented aluminum-plastic film in the assembly fixture with the dent facing upwards, place the electrode assembly in the dent, and apply external force to press it. Then cover the electrode assembly with another dented aluminum-plastic film with the dent facing downwards, and heat seal the four edges of the two aluminum-plastic films by hot pressing. Part of the negative electrode adapter 60 and part of the positive electrode adapter 50 protrude from the shell 20. After liquid injection, vacuum sealing, standing, hot pressing formation, shaping and other processes, the secondary battery is obtained.

[0118] The preparation process of the secondary battery 100 in Comparative Example 1 is basically the same as that in Example 1. The difference is that the negative electrode current collector 11 in Comparative Example 1 is not treated and the dyne value is different from that in Example 1.

[0119] The secondary battery 100 in Examples 2 to 25 is basically the same as that in Example 1. The difference is that some parameters of the secondary battery 100 in Examples 2 to 25 are different from those in Example 1. The specific differences are recorded in the table.

[0120] All electrode components in each experimental group underwent a withstand voltage test (Hi-pot test), which included the following steps:

[0121] Connect the electrode assembly to the high-voltage output device, detect the leakage current generated by the secondary battery under the 100KV test voltage output by the high-voltage device, and then calculate the resistance value: resistance value = test voltage / leakage current.

[0122] The calculated resistance value is compared with the set judgment resistor. In this application, the preset value of the judgment resistor is 1 Mohm (megaohm).

[0123] If the detected resistance value is greater than or equal to the preset value of 1 Mohm, the product under test is deemed to have passed the test (OK).

[0124] If the detected resistance value is less than the preset value of 1 Mohm, the test voltage is cut off instantly and the product under test is judged to fail the test (NG);

[0125] The number of secondary batteries that passed the test is X1, and the test pass rate = X1 / 100 × 100%, which is also known as the Hi-pot success rate.

[0126] The principle of the Hi-pot test is that if the second coating 13 does not peel off or the amount of peeling off is not significant, the detected resistance value is greater than or equal to the predetermined value because the electrode assembly, the positive electrode 20 and the negative electrode 10 are in an insulating state. If the amount of peeling off the second coating 13 is too large, causing an internal short circuit in the electrode assembly, the detected resistance value is less than the predetermined value. Therefore, the peeling status of the second coating 13 can be reflected by the resistance value.

[0127] After the Hi-pot test, 20 secondary batteries were randomly selected from each experimental group for the peel test, and another 5 secondary batteries were randomly selected to observe the S1 / S2 values.

[0128] The peel test process includes the following steps:

[0129] The negative electrode ear bundle 1121 can be connected to the negative electrode adapter 60 and cut off from the negative electrode sheet 10 as a sample. Select two adjacent layers from the sample (which can be the empty foil part 112, or the negative electrode adapter 60 and the empty foil part 112), and mark them as sample 1 and sample 2. Use double-sided tape to stick sample 1 to the steel plate base and place the steel plate on a high-speed rail tensile testing machine. Use a clamp to hold one end of sample 2 and peel it off at a tensile speed of 10 mm / min until the weld position is separated. Record the area of ​​sample 2 remaining on the surface of sample 1 after peeling. If the remaining area is less than 10% of the overall weld, it is considered a cold weld. Repeat the above steps six times by selecting different adjacent two layers. Randomly select adjacent empty foil areas 112 for testing five times, and adapter 60 and adjacent empty foil areas 112 for testing once. If a cold weld occurs in any of the six tests, the secondary battery will be judged as failing the test (NG).

[0130] The number of lithium-ion batteries that passed the test was X2, and the pass rate was X2 / 20, which is also the welding quality rate.

[0131] The observation process for S1 / S2 includes the following steps:

[0132] The negative electrode 10 in the secondary battery 100 was disassembled, and a 10mm x 10mm sample was cut and observed under an electron microscope.

[0133] The first baseline is determined using the method described above. A second baseline 134, parallel to the first baseline 133, is drawn as a reference line. The distance between the first baseline 133 and the second baseline 134 is 1 mm. The area between the first baseline 133 and the second baseline 134 is named the first region 135. The first region 135 is divided into a first sub-region 1351 and a second sub-region 1352 by a first side 131. Along the second direction Y, the first sub-region 1351 is closer to the empty foil portion 112 than the second sub-region 1352. The area of ​​the first sub-region 1351 is S1, and the area of ​​the second sub-region 1352 is S2. S1 / S2 is calculated and averaged for each group of five secondary batteries 100. The value of S1 / S2 reflects the degree of peeling of the second coating 13. The less the second coating peels off, the closer the first side 131 is to a straight line, and the smaller the value of S1 / S2.

[0134] After the experiment, Tables 1 and 2 were compiled based on the set parameters and experimental results.

[0135] Table 1

[0136] As shown in Table 1, the secondary batteries 100 in Examples 1 to 6 satisfy 30mN / m≤Dyn. Compared with Comparative Example 1, the average value of S1 / S2 of the secondary batteries 100 in Examples 1 to 17 is smaller, and the Hi-pot test pass rate is higher. It can be seen that setting Dyn≥30mN / m ensures that the dyne value of the area in direct contact between the negative electrode current collector 11 and the second coating 13 is not too small, which is beneficial to improving the adhesion between the negative electrode current collector 11 and the second coating 13. It is also beneficial to improve the wettability of the first coating 12 on the negative electrode current collector 11 and increase the coverage area of ​​the first coating 12 on the main body 111, thereby reducing the possibility of the second coating 13 falling off.

[0137] In Examples 3 to 16, the secondary battery 100 satisfies 34mN / m≤Dyn≤60mN / m. Compared with Examples 1 and 2, the average value of S1 / S2 of the secondary battery 100 in Examples 3 to 16 is smaller, and the Hi-pot test pass rate is higher. It can be seen that setting Dyn≥34mN / m is beneficial to further improve the adhesion between the negative electrode current collector 11 and the second coating 13 and reduce the possibility of the second coating 13 falling off. Compared with Example 17, the welding efficiency of the secondary battery 100 in Examples 3 to 16 is higher. It can be seen that setting Dyn≤60mN / m is beneficial to reduce the possibility of adhesive residue remaining in the second part 1112 during the removal of adhesive tape, so as to reduce the risk of adhesive residue affecting the welding quality of the empty foil part 112.

[0138] In Examples 6 to 11, the secondary battery 100 satisfies 40mN / m≤Dyn≤50mN / m. Compared with Examples 3 to 5, the average value of S1 / S2 of the secondary battery 100 in Examples 6 to 11 is smaller, and the Hi-pot test pass rate is higher. It can be seen that setting Dyn≥40mN / m is beneficial to further improve the adhesion between the negative electrode current collector 11 and the second coating 13 and reduce the possibility of the second coating 13 falling off. Compared with Examples 12 to 16, the welding efficiency of the secondary battery 100 in Examples 6 to 11 is higher. It can be seen that setting Dyn≤50mN / m is beneficial to further reduce the possibility of adhesive residue remaining in the second part 1112 during the removal of adhesive tape, so as to further reduce the risk of adhesive residue affecting the welding quality of the empty foil part 112.

[0139] Table 2

[0140] It should be noted that for examples where D1 is less than 1 μm, the adhesive tape used in the preparation process is too thin and narrow to be compatible with production equipment, and therefore is not suitable for mass production and experimentation. Therefore, in the examples, D1 = 1 μm is used as the lower limit of the experimental parameter.

[0141] As can be seen from Table 2, the secondary batteries 100 in Examples 18 to 24 satisfy D1≤60μm. Compared with Example 25, the average value of S1 / S2 of the secondary batteries in Examples 18 to 24 is lower, and the Hi-pot test pass rate is higher. It can be seen that by setting D1≤60μm, the area of ​​the first surface 11a not covered by the first coating 12 will not be too large, which is beneficial to reducing the risk of the second coating 13 falling off.

[0142] Those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of this application.

Claims

1. A secondary battery, characterized in that, The device includes a negative electrode sheet, which comprises a negative electrode current collector, a first coating, and a second coating. Along a first direction, the first coating is disposed between the negative electrode current collector and the second coating, and the first coating is bonded and fixed to the negative electrode current collector and the second coating, respectively. The second coating comprises a negative electrode active material. The first direction is the thickness direction of the negative electrode sheet. Along the first direction, the negative electrode current collector comprises a first surface and a second surface disposed opposite to each other. The negative electrode current collector includes an integrally formed main body and an empty foil portion. The empty foil portion is used for electrical connection with an external circuit. The empty foil portion is located on one side of the main body along a second direction, which is perpendicular to the first direction. The main body includes a first part and a second part connected sequentially along the second direction. The second part is located between the first part and the empty foil portion. Along the first direction, a second coating and a first coating are sequentially stacked on the first surface of the first part, and the second coating is stacked on the first surface of the second part. Along the second direction, the second coating extends beyond the first coating in a direction closer to the empty foil portion; The dyne value of the second part is Dyn, where Dyn ≥ 30 mN / m.

2. The secondary battery as described in claim 1, characterized in that, 34mN / m≤Dyn≤60mN / m.

3. The secondary battery as described in claim 2, characterized in that, 40mN / m≤Dyn≤50mN / m.

4. The secondary battery as described in any one of claims 1-3, characterized in that, The dyne value of the first part is equal to the dyne value of the second part.

5. The secondary battery as described in claim 1, characterized in that, Along the first direction, the thickness of the negative electrode current collector is T, where 1 μm ≤ T ≤ 30 μm.

6. The secondary battery as described in any one of claims 1-5, characterized in that, The material of the negative electrode current collector includes one of copper, copper-nickel alloy, or copper-chromium alloy.

7. The secondary battery as described in any one of claims 1-6, characterized in that, The first surface of the second portion is configured to undergo corona treatment, such that the first surface of the second portion has a grid pattern.

8. The secondary battery as described in any one of claims 1-7, characterized in that, Viewed along the first direction, the second coating includes a first side and a second side disposed opposite to each other along the second direction. Compared to the second side, the first side is closer to the empty foil portion. The first side is a wavy curve. The first side has a first reference point that is closest to the empty foil portion along the second direction. The tangent of the first side extending along the third direction through the first reference point is the first reference line. The first reference line is a reference line. The first coating includes a third side and a fourth side disposed opposite to each other along the second direction. Compared with the fourth side, the third side is closer to the empty foil portion, and the third side is a wavy curve. Along the second direction, the average distance from a point on the third side to the first baseline is D1, where D1 ≤ 60 μm.

9. The secondary battery as described in claim 8, characterized in that, D1≥1μm.

10. The secondary battery according to any one of claims 1-9, characterized in that, The secondary battery further includes a positive electrode and a separator, wherein the positive electrode, the separator, and the negative electrode are stacked along the first direction, and the separator is located between the positive electrode and the negative electrode. Along the first direction, the orthographic projection of the second portion lies outside the range of the orthographic projection of the positive electrode sheet.

11. The secondary battery according to any one of claims 1-10, characterized in that, Based on the quality of the second coating, the mass percentage of the negative electrode active material is M, where 92% ≤ M ≤ 99.5%.

12. The secondary battery as described in any one of claims 1-11, characterized in that, The materials of the first coating include conductive agents and adhesives; The conductive agent is made of at least one of carbon nanotubes, graphene, graphene oxide, or conductive carbon black. The adhesive material includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyimide, polyaniline, or polyacrylonitrile.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-12.

14. A method for preparing a secondary battery, used to prepare a secondary battery as described in any one of claims 1-12, characterized in that, Includes the following steps: A negative electrode current collector is selected, the negative electrode current collector including a first surface and a second surface disposed opposite to each other along its thickness direction; Adhesive tape is applied to the first surface, and the portion of the negative electrode current collector not covered by the adhesive tape is the coating area; The first coating is applied to the coating area; A second coating is applied to the first coating and the adhesive tape; Remove the adhesive tape, and the area of ​​the negative electrode current collector exposed between the first coating and the second coating is the empty foil area. Cut the empty foil area to form the empty foil portion. The portion of the negative electrode current collector having a first coating and a second coating stacked on it is the first portion, and the portion of the negative electrode current collector having only a second coating stacked on it is the second portion; Before applying the adhesive tape, the first surface of the second part is subjected to corona treatment, and the dyne value of the first surface of the second part after corona treatment is not less than 30mN / m.

15. The method for preparing the negative electrode sheet as described in claim 14, characterized in that, Before applying the adhesive tape, the entire first surface of the negative electrode current collector is subjected to corona treatment, and the dyne value of the first surface of the negative electrode current collector after corona treatment is between 30 mN / m and 60 mN / m.

16. The method for preparing the negative electrode sheet as described in claim 14, characterized in that, When corona treatment is performed on the negative electrode current collector, the power is from 20W to 20000W.

17. The method for preparing the negative electrode sheet as described in claim 16, characterized in that, When corona treatment is performed on the negative electrode current collector, the power is 800W to 16000W.

18. The method for preparing a secondary battery according to any one of claims 14-17, characterized in that, When corona treatment is performed on the negative electrode current collector, the speed is from 1 m / min to 200 m / min.

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