Electrochemical device and electronic device

Abstract

An electrochemical device and an electronic device. A first material layer in the electrochemical device is disposed on a first surface of a positive electrode current collector, and a second material layer is located on the surface of the first material layer away from the positive electrode current collector; the first material layer comprises a first positive electrode active material, the first positive electrode active material comprises at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium manganese oxide, the second material layer comprises a second positive electrode active material, and the second positive electrode active material comprises at least one of lithium manganese iron phosphate or lithium iron phosphate; along the length direction of an unwound positive electrode sheet, the length of the material layer is greater than the length of the second material layer, the ending end of the first material layer is provided with a first end surface, the ending end of the second material layer is provided with a second end surface, the first end surface extends beyond the second end surface, and the length of the first material layer is less than the length of the second positive electrode active material layer. The risk of peeling of a positive electrode active material layer is reduced, and the electrochemical device has high capacity.

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 active 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 to 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 an electrode assembly including a positive electrode sheet; the positive electrode sheet comprises a positive electrode collector and a positive electrode active material layer, the positive electrode active material layer comprises a first positive electrode active material layer and a second positive electrode active material layer, the positive electrode collector comprises a first surface and a second surface, the first surface is away from the winding center of the electrode assembly and opposite to the second surface, the first positive electrode active material layer is arranged on the first surface of the positive electrode collector, the second positive electrode active material layer is arranged on the second surface of the positive electrode collector, the first positive electrode active material layer comprises a first material layer and a second material layer, the first material layer is arranged on the first surface of the positive electrode collector, the second material layer is arranged on the second surface of the positive electrode collector The layer is located on the surface of the first material layer away from the positive electrode current collector; the first 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 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 length direction of the unfolded positive electrode sheet, the length of the first material layer is greater than the length of the second material layer, the tail end of the first material layer has a first end face, the tail end of the second material layer has a second end face, the first end face extends beyond the second end face, and the length of the first material layer is less than the length of the second positive electrode active material layer. This application controls the types of the first and second positive electrode active materials, and controls the length of the first material layer to be greater than the length of the second material layer, the first end face of the tail end of the first material layer extends beyond the second end face of the tail end of the second material layer, and the length of the first material layer is less than the length of the second positive electrode active material layer, thereby reducing the risk of delamination of the positive electrode active material layer while achieving a higher capacity of the electrochemical device. In addition, the production cost of the electrochemical device is reduced.

[0008] In one embodiment of the present application, along the length direction of the unfolded positive electrode sheet, the positive electrode active material layer includes a first main portion and a first edge portion, the first edge portion is the portion of the first material layer that exceeds the second material layer, and based on the total mass of the first positive electrode active material and the second positive electrode active material in the first main portion, the mass percentage of the second positive electrode active material is 5% to 95%.

[0009] 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 first main body portion, the mass percentage of the second positive electrode active material is 5% to 60%.

[0010] In one embodiment of the present application, the distance between the first end face and the second end face is m1, where 0.5 mm ≤ m1 ≤ 5 mm. By controlling the distance between the first end face and the second end face within this range, the risk of delamination of the positive electrode active material layer is reduced, resulting in a higher capacity electrochemical device. Furthermore, the production cost of the electrochemical device is reduced.

[0011] In one embodiment of the present application, the first material layer further comprises a first conductive agent and a first binder, and based on the mass of the first 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 material layer further comprises a second conductive agent and a second binder, and based on the mass of the second 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%. By regulating the contents of the first positive electrode active material, the first conductive agent, and the first binder in the first material layer within the above ranges, and regulating the contents of the second positive electrode active material, the second conductive agent, and the second binder in the second material layer within the above ranges, the electrochemical device has a higher capacity while reducing the risk of delamination of the positive electrode active material layer.

[0012] In one embodiment of the present application, 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.

[0013] 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 ≤ 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.

[0014] In one embodiment of the present application, 14% ≤ (ab) / b ≤ 30%. Regulating 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.

[0015] In one embodiment of the present application, 120 mAh / g≤b≤140 mAh / g.

[0016] 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 2Up 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.

[0017] 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.

[0018] In one embodiment of the present application, the CB value of the electrochemical device satisfies: 1.04≤CB≤1.2.

[0019] In one embodiment of the present application, the CB value of the edge portion is ≥ the CB value of the main portion.

[0020] In one embodiment of the present application, the second positive electrode active material layer includes a third material layer and a fourth material layer, the third material layer being disposed on the second surface of the positive electrode current collector, and the fourth material layer being disposed on the surface of the third material layer away from the positive electrode current collector; along the length direction of the unfolded positive electrode sheet, the length of the third material layer is greater than the length of the fourth material layer, the tail end of the third material layer has a third end face, the tail end of the fourth material layer has a fourth end face, and the third end face extends beyond the fourth end face. By setting the length of the third material layer greater than the length of the fourth material layer and the third end face of the tail end of the third material layer extending beyond the fourth end face of the tail end of the fourth material layer, the possibility of the fourth material layer contacting the positive electrode current collector is reduced when the second positive electrode active material layer provides a higher capacity to the electrochemical device, thereby reducing the risk of delamination of the positive electrode active material layer.

[0021] In one embodiment of the present application, the length of the first material layer is less than the length of the third material layer, and / or the length of the first material layer is less than the length of the fourth material layer. This arrangement reduces the risk of delamination of the positive electrode active material layer, resulting in a higher capacity electrochemical device. Furthermore, it reduces the production cost of the electrochemical device.

[0022] In one embodiment of the present application, the distance between the third end face and the fourth end face is m2, where 0.5 mm ≤ m2 ≤ 5 mm. By regulating the distance between the third end face and the fourth end face within the above range, the risk of delamination of the positive electrode active material layer is reduced, and the electrochemical device has a higher capacity.

[0023] The second aspect of the present application provides an electronic device, which includes the electrochemical device according to any one of the aforementioned embodiments. Therefore, the electronic device has good performance.

[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 material layer so that the first 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 above-mentioned type of second positive electrode active material is selected and applied to the second material layer, which can reduce the production cost of the electrochemical device while making the electrochemical device have a higher capacity. Since the second material layer has weaker adhesion than the first material layer, the present application sets the length of the first material layer to be greater than the length of the second material layer, and the first end face of the tail end of the first material layer exceeds the second end face of the tail end of the second material layer, so that the possibility of the second material layer contacting the positive electrode current collector is reduced, thereby reducing the risk of delamination of the positive electrode active material layer. Furthermore, the length of the first material layer is shorter than that of the second positive electrode active material layer, which can reduce the coating of the positive electrode active material layer at the end of the positive electrode sheet, thereby reducing the production cost of the electrochemical device. Thus, by regulating the types of the first and second positive electrode active materials, and regulating the length of the first material layer to be greater than the length of the second material layer, the first end surface of the end of the first material layer extends beyond the second end surface of the end of the second material layer, and the length of the first material layer is shorter than the length of the second positive electrode active material layer, the electrochemical device has a higher capacity while reducing the risk of delamination of the positive electrode active material layer. 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 an improper limitation on the present application.

[0027] FIG1 is a schematic structural diagram of an electrode assembly according to an embodiment of the present application;

[0028] FIG2 is a schematic diagram of the cross-sectional structure of a positive electrode sheet after unfolding along its own length and thickness directions according to an embodiment of the present application;

[0029] FIG3 is a schematic top view of the positive electrode sheet of FIG2 ;

[0030] FIG4 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. DETAILED DESCRIPTION

[0031] 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 examples. It is apparent that the described examples 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.

[0032] 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.

[0033] The first aspect of the present application provides an electrochemical device, the electrochemical device comprising an electrode assembly including a positive electrode sheet; the positive electrode sheet comprising a positive electrode collector and a positive electrode active material layer, the positive electrode active material layer comprising a first positive electrode active material layer and a second positive electrode active material layer, the positive electrode collector comprising a first surface and a second surface, the first surface facing away from the winding center of the electrode assembly and opposite to the second surface, the first positive electrode active material layer being arranged on the first surface of the positive electrode collector, the second positive electrode active material layer being arranged on the second surface of the positive electrode collector, the first positive electrode active material layer comprising a first material layer and a second material layer, the first material layer being arranged on the first surface of the positive electrode collector, the second positive electrode active material layer being arranged on the second surface of the positive electrode collector, The second material layer is located on the surface of the first material layer away from the positive electrode current collector; the first 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 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 length direction of the unfolded positive electrode sheet, the length of the first material layer is greater than the length of the second material layer, the tail end of the first material layer has a first end face, the tail end of the second material layer has a second end face, the first end face exceeds the second end face, and the length of the first material layer is less than the length of the second positive electrode active material layer.

[0034] As shown in Figures 1 to 3, the structure of the electrode assembly 001 is a wound structure, with the winding direction indicated by W. The electrode assembly 001 includes a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30 disposed between the positive electrode sheet 10 and the negative electrode sheet 20. It should be understood by those skilled in the art that in the electrode assembly 001, the winding direction of the positive electrode sheet 10, the negative electrode sheet 20, and the separator 30 is the same as the winding direction of the electrode assembly 001, and the winding direction of the positive electrode current collector 11 and the positive active material layer 100 in the positive electrode sheet 10 is the same as the winding direction of the electrode assembly 001. The positive electrode sheet 10 includes a positive electrode current collector 11, a first positive electrode active material layer 101, and a second positive electrode active material layer 102. The positive electrode current collector 11 includes a first surface 11a and a second surface 11b. The first surface 11a faces away from the winding center of the electrode assembly 001 and is opposite to the second surface 11b. The first positive electrode active material layer 101 includes a first material layer 121 and a second material layer 122. The first material layer 121 is disposed on the first surface 11a of the positive electrode current collector 11, and the second material layer 122 is disposed on the surface of the first material layer 121 away from the positive electrode current collector 11. The first material layer 121 is located between the second material layer 122 and the positive electrode current collector 11. The first 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 material layer 122 includes a second positive electrode active material, which includes at least one of lithium iron manganese phosphate or lithium iron phosphate. For ease of understanding, the length direction of the positive electrode sheet 10 after unfolding is defined as X, the width direction as Y, and the thickness direction as Z. It can be understood that the length, width, and thickness directions of the negative electrode sheet 20 and the separator 30 after unfolding are the same as those of the separator. Along the length direction X after the positive electrode sheet 10 is unfolded, the length L of the first material layer 121 is 121 Greater than the length L of the second material layer 122 122 The first material layer 121 has a first end surface 121a at its tail end, and a second material layer 122 has a second end surface 122a at its tail end. The first end surface 121a exceeds the second end surface 122a, and the length L of the first positive electrode active material layer 101 is 101 is smaller than the length L of the second positive electrode active material layer 102 102 .

[0035] The aforementioned first positive electrode active material has excellent viscosity and high gram capacity. Application of this first positive electrode active material in the first material layer ensures good adhesion between the first material layer and the positive electrode current collector, thereby reducing the risk of delamination of the positive electrode active material layer. Furthermore, it provides a high gram capacity for the electrochemical device, thereby enabling a high capacity electrochemical device. The aforementioned second positive electrode active material has high gram capacity and low cost. Application of this second positive electrode active material in the second material layer can achieve a high capacity electrochemical device while reducing the production cost. Because the second material layer has weaker adhesion to the first material layer, the present invention provides a method in which the length of the first material layer is greater than that of the second material layer, so that the first end face of the first material layer protrudes beyond the second end face of the second material layer. This reduces the likelihood of contact between the second material layer and the positive electrode current collector, thereby reducing the risk of delamination of the positive electrode active material layer. Furthermore, the length of the first material layer is shorter than that of the second positive electrode active material layer, which reduces the amount of positive electrode active material layer applied to the end of the positive electrode sheet, thereby reducing the production cost of the electrochemical device. Thus, by regulating the types of the first and second positive electrode active materials, and regulating the length of the first material layer to be greater than the length of the second material layer, the first end surface of the first material layer extends beyond the second end surface of the second material layer, and the length of the first material layer is less than the length of the second positive electrode active material layer, the electrochemical device has a higher capacity while reducing the risk of delamination of the positive electrode active material layer. Furthermore, the production cost of the electrochemical device is reduced.

[0036] In some other embodiments, along the Y direction, the end face of the other side of the positive electrode collector may also exceed the end face of the first positive electrode active material layer or the end face of the second positive electrode active material layer; or, along the Y direction, the end face of the other side of the positive electrode collector 11 may also exceed the end face of the first positive electrode active material layer or the end face of the second positive electrode active material layer.

[0037] In one embodiment of the present application, as shown in FIG3 , along the longitudinal direction X of the unfolded positive electrode sheet 10, the first positive electrode active material layer 101 includes a first main portion 12a and a first edge portion 12b. The first edge portion 12b is the portion of the first material layer 121 extending beyond the second material layer 122. The first main portion 12a refers to the portion of the first positive electrode active material layer 101 excluding the first edge portion 12b. Based on the total mass of the first and second positive electrode active materials in the first 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 controlling the mass percentage of the second positive electrode active material within the above range, the risk of delamination of the positive electrode active material layer is reduced, and the electrochemical device has a higher capacity.

[0038] 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 first main body portion, the mass percentage of the second positive electrode active material is 5% to 60%.

[0039] The present application does not particularly limit the weight percentage of the first positive electrode active material, as long as the objectives 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 first main body, the weight percentage of the first positive electrode active material is 5% to 95%. Furthermore, the weight percentage of the first positive electrode active material is 40% to 95%.

[0040] In one embodiment of the present application, the distance that the first end face extends beyond the second end face is m1, where 0.5 mm ≤ m1 ≤ 5 mm. For example, m1 is 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or any value between any two of the above numerical ranges. As shown in Figure 2, the distance that the first end face 121a extends beyond the second end face 122a is m1. Controlling the distance that the first end face extends beyond the second end face within the above range reduces the likelihood of contact between the second material layer and the positive electrode current collector, thereby reducing the risk of delamination of the positive electrode active material layer. This also ensures that the first and second material layers are applied simultaneously as much as possible in the area of ​​the positive electrode current collector where the first positive electrode active material layer is applied, thereby providing the highest possible capacity and reducing production costs. Thus, while reducing the risk of delamination of the positive electrode active material layer, the electrochemical device has a higher capacity. Furthermore, the production cost of the electrochemical device is reduced.

[0041] 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 FIG4 , 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 appreciated 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 aforementioned “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.

[0042] In one embodiment of the present application, along the length direction of the unfolded positive electrode sheet, the distance that one end of the negative electrode active material layer extends beyond the corresponding end of the positive electrode active material layer is n1, and 2mm≤n1≤15mm. For example, n1 is 2mm, 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, or any value between any two of the above numerical ranges. As shown in Figure 4, along the length direction X of the unfolded positive electrode sheet 10, the distance between one end of the negative electrode active material layer 22 and the corresponding end of the positive electrode active material layer 100, that is, the distance between the first end face 121a of the first material layer 121 in the first positive electrode active material layer 101 and the corresponding end face of the negative electrode active material layer 22 is n1. 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 aforementioned 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 likelihood of lithium deposition on the surface of the negative electrode sheet. Furthermore, the risk of increased costs associated with excessive negative electrode active material layers can be reduced, thereby lowering the production cost of the electrochemical device. This is beneficial for reducing lithium deposition and production costs of the electrochemical device while maintaining the capacity of the electrochemical device and reducing the risk of delamination of the positive electrode active material layer.

[0043] In one embodiment of the present application, the first material layer further comprises a first conductive agent and a first binder. Based on the mass of the first 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 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 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 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 material layer within the above-mentioned range, it is possible to provide a high gram capacity while ensuring a high adhesion between the first material layer and the positive electrode current collector, thereby reducing the risk of demolding of the positive electrode active material layer and providing the electrochemical device with a higher capacity.

[0044] In one embodiment of the present application, the second material layer further comprises a second conductive agent and a second binder. Based on the mass of the second 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 second binder is 0.5% to 2%. For example, based on the mass of the second 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 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 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 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 material layer and the first material layer, thereby reducing the risk of demolding of the positive electrode active material layer and providing the electrochemical device with a higher capacity.

[0045] In one embodiment of the present application, the coating weight of the positive electrode active material layer is 200 mg / 1540.24 mm 2 Up to 600mg / 1540.24mm2 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 / 1540.24mm 2 、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.

[0046] 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.

[0047] In one embodiment of the present application, 14% ≤ (ab) / b ≤ 30%. Regulating 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] In one embodiment of the present application, the CB value of the electrochemical device satisfies: 1.04≤CB≤1.2. In the present application, the value of (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) is recorded as CB. The above unit area refers to 1mm 2 Regulating 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.

[0054] In one embodiment of the present application, the CB value of the first edge portion is greater than or equal to the CB value of the first main portion. In this application, the CB value of the first edge portion is 1.08 to 1.3, and the CB value of the first main portion is 1.05 to 1.1. A CB value of the first edge portion that is less than or equal to the CB value of the first main portion is beneficial for improving the dynamics 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.

[0055] In one embodiment of the present application, as shown in FIG2 , the second positive electrode active material layer 102 includes a third material layer 123 and a fourth material layer 124. The third material layer 123 is disposed on the second surface 11 b of the positive electrode current collector 11, and the fourth material layer 124 is disposed on the surface of the third material layer 123 away from the positive electrode current collector 11. Along the longitudinal direction X after the positive electrode sheet 10 is unfolded, the length L of the third material layer 123 is 123 Greater than the length L of the fourth material layer 124 124 The end of the third material layer 123 has a third end surface 123a, and the end of the fourth material layer 124 has a fourth end surface 124a, with the third end surface 123a extending beyond the fourth end surface 124a. By setting the length of the third material layer to be greater than the length of the fourth material layer, and the third end surface of the end of the third material layer extending beyond the fourth end surface of the end of the fourth material layer, the likelihood of the fourth material layer contacting the positive electrode current collector is reduced when the second positive electrode active material layer provides a higher capacity for the electrochemical device, thereby reducing the risk of delamination of the positive electrode active material layer.

[0056] In one embodiment of the present application, the length of the first material layer is less than the length of the third material layer. In one embodiment of the present application, the length of the first material layer is less than the length of the fourth material layer. In one embodiment of the present application, the length of the first material layer is less than the length of the third material layer, and the length of the first material layer is less than the length of the fourth material layer. For example, as shown in FIG. 2 , the length L of the first material layer 121 is less than the length L of the third material layer. 121 Less than the length L of the third material layer 123 123 , and the length L of the first material layer 121 121 Less than the length L of the fourth material layer 124 124 By adjusting the length of the first material layer to be shorter than the length of the third material layer, and / or adjusting the length of the first material layer to be shorter than the length of the fourth material layer, the risk of delamination of the positive electrode active material layer is reduced, and the electrochemical device has a higher capacity. Furthermore, the production cost of the electrochemical device is reduced.

[0057] In one embodiment of the present application, as shown in FIG2 , the distance that the third end face 121b exceeds the fourth end face 122b is m2, 0.5mm≤m2≤5mm. For example, m2 is 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, or any value between any two of the above numerical ranges. By regulating the distance that the third end face exceeds the fourth end face within the above range, the possibility of the fourth material layer contacting the positive electrode current collector is reduced, thereby reducing the risk of the second positive electrode active material layer delaminating. It also allows the first material layer and the second material layer to be coated simultaneously as much as possible in the area on the positive electrode current collector where the second positive electrode active material layer is coated, so as to provide the highest possible capacity and reduce production costs. As a result, the electrochemical device has a higher capacity while reducing the risk of delamination of the positive electrode active material layer.

[0058] In one embodiment of the present application, the third material layer includes a first positive electrode active material, and the fourth material layer includes a second positive electrode active material. The first positive electrode active material is applied to the third material layer so that the third material layer and the positive electrode current collector can have good adhesion, thereby reducing the risk of demolding 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 is applied to the fourth material layer, which can reduce the production cost of the electrochemical device while giving the electrochemical device a higher capacity. As a result, the risk of demolding of the positive electrode active material layer can be reduced, the production cost of the electrochemical device can be reduced, and the capacity of the electrochemical device can be increased.

[0059] In one embodiment of the present application, the third material layer further includes a first conductive agent and a first binder. Based on the mass of the third 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 third 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 third 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 third 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 third material layer within the above-mentioned range, it is possible to provide a high gram capacity while ensuring a high adhesion between the third material layer and the positive electrode current collector, thereby reducing the risk of demolding of the positive electrode active material layer and providing the electrochemical device with a higher capacity.

[0060] In one embodiment of the present application, the fourth material layer further comprises a second conductive agent and a second binder. Based on the mass of the fourth 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 second binder is 0.5% to 2%. For example, based on the mass of the fourth 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 fourth 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 fourth 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 fourth material layer within the above-mentioned range, it is possible to provide a higher gram capacity and lower production cost while having a higher adhesion force between the fourth material layer and the third material layer, thereby reducing the risk of demolding of the positive electrode active material layer and providing the electrochemical device with a higher capacity.

[0061] 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.

[0062] In one embodiment of the present application, along the length direction of the unfolded positive electrode sheet, the second positive electrode active material layer includes a second main portion and a second edge portion, the second edge portion is the portion of the third material layer that exceeds the fourth material layer, and the CB value of the second edge portion is ≥ the CB value of the second main portion. The above-mentioned second main portion refers to the other portions of the second positive electrode active material layer other than the second edge portion. In the present application, the CB value of the second edge portion is 1.08 to 1.3, and the CB value of the second main portion is 1.05 to 1.1. The CB value of the second edge portion is greater than the CB value of the second main portion, which is beneficial to improving the kinetics of the edge position of the electrochemical device and overcoming the problem that the kinetics of the edge portion is inferior to that of the main portion due to its relative relaxation.

[0063] In one embodiment of the present application, the mass percentage of the first positive electrode active material in the first main body is the same as the mass percentage of the first positive electrode active material in the second main body; the mass percentage of the second positive electrode active material in the first main body is the same as the mass percentage of the second positive electrode active material in the second main body.

[0064] 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.

[0065] The present application does not particularly limit the preparation method of the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the preparation method of the positive electrode sheet may include but is not limited to the following steps: (1) preparing a first positive electrode slurry, a second positive electrode slurry, a third positive electrode slurry and a fourth positive electrode slurry; (2) applying the first positive electrode slurry on the first surface of the positive electrode current collector, drying, to obtain a positive electrode sheet coated with the first material layer; applying the second positive electrode slurry on the surface of the first material layer away from the positive electrode current collector, drying, to obtain a positive electrode sheet coated with the first material layer and the second material layer; (3) applying the third positive electrode slurry on the second surface of the positive electrode current collector, drying, to obtain a positive electrode sheet coated with the first material layer, the second material layer and the third material layer; applying the fourth positive electrode slurry on the surface of the third material layer away from the positive electrode current collector, drying, to obtain a positive electrode sheet coated with the first material layer, the second material layer, the third material layer and the fourth material layer; and (4) cold pressing, cutting and welding the positive electrode tabs. The present application has no special restrictions on the preparation methods of the first positive electrode slurry, the second positive electrode slurry, the third positive electrode slurry, and the fourth 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 material layer and the third material layer are respectively 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 material layer and the fourth material layer are respectively within the scope of the present application, the purpose of the present application can be achieved. The present application has no special 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 special restrictions on the process parameters of cold pressing, cutting and welding 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. The present application has no special restrictions on the sizes of the above-mentioned first material layer, second material layer, third material layer, and fourth material layer, as long as the purpose of the present application can be achieved.

[0066] 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 further 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):(0.5-1.5):(1.0-1.9).

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] The second aspect of the present application provides an electronic device, which includes the electrochemical device according to any one of the aforementioned embodiments. Therefore, the electronic device has good performance.

[0073] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0074] Example

[0075] 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.

[0076] Test methods and equipment:

[0077] Gram capacity test:

[0078] (1) Test of gram capacity a of the first positive electrode active material:

[0079] 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.

[0080] (2) Test of gram capacity b of the second positive electrode active material:

[0081] 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 again with a knife, 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.

[0082] (3) Test of gram capacity c of negative electrode active material

[0083] 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.

[0084] Coating weight test:

[0085] (1) Test of coating weight of positive electrode active material layer:

[0086] 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 area where the first main part and the second main part overlapped in the positive electrode active material layer was cut out to an area of ​​1540.25 mm. 2 The positive electrode sheet sample is placed on a balance and weighed, recorded as p1, and then the positive electrode active material layer on the positive electrode sheet is washed, and the positive electrode current collector is placed on a balance and weighed, recorded as p2; the coating weight CW1 = (p1-p2) / 2.

[0087] It should be noted that the coating weight of the positive electrode active material layer in this application refers to the coating weight of the first main portion of the positive electrode active material layer. The coating weight of the second main portion of the positive electrode active material layer is the same as the coating weight of the first main portion.

[0088] Among them, the coating weight of the first material layer = CW1×N1, the coating weight of the second material layer = CW1×N2, the coating weight of the third material layer is the same as the coating weight of the first material layer, and the coating weight of the fourth material layer is the same as the coating weight of the second material layer.

[0089] (2) Test of coating weight of negative electrode active material layer:

[0090] 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 DMC and dried. The area of ​​the negative electrode was cut into 1540.25mm 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.

[0091] If the negative electrode sheet is coated with a negative electrode active material layer on one side, the coating weight = q1-q2.

[0092] If the negative electrode sheet is coated with negative electrode active material layers on both sides, the coating weight = (q1-q2) / 2.

[0093] Adhesion test:

[0094] After fully discharging the lithium-ion batteries of each embodiment and comparative example, the positive electrode sheets were disassembled and cleaned with dimethyl carbonate and cut into 4 cm × 0.5 cm samples. A 0.2 cm wide rectangular adhesive tape was attached to the first 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 first 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:

[0095] (1) Test of the main body adhesion:

[0096] For a 4cm x 0.5cm sample, use a 0.2cm wide rectangular piece of adhesive tape to cover the center of the sample.

[0097] (2) Test of edge adhesion:

[0098] 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.

[0099] Capacity test:

[0100] The lithium-ion batteries of each embodiment and comparative example were charged to 4.3V at a constant current of 0.5C, then charged to a current of 0.02C at a constant voltage of 4.3V; discharged to 2.8V at a rate of 0.2C, and the corresponding capacity was collected, which was the capacity of the lithium-ion batteries in each embodiment and comparative example.

[0101] Example 1-1

[0102] <Preparation of positive electrode sheet>

[0103] The first positive electrode active material is lithium nickel cobalt manganese oxide (NCM60-10-30, LiNi0.6 Co 0.1 Mn 0.3 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.

[0104] At the same time, the first positive electrode slurry is also used as the third positive electrode slurry.

[0105] 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.

[0106] At the same time, the second positive electrode slurry is also used as the fourth positive electrode slurry.

[0107] The first positive electrode slurry is coated on the first 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 material layer. The second positive electrode slurry is coated on the surface of the first material layer away from the positive electrode current collector and dried to obtain a positive electrode sheet coated with the first and second material layers. Thereafter, the above steps are repeated on the second surface of the aluminum foil to obtain a positive electrode sheet coated with the first, second, third and fourth material layers (as shown in Figure 2). Cold pressing, cutting and welding of positive electrode tabs are performed to obtain a positive electrode sheet with a specification of 110mm×1100mm for standby use.

[0108] Among them, the length L of the first material layer 121 =970mm, length of the second material layer L 122 =969mm. The length of the third material layer L 123 =1000mm, length of the fourth material layer L 124 =999mm. The distance m1 of the first end face beyond the second end face is 1mm, and the distance m2 of the third end face beyond the fourth end face is 1mm. 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 mm2 Based 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 material layer = CW1×N1=260×30% / 2=39mg / 1540.24mm 2 , coating weight of the second material layer = CW1×N2=260×70% / 2=91mg / 1540.24mm 2 , the coating weight of the third material layer is the same as the coating weight of the first material layer, and the coating weight of the fourth material layer is the same as the coating weight of the second material layer.

[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 size of 116 mm × 1050 mm for future use.

[0111] The length of the negative electrode active material layer is 1020 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, wherein the first surface of the positive current collector in the positive electrode sheet is closer to the outside of the electrode assembly than the second surface. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. The lithium-ion battery is produced through vacuum packaging, static standing, formation, degassing, and trimming. Formation step: 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 1-6

[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 length of the second material layer changes accordingly, while the length of the first material layer remains unchanged. When m2 changes, the length of the fourth material layer changes accordingly, while the length of the third material layer remains unchanged.

[0121] Examples 1-7

[0122] <Preparation of positive electrode sheet>

[0123] 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.

[0124] The rest is the same as Example 1-1.

[0125] Examples 1-8

[0126] <Preparation of positive electrode sheet>

[0127] 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.

[0128] The rest is the same as Example 1-1.

[0129] Examples 1-9

[0130] <Preparation of positive electrode sheet>

[0131] 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.

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

[0133] Example 2-1 to Example 2-8

[0134] Except for adjusting the preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0135] 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.

[0136] Example 3-1 to Example 3-18

[0137] Except for adjusting the preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0138] Among them, in Examples 3-13 to 3-15, when the coating weight CW1 of the positive electrode active material layer changes, the coating weight of the first material layer changes according to the formula CW1×N1, the coating weight of the second material layer changes according to the formula CW1×N2, the coating weight of the third material layer is the same as the coating weight of the first material layer, and the coating weight of the fourth material layer is the same as the coating weight of the second material layer.

[0139] Comparative Example 1 and Comparative Example 3

[0140] Except for adjusting the preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0141] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0142] Table 1

[0143] Note: “\” in Table 1 indicates no corresponding parameter.

[0144] As can be seen from Examples 1-1 to 1-9, Comparative Examples 1 and 2, the embodiments of the present application, by selecting the first positive electrode active material and the second positive electrode active material within the scope of the present application, and adjusting the length of the first material layer to be greater than the length of the second material layer, the first end face to extend beyond the second end face, and the length of the first material layer to be less than the length of the second positive electrode active material layer, the positive electrode sheet has higher body adhesion and edge adhesion, and the lithium-ion battery has a higher capacity, indicating that the risk of delamination of the positive electrode active material layer is reduced, and the lithium-ion battery has a higher capacity. In contrast, the lithium-ion batteries in Comparative Examples 1 and 2, which do not select the first positive electrode active material and the second positive electrode active material within the scope of the present application, or in which the length of the first material layer is not greater than the length of the second material layer, and the first end face does not extend beyond the second end face, have lower body adhesion and / or edge adhesion in their positive electrode sheets, indicating that the lithium-ion battery has not been able to reduce the risk of delamination of the positive electrode active material layer while maintaining a high capacity.

[0145] 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 1-1 to 1-6, electrochemical devices with a distance m1 between the first end face and the second end face, and a distance m2 between the third end face and the fourth end face, within the scope of this application, exhibit high body and edge adhesion, as well as high capacity. This indicates that while maintaining good capacity, the positive electrode active material layer has a low risk of delamination. While the capacity of the lithium-ion battery of Example 1-5 is higher than that of Examples 1-1 to 1-4, 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.

[0146] 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, 1-7, and 1-9, 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.

[0147] Table 2

[0148] 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.

[0149] 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.

[0150] Table 3

[0151] 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.

[0152] 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, 3-5, and 3-8, the electrochemical device 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 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 delamination and the lithium-ion battery has a higher capacity. Among them, although the capacity of the lithium-ion batteries of Examples 3-4, 3-5, 3-7, and 3-8 is higher than that of Examples 1-1 and 3-1, the production cost of the lithium-ion batteries of Examples 3-4, 3-5, 3-7, and 3-8 is higher, which is not conducive to industrial mass production.

[0153] The gram capacity c of the negative electrode active material usually 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 this application has a 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 delamination and the lithium-ion battery has a higher capacity. Among them, although the capacity of the lithium-ion batteries of Examples 3-11 and 3-12 is the same as that of Examples 1-1, 3-9 and 3-10, the production cost of the lithium-ion batteries of Examples 3-11 and 3-12 is higher, which is not conducive to industrial mass production.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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 an electrode assembly including a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer, the positive active material layer comprising a first positive active material layer and a second positive active material layer, the first positive active material layer being disposed on a first surface of the positive current collector, the second positive active material layer being disposed on a second surface of the positive current collector, the first surface being away from the winding center of the electrode assembly and opposite to the second surface, the first positive active material layer comprising a first material layer and a second material layer, the first material layer being disposed on the first surface of the positive current collector, the second material layer being disposed on a surface of the first material layer away from the positive current collector; The first 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 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 length direction of the positive electrode sheet after unfolding, the length of the first material layer is greater than the length of the second material layer, the tail end of the first material layer has a first end face, the tail end of the second material layer has a second end face, the first end face exceeds the second end face, and the length of the first material layer is less than the length of the second positive electrode active material layer.

2. The electrochemical device according to claim 1, wherein: The distance that the first end face exceeds the second end face is m1, and 0.5 mm≤m1≤5 mm.

3. The electrochemical device according to claim 1, wherein The first material layer further includes a first conductive agent and a first binder. Based on the mass of the first 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 material layer also includes a second conductive agent and a second binder. Based on the mass of the second 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%.

4. 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 the following: 10%≤(ab) / b≤75%, 160 mAh / g≤a≤210 mAh / g.

5. The electrochemical device according to claim 4, wherein: 14%≤(ab) / b≤30%.

6. The electrochemical device according to claim 4, wherein: 120mAh / g≤b≤140mAh / g.

7. The electrochemical device according to claim 1, wherein: Along the length direction of the positive electrode sheet after unfolding, the positive electrode active material layer includes a first main body portion and a first edge portion, and the first edge portion is a portion of the first material layer that exceeds the second 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 first main body portion.

8. The electrochemical device according to claim 7, 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 first main body portion.

9. The electrochemical device according to claim 7, wherein: The CB value of the electrochemical device satisfies: 1.04≤CB≤1.

2.

10. The electrochemical device according to claim 9, wherein The CB value of the first edge portion is ≥ the CB value of the first main body portion.

11. The electrochemical device according to claim 1, wherein 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 1, wherein The electrode assembly 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 .

13. The electrochemical device according to claim 12, 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.

14. The electrochemical device according to any one of claims 1 to 13, wherein: The second positive electrode active material layer includes a third material layer and a fourth material layer, the third material layer is arranged on the second surface of the positive electrode current collector, and the fourth material layer is arranged on the surface of the third material layer away from the positive electrode current collector; Along the length direction of the unfolded positive electrode sheet, the length of the third material layer is greater than that of the fourth material layer, the tail end of the third material layer has a third end face, the tail end of the fourth material layer has a fourth end face, and the third end face exceeds the fourth end face.

15. The electrochemical device according to claim 14, wherein: The length of the first material layer is shorter than the length of the third material layer, and / or the length of the first material layer is shorter than the length of the fourth material layer.

16. The electrochemical device according to claim 14, wherein: The distance that the third end face exceeds the fourth end face is m2, 0.5mm≤m2≤5mm.

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

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