Electrochemical apparatus and electronic apparatus

Abstract

An electrochemical apparatus and an electronic apparatus. A first positive electrode active material layer in the electrochemical apparatus is disposed on a surface of a positive electrode current collector, and a second positive electrode active material layer is located on a surface of the first positive electrode active material layer distant from the positive electrode current collector. A first positive electrode active material in the first positive electrode active material layer comprises at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium manganate; and a second positive electrode active material in the second positive electrode active material layer comprises at least one of lithium iron manganese phosphate or lithium iron phosphate. Along a width direction of an unfolded positive electrode plate, the first positive electrode active material layer comprises a first end face, and a third end face opposite the first end face, and the second positive electrode active material layer comprises a second end face, and a fourth end face opposite the second end face, the first end face extending past the second end face, and the fourth end face not extending past the third end face.

Description

Electrochemical devices and electronic devices Technical Field

[0001] The present application relates to the field of electrochemistry, and in particular to an electrochemical device and an electronic device. Background Art

[0002] Electrochemical devices, such as lithium-ion batteries, boast high energy density, low maintenance, low self-discharge, long cycle life, no memory effect, stable operating voltage, and environmental friendliness. They are widely used in portable electronic devices (such as mobile phones, laptops, and cameras), power tools, and electric vehicles. With the rapid advancement of technology and the diversification of market demands, demands for lithium-ion batteries are increasing, such as thinner and lighter weight, improved safety, and higher capacity.

[0003] The positive electrode sheet is a critical component in lithium-ion batteries. However, existing positive electrode sheets suffer from weak adhesion between the positive active material layer and the positive current collector, leading to a high risk of delamination of the positive electrode material layer. Therefore, developing a lithium-ion battery that can reduce the risk of delamination of the positive active material layer is particularly important.

[0004] Summary of the Invention

[0005] The purpose of the present application is to provide an electrochemical device and an electronic device, which can reduce the risk of delamination of the positive electrode active material layer while taking into account the capacity of the electrochemical device.

[0006] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides an electrochemical device, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer being arranged on the surface of the positive electrode current collector, and the second positive electrode active material layer being arranged on the surface of the first positive electrode active material layer away from the positive electrode current collector; the first positive electrode active material layer comprising a first positive electrode active material, the first positive electrode active material comprising at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide or lithium manganate, the second positive electrode active material layer comprising a first positive electrode active material, the first positive electrode active material comprising at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide or lithium manganate, The positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material including at least one of lithium manganese iron phosphate or lithium iron phosphate; along the width direction of the unfolded positive electrode sheet, the first positive electrode active material layer includes a first end face and a third end face opposite the first end face, and the second positive electrode active material layer includes a second end face and a fourth end face opposite the second end face, the first end face and the second end face are located on a first side of the positive electrode sheet, the third end face and the fourth end face are located on a second side of the positive electrode sheet, and the first side and the second side are opposite; along the width direction of the unfolded positive electrode sheet, the first end face extends beyond the second end face, and the fourth end face does not extend beyond the third end face. By setting the first end face to extend beyond the second end face and the fourth end face to extend beyond the third end face along the width direction of the unfolded positive electrode sheet, the present application reduces the possibility of the second positive electrode active material layer contacting the positive electrode current collector, thereby reducing the risk of delamination of the edge portion of the positive electrode active material layer along the width direction. Thus, by regulating the types of the first and second positive electrode active materials, and regulating the first end face to extend beyond the second end face, and the fourth end face to not extend beyond the third end face, the present application enables the electrochemical device to maintain its capacity while reducing the risk of delamination of the positive electrode active material layer. Furthermore, the production cost of the electrochemical device is reduced.

[0008] In one embodiment of the present application, along the thickness direction of the unfolded positive electrode sheet, the projection of the second positive electrode active material layer on the positive electrode current collector is located within the projection of the first positive electrode active material layer on the positive electrode current collector, which can further reduce the risk of demolding of the second positive electrode active material layer.

[0009] In one embodiment of the present application, along the width direction of the unfolded positive electrode sheet, the positive electrode active material layer includes a main portion and an edge portion, and the edge portion is the portion where the first positive electrode active material layer exceeds the second positive electrode active material layer; based on the total mass of the first positive electrode active material and the second positive electrode active material in the main portion, the mass percentage of the second positive electrode active material is 5% to 95%.

[0010] In one embodiment of the present application, based on the total mass of the first positive electrode active material and the second positive electrode active material in the main body, the mass percentage of the second positive electrode active material is 5% to 60%.

[0011] In one embodiment of the present application, the distance between the first end face and the second end face is m1, where 0.2 mm ≤ m1 ≤ 2 mm. By regulating the distance between the first end face and the second end face within the above range, the electrochemical device can maintain its capacity while reducing the risk of delamination of the positive electrode active material layer, and also reduce the production cost of the electrochemical device.

[0012] In one embodiment of the present application, the distance between the third end face and the fourth end face is m2, where 0.2 mm ≤ m2 ≤ 2 mm. By regulating the distance between the third end face and the fourth end face within the above range, the electrochemical device can maintain its capacity while reducing the risk of delamination of the positive electrode active material layer, and also reduce the production cost of the electrochemical device.

[0013] In one embodiment of the present application, the first positive electrode active material layer further comprises a first conductive agent and a first binder, wherein, based on the mass of the first positive electrode active material layer, the mass percentage of the first positive electrode active material is 95% to 98%, the mass percentage of the first conductive agent is 0.5% to 3%, and the mass percentage of the first binder is 0.5% to 3%; and / or, the second positive electrode active material layer further comprises a second conductive agent and a second binder, wherein, based on the mass of the second positive electrode active material layer, the mass percentage of the second positive electrode active material is 95% to 98%, the mass percentage of the second conductive agent is 0.6% to 3%, and the mass percentage of the first binder is 0.5% to 2%. The contents of the first positive electrode active material, the first conductive agent, and the first binder in the first positive electrode active material layer are controlled within the above ranges, and the contents of the second positive electrode active material, the second conductive agent, and the second binder in the second positive electrode active material layer are controlled within the above ranges, so that the electrochemical device can maintain its capacity while reducing the risk of delamination of the positive electrode active material layer.

[0014] In one embodiment of the present application, in the main body portion, the coating weight of the positive electrode active material layer is 200 mg / 1540.24 mm 2 Up to 600mg / 1540.24mm 2 By regulating the coating weight of the positive electrode active material layer within the above range, the positive electrode active material layer can have more positive electrode active material, thereby providing a higher capacity for the electrochemical device.

[0015] In one embodiment of the present application, the gram capacity of the first positive electrode active material is a, and the gram capacity of the second positive electrode active material is b, satisfying the following conditions: 10% ≤ (ab) / b×100% ≤ 75%, and 160 mAh / g ≤ a ≤ 210 mAh / g. Regulating the value of (ab) / b×100% and the gram capacity a of the first positive electrode active material within the above range is beneficial for reducing the production cost of the electrochemical device while taking into account the capacity of the electrochemical device and reducing the risk of delamination of the positive electrode active material layer.

[0016] In one embodiment of the present application, 14% ≤ (ab) / b×100% ≤ 30%. Controlling the value of (ab) / b×100% within the above range is beneficial for further reducing the production cost of the electrochemical device while taking into account the capacity of the electrochemical device and reducing the risk of delamination of the positive electrode active material layer.

[0017] In one embodiment of the present application, 120 mAh / g≤b≤140 mAh / g.

[0018] In one embodiment of the present application, the electrochemical device further comprises a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the coating weight of the negative electrode active material layer being 100 mg / 1540.24 mm 2 Up to 300mg / 1540.24mm 2 By regulating the coating weight of the negative electrode active material layer within the above range, a higher capacity can be provided for the negative electrode active material layer, thereby enabling the electrochemical device to have a higher capacity.

[0019] In one embodiment of the present application, the negative electrode active material layer includes a negative electrode active material having a gram capacity of 280 mAh / g to 420 mAh / g. Regulating the gram capacity of the negative electrode active material within the above range is beneficial for providing a higher capacity for the electrochemical device.

[0020] In one embodiment of the present application, the CB value of the electrochemical device satisfies: 1.04≤CB≤1.2.

[0021] In one embodiment of the present application, along the width direction of the positive electrode sheet, the positive electrode active material layer includes a main portion and an edge portion, the edge portion is the portion where the first positive electrode active material layer exceeds the second positive electrode active material layer, and the CB value of the edge portion is ≥ the CB value of the main portion.

[0022] In one embodiment of the present application, along the length direction of the unfolded positive electrode sheet, the length of the first positive electrode active material layer is greater than the length of the second positive electrode active material layer.

[0023] A second aspect of the present application provides an electronic device comprising the electrochemical device described in any of the aforementioned embodiments.

[0024] Beneficial effects of the embodiments of the present application:

[0025] The embodiments of the present application provide an electrochemical device and an electronic device, wherein the first positive electrode active material in the electrochemical device has good viscosity and high gram capacity. The first positive electrode active material is applied to the first positive electrode active material layer, so that the first positive electrode active material layer and the positive electrode current collector can have good adhesion, thereby reducing the risk of the positive electrode active material layer delamination, and can provide a higher gram capacity for the electrochemical device, so that the electrochemical device has a high capacity. The second positive electrode active material has the characteristics of high gram capacity and low cost. The second positive electrode active material is selected and applied to the second positive electrode active material layer, which can reduce the production cost of the electrochemical device while taking into account the capacity of the electrochemical device. Because the second positive electrode active material layer has weaker adhesion than the first positive electrode active material layer, the embodiments of the present application reduce the possibility of the second positive electrode active material layer contacting the positive electrode current collector by setting the first end face beyond the second end face and the fourth end face not beyond the third end face along the width direction of the unfolded positive electrode sheet, thereby reducing the risk of delamination of the edge portion of the positive electrode active material layer. Furthermore, by regulating the types of the first and second positive electrode active materials, and by regulating the first end surface to extend beyond the second end surface and the fourth end surface to not extend beyond the third end surface, the present embodiment of the present invention reduces the risk of delamination of the positive electrode active material layer while maintaining the required capacity of the electrochemical device. Furthermore, the production cost of the electrochemical device is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0027] FIG1 is a schematic diagram of the cross-sectional structure of a positive electrode sheet along its thickness direction after unfolding according to an embodiment of the present application;

[0028] FIG2 is a schematic top view of the positive electrode sheet of FIG1 ;

[0029] FIG3 is a schematic diagram of the cross-sectional structure of a positive electrode sheet along its thickness direction after unfolding according to another embodiment of the present application;

[0030] FIG4 is a schematic top view of the positive electrode sheet of FIG3 ;

[0031] FIG5 is a schematic diagram of the cross-sectional structure of the positive electrode active material layer and the negative electrode active material layer along their thickness direction according to one embodiment of the present application;

[0032] FIG6 is a schematic diagram of the cross-sectional structure of the positive electrode active material layer and the negative electrode active material layer along their thickness direction according to another embodiment of the present application;

[0033] FIG7 is a schematic top view of an unfolded positive electrode sheet according to another embodiment of the present application. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and by enumerating embodiments. It is apparent that the embodiments described are only a portion of the embodiments of this application, rather than all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0035] It should be noted that, in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0036] According to a first aspect of the present application, an electrochemical device is provided. The electrochemical device includes a positive electrode sheet, the positive electrode sheet including a positive electrode current collector, and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer. The first positive electrode active material layer is disposed on a surface of the positive electrode current collector, and the second positive electrode active material layer is disposed on a surface of the first positive electrode active material layer away from the positive electrode current collector. The first positive electrode active material layer includes a first positive electrode active material, the first positive electrode active material including at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium manganese oxide. The second positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material including at least one of lithium iron manganese phosphate or lithium iron phosphate. Along the width of the unfolded positive electrode sheet, the first positive electrode active material layer includes a first end face and a third end face opposite the first end face, and the second positive electrode active material layer includes a second end face and a fourth end face opposite the second end face. The first and second end faces are located on a first side of the positive electrode sheet, and the third and fourth end faces are located on a second side of the positive electrode sheet, with the first side opposing the second side. Those skilled in the art will understand that, along the width of the unfolded positive electrode sheet, the first and second end faces are located on one side of the positive electrode sheet, and the third and fourth end faces are located on the other side of the positive electrode sheet. The first end face of the positive electrode sheet extends beyond the second end face, while the fourth end face does not extend beyond the third end face. The phrase "does not extend beyond" can be understood to mean that, along the width of the unfolded positive electrode sheet, the fourth end face is flush with the third end face, or that the third end face extends beyond the fourth end face. For example, in some embodiments, along the width of the unfolded positive electrode sheet, the fourth end face is flush with the third end face. In this application, the term "flush" should be understood to mean approximately flush. Those skilled in the art will understand that, ideally, the fourth end face and the third end face are flush. However, in actual production applications, due to factors such as production processes and operator operation, these may not be strictly flush in some cases, but rather approximately flush. In other embodiments, along the width direction of the expanded positive electrode sheet, the third end surface exceeds the fourth end surface.

[0037] As shown in Figures 1 to 4, for ease of understanding, a three-dimensional rectangular coordinate system is established with the length direction of the positive electrode sheet 10 as the X direction, the width direction of the positive electrode sheet 10 as the Y direction, and the thickness direction of the positive electrode sheet 10 as the Z direction when the positive electrode sheet 10 is unfolded. It can be understood that, when the positive electrode sheet 10 is unfolded, the length, width, and thickness directions of the positive electrode collector 11, the positive electrode active material layer 12, the first positive electrode active material layer 121, and the second positive electrode active material layer 122 are the same as those of the positive electrode sheet 10. The above-mentioned "positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector" means that, in some embodiments, as shown in Figures 1 and 3, the positive electrode sheet 10 includes a positive electrode current collector 11 and positive electrode active material layers 12 disposed on both surfaces of the positive electrode current collector 11. In other embodiments, the positive electrode sheet 10 also includes a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on one surface of the positive electrode current collector 11. The above-mentioned "surface" can be a partial area of ​​the surface of the positive electrode current collector 11, or it can be the entire area of ​​the surface of the positive electrode current collector 11.

[0038] As shown in Figures 1 and 3, the positive electrode active material layer 12 includes a first positive electrode active material layer 121 and a second positive electrode active material layer 122. The first positive electrode active material layer 121 is disposed on the surface of the positive electrode current collector 11, and the second positive electrode active material layer 122 is disposed on the surface of the first positive electrode active material layer 121 away from the positive electrode current collector 11. The first positive electrode active material layer 121 includes a first positive electrode active material, which includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium manganese oxide. The second positive electrode active material layer 122 includes a second positive electrode active material, which includes at least one of lithium iron manganese phosphate or lithium iron phosphate. Along the width direction Y of the unfolded positive electrode sheet 10, the first positive electrode active material layer 121 includes a first end face 121a and a third end face 121b opposite the first end face 121a. The second positive electrode active material layer 122 includes a second end face 122a and a fourth end face 122b opposite the second end face 122a. The first end face 121a and the second end face 122a are located on the first side of the positive electrode sheet 10, and the third end face 121b and the fourth end face 122b are respectively located on the second side of the positive electrode sheet 10, with the first side and the second side opposite each other. For example, in some embodiments, as shown in FIG1 , the first end face 121a extends beyond the second end face 122a, and the fourth end face 122b is flush with the third end face 121b. In other embodiments, as shown in FIG3 , the first end face 121a extends beyond the second end face 122a, and the third end face 121b extends beyond the fourth end face 122b. In some other embodiments, along the Y direction in Figures 1, 2, and 7, the other side of the positive electrode current collector 11 may also extend beyond the third end surface 121b, or, along the X direction in Figures 2 and 7, at least one end surface of the positive electrode current collector 11 may also extend beyond the end surface of the first positive electrode active material layer 121. In some other embodiments, along the X direction in Figure 4, at least one end surface of the positive electrode current collector 11 may also extend beyond the end surface of the first positive electrode active material layer 121.

[0039] The first positive electrode active material of the above type has good viscosity and high gram capacity. When the first positive electrode active material of the above type is applied to the first positive electrode active material layer, the first positive electrode active material layer and the positive electrode current collector can have good adhesion, thereby reducing the risk of delamination of the positive electrode active material layer, and can provide a higher gram capacity for the electrochemical device, so that the electrochemical device has a high capacity. The second positive electrode active material of the above type has the characteristics of high gram capacity and low cost. When the second positive electrode active material of the above type is selected and applied to the second positive electrode active material layer, the production cost of the electrochemical device can be reduced while taking into account the capacity of the electrochemical device. Since the second positive electrode active material layer has weaker adhesion than the first positive electrode active material layer, the present application reduces the possibility of contact between the second positive electrode active material layer and the positive electrode current collector by setting the first end face beyond the second end face and the fourth end face not beyond the third end face along the width direction of the unfolded positive electrode sheet, thereby reducing the risk of delamination of the edge portion of the positive electrode active material layer. Thus, by regulating the types of the first and second positive electrode active materials, and regulating the first end face to extend beyond the second end face, and the fourth end face to not extend beyond the third end face, the present application enables the electrochemical device to maintain its capacity while reducing the risk of delamination of the positive electrode active material layer. Furthermore, the production cost of the electrochemical device is reduced.

[0040] In one embodiment of the present application, along the thickness direction Z after the positive electrode sheet is unfolded, the projection of the second positive electrode active material layer on the positive electrode current collector is located within the projection of the first positive electrode active material layer on the positive electrode current collector. As shown in Figures 2 and 4, the projection of the second positive electrode active material layer 122 on the positive electrode current collector 11 is located within the projection of the first positive electrode active material layer 121 on the positive electrode current collector 11. It can also be understood that, along the thickness direction of the positive electrode sheet, the projected area of ​​the second positive electrode active material layer 122 on the positive electrode current collector 11 is smaller than the projected area of ​​the first positive electrode active material layer 121 on the positive electrode current collector 11. Through the above arrangement, the first positive electrode active material layer is in contact with the positive electrode current collector, reducing the possibility of the second positive electrode active material layer contacting the positive electrode current collector, thereby reducing the risk of delamination of the edge portion of the positive electrode active material layer.

[0041] In one embodiment of the present application, as shown in Figures 2 and 4 , along the width direction Y of the unfolded positive electrode sheet 10, the positive electrode active material 12 includes a main portion 12a and an edge portion 12b. The edge portion 12b is the portion of the first positive electrode active material layer 121 that extends beyond the second positive electrode active material layer 122. The main portion 12a refers to the portion of the positive electrode active material layer 12 other than the edge portion 12b. Based on the total mass of the first and second positive electrode active materials in the main portion, the mass percentage of the second positive electrode active material is 5% to 95%. For example, the mass percentage of the second positive electrode active material is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any value between any two of the above ranges. By regulating the mass percentage of the second positive electrode active material within the above range, the electrochemical device has a lower production cost while reducing the risk of delamination of the positive electrode active material layer and taking into account its own capacity.

[0042] The present application does not particularly limit the weight percentage of the first positive electrode active material, as long as the purpose of the present application can be achieved. For example, based on the total weight of the first positive electrode active material and the second positive electrode active material in the main body, the weight percentage of the first positive electrode active material is 5% to 95%.

[0043] In one embodiment of the present application, the mass percentage of the second positive electrode active material is 5% to 60% based on the total mass of the first positive electrode active material and the second positive electrode active material in the main body. Controlling the mass percentage of the second positive electrode active material within this range can further increase the capacity of the electrochemical device while reducing the risk of delamination of the positive electrode active material layer and production costs.

[0044] In one embodiment of the present application, as shown in Figure 1, the distance by which the first end face 121a extends beyond the second end face 122a is m1, where 0.2 mm ≤ m1 ≤ 2 mm. For example, m1 is 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm, or any value between any two of the aforementioned ranges. Controlling the distance by which the first end face extends beyond the second end face within the aforementioned range reduces the likelihood of contact between the second positive electrode active material layer and the positive electrode current collector, thereby reducing the risk of delamination at the edges of the positive electrode active material layer. This also ensures that the first and second positive electrode active material layers are applied simultaneously to the positive electrode current collector in the area where the positive electrode active material layer is applied, thereby providing the highest possible capacity and reducing production costs. Thus, the electrochemical device maintains its capacity while reducing the risk of delamination of the positive electrode active material layer. Furthermore, the production cost of the electrochemical device is reduced.

[0045] In one embodiment of the present application, as shown in FIG3 , the distance by which the third end face 121b extends beyond the fourth end face 122b is m2, where 0.2 mm ≤ m2 ≤ 2 mm. For example, m2 is 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm, or any value between any two of the above ranges. Controlling the distance by which the third end face extends beyond the fourth end face within the above range reduces the likelihood of contact between the second positive electrode active material layer and the positive electrode current collector, thereby reducing the risk of delamination at the edge of the positive electrode active material layer. This also ensures that the first and second positive electrode active material layers are applied simultaneously in the area of ​​the positive electrode current collector where the positive electrode active material layer is applied, thereby providing the highest possible capacity and reducing production costs. Thus, the electrochemical device maintains its inherent capacity while reducing the risk of delamination of the positive electrode active material layer.

[0046] In one embodiment of the present application, m2 is the same as m1. In another embodiment of the present application, m2 is different from m1.

[0047] In one embodiment of the present application, the electrochemical device further comprises a negative electrode plate, which comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. For example, in some embodiments, as shown in FIG5 , the negative electrode plate 20 comprises a negative electrode current collector 21 and a negative electrode active material layer 22 disposed on both surfaces of the negative electrode current collector 21. It will be understood by those skilled in the art that, in other embodiments, the negative electrode active material layer 22 may also be disposed on one surface of the negative electrode current collector 21. The above-mentioned “surface” may be a partial area of ​​the surface of the negative electrode current collector 21 or the entire area of ​​the surface of the negative electrode current collector 21. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0048] In one embodiment of the present application, as shown in FIG5 , along the width direction Y after the positive electrode sheet 10 is unfolded, the distance n1 by which one end of the negative electrode active material layer 22 extends beyond the corresponding end of the positive electrode active material layer 12 satisfies the following conditions: 1 mm ≤ n1 ≤ 10 mm. For example, n1 is 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, or any value between any two of the above numerical ranges. By regulating the distance by which one end of the negative electrode active material layer extends beyond the corresponding end of the positive electrode active material layer within the above range, the negative electrode active material layer can provide more locations for embedding lithium released from the positive electrode active material layer, thereby reducing the possibility of lithium plating on the surface of the negative electrode sheet. Furthermore, the risk of increased costs due to excessive negative electrode active material layers can be reduced, thereby reducing the production cost of the electrochemical device. This is beneficial for reducing lithium plating and production costs of the electrochemical device while taking into account the capacity of the electrochemical device and reducing the risk of delamination of the positive electrode active material layer.

[0049] In one embodiment of the present application, as shown in FIG6 , along the width direction Y after the positive electrode sheet 10 is unfolded, the distance that the other end of the negative electrode active material layer 22 extends beyond the corresponding end of the positive electrode active material layer 12 is n2, 1mm≤n2≤10mm. For example, n2 is 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, or any value between any two of the above numerical ranges. By regulating the distance that the other end of the negative electrode active material layer extends beyond the corresponding end of the positive electrode active material layer within the above range, the negative electrode active material layer can provide more locations to embed lithium released from the positive electrode active material layer, thereby reducing the possibility of lithium plating on the surface of the negative electrode sheet, and can reduce the risk of cost increase caused by excessive negative electrode active material layers, thereby reducing the production cost of the electrochemical device. As a result, it is beneficial to reduce the lithium plating phenomenon and production cost of the electrochemical device while taking into account the capacity of the electrochemical device and reducing the risk of delamination of the positive electrode active material layer.

[0050] It can be understood that the length direction, width direction and thickness direction of the negative electrode sheet, the negative electrode current collector and the negative electrode active material layer are the same as those of the positive electrode sheet.

[0051] In one embodiment of the present application, the first positive electrode active material layer further comprises a first conductive agent and a first binder. Based on the mass of the first positive electrode active material layer, the mass percentage of the first positive electrode active material is 95% to 98%, the mass percentage of the first conductive agent is 0.5% to 3%, and the mass percentage of the first binder is 0.5% to 3%. For example, based on the mass of the first positive electrode active material layer, the mass percentage of the first positive electrode active material is 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, or any value between any two of the above numerical ranges. For example, based on the mass of the first positive electrode active material layer, the mass percentage of the first conductive agent is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any value between any two of the above numerical ranges. For example, based on the mass of the first positive electrode active material layer, the mass percentage of the first binder is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any value between any two of the above numerical ranges. By regulating the contents of the first positive electrode active material, the first conductive agent and the first binder in the first positive electrode active material layer within the above-mentioned range, it is possible to provide a high gram capacity while ensuring a high adhesion between the first positive electrode active material layer and the positive electrode current collector, so that the electrochemical device can take into account its own capacity while reducing the risk of delamination of the positive electrode active material layer.

[0052] In one embodiment of the present application, the second positive electrode active material layer further includes a second conductive agent and a second binder. Based on the mass of the second positive electrode active material layer, the mass percentage of the second positive electrode active material is 95% to 98%, the mass percentage of the second conductive agent is 0.6% to 3%, and the mass percentage of the first binder is 0.5% to 2%. For example, based on the mass of the second positive electrode active material layer, the mass percentage of the second positive electrode active material is 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, or any value between any two of the above numerical ranges. For example, based on the mass of the second positive electrode active material layer, the mass percentage of the second conductive agent is 0.6%, 1%, 1.5%, 2%, 2.5%, 3%, or any value between any two of the above numerical ranges. For example, based on the mass of the second positive electrode active material layer, the mass percentage of the second binder is 0.5%, 1%, 1.5%, 2%, or any value between any two of the above numerical ranges. By regulating the contents of the second positive electrode active material, the second conductive agent and the second binder in the second positive electrode active material layer within the above-mentioned range, it is possible to provide a higher gram capacity and lower production cost while ensuring a higher adhesion between the second positive electrode active material layer and the first positive electrode active material layer, thereby enabling the electrochemical device to take into account its own capacity while reducing the risk of delamination of the positive electrode active material layer.

[0053] The present application does not particularly limit the types of the first conductive agent, the first binder, the second conductive agent, and the second binder, as long as they can achieve the purpose of the present application. For example, the first conductive agent and the second conductive agent are each independently selected from at least one of conductive carbon black, conductive carbon nanotubes, carbon fibers, conductive graphite, or graphene. For example, the first binder and the second binder are each independently selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyacrylic acid, polyethyl acrylate, polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, or polyurethane.

[0054] In one embodiment of the present application, in the main body portion, the coating weight of the positive electrode active material layer is 200 mg / 1540.24 mm 2 Up to 600mg / 1540.24mm 2 For example, the coating weight of the positive electrode active material layer is 200 mg / 1540.24 mm 2 、250mg / 1540.24mm 2 、300mg / 1540.24mm 2 、350mg / 1540.24mm 2 , 400mg / 1540.24mm 2 、450mg / 1540.24mm 2 、500mg / 1540.24mm2 、550mg / 1540.24mm 2 、600mg / 1540.24mm 2 or any value between any two of the above numerical ranges. By controlling the coating weight of the positive electrode active material layer within the above range, the content of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer is relatively high, enabling the positive electrode active material layer to have more positive electrode active material, thereby providing a higher capacity for the electrochemical device.

[0055] In one embodiment of the present application, the gram capacity of the first positive electrode active material is a, and the gram capacity of the second positive electrode active material is b, satisfying: 10% ≤ (ab) / b × 100% ≤ 75%, 160 mAh / g ≤ a ≤ 210 mAh / g. For example, the value of (ab) / b × 100% is 10%, 14%, 20%, 30%, 40%, 50%, 60%, 70%, 75% or any value between any two of the above numerical ranges. For example, a is 160 mAh / g, 170 mAh / g, 180 mAh / g, 190 mAh / g, 200 mAh / g, 210 mAh / g or any value between any two of the above numerical ranges. By regulating the value of (ab) / b × 100% and the gram capacity a of the first positive electrode active material within the above range, the first positive electrode active material and the second positive electrode active material can work synergistically, and the production cost of the positive electrode active material layer can be reduced while the positive electrode active material layer has a higher capacity. This is beneficial for reducing the production cost of the electrochemical device while taking into account the capacity of the electrochemical device and reducing the risk of delamination of the positive electrode active material layer.

[0056] In one embodiment of the present application, 14% ≤ (ab) / b×100% ≤ 30%. Controlling the value of (ab) / b×100% within the above range is beneficial for further reducing the production cost of the electrochemical device while taking into account the capacity of the electrochemical device and reducing the risk of delamination of the positive electrode active material layer.

[0057] In one embodiment of the present application, 120 mAh / g ≤ b ≤ 140 mAh / g. For example, b is 120 mAh / g, 125 mAh / g, 130 mAh / g, 135 mAh / g, 140 mAh / g, or any value between any two of the foregoing ranges. Controlling the gram capacity b of the second positive electrode active material within the foregoing range is beneficial for further increasing the capacity of the electrochemical device.

[0058] The present application does not particularly limit the method for regulating the gram capacity of the first positive electrode active material and the second positive electrode active material, as long as the purpose of the present application can be achieved. For example, this can be achieved by regulating the types of the first positive electrode active material and the second positive electrode active material.

[0059] In one embodiment of the present application, the coating weight of the negative electrode active material layer is 100 mg / 1540.24 mm 2 Up to 300mg / 1540.24mm 2 For example, the coating weight of the negative electrode active material layer is 100 mg / 1540.24 mm 2 、140mg / 1540.24mm 2 、180mg / 1540.24mm 2 , 220mg / 1540.24mm 2 、260mg / 1540.24mm 2 、300mg / 1540.24mm 2 or any value between any two of the above numerical ranges. By controlling the coating weight of the negative electrode active material layer within the above range, a higher content of negative electrode active material in the negative electrode active material layer can provide a higher capacity for the negative electrode active material layer, thereby enabling the electrochemical device to have a higher capacity.

[0060] In one embodiment of the present application, the negative electrode active material layer includes a negative electrode active material, and the gram capacity of the negative electrode active material is 280 mAh / g to 420 mAh / g. For example, the gram capacity of the negative electrode active material is 280 mAh / g, 300 mAh / g, 320 mAh / g, 340 mAh / g, 360 mAh / g, 380 mAh / g, 400 mAh / g, 420 mAh / g, or any value between any two of the above ranges. Regulating the gram capacity of the negative electrode active material within the above range is beneficial for providing a higher capacity for the electrochemical device.

[0061] The present application does not particularly limit the method for regulating the gram capacity of the negative electrode active material, as long as the purpose of the present application can be achieved. For example, this can be achieved by regulating the type of negative electrode active material.

[0062] In one embodiment of the present application, the CB value of the electrochemical device satisfies: 1.04≤CB≤1.2. For example, CB is 1.04, 1.08, 1.12, 1.16, 1.2 or any value between any two of the above numerical ranges. In the present application, CB = (gram capacity of negative electrode active material × mass of negative electrode active material per unit area of ​​negative electrode sheet) / (gram capacity of first positive electrode active material × mass of first positive electrode active material per unit area of ​​positive electrode sheet + gram capacity of second positive electrode active material × mass of second positive electrode active material per unit area of ​​positive electrode sheet). The above unit area refers to 1mm 2Regulating the CB value within the above range is beneficial for embedding all the lithium released from the positive electrode sheet of the electrochemical device into the negative electrode sheet under current actual production capacity, thereby reducing the occurrence of lithium plating in the electrochemical device and improving the cycle performance of the electrochemical device; while also minimizing the amount of negative electrode active material in the negative electrode sheet, thereby reducing the production cost of the electrochemical device.

[0063] In one embodiment of the present application, the CB value of the edge portion is greater than or equal to the CB value of the main portion. In this application, the CB value of the edge portion is 1.08 to 1.3, while the CB value of the main portion is 1.05 to 1.1. A CB value of the edge portion greater than or equal to the CB value of the main portion is beneficial for improving the kinetics at the edge of the electrochemical device, overcoming the problem of the edge portion having less dynamics than the main portion due to its greater relaxation.

[0064] In one embodiment of the present application, as shown in FIG7 , along the longitudinal direction X of the unfolded positive electrode sheet 10 , the length L of the first positive electrode active material layer 121 is 121 Greater than the length L of the second positive active material layer 122 122 Through the above arrangement, the possibility of the second positive electrode active material layer contacting the positive electrode current collector can be reduced in both the length and width directions after the positive electrode sheet is unfolded, thereby further reducing the risk of the edge portion of the positive electrode active material layer peeling off.

[0065] The present application has no particular restrictions on the type of positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector can include aluminum foil, aluminum alloy foil, etc.

[0066] The present application does not impose any particular restrictions on the method for preparing the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the positive electrode sheet may include but is not limited to the following steps: (1) preparing a first positive electrode slurry and a second positive electrode slurry; (2) applying the first positive electrode slurry to one surface of a positive electrode current collector, drying the first positive electrode slurry to obtain a positive electrode sheet coated with the first positive electrode active material layer on one side, and applying the second positive electrode slurry to the surface of the first positive electrode active material layer away from the positive electrode current collector, drying the second positive electrode sheet coated with the first positive electrode active material layer and the second positive electrode active material layer on one side; (3) repeating step (2), applying the first positive electrode slurry and the second positive electrode slurry to the other surface of the positive electrode current collector to obtain a positive electrode sheet coated with the first positive electrode active material layer and the second positive electrode active material layer on both sides; (4) cold pressing, cutting, and welding the positive electrode tabs. The present application has no particular restrictions on the preparation method of the first positive electrode slurry and the second positive electrode slurry in the above step (1). As long as the contents of the first positive electrode active material, the first conductive agent and the first binder in the first positive electrode active material layer are within the scope of the present application, and the contents of the second positive electrode active material, the second conductive agent and the second binder in the second positive electrode active material layer are within the scope of the present application, the purpose of the present application can be achieved. The present application has no particular restrictions on the temperature and time of the drying in the above step (2). Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the process parameters of cold pressing, cutting and welding the positive electrode ears in the above step (4). Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0067] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam or copper foam, etc. The present application has no particular restrictions on the type of negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microbeads, tin-based materials, silicon-based materials, lithium titanate, transition metal nitride or natural flake graphite, etc. Optionally, the negative electrode active material layer also includes at least one of a negative electrode conductive agent, a thickener, and a negative electrode binder. The present application has no particular restrictions on the types of negative electrode conductive agent, thickener and negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the mass ratio of the negative electrode active material, negative electrode conductive agent, thickener and negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the mass ratio of the negative electrode active material, the negative electrode conductor, the thickener and the negative electrode binder in the negative electrode active material layer is (97-98):(0-1.5):(0-1.5):(1.0-1.9).

[0068] The thickness of the negative electrode current collector and the negative electrode active material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 5 μm to 20 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm.

[0069] The electrochemical device of the present application also includes a diaphragm, which is arranged between the positive electrode sheet and the negative electrode sheet to separate the positive electrode sheet and the negative electrode sheet. The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0070] In one embodiment of the present application, the electrochemical device further comprises a packaging bag and an electrolyte, wherein the electrolyte, positive electrode sheet, separator, and negative electrode sheet are contained in the packaging bag. The present application does not particularly limit the packaging bag and electrolyte. Those skilled in the art may select packaging bags and electrolytes known in the art as needed, as long as they can achieve the objectives of the present application.

[0071] The present application does not particularly limit the type of electrochemical device, and it can include any device that undergoes an electrochemical reaction. For example, the electrochemical device can include, but is not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), sodium ion secondary batteries (sodium ion batteries), lithium polymer secondary batteries, and lithium ion polymer secondary batteries.

[0072] The present application does not particularly limit the preparation method of the electrochemical device, and any preparation method known in the art may be selected as long as the purpose of the present application can be achieved. For example, the preparation method of the electrochemical device includes but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and winding, folding, etc. as needed to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the bag to obtain the electrochemical device; or stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the bag to obtain the electrochemical device.

[0073] A second aspect of the present application provides an electronic device comprising the electrochemical device described in any of the aforementioned embodiments.

[0074] The electronic devices of the present application are not particularly limited and may be any electronic device known in the art. For example, the electronic devices may include, but are not limited to, laptop computers, pen-based computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0075] Example

[0076] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

[0077] Test methods and equipment:

[0078] Gram capacity test:

[0079] (1) Test of gram capacity b of the second positive electrode active material:

[0080] First, the positive electrode sheet is removed from the fully charged lithium-ion battery, and the electrolyte in the positive electrode sheet is dried in an electric oven at a temperature of 60°C; then, the second positive electrode active material powder is scraped from the positive electrode sheet with a knife, the weight m1 = 100 mg is weighed on a balance, and it is immersed in a hydrochloric acid solution (mass fraction 10%) for 3 hours; then, the remaining solid matter is filtered out, and the solid matter is baked in an electric oven at a temperature of 60°C for 24 hours, and the solid weight m2 is weighed; (m1-m2) / m1 is calculated, which is the mass ratio x of the second positive electrode active material in the original positive electrode sheet formula. The second positive electrode active material powder was scraped from the positive electrode sheet with a knife again, and the weight m3 = 100 mg was measured on a balance. It was mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) in a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 65wt%, and stirred evenly. The slurry was evenly coated on the positive electrode current collector aluminum foil. After the positive electrode sheet was dried, the positive electrode sheet was assembled with the metal lithium sheet, separator, and electrolyte to form a button cell. Finally, it was charged at a constant current rate of 0.1C to 4.3V, charged at a constant voltage of 4.3V to 0.02C, and then discharged at a constant current rate of 0.1C to 2.8V to obtain the effective capacity of the button cell. The effective capacity was divided by the effective active material powder weight m4 (m4 = m3 × x) to obtain the gram capacity of the second positive electrode active material. The electrolyte is the same as that in Example 1-1.

[0081] (2) Test of gram capacity a of the first positive electrode active material:

[0082] First, the positive electrode sheet is removed from the fully charged lithium-ion battery, and the electrolyte in the positive electrode sheet is dried in an electric oven at a temperature of 60°C; after scraping off the second positive electrode active material layer from the positive electrode sheet with a knife, the first positive electrode active material powder is scraped off with a knife, and the weight m1 = 100 mg is weighed on a balance, and it is immersed in a hydrochloric acid solution (mass fraction 10%) for 3 hours; then, the remaining solid matter is filtered out, and the solid matter is baked in an electric oven at a temperature of 60°C for 24 hours, and the solid weight m2 is weighed; (m1-m2) / m1 is calculated, which is the mass ratio x of the first positive electrode active material in the original sheet formula. The first positive electrode active material powder was scraped from the positive electrode sheet with a knife again, and the weight m3 = 100 mg was measured on a balance. It was mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) in a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 65 wt%, and stirred evenly. The slurry was evenly coated on the aluminum foil on the positive electrode current collector. After the electrode sheet was dried, the electrode sheet was assembled with the metal lithium sheet, separator, and electrolyte to form a button cell. Finally, it was charged at a constant current rate of 0.1C to 4.3V, charged at a constant voltage of 4.3V to 0.02C, and then discharged at a constant current rate of 0.1C to 2.8V to obtain the effective capacity of the button cell. The effective capacity was divided by the effective active material powder weight m4 (m4 = m3 × x) to obtain the gram capacity of the first positive electrode active material. The electrolyte is the same as that in Example 1-1.

[0083] (3) Test of gram capacity c of negative electrode active material

[0084] First, the negative electrode sheet was removed from the fully charged lithium-ion battery, soaked in deionized water for 3 hours, and then dried in an electric oven at 60°C. Next, the negative electrode active material powder was scraped from the negative electrode sheet with a knife and weighed on a balance to obtain a weight of m1 = 100 mg. The powder was heated to 700°C using a thermogravimetric analyzer (inert gas mode), and the remaining powder weight m2 was recorded. The ratio (m1 - m2) / m1 was calculated as the mass fraction y of the negative electrode active material in the negative electrode sheet. The negative electrode active material powder was again scraped from the negative electrode sheet with a knife and weighed on a balance to obtain a weight of m3 = 100 mg. This powder was then mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) in a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solids content of 65 wt%, which was then stirred evenly. The slurry was evenly coated on the copper foil on the negative electrode current collector. After the negative electrode sheet was dried, it was assembled with the metal lithium sheet, separator, and electrolyte to form a button cell. Finally, the battery was charged at a constant current rate of 0.1C to 1.5V, then charged at a constant voltage rate of 1.5V to 0.02C, and then discharged at a constant current rate of 0.1C to 0V. The effective capacity of the button cell was obtained by dividing the effective capacity by the weight of the effective active material powder m4 (m4 = m3 × y). The gram capacity of the negative electrode active material was obtained by dividing the effective capacity by the weight of the effective active material powder m4 (m4 = m3 × y). The electrolyte was the same as that in Example 1-1.

[0085] Coating weight test:

[0086] (1) Test of coating weight of positive electrode active material layer:

[0087] The fully charged lithium-ion battery was disassembled to obtain the positive electrode sheet. The impurities on the surface of the positive electrode sheet were cleaned with dimethyl formate (DMC) and dried. The main part of the positive electrode active material layer was cut to an area of ​​1540.25 mm. 2 The positive electrode sheet sample is placed on a balance and weighed, which is recorded as p1. The positive electrode active material layer on the positive electrode sheet is then washed clean, and the positive electrode current collector is placed on a balance and weighed, which is recorded as p2.

[0088] If the positive electrode sheet is coated with a positive electrode active material layer on one side, the coating weight CW1 = p1 - p2;

[0089] If the positive electrode sheet is coated with a positive electrode active material layer on both sides, the coating weight CW1 = (p1-p2) / 2;

[0090] The coating weight of the first positive electrode active material layer = CW1 × N1, and the coating weight of the second positive electrode active material layer = CW1 × N2.

[0091] (2) Test of coating weight of negative electrode active material layer:

[0092] The fully charged lithium-ion battery was disassembled to obtain the negative electrode. The impurities on the surface of the negative electrode were cleaned with dimethyl formate and dried. The area of ​​the negative electrode was cut into 1540.25 mm 2 The negative electrode sheet sample is placed on a balance and weighed, which is recorded as q1. Then the negative electrode active material layer on the negative electrode sheet is washed clean, and the negative electrode current collector is placed on a balance and weighed, which is recorded as q2.

[0093] If the negative electrode sheet is coated with a negative electrode active material layer on one side, the coating weight = q1-q2.

[0094] If the negative electrode sheet is coated with negative electrode active material layers on both sides, the coating weight = (q1-q2) / 2.

[0095] Adhesion test:

[0096] After fully discharging the lithium-ion batteries of each embodiment and comparative example, the positive electrode sheets were disassembled and cleaned with dimethyl carbonate. The sheets were then cut into 4 cm × 0.5 cm samples. A rectangular tape measuring 2 cm × 0.2 cm in length × width was attached to the positive electrode active material layer. One end of the tape was connected to a dynamometer. The dynamometer was pulled until the tape tore through the positive electrode active material layer. The force reading was then read. The force reading was divided by the tape width (0.2 cm) to obtain the bonding strength. Specifically:

[0097] (1) Test of the main body adhesion:

[0098] For a 4cm x 0.5cm sample, use a 0.2cm wide rectangular piece of adhesive tape to cover the center of the sample.

[0099] (2) Test of edge adhesion:

[0100] For a 4cm x 0.5cm sample, use a 0.2cm wide rectangular adhesive tape to align the edges of the sample close to the edge.

[0101] Capacity test:

[0102] The lithium-ion batteries of the embodiments and comparative examples were charged to 4.3V at a constant current of 0.5C, and then charged to a current of 0.02C at a constant voltage of 4.3V; the lithium-ion batteries were discharged to 2.8V at a rate of 0.2C, and the corresponding capacities were collected, which were the capacities of the lithium-ion batteries in the embodiments and comparative examples.

[0103] Example 1-1

[0104] <Preparation of positive electrode sheet>

[0105] The first positive electrode active material is lithium nickel cobalt manganese oxide (NCM60-10-30, LiNi 0.6 Co 0.1 Mn0.3 O2), a first conductive agent, conductive carbon black (Super P), and conductive carbon nanotubes (CNTs), and a first binder, polyvinylidene fluoride (PVDF, weight-average molecular weight 8,000-10,000), were mixed in a mass ratio of 97.1:1.0:0.4:1.5. N-methylpyrrolidone (NMP) was added as a solvent and stirred evenly to prepare a first positive electrode slurry with a solid content of 75 wt%. The gram capacity of the first positive electrode active material, a, was 180 mAh / g.

[0106] The second positive electrode active material is lithium manganese iron phosphate (LiFe 0.4 Mn 0.6 PO4, a second conductive agent Super P, and a second binder PVDF (weight-average molecular weight 8,000-10,000) were mixed in a mass ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a second positive electrode slurry with a solid content of 65 wt%. The gram capacity of the second positive electrode active material was b = 140 mAh / g.

[0107] The first positive electrode slurry is coated on one surface of a 10μm thick positive electrode current collector aluminum foil and dried at 90°C to obtain a positive electrode sheet coated with the first positive electrode active material layer on one side. The second positive electrode slurry is coated on the surface of the first positive electrode active material layer away from the positive electrode current collector and dried to obtain a positive electrode sheet coated with the first and second positive electrode active material layers on one side. Thereafter, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with the first and second positive electrode active material layers on both sides (as shown in Figure 1). Cold pressing, cutting, and welding of positive electrode tabs are performed to obtain a positive electrode sheet with a specification of 110mm×867mm for use.

[0108] The width W of the first positive electrode active material layer is 121 =100 mm, the width of the second positive electrode active material layer W 122 =98mm. The distance m1 of the first end face beyond the second end face =2mm. The length L of the first positive electrode active material layer 121 =867 mm, the length of the second positive electrode active material layer L 122 =867mm. The compaction density of the positive electrode active material layer is 2.6g / cm 3 The coating weight of the positive electrode active material layer CW1 = 260 mg / 1540.24 mm 2Based on the total mass of the first positive electrode active material and the second positive electrode active material, the mass percentage of the first positive electrode active material N1 = 30%, and the mass percentage of the second positive electrode active material N2 = 70%. Wherein, the coating weight of the first positive electrode active material layer = CW1 × N1 = 260 × 30% = 78 mg / 1540.24 mm 2 , coating weight of the second positive electrode active material layer = CW1×N2=260×70%=182mg / 1540.24mm 2 .

[0109] <Preparation of negative electrode sheet>

[0110] The negative electrode active material artificial graphite, the negative electrode conductive agent conductive carbon black, the negative electrode binder styrene butadiene rubber (SBR, weight average molecular weight 50×10 5 ) were mixed in a mass ratio of 97:1.5:1.5, and then deionized water was added as a solvent. The mixture was stirred in a vacuum mixer until a solid content of 70 wt% and a uniform negative electrode slurry was obtained. The negative electrode slurry was evenly coated on one surface of an 8 μm thick negative electrode current collector copper foil and dried at 110°C to obtain a negative electrode sheet coated with a negative electrode active material layer on one side (130 μm thick). The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. The sheet was cold pressed, cut into pieces, and welded to the negative electrode copper tabs to obtain a negative electrode sheet with a specification of 115 mm × 880 mm for future use.

[0111] The width of the negative electrode active material layer is 105 mm, and the compaction density of the negative electrode active material layer is 1.6 g / cm 3 The gram capacity of the negative electrode active material c = 340 mAh / g. The coating weight of the negative electrode active material layer CW2 = 135 mg / 1540.24 mm 2 .

[0112] <Preparation of Separator>

[0113] A polyethylene film with a thickness of 15 μm was used.

[0114] <Preparation of Electrolyte>

[0115] In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20 to obtain an organic solvent. Then, lithium salt LiPF6 was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.5 mol / L.

[0116] <Preparation of lithium-ion batteries>

[0117] The negative electrode sheet, separator, and positive electrode sheet prepared above are stacked and wound in sequence to form a wound electrode assembly. The electrode assembly is placed in an aluminum-plastic film bag, dried, and then filled with electrolyte. The lithium-ion battery is produced through vacuum packaging, resting, formation, degassing, and trimming. Formation steps: Charge at a constant current of 0.02C to 3.3V, then at a constant current of 0.1C to 3.6V.

[0118] Example 1-2 to Example 1-5

[0119] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0120] When m1 changes, the width of the second positive electrode active material layer changes accordingly, while the width of the first positive electrode active material layer remains unchanged.

[0121] Examples 1-6

[0122] <Preparation of positive electrode sheet>

[0123] FIG3 shows a positive electrode sheet coated on both sides with the first positive electrode active material layer and the second positive electrode active material layer.

[0124] The width W of the first positive electrode active material layer is 121 =100 mm, the width of the second positive electrode active material layer W 122 =99.6mm. The distance m1 of the first end face beyond the second end face =0.2mm, and the distance m2 of the third end face beyond the fourth end face =0.2mm. The length L of the first positive electrode active material layer 121 =867 mm, the length of the second positive electrode active material layer L 122 =867mm.

[0125] The rest is the same as Example 1-1.

[0126] Example 1-7 to Example 1-10

[0127] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Examples 1-6.

[0128] When m1 and m2 change, the width of the second positive electrode active material layer changes accordingly, while the width of the first positive electrode active material layer remains unchanged.

[0129] Examples 1-11

[0130] <Preparation of positive electrode sheet>

[0131] The second positive electrode active material is adjusted to lithium iron phosphate, and the gram capacity of the second positive electrode active material is b=143 mAh / g.

[0132] The rest is the same as Example 1-1.

[0133] Examples 1-12

[0134] <Preparation of positive electrode sheet>

[0135] The first positive electrode active material is adjusted to lithium cobalt oxide, and the gram capacity of the first positive electrode active material is a=200 mAh / g.

[0136] The rest is the same as Example 1-1.

[0137] Examples 1-13

[0138] <Preparation of positive electrode sheet>

[0139] The first positive electrode active material is adjusted to lithium nickel cobalt aluminum oxide, and the gram capacity a of the first positive electrode active material is 185 mAh / g.

[0140] The rest is the same as Example 1-1.

[0141] Example 2-1 to Example 2-8

[0142] Except for adjusting the preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0143] In Examples 2-5 to 2-8, when the mass percentage of the first conductive agent changes, the mass percentages of the first conductive agent, conductive carbon black (Super P) and conductive carbon nanotubes (CNT), change according to a mass ratio of 1.0:0.4.

[0144] Example 3-1 to Example 3-18

[0145] Except for adjusting the preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0146] When the coating weight CW1 of the positive electrode active material layer changes, the coating weight of the first positive electrode active material layer changes according to the formula CW1×N1, and the coating weight of the second positive electrode active material layer changes according to the formula CW1×N2.

[0147] Comparative Example 1 and Comparative Example 2

[0148] Except for adjusting the preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0149] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0150] Table 1 Note: “\” in Table 1 indicates no corresponding parameter.

[0151] As can be seen from Examples 1-1 to 1-13, Comparative Examples 1 and 2, the embodiments of the present application, by selecting the first and second positive electrode active materials within the scope of the present application, and controlling the first end face of the first positive electrode active material layer to extend beyond the second end face of the second positive electrode active material layer, and the fourth end face of the first positive electrode active material layer to not extend beyond the third end face of the second positive electrode active material layer, result in the positive electrode sheets having higher bulk adhesion and edge adhesion, and the lithium-ion batteries having higher capacities. This indicates that the lithium-ion batteries reduce the risk of delamination of the positive electrode active material layers while maintaining high capacities. In contrast, the lithium-ion batteries in Comparative Examples 1 and 2, which do not select the first and second positive electrode active materials within the scope of the present application, or in which the first end face of the first positive electrode active material layer does not extend beyond the second end face of the second positive electrode active material layer, have lower bulk adhesion and / or edge adhesion, indicating that the lithium-ion batteries fail to maintain their own capacities while reducing the risk of delamination of the positive electrode active material layers.

[0152] The distance m1 that the first end face extends beyond the second end face generally affects the capacity of the lithium-ion battery and the risk of the positive electrode active material layer peeling off. As can be seen from Examples 1-1 to 1-5, the electrochemical device selected in which the distance m1 of the first end face extending beyond the second end face is within the scope of the present application has higher main body adhesion and edge adhesion, and also has higher capacity, indicating that the positive electrode active material layer has a lower risk of peeling off and the lithium-ion battery has a higher capacity. Among them, although the capacity of the lithium-ion battery of Example 1-4 is higher than that of Examples 1-1 to 1-3, the distance m1 that the first end face extends beyond the second end face is too small, which places high demands on the processing technology in the actual production process, will increase the production cost of the lithium-ion battery, and is not conducive to industrial mass production.

[0153] When the third end face extends beyond the fourth end face, the distance m1 between the first end face and the second end face, and the distance m2 between the third end face and the fourth end face generally affect the capacity of the lithium-ion battery and the risk of delamination of the positive electrode active material layer. As can be seen from Examples 1-6 to 1-10, electrochemical devices in which the distance m1 between the first end face and the second end face, and the distance m2 between the third end face and the fourth end face are within the scope of this application exhibit high bulk and edge adhesion, as well as high capacity, indicating a lower risk of delamination of the positive electrode active material layer and a higher capacity lithium-ion battery. While the capacity of the lithium-ion battery of Example 1-9 is higher than that of Examples 1-6 to 1-8, the distance m1 between the first end face and the second end face, and the distance m2 between the third end face and the fourth end face, are too small. This places high demands on the processing technology during actual production, increases the production cost of the lithium-ion battery, and is not conducive to industrial mass production.

[0154] The types of the first and second positive electrode active materials generally affect the capacity of lithium-ion batteries and the risk of positive electrode active material layer delamination. As can be seen from Examples 1-1, 1-11, and 1-13, electrochemical devices using first and second positive electrode active materials within the scope of this application exhibit high bulk and edge adhesion, as well as high capacity. This indicates that the positive electrode active material layer has a low risk of delamination and the lithium-ion battery has a higher capacity.

[0155] Table 2

[0156] Based on the total mass of the first and second positive electrode active materials, the mass percentage of the second positive electrode active material generally affects the capacity of the lithium-ion battery and the risk of the positive electrode active material layer delamination. As can be seen from Examples 1-1, 2-1, and 2-4, electrochemical devices using a mass percentage of the second positive electrode active material within the range of this application exhibit high bulk and edge adhesion, as well as high capacity. This indicates that the positive electrode active material layer has a low risk of delamination and the lithium-ion battery has a high capacity.

[0157] The content of the first binder in the first positive electrode active material layer and the content of the second binder in the second positive electrode active material layer generally affect the capacity of the lithium-ion battery and the risk of positive electrode active material layer delamination. As can be seen from Examples 1-1, 2-5, and 2-8, electrochemical devices with the first binder content in the first positive electrode active material layer and the second binder content in the second positive electrode active material layer within the ranges of this application exhibit high bulk and edge adhesion, as well as high capacity. This indicates that the positive electrode active material layer has a low risk of delamination and the lithium-ion battery has a high capacity.

[0158] Table 3 Note: In Table 3, the chemical formula of NCM50-20-30 is LiNi 0.5 Co 0.2 Mn 0.3 The chemical formula of O2 and NCM80-10-10 is LiNi 0.8 Co 0.1 Mn 0.1 The chemical formula of O2 and NCM33-33-33 is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The chemical formula of O2 and NCM90-5-5 is LiNi 0.9 Co 0.05 Mn 0.05 O2.

[0159] The gram capacity a of the first positive electrode active material, the gram capacity b of the second positive electrode active material, and the value of (ab) / b×100% generally affect the capacity of the lithium-ion battery and the risk of delamination of the positive electrode active material layer. As can be seen from Examples 1-1, 3-1, and 3-8, electrochemical devices using the gram capacity a of the first positive electrode active material, the gram capacity b of the second positive electrode active material, and (ab) / b×100% within the scope of this application have higher body adhesion and edge adhesion, as well as higher capacity, indicating that the positive electrode active material layer has a lower risk of delamination and the lithium-ion battery has a higher capacity. Among them, although the capacity of the lithium-ion batteries of Examples 3-2, 3-4, 3-5, and 3-8 is higher than that of Examples 1-1 and 3-1, the production cost of the lithium-ion batteries of Examples 3-2, 3-4, 3-5, and 3-8 is higher, making them unsuitable for industrial mass production. The gram capacity c of the negative electrode active material generally affects the capacity of the lithium-ion battery and the risk of delamination of the positive electrode active material layer. It can be seen from Examples 1-1, 3-9 to 3-12 that the electrochemical device using the negative electrode active material with a gram capacity c within the scope of the present application has higher main body adhesion and edge adhesion, and also has a higher capacity, indicating that the positive electrode active material layer has a lower risk of demolding and the lithium-ion battery has a higher capacity.

[0160] The coating weight of the positive electrode active material layer usually affects the capacity of the lithium-ion battery and the risk of the positive electrode active material layer peeling. It can be seen from Examples 1-1, 3-13 to 3-15 that the electrochemical device using the coating weight of the positive electrode active material layer within the scope of this application has higher main body adhesion and edge adhesion, and also has higher capacity, indicating that the positive electrode active material layer has a lower peeling risk and the lithium-ion battery has a higher capacity. Among them, although the capacity of the lithium-ion battery of Example 3-15 is higher than that of Examples 1-1, 3-13 and 3-14, the production cost of the lithium-ion battery of Example 3-15 is higher, which is not conducive to industrial mass production.

[0161] The coating weight of the negative electrode active material layer usually affects the capacity of the lithium-ion battery and the risk of the positive electrode active material layer peeling. From Examples 1-1, 3-16, and 3-18, it can be seen that the electrochemical device using the coating weight of the negative electrode active material layer within the scope of this application has higher main body adhesion and edge adhesion, and also has higher capacity, indicating that the positive electrode active material layer has a lower peeling risk and the lithium-ion battery has a higher capacity. Among them, although the capacity of the lithium-ion battery of Example 3-18 is higher than that of Examples 1-1, 3-16, and 3-17, the production cost of the lithium-ion battery of Example 3-18 is higher, which is not conducive to industrial mass production.

[0162] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0163] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0164] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device, comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer being disposed on the surface of the positive electrode current collector, and the second positive electrode active material layer being disposed on the surface of the first positive electrode active material layer away from the positive electrode current collector; The first positive electrode active material layer includes a first positive electrode active material, the first positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide or lithium manganese oxide, and the second positive electrode active material layer includes a second positive electrode active material, the second positive electrode active material includes at least one of lithium iron manganese phosphate or lithium iron phosphate; Along the width direction of the unfolded positive electrode sheet, the first positive electrode active material layer includes a first end face and a third end face opposite to the first end face, the second positive electrode active material layer includes a second end face and a fourth end face opposite to the second end face, the first end face and the second end face are located on a first side of the positive electrode sheet, the third end face and the fourth end face are located on a second side of the positive electrode sheet, and the first side is opposite to the second side; in, Along the width direction of the unfolded positive electrode sheet, the first end face exceeds the second end face, and the fourth end face does not exceed the third end face.

2. The electrochemical device according to claim 1, wherein: Along the thickness direction of the unfolded positive electrode sheet, the projection of the second positive electrode active material layer on the positive electrode current collector is located within the projection of the first positive electrode active material layer on the positive electrode current collector.

3. The electrochemical device according to claim 1, wherein The distance that the first end surface exceeds the second end surface is m1, and 0.2 mm≤m1≤2 mm.

4. The electrochemical device according to claim 1, wherein The distance that the third end face exceeds the fourth end face is m2, 0.2mm≤m2≤2mm.

5. The electrochemical device according to claim 1, wherein The first positive electrode active material layer further includes a first conductive agent and a first binder. Based on the mass of the first positive electrode active material layer, the mass percentage of the first positive electrode active material is 95% to 98%, the mass percentage of the first conductive agent is 0.5% to 3%, and the mass percentage of the first binder is 0.5% to 3%; and / or, The second positive electrode active material layer also includes a second conductive agent and a second binder. Based on the mass of the second positive electrode active material layer, the mass percentage of the second positive electrode active material is 95% to 98%, the mass percentage of the second conductive agent is 0.6% to 3%, and the mass percentage of the first binder is 0.5% to 2%.

6. The electrochemical device according to claim 1, wherein The gram capacity of the first positive electrode active material is a, and the gram capacity of the second positive electrode active material is b, satisfying: 10%≤(ab) / b×100%≤75%, 160mAh / g≤a≤210mAh / g.

7. The electrochemical device according to claim 6, wherein: 14%≤(ab) / b×100%≤30%.

8. The electrochemical device according to claim 6, wherein: 120mAh / g≤b≤140mAh / g.

9. The electrochemical device according to claim 1, wherein: Along the width direction of the unfolded positive electrode sheet, the positive electrode active material layer includes a main body portion and an edge portion, and the edge portion is a portion of the first positive electrode active material layer that exceeds the second positive electrode active material layer; The mass percentage of the second positive electrode active material is 5% to 95% based on the total mass of the first positive electrode active material and the second positive electrode active material in the main body portion.

10. The electrochemical device according to claim 9, wherein: The mass percentage of the second positive electrode active material is 5% to 60% based on the total mass of the first positive electrode active material and the second positive electrode active material in the main body portion.

11. The electrochemical device according to claim 9, wherein: In the main body, the coating weight of the positive electrode active material layer is 200 mg / 1540.24 mm 2 Up to 600mg / 1540.24mm 2 .

12. The electrochemical device according to claim 9, wherein: The CB value of the electrochemical device satisfies: 1.04≤CB≤1.

2.

13. The electrochemical device according to claim 12, wherein: The CB value of the edge portion is ≥ the CB value of the main portion.

14. The electrochemical device according to claim 1, wherein The electrochemical device further comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the coating weight of the negative electrode active material layer is 100 mg / 1540.24 mm 2 Up to 300mg / 1540.24mm 2 .

15. The electrochemical device according to claim 14, wherein: The negative electrode active material layer includes a negative electrode active material, and the gram capacity of the negative electrode active material is 280 mAh / g to 420 mAh / g.

16. The electrochemical device according to any one of claims 1 to 15, wherein: Along the length direction of the unfolded positive electrode sheet, the length of the first positive electrode active material layer is greater than the length of the second positive electrode active material layer.

17. An electronic device comprising the electrochemical device according to any one of claims 1 to 16.

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