Electrochemical device and electric equipment

Abstract

The negative electrode sheet of the electrochemical device comprises a first active material layer, a first current collector and a second active material layer; the first coating layer and the second coating layer of the first active material layer are arranged in a staggered manner in the length direction, so that the first active material layer has a first single-layer part and a second single-layer part; the first active material layer and the second active material layer are also arranged in a staggered manner in the length direction, so that the two ends of the negative electrode sheet are respectively a first single-sided coating part and a second single-sided coating part, and the length of the first single-sided coating part is greater than the length of the second single-sided coating part. By arranging the first active material layer of the negative electrode sheet in a staggered manner and arranging the first active material layer and the second active material layer in a staggered manner, the risk of the end thickness of the first active material layer and the end thickness of the negative electrode sheet being too large can be reduced, so as to solve the problem that the first current collector is broken due to the end thickness being too large during the rolling process of the negative electrode sheet, and the probability of the negative electrode sheet being broken during the rolling process is reduced.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrochemical device and electrical equipment. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and portability, are widely used in various energy storage fields. The negative electrode in a lithium-ion battery typically includes a current collector and active material layers coated on both surfaces of the current collector. In existing technologies, to improve production efficiency, large rolls of electrode sheets are usually produced continuously, and then slit according to the battery's design dimensions to obtain the corresponding electrode sheets. During the continuous production of the electrode rolls, when the active material is continuously coated, the active material layers on the two surfaces of the current collector are aligned at least one end along the length of the current collector. This alignment at the end of the active material layer makes it very easy for overpressure to occur during subsequent cold pressing and rolling, causing damage to the current collector. This leads to strip breakage of the negative electrode sheet during subsequent processing, resulting in low yield and increased costs. Furthermore, the active material layers of the slit electrode sheets are also typically aligned vertically at at least one end. After being wound into electrode assemblies, they are prone to breakage and burr formation in the empty foil area next to the alignment point during subsequent hot pressing, affecting safety performance. Summary of the Invention

[0003] The main technical problem solved by this application is to provide an electrochemical device and electrical equipment that can effectively solve the problems of current collectors being easily damaged and failing during continuous production of electrode rolls and cold pressing, as well as the problems of current collectors being easily damaged during the hot pressing process of electrode sheets in the process of preparing them into battery cells.

[0004] In a first aspect, this application provides an electrochemical device comprising a positive electrode, a separator, and a negative electrode. The separator is disposed between the negative electrode and the positive electrode. The positive electrode, separator, and negative electrode are stacked and wound to form a wound electrode assembly. The negative electrode comprises a first active material layer, a first current collector, and a second active material layer, with the first current collector disposed between the first and second active material layers. The first active material layer comprises a first coating and a second coating, with the second coating disposed between the first coating and the first current collector. Along the length direction of the negative electrode, the first coating has opposing first and second ends, and the second coating has opposing first and second ends, wherein the first ends of the first coating and the first ends of the second coating are at the same end of the first active material layer. Along a first direction, the first end of the second coating extends beyond the first end of the first coating, giving the first active material layer a first monolayer portion; and / or, along a second direction, the second end of the second coating extends beyond the second end of the first coating, giving the first active material layer a second monolayer portion; both the first and second directions are the length directions of the negative electrode, but are opposite to each other. Along the length of the negative electrode sheet, the negative electrode sheet has a first single-sided coating portion. The first single-sided coating portion is a region on the negative electrode sheet where a first active material layer or a second active material layer is disposed only on the surface of the negative electrode sheet on one side of the first current collector, and the surface of the negative electrode sheet on the other side of the first current collector corresponds to a first blank current collector region. Along the length of the negative electrode sheet, the negative electrode sheet also has a second single-sided coating portion. The second single-sided coating portion is a region on the negative electrode sheet where a first active material layer or a second active material layer is disposed only on the surface of the negative electrode sheet on one side of the first current collector, and the surface of the negative electrode sheet on the other side of the first current collector corresponds to a second blank current collector region. The first single-sided coating portion is close to the winding center of the wound electrode assembly, and the second single-sided coating portion is far from the winding center of the wound electrode assembly. Furthermore, the length L1 of the first single-sided coating portion is greater than the length L2 of the second single-sided coating portion.

[0005] The electrochemical device of this application sets the ends of the first coating and the second coating of the first active material layer in the negative electrode sheet to be staggered, that is, the second coating extends beyond the first coating along the first direction or the second direction. This can reduce the risk of the end thickness of the first active material layer becoming thicker due to the alignment of the ends of the first coating and the second coating. This effectively solves the problem that the two ends of the first active material layer in the length direction are prone to overpressure during the rolling process of the negative electrode sheet, which can cause the first current collector to break. It also reduces the probability of strip breakage during the rolling process of the negative electrode sheet and improves the production yield of the negative electrode sheet.

[0006] The negative electrode of the electrochemical device of this application has a first single-sided coating portion and a second single-sided coating portion arranged opposite to each other at both ends in the length direction. The first single-sided coating portion and the second single-sided coating portion can further reduce the thickness between the same ends of the first active material layer and the second active material layer, preventing the negative electrode from breaking during cold pressing. At the same time, after the negative electrode is subsequently wound into an electrode assembly, when the electrode assembly is hot-pressed, the risk of the first current collector being damaged by excessive hot pressing due to the alignment of the ends of the first active material layer and the second active material layer and the increase in overall thickness is reduced.

[0007] In some embodiments, the second active material layer includes a third coating and a fourth coating, with the fourth coating disposed between the third coating and the first current collector. Along the length of the negative electrode sheet, the third coating has opposing first and second ends, and the fourth coating also has opposing first and second ends, wherein the first ends of the third and fourth coatings, and the first ends of the first and second coatings are at the same end of the negative electrode sheet. Along a first direction, the first end of the fourth coating extends beyond the first end of the third coating, and the second active material layer has a third monolayer portion; and / or, along a second direction, the second end of the fourth coating extends beyond the second end of the third coating, and the second active material layer has a fourth monolayer portion. By also configuring the second active material layer with the same double-layer coating and end-misalignment structure as the first active material layer, the thickness of the active material layer at the same end of the negative electrode sheet can be further avoided, further reducing the probability of strip breakage during rolling of the negative electrode sheet.

[0008] In some embodiments, the first blank current collector region and the second blank current collector region are located on the same side surface of the first current collector. This structure, where the first blank current collector and the second blank current collector are located on the same side surface of the first current collector, facilitates the application of active material layers of the same size across each surface of the first current collector during electrode roll production, enabling continuous production.

[0009] In some embodiments, along the length direction of the negative electrode sheet, the length L3 of the first monolayer portion satisfies: 3mm≤L3≤100mm; and / or, along the length direction of the negative electrode sheet, the length L4 of the second monolayer portion satisfies: 3mm≤L4≤100mm.

[0010] In some embodiments, along the length direction of the negative electrode sheet, the length L3 of the first monolayer portion satisfies: 3mm≤L3≤10mm; and / or, along the length direction of the negative electrode sheet, the length L4 of the second monolayer portion satisfies: 3mm≤L4≤10mm.

[0011] In some embodiments, the length L1 of the first single-sided coating portion and the length L2 of the second single-sided coating portion satisfy the following conditions: 60mm≤L1≤100mm, 3mm≤L2≤5mm.

[0012] Secondly, this application provides an electrochemical device, comprising a positive electrode, a separator, and a negative electrode. The separator is disposed between the negative electrode and the positive electrode. The positive electrode, separator, and negative electrode are stacked to form a stacked electrode assembly. The negative electrode includes a first active material layer, a first current collector, and a second active material layer, with the first current collector disposed between the first and second active material layers. The first active material layer includes a first coating and a second coating. The second coating is disposed between the first coating and the first current collector. Along the length direction of the negative electrode, the first coating has opposing first and second ends, and the second coating has opposing first and second ends, wherein the first ends of the first coating and the first ends of the second coating are at the same end of the first active material layer. Along a first direction, the first end of the second coating extends beyond the first end of the first coating, giving the first active material layer a first monolayer portion; and / or, along a second direction, the second end of the second coating extends beyond the second end of the first coating, giving the first active material layer a second monolayer portion; both the first and second directions are the length directions of the negative electrode, but they are opposite. Along the length of the negative electrode sheet, the negative electrode sheet has a first single-sided coating portion. The first single-sided coating portion is a region on the negative electrode sheet where a first active material layer or a second active material layer is disposed only on the surface of the negative electrode sheet on the side of the first current collector, and the surface of the negative electrode sheet on the other side of the first current collector corresponds to a first blank current collector region. Along the length of the negative electrode sheet, the negative electrode sheet also has a second single-sided coating portion. The second single-sided coating portion is a region on the negative electrode sheet where a first active material layer or a second active material layer is disposed only on the surface of the negative electrode sheet on the side of the first current collector, and the surface of the negative electrode sheet on the other side of the first current collector corresponds to a second blank current collector region. The lengths L1 of the first single-sided coating portion and L2 of the second single-sided coating portion satisfy: 3mm ≤ L1 ≤ 5mm and 3mm ≤ L2 ≤ 5mm, respectively.

[0013] In some embodiments, the second active material layer includes a third coating and a fourth coating, the fourth coating being disposed between the third coating and the first current collector. Along the length direction of the negative electrode sheet, the third coating has opposing first and second ends, and the fourth coating also has opposing first and second ends, wherein the first ends of the third and fourth coatings, and the first ends of the first and second coatings are at the same end of the negative electrode sheet. Along a first direction, the first end of the fourth coating extends beyond the first end of the third coating, giving the second active material layer a third monolayer portion; and / or, along a second direction, the second end of the fourth coating extends beyond the second end of the third coating, giving the second active material layer a fourth monolayer portion.

[0014] In some embodiments, the first blank current collector area and the second blank current collector area are located on the same side surface of the first current collector.

[0015] In some embodiments, along the length direction of the negative electrode sheet, the length L3 of the first monolayer portion satisfies: 3mm≤L3≤100mm; and / or, along the length direction of the negative electrode sheet, the length L4 of the second monolayer portion satisfies: 3mm≤L4≤100mm.

[0016] In some embodiments, along the length direction of the negative electrode sheet, the length L3 of the first monolayer portion satisfies: 3mm≤L3≤10mm; and / or, along the length direction of the negative electrode sheet, the length L4 of the second monolayer portion satisfies: 3mm≤L4≤10mm.

[0017] Thirdly, this application provides an electrical device that includes any of the aforementioned electrochemical devices, the electrochemical devices being used to provide electrical energy to the electrical device. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the specific embodiments of this application, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0019] Figure 1 This is a schematic diagram of the existing technology for producing large rolls of negative electrode sheets.

[0020] Figure 2 This is a cross-sectional view of the wound electrode assembly in the electrochemical device of this application embodiment.

[0021] Figure 3 This is a cross-sectional view of the unfolded negative electrode sheet according to an embodiment of this application.

[0022] Figure 4 This is a cross-sectional view of the unfolded negative electrode sheet according to another embodiment of this application.

[0023] Figure 5 This application is one embodiment of an electrochemical device in which... Figure 2 A magnified view of part A.

[0024] Figure 6 Another embodiment of the electrochemical device in this application Figure 2 A magnified view of part A. Detailed Implementation

[0025] To facilitate understanding of this application, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. It should be noted that the terms "upper," "lower," "inner," "outer," "vertical," and "horizontal," etc., used in this specification to indicate the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0027] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0028] Please see Figure 1 In existing technologies, to improve production efficiency, large rolls of negative electrode sheets 1000 are typically produced continuously. Then, the sheet rolls are slit according to the battery design dimensions to obtain corresponding negative electrode sheets 10, for example, smaller negative electrode sheets 10 are cut at the DD position. During the continuous production of the negative electrode sheet rolls 1000, when the active material layers 11 and 13 are continuously coated, the negative electrode active material layers 11 and 13 on the two surfaces of the current collector 12 are aligned at least at one end along the length of the negative electrode current collector 12, such as... Figure 1 As shown in section E, since the current collector 12 of the negative electrode sheet 10 is usually made of copper foil, the alignment of the relatively soft negative electrode active material layer at the end is very prone to over-pressure during subsequent cold pressing and rolling, causing damage to the negative electrode current collector 12. This leads to strip breakage of the negative electrode sheet 10 during subsequent processing, resulting in low yield and increased costs. Furthermore, in the negative electrode sheet 10 slit by the negative electrode sheet roll 1000, the negative electrode active material layer is usually aligned vertically at at least one end of the electrode sheet. After being wound into an electrode assembly, it is also prone to breakage and burr formation in the empty foil area next to the alignment point during subsequent hot pressing, affecting safety performance.

[0029] This application employs a structure in which two or more layers of active material are coated on the surface of the current collector, and the two ends of the two or more layers of active material are staggered along the length of the negative electrode 10. This structure can effectively solve the problem of strip breakage in the negative electrode during subsequent processing in the prior art.

[0030] In some embodiments, please refer to Figure 2 and Figure 3 The negative electrode 10 includes a first active material layer 11, a first current collector 12, and a second active material layer 13, with the first current collector 12 disposed between the first active material layer 11 and the second active material layer 13. The first active material layer 11 and the second active material layer 13 can be directly coated onto the surface of the first current collector 12, or they can be indirectly coated onto the surface of the first current collector 12 through other coatings. The first active material layer 11 has a double-layer coating structure, including a first coating layer 111 and a second coating layer 112, with the second coating layer 112 disposed between the first coating layer 111 and the first current collector 12. Along the length of the negative electrode 10, the first coating 111 has a first end 111a and a second end 111b, and the second coating 112 has a first end 112a and a second end 112b. The first end 111a of the first coating 111 and the first end 112a of the second coating 112 are at the same end of the first active material layer 11, and the second end 111b of the first coating 111 and the second end 112b of the second coating 112 are at the other end of the first active material layer 11.

[0031] The first coating 111 and the second coating 112 are offset at their ends along the length of the negative electrode 10. Specifically, along the first direction X1, the first end 112a of the second coating 112 extends beyond the first end 111a of the first coating 111, so that a first monolayer portion M1 is formed at the end of the first active material layer 11; and / or, along the second direction X2, the second end 112b of the second coating 112 extends beyond the second end 111b of the first coating 111, so that a second monolayer portion M2 is formed at the other end of the first active material layer 11. Wherein, both the first direction X1 and the second direction X2 are along the length of the negative electrode 10, only their directions are opposite.

[0032] The applicant of this application discovered that during the coating process of the active material layer, the thickness of the initial section is usually slightly greater than that of the middle and final sections, especially the initial end of the initial section. Therefore, the negative electrode sheet 10 of this application sets the ends of the first coating layer 111 and the second coating layer 112 in the first active material layer 11 to be staggered, that is, along the first direction X1 or the second direction X2, the second coating layer 112 extends beyond the first coating layer 111. This avoids the end of the first active material layer 11 becoming thicker due to the alignment of the ends of the first coating layer 111 and the second coating layer 112, thereby effectively solving the problem that the two ends of the active material layer in the length direction are prone to overpressure during the rolling process of the negative electrode sheet 10, which can cause the first current collector 12 to break. This reduces the probability of strip breakage during the rolling process of the negative electrode sheet 10 and improves the production yield of the negative electrode sheet 10.

[0033] In some embodiments, the temperature coefficient of the first coating 111 is greater than that of the second coating 112. Both the first coating 111 and the second coating 112 contain graphite, and the temperature coefficient of graphite is positively correlated with its kinetic performance; the higher the temperature coefficient of graphite, the better its kinetic performance and the better the activity of its molecules. Therefore, by placing the first coating 111, which has better kinetic performance, on the outer side, the interface problem of the negative electrode 10 can be effectively solved, and the reaction efficiency of the first active material layer 11 can be improved. Meanwhile, the second coating 112, which has a relatively lower temperature coefficient, has a higher energy density. Placing the second coating 112 on the side closer to the first current collector 12 can ensure that the first active material layer 11 can have a higher energy density. In other words, by setting the structure of the first coating 111 and the second coating 112 with different kinetic performance, this application can both improve the kinetic performance of the first active material layer 11 and enable the first active material layer 11 to have a higher energy density.

[0034] Since the temperature coefficient of the first coating 111 is greater than that of the second coating 112, the kinetic properties and energy density of the first coating 111 are different from those of the second coating 112. Furthermore, the compaction density and critical compaction density of the first coating 111 and the second coating 112 are also different. Therefore, it is difficult to process the end of the first active material layer 11 by thinning after coating. Thus, in the embodiments of this application, the first coating 111 and the second coating 112 are arranged in a staggered structure at the end of the first active material layer 11, which can effectively avoid the problem of excessive thickness at the end of the first active material layer 11 and reduce the probability that the first current collector 12 is easily crushed and fails during the cold pressing process.

[0035] In some embodiments, please refer to Figure 3Along the first direction X1, the length L3 of the first single-layer portion M1 satisfies: 3mm ≤ L3 ≤ 100mm; and / or, along the second direction X2, the length L4 of the second single-layer portion M2 satisfies: 3mm ≤ L4 ≤ 100mm. By controlling the lengths of the first single-layer portion M1 and the second single-layer portion M2 to be above 3mm, a certain misalignment length can be achieved between the first coating 111 and the second coating 112, thereby effectively solving the problem of the relatively thick end of the first active material layer 11. Of course, in order to ensure the energy density of the negative electrode 10, the misalignment length between the first coating 111 and the second coating 112 does not need to be too long, that is, the length L3 of the first single-layer portion M1 satisfies: 3mm ≤ L3 ≤ 10mm; and / or, along the second direction X2, the length L4 of the second single-layer portion M2 satisfies: 3mm ≤ L4 ≤ 10mm.

[0036] In a further embodiment, when the ratio of the coating weight per unit area of ​​the first coating 111 to the coating weight per unit area of ​​the second coating 112 is (1:1), the length L3 of the first single-layer portion M1 and the length L4 of the second single-layer portion M2 satisfy: L3≥3mm, L4≥3mm. When the ratio of the coating weight per unit area of ​​the first coating 111 to the coating weight per unit area of ​​the second coating 112 is (1:2), the length L3 of the first single-layer portion M1 and the length L4 of the second single-layer portion M2 satisfy: L3≥4mm, L4≥4mm. When the ratio of the coating weight per unit area of ​​the first coating 111 to the coating weight per unit area of ​​the second coating 112 is (1:4), the length L3 of the first single-layer portion M1 and the length L4 of the second single-layer portion M2 satisfy: L3≥5mm, L4≥5mm. By adjusting the relationship between the unit area coating weight and the misalignment length at the end of the first coating 111 and the second coating 112, the first active material layer 11 can have both good kinetic performance and high energy density. In addition, it can effectively solve the problem that the first current collector 12 is crushed and damaged due to excessive local thickness at the end of the first active material layer 11.

[0037] In some embodiments, the second active material layer 13 can be a single-layer coating structure, or a double-layer or multi-layer coating structure. As an example, please refer to... Figure 3The second active material layer 13 has a double-layer coating structure. The second active material layer 13 includes a third coating layer 131 and a fourth coating layer 132, with the fourth coating layer 132 disposed between the third coating layer 131 and the first current collector 12. Along the length direction of the negative electrode sheet 10, the third coating layer 131 has opposing first ends 131a and second ends 131b, and the fourth coating layer 132 has opposing first ends 132a and second ends 132b, wherein the first ends 111a of the first coating layer 111, 112a of the second coating layer 112, 131a of the third coating layer 131, and 132a of the fourth coating layer 132 are at the same end of the negative electrode sheet 10.

[0038] The third coating 131 and the fourth coating 132 are offset at their ends along the length of the negative electrode 10. Specifically, along the first direction X1, the first end 132a of the fourth coating 132 extends beyond the first end 131a of the third coating 131, so that a third monolayer portion M3 is formed at the end of the second active material layer 13; and / or, along the second direction X2, the second end 132b of the fourth coating 132 extends beyond the second end 131b of the third coating 131, so that a fourth monolayer portion M4 is formed at the other end of the second active material layer 13. The first direction X1 and the second direction X2 are both along the length of the negative electrode 10, only their directions are opposite.

[0039] In this application, the negative electrode 10 has its ends of the third coating 131 and the fourth coating 132 in the second active material layer 13 staggered, i.e., the fourth coating 132 extends beyond the third coating 131 along the first direction X1 or the second direction X2. This avoids the end thickness of the second active material layer 13 from being aligned with the ends of the third coating 131 and the fourth coating 132, thus effectively solving the problem that overpressure can easily occur at the two ends of the active material layer in the length direction during the rolling process of the negative electrode 10, which can lead to damage to the first current collector 12. This reduces the probability of strip breakage during the rolling process of the negative electrode 10 and improves the production yield of the negative electrode 10.

[0040] In some embodiments, please refer to Figure 3Along the first direction X1, the length L5 of the third single-layer portion M3 satisfies: 3mm ≤ L5 ≤ 100mm; and / or, along the second direction X2, the length L6 of the fourth single-layer portion M4 satisfies: 3mm ≤ L6 ≤ 100mm. By controlling the lengths of the third single-layer portion M3 and the fourth single-layer portion M4 to be above 3mm, a certain misalignment length can be achieved between the third coating 131 and the fourth coating 132, thereby effectively solving the problem of the relatively thick end of the second active material layer 13. Of course, in order to ensure the energy density of the negative electrode 10, the misalignment length between the third coating 131 and the fourth coating 132 does not need to be too long, that is, the length L5 of the third single-layer portion M3 satisfies: 3mm ≤ L5 ≤ 10mm; and / or, along the second direction X2, the length L6 of the fourth single-layer portion M4 satisfies: 3mm ≤ L6 ≤ 10mm.

[0041] In some embodiments, the temperature coefficient of the third coating 131 is greater than that of the fourth coating 132. Both the third coating 131 and the fourth coating 132 contain graphite, and the temperature coefficient of graphite is positively correlated with its kinetic performance; the higher the temperature coefficient of graphite, the better its kinetic performance and the better the activity of its molecules. Therefore, using the third coating 131, which has better kinetic performance, on the outer side can effectively solve the interface problem of the negative electrode 10 and improve the reaction efficiency of the second active material layer 13. Meanwhile, the fourth coating 132, which has a relatively lower temperature coefficient, has a higher energy density. Placing the fourth coating 132 on the side closer to the first current collector 12 can ensure that the second active material layer 13 can have a high energy density. In other words, by setting the structure of the third coating 131 and the fourth coating 132 with different kinetic performances, this application can both improve the kinetic performance of the second active material layer 13 and enable the second active material layer 13 to have a high energy density.

[0042] In some embodiments, in the length direction of the negative electrode sheet 10, in addition to the first coating 111 and the second coating 112 in the first active material layer 11 being misaligned, and / or the third coating 131 and the fourth coating 132 in the second active material layer 13 being misaligned, the two ends of the first active material layer 11 and the second active material layer 13 may also be misaligned.

[0043] As an example, please refer to Figure 4 Along the length of the negative electrode 10, the negative electrode 10 includes a first single-sided coating portion 10a, a middle portion 10b, and a second single-sided coating portion 10c. The first single-sided coating portion 10a and the second single-sided coating portion 10c are disposed opposite to each other at both ends of the middle portion 10b.

[0044] The first single-sided coating portion 10a is characterized by having a first active material layer 11 or a second active material layer 13 deposited on one side of the surface of the first current collector 12 at one end along the length of the negative electrode sheet 10, and the opposite side of the surface of the first current collector 12 corresponding to the area of ​​the first blank current collector region 121. In other words, at the first single-sided coating portion 10a, the other side of the surface of the first current collector 12 does not have the first active material layer 11 or the second active material layer 13 deposited.

[0045] Similarly, the second single-sided coating portion 10c is as follows: at the other end of the negative electrode sheet 10 along its length, a first active material layer 11 or a second active material layer 13 is provided only on one side of the surface of the first current collector 12, and the surface on the opposite side of the first current collector 12 corresponds to the area of ​​the second blank current collector region 122. That is, at the second single-sided coating portion 10c, the first active material layer 11 or the second active material layer 13 is not provided on the surface of the other side of the first current collector 12.

[0046] It is worth noting that in the first single-sided coating portion 10a and the second single-sided coating portion 10c described above, only the first active material layer 11 or the second active material layer 13 is provided on one of the surfaces of the first current collector 12. The phrase "only provided" refers to both the first active material layer 11 and the second active material layer 13, meaning that only one of them is coated. However, other coatings, such as conductive layers, safety layers, adhesive tape, etc., can also be coated on the two surfaces of the first current collector 12.

[0047] This embodiment of the application provides a first single-sided coating portion 10a and a second single-sided coating portion 10c at the two ends of the negative electrode sheet 10. That is, along the first direction X1, the first active material layer 11 extends beyond the second active material layer 13, or the second active material layer 13 extends beyond the first active material layer 11; and along the second direction X2, the first active material layer 11 extends beyond the second active material layer 13, or the second active material layer 13 extends beyond the first active material layer 11. In other words, the first active material layer 11 and the second active material layer 13 at the two ends of the negative electrode sheet 10 are staggered. This avoids the problem of local thickness increase caused by the first active material layer 11 and the second active material layer 13 being aligned at their ends. This effectively solves the problem of overpressure at the two ends of the negative electrode sheet 10 during the rolling process, which can easily lead to damage to the first current collector 12. It also reduces the probability of strip breakage in the negative electrode sheet 10 and improves the production yield of the negative electrode sheet 10.

[0048] The following description uses examples where the second active material layer 13 extends beyond the first active material layer 11 along the first direction X1 and along the second direction X2.

[0049] Please see Figure 4 In some embodiments, along the length direction of the negative electrode sheet 10, the length L1 of the first single-sided coating portion 10a satisfies: 3mm ≤ L1 ≤ 100mm. Along the length direction of the negative electrode sheet 10, the length L2 of the second single-sided coating portion 10c satisfies: 3mm ≤ L2 ≤ 100mm. By setting the first active material layer 11 and the second active material layer 13 with a misalignment length of 3mm or more, the negative electrode sheet 10 can avoid end-to-end alignment during cold pressing, thus preventing local thickness increases at the ends. This solves the problem of the first current collector 12 being damaged due to excessive force at the ends, leading to local or even overall crushing failure of the first current collector 12, while also considering the energy density and production cost of the secondary battery.

[0050] When the aforementioned negative electrode 10 is applied in a stacked electrode assembly 100, the lengths L1 of the first single-sided coating portion 10a and L2 of the second single-sided coating portion 10c can be relatively small, for example, 3mm≤L1≤5mm and 3mm≤L2≤5mm. Since a misalignment length of 3mm between the first active material layer 11 and the second active material layer 13 can solve the problem of the first current collector 12 being easily damaged during rolling, the misalignment length between the first active material layer 11 and the second active material layer 13 can be appropriately increased to reduce processing difficulty. However, to ensure that the negative electrode 10 has a high energy density, the misalignment length between the first active material layer 11 and the second active material layer 13 should not be set too long.

[0051] When the aforementioned negative electrode 10 is applied in a wound electrode assembly 100, the length of the portion of the first single-sided coating 10a and the second single-sided coating 10c located at the winding center can be larger, while the length of the portion farther from the winding center can be smaller. For an example, please refer to... Figure 2 and Figure 4The first single-sided coating portion 10a of the negative electrode 10 is located at the winding center, and its length L1 satisfies 60mm≤L1≤100mm. The second single-sided coating portion 10c of the negative electrode 10 is far from the winding center, and its length L2 satisfies 3mm≤L2≤5mm. At the winding center of the electrode assembly 100, since there is no corresponding positive electrode 20 on the inner side of the negative electrode 10, the active material on the inner side of the negative electrode 10 cannot participate in the electrochemical reaction. Therefore, in order to reduce the weight of the electrode assembly 100 and increase the energy density of the electrode assembly 100, the inner side of the end of the negative electrode 10 located at the winding center is usually set as an empty foil area 123, that is, no active material is coated. At the winding center of the electrode assembly 100, there is a corresponding positive electrode 20 on the outer side of the negative electrode 10. Therefore, an active material layer is provided on the outer side of the negative electrode 10, which can participate in the electrochemical reaction with the active material layer on the positive electrode 20. That is, the first single-sided coating portion 10a constitutes a staggered arrangement of the active material layers on the two side surfaces of the first current collector 12. In addition, since the length of the empty foil area 123 at the winding center of the negative electrode 10 is positively correlated with the width of the finished electrochemical device, that is, the longer the length of the empty foil area 123, the wider the corresponding electrochemical device, in some embodiments, the length L1 of the first single-sided coating portion 10a of the negative electrode 10 can be a large value.

[0052] Please see Figure 2 , Figure 5 and Figure 6 At the end of the negative electrode 10 away from the winding center of the electrode assembly 100, there are corresponding positive electrode 20s on both its inner and outer surfaces. Therefore, a first active material layer 11 and a second active material layer 13 should be provided on both sides of the end of the negative electrode 10. However, in order to avoid the first active material layer 11 and the second active material layer 13 being aligned at the end of the negative electrode 10, which would lead to an increase in its local thickness, the first active material layer 11 and the second active material layer 13 can be set in a staggered manner. That is, the length L2 of the second single-sided coating portion 10c can be 3 mm or more. However, considering the processing difficulty and the need to ensure energy density, the length L2 of the second single-sided coating portion 10c can be appropriately increased, for example, 3 mm ≤ L2 ≤ 5 mm.

[0053] In some embodiments, please refer to Figure 4 The first blank current collector region 121 and the second blank current collector region 122 of the negative electrode 10 can be located on the same side surface of the first current collector 12. Alternatively, they can be located on opposite sides of the first current collector 12, that is, the first blank current collector region 121 is located on one of the surfaces of the first current collector 12, while the second blank current collector region 122 is located on the other surface of the first current collector 12, with the two surfaces of the first current collector 12 arranged opposite to each other.

[0054] The following explanation uses the application of the negative electrode 10 in a wound electrode assembly 100 as an example. Please refer to... Figure 2 The first single-sided coating portion 10a of the negative electrode 10 is located at the winding center of the electrode assembly 100, and the first blank current collector region 121 is located on the inner surface of the first current collector 12. The second single-sided coating portion 10c of the negative electrode 10 is located away from the winding center of the electrode assembly 100. At this time, as... Figure 5 As shown, the second blank current collector region 122 can be located on the inner surface of the first current collector 12, or, as... Figure 6 As shown, the second blank current collector region 122 can be located on the outer surface of the first current collector 12. It is worth noting that, due to the presence of the second blank current collector region 122, the coating length of the active material layer in the positive electrode plate 20 and the area corresponding to the second blank current collector region 122 in the electrode assembly 100 can be appropriately reduced, ensuring that the negative electrode active material layer on the negative electrode plate 10 can completely cover the positive electrode active material layer on the positive electrode plate 20. This effectively avoids the phenomenon of lithium plating caused by the inability of free lithium ions at the location of the second blank current collector region 122 to be embedded in the active material layer of the negative electrode plate 10.

[0055] In the above embodiments, along the length of the negative electrode 10, the two ends of the negative electrode 10 are respectively a first single-sided coating portion 10a and a second single-sided coating portion 10c. In other embodiments, please refer to... Figure 4 The two ends of the negative electrode 10 can also be empty foil areas 123, that is, neither of the two surfaces of the first current collector 12 is coated with the first active material layer 11 and the second active material layer 13.

[0056] This application also provides an electrochemical device, which includes a housing, an electrode assembly 100, a positive electrode tab, and a negative electrode tab. The housing has a receiving cavity for housing the electrode assembly 100. Both the positive and negative electrode tabs are electrically connected to the electrode assembly 100 and extend outside the housing. The receiving cavity is filled with an electrolyte for the electrode assembly 100 to undergo an electrochemical reaction. The electrode assembly 100 includes a positive electrode plate 20, a separator 30, and a negative electrode plate 10. The separator 30 separates the positive electrode plate 20 and the negative electrode plate 10. The structure and function of the negative electrode plate 10 can be referred to the above embodiments and will not be repeated here.

[0057] In some embodiments, to ensure that lithium ions can be smoothly embedded into the active material layer of the negative electrode 10 and to prevent lithium plating, the coating length of the active material layer on the negative electrode 10 typically needs to be greater than the length of the active material layer on the positive electrode 20. For example, please refer to... Figure 2 and Figure 5The positive electrode 20 includes a second current collector 21, a third active material layer 22, and a fourth active material layer 23. The third active material layer 22 is disposed on the inner surface of the second current collector 21 near the winding center of the electrode assembly 100, and the fourth active material layer 23 is disposed on the outer surface of the second current collector 21 away from the winding center of the electrode assembly 100. When the second blank current collector region 122 of the negative electrode 10 is located on the inner surface, the length of the fourth active material layer 23 can be appropriately reduced, thereby ensuring that the first active material layer 11 can extend beyond the fourth active material layer 23. (See also...) Figure 2 and Figure 6 When the second blank current collector region 122 of the negative electrode 10 is located on the outer surface, the length of the third active material layer 22 can be appropriately reduced, thereby ensuring that the second active material layer 13 can extend beyond the third active material layer 22.

[0058] This application also provides an electrical device, which includes the electrochemical device from any of the above embodiments, and the electrochemical device provides electrical energy to the electrical device. The structure and function of the electrochemical device can be found in the above embodiments, and will not be repeated here.

[0059] The negative electrode 10 of this application embodiment includes a first active material layer 11, a first current collector 12, and a second active material layer 13, with the first current collector 12 disposed between the first active material layer 11 and the second active material layer 13. Along a first direction X1, the first end 112a of the second coating 112 extends beyond the first end 111a of the first coating 111, such that a first monolayer portion is formed at the end of the first active material layer 11; and / or, along a second direction X2, the second end 112b of the second coating 112 extends beyond the second end 111b of the first coating 111, such that a second monolayer portion is formed at the other end of the first active material layer 11. The negative electrode 10 of this application achieves this by setting the two ends of the first coating 111 and the second coating 112 in the first active material layer 11 to be staggered, that is, along the first direction X1 or the second direction X2, the second coating 112 extends beyond the first coating 111. This avoids the end of the first active material layer 11 becoming thicker due to the alignment of the ends of the first coating 111 and the second coating 112. This effectively solves the problem that the two ends of the active material layer in the length direction are prone to overpressure during the rolling process of the negative electrode sheet 10, which can cause the first current collector 12 to break. It also reduces the probability of strip breakage during the rolling process of the negative electrode sheet 10 and improves the production yield of the negative electrode sheet 10.

[0060] To facilitate understanding of the technical concept and effects of this application, an experiment will be conducted below using a lithium-ion battery as an example.

[0061] Experiment 1: [Preparation of Large Rolls of Negative Electrode Sheets] Example 1 Artificial graphite (specific capacity = 360 mAh / g) and carboxymethyl cellulose (CMC, weight average molecular weight 7.0 × 10⁻⁶) were used. 5 ), and the binder is styrene-butadiene rubber (SBR, with a weight-average molecular weight of 5×10⁻⁶). 6 The mixture was prepared according to a mass ratio of 97.8:1.2:1, and then deionized water was added as a solvent. The mixture was stirred under vacuum until a first coating slurry with a solid content of 50wt% and a uniform system was obtained.

[0062] Artificial graphite (specific capacity = 360 Ah / g), carboxymethyl cellulose (CMC, weight average molecular weight 7.0 × 10⁻⁶) and other materials were used. 5 ), and the binder is styrene-butadiene rubber (SBR, with a weight-average molecular weight of 5×10⁻⁶). 6 The mixture was prepared according to a mass ratio of 97.5:1.2:1.3, and then deionized water was added as a solvent. The mixture was stirred under vacuum until a second coating slurry with a solid content of 50wt% and a uniform system was obtained.

[0063] A first and second coating slurry are simultaneously and uniformly coated onto one surface of an 8µm thick copper foil (tensile strength = 500MPa) for the negative electrode current collector using a dual-cavity extrusion coating die. The foil is then dried at 90°C to obtain a large roll of negative electrode sheet with both the first and second coatings applied to one side. The second coating is located between the first coating and the copper foil. The above steps are then repeated on the other surface of the copper foil, followed by cold pressing to form a large roll of semi-finished negative electrode sheet with double-sided coatings of the negative electrode active material (first and second coatings). The semi-finished negative electrode sheet is then baked at 290°C for 10 hours and cooled to room temperature in an environment with <5% humidity. Before cold pressing, both the first and second coatings are 50µm thick.

[0064] like Figure 3 As shown, the negative electrode 10 includes a first active material layer 11, a first current collector 12, and a second active material layer 13, with the first current collector 12 disposed between the first active material layer 11 and the second active material layer 13. The first active material layer 11 includes a first coating layer 111 and a second coating layer 112, with the second coating layer 112 disposed between the first coating layer 111 and the first current collector 12. The first end 112a of the second coating layer 112 extends beyond the first end 111a of the first coating layer 111 to form a first monolayer portion M1, and the second end 112b of the second coating layer 112 extends beyond the second end 111b of the first coating layer 111 to form a second monolayer portion M2.

[0065] The length L3 of the first single-layer part M1 is 3mm, and the length L4 of the second single-layer part M2 is 3mm.

[0066] Examples 2-6: Except for the length L3 of the first single-layer part M1 and the length L4 of the second single-layer part M2, the other parameters are the same as in Example 1. Please refer to Table 1 below for details.

[0067] Example 7: Based on the negative electrode structure of Example 1, as follows... Figure 3 As shown, the second active material layer 13 includes a third coating 131 and a fourth coating 132, with the fourth coating 132 disposed between the third coating 131 and the first current collector 12. The first end 132a of the fourth coating 132 extends beyond the first end 131a of the third coating 131 to form a third monolayer portion M3; the second end 132b of the fourth coating 132 extends beyond the second end 131b of the third coating 131 to form a fourth monolayer portion M4.

[0068] Among them, the length L5 of the third single-layer part M3 is 3mm, and the length L6 of the fourth single-layer part M4 is 3mm.

[0069] Examples 8-10: Except for the length L5 of the third single-layer part M3 and the length L6 of the fourth single-layer part M4, the other parameters are the same as those in Example 7. Please refer to Table 1 below for details.

[0070] Example 11: Based on the negative electrode structure of Example 1, as follows... Figure 4 As shown, along the length of the negative electrode sheet, the first active material layer and the second active material layer are staggered to form a first single-sided coating portion at one end of the negative electrode sheet, wherein the length L1 of the first single-sided coating portion is 3mm.

[0071] Examples 12-14: Except for the length L1 of the first single-sided coating portion, the other parameters are the same as those in Example 11. Please refer to Table 1 below for details.

[0072] Example 15: Based on the negative electrode structure of Example 13, as follows... Figure 4 As shown, along the length of the negative electrode sheet, the two ends of the first active material layer and the second active material layer are staggered to form a first single-sided coating portion and a second single-sided coating portion at the two ends of the negative electrode sheet, respectively. The length L1 of the first single-sided coating portion is 60 mm, and the length L2 of the second single-sided coating portion is 3 mm.

[0073] Examples 16-18: Except for the length L2 of the second single-sided coating portion, the other parameters are the same as those in Example 15. Please refer to Table 1 below for details.

[0074] Examples 19-20: Except for the length L5 of the third single-layer part M3 and the length L6 of the fourth single-layer part M4, the other parameters are the same as those in Example 16. Please refer to Table 1 below for details.

[0075] Comparative Example 1: Along the length of the negative electrode sheet, the two ends of the first coating and the second coating in the first active material layer are aligned, that is, there is no first monolayer and / or second monolayer in the first active material layer. The other parameters are the same as in Example 1. Please refer to Table 1 below for details.

[0076] Breakage rate test method: Take approximately 1000 meters of coated negative electrode sheet after winding, and perform cold pressing on a cold press. The compaction density of the electrode sheet is set to 1.7 g / cm³. 3 If the total length of tape before cold pressing is Y, and the length of tape lost due to tape breakage during cold pressing is Y', then the tape breakage rate during cold pressing = Y' / Y × 100%.

[0077] Table 1

[0078] Conclusion: Comparative Example 1 and Examples 1-10 show that the structure in which one or both ends of the first and second coating layers on the negative electrode sheet are staggered can effectively reduce the breakage rate of the negative electrode sheet during the production of large rolls, thereby improving the continuity of large roll production and product quality. According to Examples 11-20, the structure in which one or both ends of the first and second active material layers on both sides of the first current collector on the negative electrode sheet are staggered can further reduce the breakage rate of the negative electrode sheet during the production of large rolls, thereby improving the continuity of large roll production and product quality.

[0079] Experiment 2: [Lithium-ion Battery Hot-Pressure Pass Rate Test] <Preparation of Negative Electrode Sheets> Large rolls of negative electrode sheets from Comparative Example 1, Example 1, and Example 15 were cut to obtain three types of negative electrode sheets suitable for manufacturing lithium-ion batteries, each with a single-sided coating thickness of 90 μm and a width × length of 76 mm × 860 mm. A 12 mm × 35 mm negative electrode tab groove was laser-cut into the negative electrode sheet, and a negative electrode tab with a thickness of 110 μm and a width × length of 8 mm × 55 mm was welded into the negative electrode tab groove.

[0080] <Preparation of the positive electrode> The positive electrode active material is lithium iron phosphate, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10⁻⁶). 5The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone (NMP) added as a solvent. The mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was obtained. The positive electrode slurry was uniformly coated onto one surface of a 6 μm thick aluminum foil used as a positive electrode current collector, and dried at 90°C to obtain a positive electrode sheet with a single-sided coating of positive active material (80 μm thick). The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material. After cold pressing and slitting, a 10 mm diameter was laser-cut into the positive electrode sheet. A 35mm positive electrode tab slot is provided, in which a 116µm thick weld with a width × length of 5mm is placed. The 55mm positive electrode tab is made to a specification of 74mm. 851mm positive electrode sheet is ready for use.

[0081] The diaphragm is made of a porous polyethylene (PE) membrane with a thickness of 8 μm.

[0082] <Preparation of Electrolyte> In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0083] <Preparation of Lithium-ion Batteries> The separator, positive electrode, separator, and negative electrode prepared above are stacked in sequence and wound to obtain an electrode assembly. The first single-sided coating of the negative electrode is close to the winding center of the wound electrode assembly, and the second single-sided coating of the negative electrode is away from the winding center of the wound electrode assembly. The electrode assembly is hot-pressed at a pressure of 5 MPa, a temperature of 65°C, and a holding time of 10 s. The electrode assembly is placed in an outer packaging aluminum-plastic film, and after dehydration at 80°C, electrolyte is injected and the assembly is sealed. After formation, degassing, and shaping processes, a lithium-ion battery is obtained. Among them, three different lithium batteries are prepared by using different negative electrode sheets obtained in Comparative Example 1, Example 1, and Example 13. Ion battery.

[0084] Following the above steps, 10 of each of the three different lithium-ion batteries were prepared, and these 30 lithium-ion batteries were subjected to a hot-pressing test (hot-pressing conditions: pressure 0.25 MPa, temperature 65℃, time 4 s). After the experiment, the lithium... The number of damaged negative electrode current collectors was recorded after disassembling the ion battery, as shown in Table 2 below.

[0085] Table 2

[0086] Conclusion: Based on the above experimental results, it can be seen that the negative electrode sheet in the electrode assembly adopts a structure in which one or both ends of the first and second coating layers are staggered on one side, which can effectively improve the pass rate of lithium-ion batteries in hot-pressing tests. Furthermore, the negative electrode sheet in the electrode assembly adopts a structure in which one or both ends of the first and second active material layers on both sides of the first current collector are staggered, which can further improve the pass rate of lithium-ion batteries in hot-pressing tests, thereby improving the safety performance of lithium-ion batteries.

[0087] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. An electrochemical device, characterized in that, It includes a positive electrode, a separator, and a negative electrode, wherein the separator is disposed between the negative electrode and the positive electrode, and the positive electrode, the separator, and the negative electrode are stacked and wound to form a wound electrode assembly; The negative electrode sheet includes a first active material layer, a first current collector, and a second active material layer, wherein the first current collector is disposed between the first active material layer and the second active material layer; The first active material layer includes a first coating and a second coating. The second coating is disposed between the first coating and the first current collector. Along the length direction of the negative electrode sheet, the first coating has a first end and a second end opposite to each other, and the second coating has a first end and a second end opposite to each other. The first end of the first coating and the first end of the second coating are at the same end of the first active material layer. Along a first direction, the first end of the second coating extends beyond the first end of the first coating, so that the first active material layer has a first monolayer portion; and / or, along a second direction, the second end of the second coating extends beyond the second end of the first coating, so that the first active material layer has a second monolayer portion; the first direction and the second direction are both the length directions of the negative electrode sheet, and the first direction and the second direction are opposite; Along the length of the negative electrode sheet, the negative electrode sheet has a first single-sided coating portion. The first single-sided coating portion is a region on the negative electrode sheet where the first active material layer or the second active material layer is provided only on the surface of the first current collector side, and the surface of the other side of the first current collector corresponds to the first blank current collector area. Along the length of the negative electrode sheet, the negative electrode sheet has a second single-sided coating portion. The second single-sided coating portion is a region on the negative electrode sheet where the first active material layer or the second active material layer is disposed only on the surface of the first current collector side, and the surface of the other side of the first current collector corresponds to the second blank current collector area. The first single-sided coating portion is close to the winding center of the wound electrode assembly, the second single-sided coating portion is far from the winding center of the wound electrode assembly, and the length L1 of the first single-sided coating portion is greater than the length L2 of the second single-sided coating portion.

2. The electrochemical device according to claim 1, characterized in that, The second active material layer includes a third coating and a fourth coating. The fourth coating is disposed between the third coating and the first current collector along the length direction of the negative electrode sheet. The third coating has a first end and a second end opposite to each other, and the fourth coating has a first end and a second end opposite to each other. The first end of the third coating, the first end of the fourth coating, the first end of the first coating, and the first end of the second coating are at the same end of the negative electrode sheet. Along a first direction, the first end of the fourth coating extends beyond the first end of the third coating, and the second active material layer has a third monolayer portion; and / or, along a second direction, the second end of the fourth coating extends beyond the second end of the third coating, and the second active material layer has a fourth monolayer portion.

3. The electrochemical device according to claim 1 or 2, characterized in that, The first blank current collector area and the second blank current collector area are located on the same side surface of the first current collector.

4. The electrochemical device according to claim 1 or 2, characterized in that, Along the length direction of the negative electrode sheet, the length L3 of the first single-layer portion satisfies: 3mm≤L3≤100mm; And / or, Along the length direction of the negative electrode sheet, the length L4 of the second single-layer portion satisfies: 3mm≤L4≤100mm.

5. The electrochemical device according to claim 1 or 2, characterized in that, Along the length direction of the negative electrode sheet, the length L3 of the first single-layer portion satisfies: 3mm≤L3≤10mm; And / or, Along the length direction of the negative electrode sheet, the length L4 of the second single-layer portion satisfies: 3mm≤L4≤10mm.

6. The electrochemical device according to claim 1 or 2, characterized in that, The lengths L1 of the first single-sided coating portion and L2 of the second single-sided coating portion satisfy the following conditions: 60mm≤L1≤100mm and 3mm≤L2≤5mm, respectively.

7. An electrochemical device, characterized in that, It includes a positive electrode, a separator, and a negative electrode, wherein the separator is disposed between the negative electrode and the positive electrode, and the positive electrode, the separator, and the negative electrode are stacked to form a stacked electrode assembly; The negative electrode sheet includes a first active material layer, a first current collector, and a second active material layer, wherein the first current collector is disposed between the first active material layer and the second active material layer; The first active material layer includes a first coating and a second coating. The second coating is disposed between the first coating and the first current collector. Along the length direction of the negative electrode sheet, the first coating has a first end and a second end opposite to each other, and the second coating has a first end and a second end opposite to each other. The first end of the first coating and the first end of the second coating are at the same end of the first active material layer. Along a first direction, the first end of the second coating extends beyond the first end of the first coating, so that the first active material layer has a first monolayer portion; and / or, along a second direction, the second end of the second coating extends beyond the second end of the first coating, so that the first active material layer has a second monolayer portion; the first direction and the second direction are both the length directions of the negative electrode sheet, and the first direction and the second direction are opposite; Along the length of the negative electrode sheet, the negative electrode sheet has a first single-sided coating portion. The first single-sided coating portion is a region on the negative electrode sheet where the first active material layer or the second active material layer is provided only on the surface of the first current collector side, and the surface of the other side of the first current collector corresponds to the first blank current collector area. Along the length of the negative electrode sheet, the negative electrode sheet has a second single-sided coating portion. The second single-sided coating portion is a region on the negative electrode sheet where the first active material layer or the second active material layer is disposed only on the surface of the first current collector side, and the surface of the other side of the first current collector corresponds to the second blank current collector area. The lengths L1 of the first single-sided coating portion and L2 of the second single-sided coating portion satisfy the following conditions: 3mm≤L1≤5mm, 3mm≤L2≤5mm.

8. The electrochemical device according to claim 7, characterized in that, The second active material layer includes a third coating and a fourth coating. The fourth coating is disposed between the third coating and the first current collector along the length direction of the negative electrode sheet. The third coating has a first end and a second end opposite to each other, and the fourth coating has a first end and a second end opposite to each other. The first end of the third coating, the first end of the fourth coating, the first end of the first coating, and the first end of the second coating are at the same end of the negative electrode sheet. Along a first direction, the first end of the fourth coating extends beyond the first end of the third coating, so that the second active material layer has a third monolayer portion; and / or, along a second direction, the second end of the fourth coating extends beyond the second end of the third coating, so that the second active material layer has a fourth monolayer portion.

9. The electrochemical device according to claim 7 or 8, characterized in that, The first blank current collector area and the second blank current collector area are located on the same side surface of the first current collector.

10. The electrochemical device according to claim 7 or 8, characterized in that, Along the length direction of the negative electrode sheet, the length L3 of the first single-layer portion satisfies: 3mm≤L3≤100mm; And / or, Along the length direction of the negative electrode sheet, the length L4 of the second single-layer portion satisfies: 3mm≤L4≤100mm.

11. The electrochemical device according to claim 7 or 8, characterized in that, Along the length direction of the negative electrode sheet, the length L3 of the first single-layer portion satisfies: 3mm≤L3≤10mm; And / or, Along the length direction of the negative electrode sheet, the length L4 of the second single-layer portion satisfies: 3mm≤L4≤10mm.

12. An electrical appliance, characterized in that, Includes the electrochemical device according to any one of claims 1-11.

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