Negative plate and preparation method thereof, electrode assembly, battery monomer, battery device and electric equipment

Abstract

The invention relates to a negative plate and a preparation method thereof, an electrode assembly, a battery monomer, a battery device and electric equipment. A first active material layer is provided with a first coating area and second coating areas located on the two sides of the first coating area; the average weight of the active substances in the unit area in the first coating region in the middle is greater than the average weight of the active substances in the unit area in the second coating regions on the two sides, so that the ion embedding capability in the first coating region is higher than that in the second coating regions on the two sides; the embedding degree difference of metal ions in different positions of the negative plate in the later period of circulation is made up, the probability of lithium precipitation in the middle of the negative plate is effectively reduced, and the service life of the single battery is prolonged.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to negative electrode sheets and preparation methods thereof, electrode assemblies, battery cells, battery devices and electrical equipment. Background Art

[0002] The electrode is a component that undergoes electrochemical reactions in a battery cell, and is divided into a negative electrode and a positive electrode. During the charge and discharge process, the negative active material of the negative electrode and the positive active material of the positive electrode react with the electrolyte to achieve energy storage or energy supply. However, due to the limitations of the structural design of traditional negative electrode sheets, lithium deposition is prone to occur in the middle of the negative electrode during charge and discharge, which reduces the service life of the battery cell. Summary of the invention

[0003] Based on this, it is necessary to provide a negative electrode sheet and a preparation method thereof, an electrode assembly, a battery cell, a battery device and electrical equipment to reduce the probability of lithium plating and increase the service life of the battery cell.

[0004] In the first aspect, the present application provides a negative electrode sheet, wherein at least one surface of the negative electrode sheet along its own thickness direction includes a first active material layer; wherein the first active material layer includes a first coating area and second coating areas respectively arranged on opposite sides of the first coating area along a preset direction, and the average weight of the active material per unit area in the first coating area is greater than the average weight of the active material per unit area in each second coating area.

[0005] The above-mentioned negative electrode sheet is respectively provided with a first coating area and second coating areas on both sides of the first coating area on the first active material layer, and the average weight of active material per unit area in the first coating area in the middle is greater than the average weight of active material per unit area in the second coating areas on both sides, so that the capacity for ion embedding in the first coating area is larger than that in the second coating areas on both sides, which makes up for the difference in the embedding degree of metal ions in different positions of the negative electrode sheet in the late stage of the cycle, effectively reduces the probability of lithium deposition in the middle of the negative electrode sheet, and improves the service life of the battery cell.

[0006] In some embodiments, the average weight of active material per unit area in the first coating area is recorded as CW1, and the average weight of active material per unit area in each second coating area is recorded as CW2, wherein 1<CW1 / CW2≤2. In this design, the ratio between the average weight of active material per unit area in the first coating area and the average weight of active material per unit area in the second coating area is controlled between 1 and 2, so that the capacity for ion embedding in the first coating area is increased, the probability of lithium deposition in the middle of the negative electrode sheet is reduced, and the service life of the battery cell is extended.

[0007] In some embodiments, CW1 / CW2 also satisfies the condition: 1<CW1 / CW2≤1.5. With such a design, the ratio between the average weight of active materials per unit area in the first coating area and the average weight of active materials per unit area in the second coating area is further controlled between 1 and 1.5. On the premise of compensating for the difference in the degree of embedding in the later stage of the cycle, the difference between active materials in different coating areas is controlled as much as possible, so that the performance of the battery cell is more stable.

[0008] In some embodiments, in at least one second coating area, the weight per unit area of ​​the active material increases from the side of the second coating area away from the first coating area to the side of the second coating area close to the first coating area. This design is convenient for effectively compensating for the difference in the degree of metal ion embedding between the middle and edge of the negative electrode sheet, reducing the probability of lithium plating and extending the service life of the battery cell.

[0009] In some embodiments, in at least one second coating area, the thickness of the active material gradually increases from the side of the second coating area away from the first coating area to the side of the second coating area close to the first coating area. In this way, the thickness of the active material in the second coating area is designed to be larger as it approaches the first coating area, so that the weight of the active material increases from the edge to the middle of the negative electrode sheet, making up for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet, reducing the probability of lithium plating, and effectively extending the service life of the battery cell.

[0010] In some embodiments, the first coating area includes a first line intersecting with a preset direction, and the weight per unit area of ​​the active material increases from at least one side of the first coating area close to the second coating area to the first line. In this design, in the first coating area, the weight per unit area of ​​the active material increases as it approaches the first line, effectively compensating for the insufficient embedding degree at the first line, thereby effectively reducing the probability of lithium precipitation.

[0011] In some embodiments, the thickness of the active material gradually increases from at least one side of the first coating area close to the second coating area to the first line. In this way, the thickness of the active material in the first coating area is designed to be larger as it approaches the first line, thereby compensating for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet, reducing the probability of lithium deposition in the middle of the negative electrode sheet, and effectively extending the service life of the battery cell.

[0012] In some embodiments, the first line overlaps with the center line of the first active material layer along a preset direction. In this design, the first coating area is arranged in the middle of the negative electrode sheet, which is convenient for increasing the ion embedding capacity in the middle of the negative electrode sheet, reducing the probability of lithium deposition in the middle, and improving the service life of the battery cell.

[0013] In some embodiments, the size of the first coating area along the preset direction is recorded as W1, where 5mm≤W1≤100mm. In this design, the size of the first coating area along the preset direction is controlled between 5mm and 100mm, which is convenient for accurately increasing the embedding capacity of the effective area on the negative electrode sheet and effectively improving the lithium deposition problem in the middle of the negative electrode sheet.

[0014] In some embodiments, the active material of the first active material layer includes at least one of a carbon material and a silicon material. Such a design is convenient for effectively improving the lithium deposition problem of battery cells containing carbon or silicon systems and increasing the service life of the battery cells.

[0015] In some embodiments, the negative electrode sheet further includes a first current collector, and the first active material layer is disposed on at least one surface of the first current collector. With such a design, the first current collector is introduced to facilitate the formation of different active material weights at different positions of the first current collector, thereby compensating for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet and reducing the probability of lithium precipitation.

[0016] In some embodiments, the first current collector includes a main body and a tab disposed at at least one end of the main body along a preset direction, and the first active material layer is disposed on at least one surface of the main body. In this design, the first current collector is designed as a main body and a tab, which facilitates the transmission of electric energy between the negative electrode sheet and the outside; at the same time, the preset direction is designed as the distribution direction between the main body and the tab, so that the first coating area and the second coating area in the wound electrode assembly are distributed in sequence along the height direction of the electrode assembly, effectively reducing the probability of lithium deposition in the middle of the negative electrode sheet.

[0017] In some embodiments, the average weight of active material per unit area in the first coating area is 0.1 g / 1540.25 mm 2 ~0.25g / 1540.25mm 2 With this design, the average weight of active material per unit area in the first coating area is controlled at 0.1 g / 1540.25 mm 2 ~0.25g / 1540.25mm 2 In order to meet the effective embedding of metal ions in the middle of the negative electrode during the cycle charge and discharge, the probability of lithium precipitation is effectively reduced.

[0018] In second aspect, the present application provides a method for preparing a negative electrode sheet, the method comprising: providing a first current collector; forming a first active material layer on at least one surface of the first current collector, and controlling the average weight of active material per unit area in a first coating area of ​​the first active material layer to be greater than the average weight of active material per unit area in a second coating area of ​​the first active material layer, wherein the first active material layer comprises a first coating area and second coating areas respectively arranged on opposite sides of the first coating area along a preset direction.

[0019] In the above-mentioned method for preparing the negative electrode sheet, a first active material layer is arranged on the first current collector, and a first coating area and second coating areas located on both sides of the first coating area are respectively arranged on the first active material layer. Since the average weight of active materials per unit area in the first coating area located in the middle is greater than the average weight of active materials per unit area in the second coating areas on both sides, the capacity for ion embedding in the first coating area is greater than that in the second coating areas on both sides, which makes up for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet in the later stage of the cycle, effectively reduces the probability of lithium deposition in the middle of the negative electrode sheet, and improves the service life of the battery cell.

[0020] In some embodiments, the step of forming a first active material layer on at least one surface of the first current collector includes: on the surface of the first current collector, an active material coating operation is performed at preset intervals along a preset direction, and the coating parameter in each coating operation is larger as it is closer to the center line of the first active material layer, wherein the coating parameter includes at least one of the coating time and the flow rate of the active material, and the center line of the first active material layer is located in the first coating area. In this way, the coating parameter in each coating operation is designed to be larger as it is closer to the center line of the first active material layer, so that the weight of the active material shows an increasing trend from the edge to the middle of the negative electrode sheet, compensating for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet, reducing the probability of lithium precipitation, and effectively extending the service life of the battery cell.

[0021] In some embodiments, the preset spacing is 5 mm to 100 mm. In this way, the preset spacing is designed to be between 5 mm and 100 mm, which is convenient for controlling the weight of the coated active material at intervals to achieve different weights of the active material at different positions.

[0022] In a third aspect, the present application provides an electrode assembly, the electrode assembly comprising a positive electrode sheet, a separator and any one of the negative electrode sheets above, wherein the positive electrode sheet and the negative electrode sheet are separated by a separator.

[0023] In some embodiments, at least one surface of the positive electrode sheet along its thickness direction includes a second active material layer; wherein the second active material layer includes a third coating area opposite to the first coating area and a fourth coating area opposite to the second coating area, and the average weight of the active material per unit area in the third coating area is less than the average weight of the active material per unit area in each fourth coating area. Such a design is conducive to increasing the CB value of the middle part of the electrode assembly, facilitating the full embedding of metal ions in the middle part of the electrode assembly, and reducing the risk of lithium precipitation.

[0024] In some embodiments, the average weight of active material per unit area in the third coating area is recorded as CW3, and the average weight of active material per unit area in each fourth coating area is recorded as CW4, wherein 0.5≤CW3 / CW4<1. With such a design, the ratio between the average weight of active material per unit area in the third coating area and the average weight of active material per unit area in the fourth coating area is controlled between 0.5 and 1, so that the metal ions in the third coating area are relatively reduced, the probability of lithium deposition in the middle is reduced, and the service life of the battery cell is extended.

[0025] In some embodiments, CW3 / CW4 also satisfies the condition: 0.7≤CW3 / CW4<1. With such a design, the ratio between the average weight of active materials per unit area in the third coating area and the average weight of active materials per unit area in the fourth coating area is further controlled between 0.7 and 1. On the premise of compensating for the difference in the degree of embedding in the later stage of the cycle, the difference between active materials in different coating areas is controlled as much as possible, so that the performance of the battery cell is more stable.

[0026] In some embodiments, in at least one fourth coating area, the weight per unit area of ​​the active material decreases from the side of the fourth coating area away from the third coating area to the side of the fourth coating area close to the second coating area. In this way, the weight per unit area of ​​the active material in the fourth coating area is reduced as it approaches the third coating area, so that the weight of the active material decreases from the edge to the middle of the positive electrode sheet, reducing the probability of lithium deposition in the middle of the electrode assembly and effectively extending the service life of the battery cell.

[0027] In some embodiments, in at least one second coating area, the thickness of the active material gradually decreases from the side of the fourth coating area away from the third coating area to the side of the fourth coating area close to the third coating area. In this way, the thickness of the active material in the fourth coating area is reduced as it approaches the third coating area, so that the weight of the active material shows a decreasing trend from the edge to the middle of the positive electrode sheet, reducing the aggregation of metal ions in the middle, reducing the probability of lithium precipitation, and effectively extending the service life of the battery cell.

[0028] In some embodiments, the third coating area includes a second line intersecting with a preset direction, and the weight per unit area of ​​the active material decreases from at least one side of the third coating area close to the fourth coating area to the second line. In this way, in the third coating area, the weight per unit area of ​​the active material decreases as it approaches the second line, reducing the aggregation of metal ions in the middle, thereby effectively compensating for the insufficient embedding degree at the second line, thereby effectively reducing the probability of lithium precipitation.

[0029] In some embodiments, the dimension of the third coating area along the preset direction is recorded as W2, where 5 mm ≤ W2 ≤ 100 mm. In this way, the thickness of the active material in the third coating area is designed to be smaller as it is closer to the second line, thereby reducing the central aggregation of metal ions, reducing the probability of lithium precipitation in the middle of the positive electrode sheet, and effectively extending the service life of the battery cell.

[0030] In a fourth aspect, the present application provides a battery cell, wherein the battery cell comprises any one of the electrode assemblies described above.

[0031] In a fifth aspect, the present application provides a battery device, which includes the above battery cells.

[0032] In a sixth aspect, the present application provides an electrical device, which includes the above battery cell or the above battery device. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the structure of a vehicle provided for some embodiments of the present application.

[0034] Figure 2 An exploded view of a battery device provided in accordance with some embodiments of the present application.

[0035] Figure 3 A schematic diagram of the exploded structure of a battery cell provided in some embodiments of the present application.

[0036] Figure 4 A one-view diagram of the structure of the negative electrode sheet provided in some embodiments of the present application.

[0037] Figure 5 Structural cross-section of the negative electrode sheet provided in some embodiments of the present application Figure 1 .

[0038] Figure 6 Structural cross-section of the negative electrode sheet provided in some embodiments of the present application Figure 2 .

[0039] Figure 7 Another perspective view of the structure of the negative electrode sheet provided in some embodiments of the present application.

[0040] Figure 8 A schematic diagram of the manufacturing process of the negative electrode sheet provided in some embodiments of the present application.

[0041] Fig. 9 A schematic diagram of preset interval coating on a negative electrode sheet provided in some embodiments of the present application.

[0042] Fig.10 A partial structural cross-sectional view of an electrode assembly provided in some embodiments of the present application.

[0043] Fig.11Structural cross-section of the positive electrode sheet provided in some embodiments of the present application Figure 1 .

[0044] Fig.12 Structural cross-section of the positive electrode sheet provided in some embodiments of the present application Figure 2 .

[0045] 1000, vehicle; 100, battery device; 200, controller; 300, motor; 10, battery cell; 20, housing; 201, first part; 202, second part; 1, electrode assembly; 11, negative electrode sheet; 111, first current collector; 11a, main body; 11b, pole ear; 112, first active material layer; 11c, first coating area; 11d, first line; 11e, second coating area; 12, positive electrode sheet; 121, second current collector; 122, second active material layer; 12a, third coating area; 12b, second line; 12c, fourth coating area; X, preset direction; 13, diaphragm; 2, end cap; 21, electrode terminal; 3, housing; 31, opening. DETAILED DESCRIPTION

[0046] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0047] In the description of the present application, it should be understood that if the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or position relationship indicated by these terms is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0048] In addition, if the terms "first" or "second" appear, these terms are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, if the term "plurality" appears, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0049] In this application, unless otherwise clearly specified and limited, if the terms "installed", "connected", "connected", "fixed" and the like appear, these terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0050] In the present application, unless otherwise clearly specified and limited, if there is a description that a first feature is "above" or "below" a second feature, etc., or similar descriptions appear, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "above" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0051] It should be noted that if an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. If an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. If any, the terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in this application are for illustrative purposes only and do not represent the only implementation method.

[0052] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0053] The electrode assembly is the part where the electrochemical reaction occurs in the battery cell, and it mainly includes the negative electrode sheet and the positive electrode sheet. During the charge and discharge process, the negative electrode active material of the negative electrode sheet and the positive electrode active material of the positive electrode sheet react with the electrolyte to achieve energy storage or energy supply. However, during the cyclic charge and discharge process of the battery cell, lithium deposition is prone to occur in the middle of the negative electrode sheet, which reduces the service life of the battery cell.

[0054] Based on this, in order to solve the problem that traditional battery cells are prone to lithium deposition in the middle of the negative electrode sheet during the charge and discharge process, the present application provides a negative electrode sheet, wherein a first coating area and second coating areas on both sides of the first coating area are respectively arranged on the first active material layer, and the average weight of active material per unit area in the first coating area in the middle is greater than the average weight of active material per unit area in the second coating areas on both sides, so that the capacity for ion embedding in the first coating area is larger than that in the second coating areas on both sides, thereby compensating for the difference in the degree of embedding of metal ions in different positions of the negative electrode sheet in the late stage of the cycle, effectively reducing the probability of lithium deposition in the middle of the negative electrode sheet, and improving the service life of the battery cell.

[0055] The battery cells disclosed in the embodiments of the present application can be used, but not limited to, in electrical devices such as vehicles, ships or aircraft. A power supply system comprising the battery cells and battery devices disclosed in the present application can be used to form the electrical device.

[0056] The embodiment of the present application provides an electric device using a battery device as a power source, and the electric device may be, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, for example, a game console, an electric car toy, an electric ship toy, an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, a spacecraft, etc.

[0057] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0058] Please refer to Figure 1 , Figure 1A schematic diagram of the structure of a vehicle 1000 provided for some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery device 100 is provided inside the vehicle 1000, and the battery device 100 may be provided at the bottom, head or tail of the vehicle 1000. The battery device 100 may be used to power the vehicle 1000, for example, the battery device 100 may be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, and the controller 200 is used to control the battery device 100 to power the motor 300, for example, for starting, navigating and driving the vehicle 1000.

[0059] In some embodiments of the present application, the battery device 100 can not only serve as an operating power source for the vehicle 1000, but also serve as a driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0060] Please refer to Figure 2 , Figure 2 An exploded view of a battery device 100 provided in some embodiments of the present application. The battery device 100 includes a box body 20 and a battery cell 10, and the battery cell 10 is contained in the box body 20. Among them, the box body 20 is used to provide a storage space for the battery cell 10, and the box body 20 can adopt a variety of structures. In some embodiments, the box body 20 may include a first part 201 and a second part 202, and the first part 201 and the second part 202 cover each other, and the first part 201 and the second part 202 jointly define a storage space for accommodating the battery cell 10. The second part 202 may be a hollow structure with one end open, and the first part 201 may be a plate-like structure, and the first part 201 covers the open side of the second part 202, so that the first part 201 and the second part 202 jointly define a storage space; the first part 201 and the second part 202 may also be hollow structures with one side open, and the open side of the first part 201 covers the open side of the second part 202. Of course, the box body 20 formed by the first part 201 and the second part 202 can be in various shapes, such as a cylinder, a cuboid, etc.

[0061] In the battery device 100, there may be multiple battery cells 10, and the multiple battery cells 10 may be connected in series, in parallel, or in a mixed connection. A mixed connection means that the multiple battery cells 10 are both connected in series and in parallel. The multiple battery cells 10 may be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 10 is accommodated in the box 20; of course, the battery device 100 may also be a battery device 100 module in which multiple battery cells 10 are first connected in series, in parallel, or in a mixed connection, and then the multiple battery device 100 modules are connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 20. The battery device 100 may also include other structures, for example, the battery device 100 may also include a busbar component for realizing electrical connection between the multiple battery cells 10.

[0062] Each battery cell 10 may be a secondary battery or a primary battery, or a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 10 may be cylindrical, flat, rectangular, or in other shapes.

[0063] Please refer to Figure 3 , Figure 3 The schematic diagram of the exploded structure of the battery cell 10 provided in some embodiments of the present application. The battery cell 10 refers to the smallest unit constituting the battery device 100. Figure 3 The battery cell 10 includes an end cover 2, a shell 3, an electrode assembly 1 and other functional components.

[0064] The end cap 2 refers to a component that covers the opening 31 of the shell 3 to isolate the internal environment of the battery cell 10 from the external environment. Without limitation, the shape of the end cap 2 can be adapted to the shape of the shell 3 to match the shell 3. Optionally, the end cap 2 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the end cap 2 is not easily deformed when squeezed and collided, so that the battery cell 10 can have a higher structural strength and the safety performance can also be improved. Functional components such as electrode terminals 21 can be provided on the end cap 2. The electrode terminal 21 can be used to electrically connect to the electrode assembly 1 for outputting or inputting electrical energy of the battery cell 10. In some embodiments, the end cap 2 can also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 10 reaches a threshold. The material of the end cap 2 can also be a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not impose special restrictions on this. In some embodiments, an insulating member may be provided inside the end cap 2, and the insulating member may be used to isolate the electrical connection components in the housing 3 from the end cap 2 to reduce the risk of short circuit. For example, the insulating member may be plastic, rubber, or the like.

[0065] The shell 3 is a component used to cooperate with the end cap 2 to form the internal environment of the battery cell 10, wherein the formed internal environment can be used to accommodate the electrode assembly 1, the electrolyte and other components. The shell 3 and the end cap 2 can be independent components, and an opening 31 can be set on the shell 3, and the internal environment of the battery cell 10 is formed by covering the opening 31 with the end cap 2 at the opening 31. Without limitation, the end cap 2 and the shell 3 can also be integrated. Specifically, the end cap 2 and the shell 3 can form a common connection surface before other components are put into the shell, and when the interior of the shell 3 needs to be encapsulated, the end cap 2 is covered with the shell 3. The shell 3 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 3 can be determined according to the specific shape and size of the electrode assembly 1. The material of the shell 3 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0066] The electrode assembly 1 is a component in the battery cell 10 where an electrochemical reaction occurs. One or more electrode assemblies 1 may be contained in the housing 3. The electrode assembly 1 is mainly formed by winding or stacking a positive electrode sheet 12 and a negative electrode sheet 11, and a separator 13 is usually provided between the positive electrode sheet 12 and the negative electrode sheet 11. The parts of the positive electrode sheet 12 and the negative electrode sheet 11 with active materials constitute the main body of the electrode assembly 1, and the parts of the positive electrode sheet 12 and the negative electrode sheet 11 without active materials each constitute a tab 11b. The positive tab 11b and the negative tab 11b may be located together at one end of the main body or at both ends of the main body respectively. During the charge and discharge process of the battery device 100, the positive active material and the negative active material react with the electrolyte, and the tab 11b is connected to the electrode terminal 21 to form a current loop.

[0067] According to some embodiments of this application, please refer to Figure 4 The present application provides a negative electrode sheet 11, wherein at least one surface of the negative electrode sheet 11 along its thickness direction includes a first active material layer 112; wherein the first active material layer 112 includes a first coating area 11c and second coating areas 11e respectively arranged on opposite sides of the first coating area 11c along a preset direction X, and the average weight of the active material per unit area in the first coating area 11c is greater than the average weight of the active material per unit area in each second coating area 11e.

[0068] The first active material layer 112 refers to the active material located on the surface of the negative electrode sheet 11. The active material may be made of a variety of materials. As a non-limiting example, the first active material layer 112 may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, etc. The silicon-based material may include one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds, and silicon alloys.

[0069] The first active material layer 112 may be located on one surface of the negative electrode sheet 11, or may be disposed on two opposite sides of the negative electrode sheet 11. In some specific examples, the negative electrode sheet 11 further includes a first current collector 111, and the first active material layer 112 is disposed on at least one surface of the first current collector 111.

[0070] It is understandable that in the first active material layer 112, the second coating area 11e is provided on both sides of the first coating area 11c, which means that the first coating area 11c is closer to the middle of the first active material layer 112 than the second coating area 11e. During the charge and discharge cycle of the battery cell 10, some metal ions will converge toward the middle of the negative electrode sheet 11, causing the metal ions to easily precipitate lithium in the middle of the negative electrode sheet 11. To this end, the present embodiment increases the average weight of active material per unit area in the first coating area 11c, increases the capacity for ion embedding in the first coating area 11c, and reduces the probability of lithium precipitation in the middle of the negative electrode sheet 11.

[0071] Among them, the average weight of active material per unit area can be understood as the average surface density of the active material. In order to achieve that the average surface density of the first coating area 11c is greater than the average surface density of the second coating area 11e, there are many ways, such as: when the thickness of the active material in the first coating area 11c and the second coating area 11e is the same, the compaction degree in the first coating area 11c is greater than the compaction degree in the second coating area 11e; or, when the compaction degree of the active material in the first coating area 11c and the second coating area 11e is the same, the thickness of the active material in the first coating area 11c is greater than the thickness of the active material in the second coating area 11e.

[0072] In addition, the active material in the first coating area 11c may be consistent or inconsistent along the preset direction X, for example, the thickness or compaction degree of the active material in the first coating area 11c first increases and then decreases along the preset direction X. Similarly, the active material in the second coating area 11e may be consistent or inconsistent along the preset direction X, for example, the thickness or compaction degree of the active material in the second coating area 11e gradually decreases or increases along the preset direction X.

[0073] It should also be noted that the ratio of the size of the first coating area 11c and the second coating area 11e along the preset direction X can be determined according to the size of the negative electrode sheet 11. At the same time, in some embodiments, the midline of the first active material layer 112 along the preset direction X is located in the first coating area 11c; and the end of the second coating area 11e away from the first coating area 11c can be located at one end of the first active material layer 112 along the preset direction X. In addition, the preset direction X can be the length direction of the negative electrode sheet 11 or the width direction. If the electrode assembly 1 is a winding structure, the preset direction X can be set as the width direction of the negative electrode sheet 11, so that when winding along the length direction, the first coating area 11c and the second coating area 11e can be distributed in sequence along the height direction of the electrode assembly 1, which is convenient for effectively improving the lithium deposition problem in the middle of the electrode assembly 1. In addition, the width direction of the negative electrode sheet 11 can be understood as: at least one end of the negative electrode sheet 11 along its own width direction includes a pole ear 11b.

[0074] Such a design makes the capacity for ion embedding in the first coating area 11c greater than that in the second coating areas 11e on both sides, compensating for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet 11 in the later stage of the cycle, effectively reducing the probability of lithium deposition in the middle of the negative electrode sheet 11, and improving the service life of the battery cell 10.

[0075] According to some embodiments of the present application, optionally, please refer to Figure 5 The average weight of active material per unit area in the first coating area 11c is recorded as CW1, and the average weight of active material per unit area in each second coating area 11e is recorded as CW2, wherein 1<CW1 / CW2≤2.

[0076] The ratio between the average weight of active material per unit area in the first coating area 11c and the average weight of active material per unit area in the second coating area 11e can be between 1 and 2, for example, but not limited to, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc.

[0077] In addition, in some examples, the ratio of the weight of the active material on the midline of the first coating area 11 c along the preset direction X to the weight of the active material at one end of the second coating area 11 e away from the first coating area 11 c may be 1-2.

[0078] With such a design, the ratio between the average weight of active material per unit area in the first coating area 11c and the average weight of active material per unit area in the second coating area 11e is controlled between 1 and 2, thereby increasing the capacity for ion embedding in the first coating area 11c, reducing the probability of lithium deposition in the middle of the negative electrode sheet 11, and extending the service life of the battery cell 10.

[0079] According to some embodiments of the present application, optionally, CW1 / CW2 further satisfies the condition: 1<CW1 / CW2≤1.5.

[0080] The ratio between the average weight of active material per unit area in the first coating area 11c and the average weight of active material per unit area in the second coating area 11e can be further taken between 1 and 1.5, for example, but not limited to, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc.

[0081] In addition, in some examples, the ratio of the weight of the active material on the midline of the first coating area 11 c along the preset direction X to the weight of the active material at one end of the second coating area 11 e away from the first coating area 11 c may be 1-1.5.

[0082] With such a design, the ratio between the average weight of active material per unit area in the first coating area 11c and the average weight of active material per unit area in the second coating area 11e is further controlled between 1 and 1.5. On the premise of being able to compensate for the difference in embedding degree in the later stage of the cycle, the difference between active materials in different coating areas is controlled as much as possible, so that the performance of the battery cell 10 is more stable.

[0083] According to some embodiments of the present application, optionally, please refer to Figure 5 and Figure 6 In at least one second coating area 11e, the weight per unit area of ​​the active substance tends to increase from the side of the second coating area 11e far from the first coating area 11c to the side of the second coating area 11e close to the first coating area 11c.

[0084] It should be noted that the average weight of active substances per unit area in the second coating area 11e refers to the ratio of the weight of all active substances in the second coating area 11e to the area of ​​the second coating area 11e, and the weight per unit area in the second coating area 11e refers to the weight of active substances corresponding to each unit area in the second coating area 11e along the preset direction X. The average weight of active substances per unit area in the second coating area 11e can be regarded as the average weight of active substances per unit area in the second coating area 11e.

[0085] The closer the weight per unit area in the second coating area 11e is to the first coating area 11c, the greater its value. Taking the same compaction degree as an example, the closer the thickness of the active material in the second coating area 11e is to the first coating area 11c, the greater its value; taking the same thickness as an example, the closer the compaction degree of the active material in the second coating area 11e is to the first coating area 11c, the greater its value.

[0086] In addition, the weight of the active material on one end of the second coating area 11e close to the first coating area 11c is equal to the weight of the active material on one end of the first coating area 11c close to the second coating area 11e, so that the weight of the active material at the junction between the first coating area 11c and the second coating area 11e is smoothly transitioned.

[0087] It can be known that the increasing trend means that the unit area weight of the active substance in the second coating area 11e can increase linearly along the preset direction X, or increase in a curve, such as a normal distribution; of course, it can also increase in a step-by-step manner, for example: gradually increase first, then remain unchanged, and then gradually increase.

[0088] Such a design can effectively make up for the difference in the embedding degree of metal ions between the middle and the edge of the negative electrode sheet 11 , reduce the probability of lithium plating, and extend the service life of the battery cell 10 .

[0089] According to some embodiments of the present application, optionally, please refer to Figure 5 and Figure 6 In at least one second coating region 11e, the thickness of the active material gradually increases from a side of the second coating region 11e far from the first coating region 11c to a side of the second coating region 11e close to the first coating region 11c.

[0090] It can be seen that in the second coating area 11e, the thickness of the active material gradually increases along the preset direction X and toward one side of the first coating area 11c, so that the weight of the active material per unit area closer to the first coating area 11c is greater, which can effectively make up for the difference in the embedding degree of the middle part of the negative electrode sheet 11 and improve the lithium precipitation problem. In some examples, in the two second coating areas 11e, the thickness of the active material gradually increases from the side of the second coating area 11e away from the first coating area 11c to the side of the second coating area 11e close to the first coating area 11c.

[0091] In this way, the thickness of the active material in the second coating area 11e is designed to be larger as it is closer to the first coating area 11c, so that the weight of the active material increases from the edge to the middle of the negative electrode sheet 11, compensating for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet 11, reducing the probability of lithium plating, and effectively extending the service life of the battery cell 10.

[0092] According to some embodiments of the present application, optionally, please refer to Figure 5 The first coating area 11c includes a first line 11d intersecting the preset direction X, and the unit area weight of the active material increases from at least one side of the first coating area 11c close to the second coating area 11e to the first line 11d.

[0093] The first line 11d may be located on the midline of the first coating area 11c along the preset direction X, or may be located on one side of the midline of the first coating area 11c along the preset direction X. In the first coating area 11c, the weight per unit area of ​​the active material increases from at least one side of the first coating area 11c close to the second coating area 11e to the first line 11d, indicating that the weight of the active material on the first line 11d is relatively large, which can more effectively compensate for the insufficient embedding degree at the first line 11d, thereby effectively reducing the probability of lithium precipitation.

[0094] For some examples, see Figure 5 , the weight per unit area of ​​the active material increases from any side of the first coating area 11c close to the second coating area 11e to the first line 11d, and the first line 11d is located on the midline of the first active material layer 112 along the preset direction X. The increasing trend means that the weight per unit area of ​​the active material in the second coating area 11e can increase in a straight line or in a curve along the preset direction X; of course, it can also increase in a step-by-step manner, such as: gradually increasing first, then unchanged, and then gradually increasing.

[0095] It is understandable that the first line 11d of the present embodiment is located in the first coating area 11c, so the first line 11d not only intersects with the preset direction X, but is also perpendicular to the thickness direction of the negative electrode sheet 11. In some examples, the first line 11d, the preset direction X, and the thickness direction of the negative electrode sheet 11 are perpendicular to each other.

[0096] With such a design, in the first coating area 11 c , the weight per unit area of ​​the active material increases as it is closer to the first line 11 d , thereby effectively compensating for the insufficient embedding degree at the first line 11 d , thereby effectively reducing the probability of lithium deposition.

[0097] According to some embodiments of the present application, optionally, please refer to Figure 5 , the thickness of the active material gradually increases from at least one side of the first coating area 11c close to the second coating area 11e to the first line 11d.

[0098] It can be seen that in the first coating area 11c, the thickness of the active material gradually increases along the preset direction X and toward one side of the first line 11d, so that the closer to the middle of the first coating area 11c, the greater the weight of the active material per unit area, which can effectively make up for the difference in the embedding degree of the middle part of the negative electrode sheet 11 and improve the lithium precipitation problem. In some examples, the thickness of the active material gradually increases from any side of the first coating area 11c close to the second coating area 11e to the first line 11d.

[0099] In this way, the thickness of the active material in the first coating area 11c is designed to be larger as it is closer to the first line 11d, thereby compensating for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet 11, reducing the probability of lithium deposition in the middle of the negative electrode sheet 11, and effectively extending the service life of the battery cell 10.

[0100] According to some embodiments of the present application, optionally, please refer to Figure 5 , the first line 11d overlaps with the center line of the first active material layer 112 along the preset direction X.

[0101] It can be seen that the first coating area 11 c is located in the middle of the negative electrode sheet 11 , and at this time, the second coating areas 11 e on both sides can be symmetrically distributed with respect to the first coating area 11 c .

[0102] With such a design, the first coating area 11 c is disposed in the middle of the negative electrode sheet 11 , so as to increase the ion embedding capacity of the middle of the negative electrode sheet 11 , reduce the probability of lithium deposition in the middle, and increase the service life of the battery cell 10 .

[0103] According to some embodiments of the present application, optionally, a dimension of the first coating area 11 c along a preset direction X is recorded as W1, wherein 5 mm≤W1≤100 mm.

[0104] The size of the first coating area 11c along the preset direction X may be between 5 mm and 100 mm, for example, but not limited to, 5 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, etc.

[0105] With such a design, the size of the first coating area 11 c along the preset direction X is controlled between 5 mm and 100 mm, so as to accurately increase the embedding capacity of the effective area on the negative electrode sheet 11 and effectively improve the lithium deposition problem in the middle of the negative electrode sheet 11 .

[0106] According to some embodiments of the present application, optionally, the active material of the first active material layer 112 includes at least one of a carbon material and a silicon material.

[0107] It can be known that the carbon material may be but not limited to artificial graphite, natural graphite, soft carbon, hard carbon, etc. The silicon material may be but not limited to elemental silicon, silicon oxide, silicon nitrogen compound, silicon alloy, etc. Of course, the carbon material and the silicon material may be compounded, such as silicon carbon compound, etc.

[0108] Such a design can effectively improve the lithium deposition problem of the battery cell 10 containing carbon or silicon, and increase the service life of the battery cell 10.

[0109] According to some embodiments of the present application, optionally, please refer to Figure 5The negative electrode sheet 11 further includes a first current collector 111 , and the first active material layer 112 is disposed on at least one surface of the first current collector 111 .

[0110] The first current collector 111 is a structure that not only provides support for the active material, but also collects the current generated by the active material for external output. It can be a metal structure, such as copper metal foil, etc.; it can also be a composite current collector. The first active material layer 112 can be disposed on one surface of the first current collector 111, or on two opposite surfaces of the first current collector 111.

[0111] Such a design and the introduction of the first current collector 111 facilitate the formation of different active material weights at different positions of the first current collector 111, thereby compensating for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet 11 and reducing the probability of lithium plating.

[0112] According to some embodiments of the present application, optionally, please refer to Figure 7 The first current collector 111 includes a main body 11 a and a tab 11 b disposed at at least one end of the main body 11 a along a preset direction X, and the first active material layer 112 is disposed on at least one surface of the main body 11 a .

[0113] The main body 11a refers to a structure in which an active material is coated in the first current collector 111, and the tab 11b refers to a structure in which an active material is not coated in the first current collector 111. When the first current collector 111 is a metal current collector, the material of the tab 11b is also only a metal material. When the first current collector 111 is a composite current collector, the tab 11b includes an insulating support layer and a conductive layer disposed on the insulating support layer. At the same time, there are various structural forms of the tab 11b on the first current collector 111, for example: the tab 11b on the first current collector 111 can be a full tab 11b, that is, a whole edge of the first current collector 111 along a preset direction X; or, the tab 11b on the first current collector 111 is a plurality of spaced-apart protrusion structures.

[0114] In this embodiment, the preset direction X is designed as the distribution direction between the main body 11a and the tab 11b, so that in the winding process, winding can be performed in a direction perpendicular to the preset direction X, so that in the formed electrode assembly 1, the first coating area 11c and the second coating area 11e are distributed in sequence along the height direction of the electrode assembly 1, so as to effectively reduce the probability of lithium deposition in the middle of the negative electrode sheet 11.

[0115] In this design, the first current collector 111 is designed to be a main body 11a and a pole ear 11b, which facilitates the transmission of electric energy between the negative electrode sheet 11 and the outside; at the same time, the preset direction X is designed as the distribution direction between the main body 11a and the pole ear 11b, so that the first coating area 11c and the second coating area 11e in the wound electrode assembly 1 are distributed sequentially along the height direction of the electrode assembly 1, effectively reducing the probability of lithium deposition in the middle of the negative electrode sheet 11.

[0116] According to some embodiments of the present application, optionally, the average weight of active material per unit area in the first coating area 11c is 0.1 g / 1540.25 mm 2 ~0.25g / 1540.25mm 2 .

[0117] The average weight of active material per unit area in the first coating area 11c can be 0.1 g / 1540.25 mm 2 ~0.25g / 1540.25mm 2 For example, it can be but not limited to 0.1g / 1540.25mm 2 , 0.12g / 1540.25mm 2 , 0.14g / 1540.25mm 2 , 0.15g / 1540.25mm 2 , 0.2g / 1540.25mm 2 , 0.22g / 1540.25mm 2 , 0.25g / 1540.25mm 2 wait.

[0118] In this way, the average weight of active material per unit area in the first coating area 11c is controlled at 0.1 g / 1540.25 mm 2 ~0.25g / 1540.25mm 2 In order to meet the effective embedding of metal ions in the middle of the negative electrode sheet 11 during the cycle charge and discharge, the probability of lithium precipitation is effectively reduced.

[0119] According to some embodiments of this application, please refer to Figure 8 The present application provides a method for preparing a negative electrode sheet 11, the method comprising:

[0120] S100, providing a first current collector 111;

[0121] S200, forming a first active material layer 112 on at least one surface of the first current collector 111, and controlling the average weight of active material per unit area in the first coating area 11c of the first active material layer 112 to be greater than the average weight of active material per unit area in the second coating area 11e of the first active material layer 112, wherein the first active material layer 112 includes a first coating area 11c and second coating areas 11e respectively arranged on opposite sides of the first coating area 11c along a preset direction X.

[0122] The first current collector 111 refers to a structure that not only provides support for the active material but also collects the current generated by the active material for external output. It can be a metal structure, such as copper metal foil, etc.; it can also be a composite current collector.

[0123] In step S200, there are many ways to form the first active material layer 112 on the first current collector 111, such as coating the active material on the first current collector 111 through a coating mold, etc. In order to achieve that the average surface density of the first coating area 11c is greater than the average surface density of the second coating area 11e, there are many ways, such as: when the thickness of the active material in the first coating area 11c and the second coating area 11e is the same, the compaction degree in the first coating area 11c is greater than the compaction degree in the second coating area 11e; or, when the compaction degree of the active material in the first coating area 11c and the second coating area 11e is the same, the thickness of the active material in the first coating area 11c is greater than the thickness of the active material in the second coating area 11e.

[0124] With this design, the capacity for ion embedding in the first coating area 11c is greater than that in the second coating areas 11e on both sides, compensating for the difference in the degree of metal ion embedding at different positions of the negative electrode sheet 11 in the later stage of the cycle, effectively reducing the probability of lithium deposition in the middle of the negative electrode sheet 11 and increasing the service life of the battery cell 10.

[0125] According to some embodiments of the present application, optionally, S200, the step of forming a first active material layer 112 on at least one surface of the first current collector 111, includes: on the surface of the first current collector 111, an active material coating operation is performed at a preset interval along a preset direction X, and a coating parameter in each coating operation is larger the closer to the center line of the first active material layer 112, wherein the coating parameter includes at least one of the coating time and the flow rate of the active material, and the center line of the first active material layer 112 is located in the first coating area 11c.

[0126] It can be seen that during the coating process, the coating device, such as a coating die head, is aligned with one end of the first current collector 111 along the preset direction X, and the active material is coated. After the coating is completed, the coating die head is controlled to move the preset spacing, and the coating of the active material is continued, and the operation is cyclical. Among them, the closer the coating device is to the center line of the first active material layer 112, the larger its coating parameters are controlled to be, for example: the closer to the center line of the first active material layer 112, the longer the coating time of each coating operation; or, the greater the flow rate of the active material in each coating operation, etc. At the same time, the preset spacing refers to the control point of the coating device on the first current collector 111, and its specific value can be determined according to the coating width of the coating device, for example: the preset spacing is equal to the coating width of the coating device, or slightly smaller than the coating width, etc.

[0127] For easier understanding of preset spacing, please refer to Fig. 9 , the preset spacing can be Fig. 9 The spacing expressed by D in the figure means that during the coating process, after the coating operation is completed at the first coating point, the coating device can be moved to the next coating point for coating operation, and the spacing between two adjacent coating points is the preset spacing.

[0128] Of course, in some other embodiments, the coating device can be controlled to move at a constant speed above the first current collector 111, and the flow rate of the active substance can be controlled to increase to the center line of the first active substance layer 112 as the first current collector 111 moves, and then the flow rate of the active substance is controlled to gradually decrease.

[0129] In this way, the coating parameters in each coating operation are designed to be larger as they are closer to the center line of the first active material layer 112, so that the weight of the active material increases from the edge to the middle of the negative electrode sheet 11, compensating for the difference in the degree of embedding of metal ions at different positions of the negative electrode sheet 11, reducing the probability of lithium plating, and effectively extending the service life of the battery cell 10.

[0130] According to some embodiments of the present application, the preset spacing is 5 mm to 100 mm.

[0131] The preset spacing may be between 5 mm and 100 mm, for example, but not limited to, 5 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, etc.

[0132] In this design, the preset spacing is designed to be between 5 mm and 100 mm, which is convenient for controlling the weight of the coated active material at intervals to achieve different weights of the active material at different positions.

[0133] According to some embodiments of this application, please refer to Fig.10The present application provides an electrode assembly 1, which includes a positive electrode sheet 12, a separator 13 and a negative electrode sheet 11 of any one of the above, and a separator 13 is provided between the positive electrode sheet 12 and the negative electrode sheet 11.

[0134] The electrode assembly 1 may be a laminated structure or a wound structure. When the electrode assembly 1 is a wound structure, it may be, but is not limited to, a columnar structure or a square flat structure.

[0135] The separator 13 is a porous plastic film that ensures that lithium ions can pass freely to form a circuit, and at the same time prevents the two electrodes from contacting each other and plays an electronic insulation role. The type can be selected from but not limited to polyethylene monolayer film, polypropylene monolayer film, etc.

[0136] In addition, the weight of the active material on the positive electrode sheet 12 can be kept consistent, or the weight of the active material can be designed differently according to different positions. For example, the weight of the active material in the middle of the positive electrode sheet 12 is lower than the weight of the active material on both sides.

[0137] Such a design and the use of the above negative electrode sheet 11 can make up for the difference in the degree of metal ion embedding at different positions of the negative electrode sheet 11 in the later stage of the cycle, effectively reduce the probability of lithium deposition in the middle of the negative electrode sheet 11, and increase the service life of the battery cell 10.

[0138] According to some embodiments of the present application, optionally, please refer to Fig.11 At least one surface of the positive electrode sheet 12 along its thickness direction includes a second active material layer 122; wherein the second active material layer 122 includes a third coating area 12a opposite to the first coating area 11c, and a fourth coating area 12c opposite to the second coating area 11e, and the average weight of active material per unit area in the third coating area 12a is less than the average weight of active material per unit area in each fourth coating area 12c.

[0139] The second active material layer 122 refers to the active material located on the surface of the positive electrode sheet 12. The materials of the active material may be various. As a non-limiting example, the first active material layer 112 may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other active materials that can be used as the positive electrode sheet 12 may also be used. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0140] The second active material layer 122 may be located on one surface of the positive electrode sheet 12, or may be disposed on opposite sides of the positive electrode sheet 12. Specifically, in some examples, the positive electrode sheet 12 further includes a second current collector 121, and the second active material layer 122 is disposed on at least one surface of the second current collector 121. The second current collector 121 may be made of a variety of materials, for example, the material of the second current collector 121 may be, but is not limited to, aluminum metal, a composite material, and the like.

[0141] It can be understood that the third coating area 12a is opposite to the first coating area 11c, and the fourth coating area 12c is opposite to the second coating area 11e, indicating that the active material in the third coating area 12a and the active material in the first coating area 11c are arranged facing each other, and the active material in the fourth coating area 12c and the active material in the second coating area 11e are arranged facing each other. At this time, the ratio of the unit area capacity of the active material in the first coating area 11c to the unit area capacity of the active material in the third coating area 12a is recorded as CB1, and the ratio of the unit area capacity of the active material in the second coating area 11e to the unit area capacity of the active material in the fourth coating area 12c is recorded as CB2, CB1 is greater than CB2, that is, the CB value in the middle of the electrode assembly 1 is greater than the CB on both sides, which is conducive to the full embedding of metal ions, such as lithium ions, in the middle of the electrode assembly 1, reducing the risk of lithium precipitation.

[0142] There are many ways to achieve that the average surface density of the third coating area 12a is lower than the average surface density of the fourth coating area 12c, such as: when the thickness of the active material in the third coating area 12a is the same as that in the fourth coating area 12c, the compaction degree in the third coating area 12a is lower than that in the fourth coating area 12c; or, when the compaction degree of the active material in the third coating area 12a is the same as that in the fourth coating area 12c, the thickness of the active material in the third coating area 12a is lower than that in the fourth coating area 12c.

[0143] In addition, the active material in the third coating area 12a may be consistent or inconsistent along the preset direction X, for example, the thickness or compaction degree of the active material in the third coating area 12a first decreases and then increases along the preset direction X. Similarly, the active material in the fourth coating area 12c may be consistent or inconsistent along the preset direction X, for example, the thickness or compaction degree of the active material in the fourth coating area 12c gradually decreases or increases along the preset direction X.

[0144] It should also be noted that the ratio of the size of the third coating area 12a and the fourth coating area 12c along the preset direction X can be determined according to the size of the positive electrode sheet 12. At the same time, in some embodiments, the midline of the second active material layer 122 along the preset direction X is located in the third coating area 12a; and the end of the fourth coating area 12c away from the third coating area 12a can be located at one end of the second active material layer 122 along the preset direction X. In addition, if the electrode assembly 1 is a winding structure, the preset direction X can be set as the width direction of the positive electrode sheet 12, so that when winding along the length direction, the third coating area 12a and the fourth coating area 12c can be distributed in sequence along the height direction of the electrode assembly 1, so as to effectively improve the lithium deposition problem in the middle of the electrode assembly 1. In addition, the width direction of the positive electrode sheet 12 can be understood as: at least one end of the positive electrode sheet 12 along its own width direction includes a pole ear 11b.

[0145] Such a design is conducive to increasing the CB value in the middle of the electrode assembly 1, which is conducive to fully embedding metal ions in the middle of the electrode assembly 1 and reducing the risk of lithium plating.

[0146] According to some embodiments of the present application, optionally, the average weight of active material per unit area in the third coating zone 12a is recorded as CW3, and the average weight of active material per unit area in each fourth coating zone 12c is recorded as CW4, wherein 0.5≤CW3 / CW4<1.

[0147] The ratio between the average weight of active material per unit area in the third coating zone 12a and the average weight of active material per unit area in the fourth coating zone 12c may be between 0.5 and 1, for example, but not limited to 0.5, 0.6, 0.7, 0.8, 0.9, etc.

[0148] With such a design, the ratio between the average weight of active material per unit area in the third coating zone 12a and the average weight of active material per unit area in the fourth coating zone 12c is controlled between 0.5 and 1, so that the metal ions in the third coating zone 12a are relatively reduced, the probability of lithium deposition in the middle is reduced, and the service life of the battery cell 10 is extended.

[0149] According to some embodiments of the present application, optionally, CW3 / CW4 further satisfies the condition: 0.7≤CW3 / CW4<1.

[0150] The ratio between the average weight of active material per unit area in the third coating zone 12a and the average weight of active material per unit area in the fourth coating zone 12c can be further taken between 0.7 and 1, for example, but not limited to 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, etc.

[0151] With such a design, the ratio between the average weight of active material per unit area in the third coating zone 12a and the average weight of active material per unit area in the fourth coating zone 12c is further controlled between 0.7 and 1. On the premise of being able to compensate for the difference in the degree of embedding in the later stage of the cycle, the difference between the active materials in different coating zones is controlled as much as possible, so that the performance of the battery cell 10 is more stable.

[0152] According to some embodiments of the present application, optionally, please refer to Fig.11 and Fig.12 In at least one fourth coating area 12c, the weight per unit area of ​​the active material decreases from the side of the fourth coating area 12c away from the third coating area 12a to the side of the fourth coating area 12c close to the second coating area 11e.

[0153] It can be understood that the average weight of active substances per unit area in the fourth coating area 12c refers to the ratio of the weight of all active substances in the fourth coating area 12c to the area of ​​the fourth coating area 12c, and the weight per unit area in the fourth coating area 12c refers to the weight of active substances corresponding to each unit area in the fourth coating area 12c along the preset direction X. Among them, the average weight of active substances per unit area in the fourth coating area 12c can be regarded as the average weight of active substances per unit area in the fourth coating area 12c.

[0154] The closer the weight per unit area in the fourth coating area 12c is to the third coating area 12a, the smaller its value is. Taking the same compaction degree as an example, the closer the thickness of the active material in the fourth coating area 12c is to the third coating area 12a, the smaller it is; taking the same thickness as an example, the closer the compaction degree of the active material in the fourth coating area 12c is to the third coating area 12a, the smaller it is.

[0155] In addition, the weight of the active material on the end of the fourth coating area 12c close to the third coating area 12a is equal to the weight of the active material on the end of the third coating area 12a close to the fourth coating area 12c, so that the weight of the active material at the junction between the third coating area 12a and the fourth coating area 12c is smoothly transitioned.

[0156] It can be known that the decreasing trend means that the unit area weight of the active material in the fourth coating area 12c can decrease linearly along the preset direction X, or can decrease in a curve; of course, it can also decrease in a step-by-step manner, for example: first gradually decrease, then remain unchanged, and then gradually decrease.

[0157] In this way, the unit area weight of the active material in the fourth coating area 12c is reduced as it approaches the third coating area 12a, so that the weight of the active material shows a decreasing trend from the edge to the middle of the positive electrode sheet 12, thereby reducing the probability of lithium deposition in the middle of the electrode assembly 1 and effectively extending the service life of the battery cell 10.

[0158] According to some embodiments of the present application, optionally, please refer to Fig.11 and Fig.12 In at least one second coating region 11e, the thickness of the active material gradually decreases from a side of the fourth coating region 12c away from the third coating region 12a to a side of the fourth coating region 12c close to the third coating region 12a.

[0159] It can be seen that in the fourth coating area 12c, the thickness of the active material gradually decreases along the preset direction X and toward one side of the third coating area 12a, so that the weight of the active material per unit area closer to the third coating area 12a is reduced, which can effectively reduce the concentration of metal ions in the positive electrode sheet 12 and improve the lithium precipitation problem. In some examples, in the two fourth coating areas 12c, the thickness of the active material gradually decreases from the side of the fourth coating area 12c away from the third coating area 12a to the side of the fourth coating area 12c close to the third coating area 12a.

[0160] In this way, the thickness of the active material in the fourth coating area 12c is reduced as it approaches the third coating area 12a, so that the weight of the active material decreases from the edge to the middle of the positive electrode sheet 12, reducing the aggregation of metal ions in the middle, reducing the probability of lithium precipitation, and effectively extending the service life of the battery cell 10.

[0161] According to some embodiments of the present application, optionally, please refer to Fig.11 and Fig.12 The third coating area 12a includes a second line 12b intersecting the preset direction X, and the unit area weight of the active material decreases from at least one side of the third coating area 12a close to the fourth coating area 12c to the second line 12b.

[0162] The second line 12b may be located on the middle line of the third coating area 12a along the preset direction X, or may be located on one side of the middle line of the third coating area 12a along the preset direction X. In the third coating area 12a, the weight per unit area of ​​the active material decreases from at least one side of the third coating area 12a close to the fourth coating area 12c to the second line 12b, indicating that the weight of the active material on the second line 12b is relatively small, which can more effectively reduce the aggregation of metal ions in the middle, thereby effectively reducing the probability of lithium precipitation.

[0163] In some examples, the weight per unit area of ​​the active material decreases from any side of the third coating area 12a close to the fourth coating area 12c to the second line 12b, and the second line 12b is located on the midline of the first active material layer 112 along the preset direction X. The decreasing trend means that the weight per unit area of ​​the active material in the fourth coating area 12c may decrease in a straight line or in a curve along the preset direction X; of course, it may also decrease in a step-by-step manner, such as first gradually decreasing, then remaining unchanged, and then gradually decreasing.

[0164] It is understandable that the second line 12b of the present embodiment is located in the third coating area 12a, so the second line 12b, in addition to intersecting with the preset direction X, is also perpendicular to the thickness direction of the positive electrode sheet 12. In some examples, the second line 12b, the preset direction X, and the thickness direction of the positive electrode sheet 12 are perpendicular to each other.

[0165] With such a design, in the third coating area 12a, the weight per unit area of ​​the active material is reduced as it is closer to the second line 12b, thereby reducing the aggregation of metal ions in the middle, thereby effectively compensating for the insufficient embedding degree at the second line 12b, and effectively reducing the probability of lithium precipitation.

[0166] According to some embodiments of the present application, optionally, please refer to Fig.11 and Fig.12 , the thickness of the active material gradually decreases from at least one side of the third coating area 12a close to the fourth coating area 12c to the second line 12b.

[0167] It can be seen that in the third coating area 12a, the thickness of the active material gradually decreases along the preset direction X and toward one side of the second line 12b, so that the closer to the middle of the third coating area 12a, the greater the weight of the active material per unit area, reducing the central convergence of metal ions and improving the lithium precipitation problem. In some examples, the thickness of the active material gradually decreases from any side of the third coating area 12a close to the fourth coating area 12c to the second line 12b.

[0168] In this way, the thickness of the active material in the third coating area 12 a is designed to be smaller as it is closer to the second line 12 b , thereby reducing the central aggregation of metal ions, reducing the probability of lithium deposition in the central part of the positive electrode sheet 12 , and effectively extending the service life of the battery cell 10 .

[0169] According to some embodiments of the present application, optionally, please refer to Fig.11 , the second line 12b overlaps with the center line of the second active material layer 122 along the preset direction X.

[0170] It can be seen that the third coating area 12a is located in the middle of the positive electrode sheet 12. At this time, the fourth coating areas 12c on both sides can be symmetrically distributed with respect to the third coating area 12a.

[0171] With such a design, the third coating area 12 a is disposed in the middle of the positive electrode sheet 12 , so as to reduce the central aggregation of metal ions, reduce the probability of lithium deposition in the middle, and increase the service life of the battery cell 10 .

[0172] According to some embodiments of the present application, optionally, please refer to Fig.11 The dimension of the third coating area 12a along the preset direction X is recorded as W2, wherein 5mm≤W2≤100mm.

[0173] The size of the third coating area 12a along the preset direction X may be between 5 mm and 100 mm, for example, but not limited to, 5 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, etc.

[0174] With such a design, the size of the third coating area 12a along the preset direction X is controlled between 5 mm and 100 mm, so as to accurately reduce the metal ion concentration in the effective area of ​​the positive electrode sheet 12 and improve the lithium deposition problem in the middle.

[0175] According to some embodiments of the present application, the present application provides a battery cell 10 , and the battery cell 10 includes any one of the above electrode assemblies 1 .

[0176] According to some embodiments of the present application, the present application provides a battery device 100 , and the battery device 100 includes the above battery cell 10 .

[0177] According to some embodiments of the present application, the present application provides an electrical device, which includes the above battery cell 10 or the above battery device 100 .

[0178] According to some embodiments of this application, please refer to Figures 4 to 12The present application provides an electrode assembly 1, which includes a negative electrode sheet 11, a positive electrode sheet 12, and a separator 13 disposed between the negative electrode sheet 11 and the positive electrode sheet 12. At least one surface of the negative electrode sheet 11 along its thickness direction includes a first active material layer 112, and the first active material layer 112 includes a first coating area 11c and second coating areas 11e located on opposite sides of the first coating area 11c. There are multiple second coating areas 11e, and the average weight of active materials per unit area in the first coating area 11c is greater than the average weight of active materials per unit area in each second coating area 11e. On any side of the first coating area 11c along a preset direction X, all the second coating areas 11e are distributed in sequence along the preset direction X, and the closer the second coating area 11e is to the first coating area 11c, the greater the average weight of active materials per unit area.

[0179] At least one surface of the positive electrode sheet 12 along the thickness direction thereof includes a second active material layer 122, and the second active material layer 122 includes a third coating area 12a and fourth coating areas 12c located on opposite sides of the third coating area 12a. There are multiple fourth coating areas 12c, and the average weight of active materials per unit area in the third coating area 12a is less than the average weight of active materials per unit area in each fourth coating area 12c. On either side of the third coating area 12a along the preset direction X, all fourth coating areas 12c are sequentially distributed along the preset direction X, and the closer the fourth coating area 12c is to the third coating area 12a, the smaller the average weight of active materials per unit area.

[0180] In order to make the purpose, technical solutions and advantages of the present application more concise and clear, the present application is described with the following specific embodiments, but the present application is by no means limited to these embodiments. The embodiments described below are only preferred embodiments of the present application and can be used to describe the present application, and cannot be understood as limiting the scope of the present application. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

[0181] In order to better illustrate the present application, the present application is further described below in conjunction with the embodiments. The following are specific embodiments.

[0182] Comparative Example 1

[0183] Preparation of negative electrode sheet 11

[0184] 1) Using graphite as the negative electrode active material, styrene-butadiene rubber as the binder, carbon black as the conductive agent, sodium carboxymethyl cellulose as the dispersant, and distilled water as the solvent, the above raw materials are stirred and mixed in a ratio of graphite:styrene-butadiene rubber:carbon black:sodium carboxymethyl cellulose=97:1.5:1:0.5 to form a negative electrode slurry with a solid content of 50%;

[0185] 2) Use extrusion coating equipment for coating. The equipment can adjust the slurry flow rate of each nozzle position (25cm interval) to make the flow rate of each nozzle position consistent, and continuously coat the negative electrode slurry on the surface of the 6μm negative electrode collector (copper foil) to form a membrane coating. The control equipment makes the average weight per unit area of ​​the solid substance be 0.150g / 1540.25mm 2 , and the thickness of the negative electrode slurry is 125 μm;

[0186] 3) The negative electrode current collector coated with the negative electrode film coating is dried, rolled, die-cut and slit to prepare a negative electrode sheet.

[0187] Preparation of positive electrode sheet 12

[0188] 1) The positive electrode active material is lithium iron phosphate LFP, the binder is polyvinylidene fluoride PVDF, the conductive agent is carbon black, and the solvent is N-methylpyrrolidone (NMP). The above materials are mixed in a mass ratio of LFP:PVDF:C=97.5:2:0.5, and the solid content of the positive electrode slurry is 0.65;

[0189] 2) Use extrusion coating equipment to continuously coat the positive electrode slurry on the surface of the 15μm positive electrode current collector (aluminum foil) to form a membrane coating with a width of 200mm. Control the equipment so that the average weight per unit area of ​​the solid substance is 0.240g / 1540.25mm 2 , and the thickness of the positive electrode slurry is 160μm;

[0190] 3) The positive electrode current collector coated with the membrane coating is dried, rolled, die-cut and slit to prepare the positive electrode sheet.

[0191] Assembling battery cells 10

[0192] The positive electrode sheet, negative electrode sheet and separator prepared in the above process are wound into an electrode assembly in the manner of negative electrode-separator-positive electrode-separator; the wound battery cell is assembled and welded with the top cover shell after hot pressing to complete the battery cell assembly. Finally, the battery cell is injected, formed, vented, sealed and other processes to complete the battery production.

[0193] Example 1

[0194] The negative electrode slurry is non-uniformly coated on both surfaces of the copper foil, the thickness of the first active material layer 112 gradually increases from the two edges to the middle of the negative electrode sheet 11 in the width direction, the thickness of the active material in the middle of the first active material layer 112 is 167 μm, the thickness of the active material at the edge of the first active material layer 112 is 83 μm, and the average weight of the active material per unit area in the middle of the first active material layer 112 is 0.2 g / 1540.25 mm 2The average weight of active material per unit area at the edge of the first active material layer 112 is 0.10 g / 1540.25 mm 2 .

[0195] Example 2

[0196] The negative electrode slurry is non-uniformly coated on both surfaces of the copper foil, the thickness of the first active material layer 112 gradually increases from the two edges to the middle of the negative electrode sheet 11 in the width direction, the thickness of the active material in the middle of the first active material layer 112 is 150 μm, the thickness of the active material at the edge of the first active material layer 112 is 100 μm, and the average weight of the active material per unit area in the middle of the first active material layer 112 is 0.18 g / 1540.25 mm 2 The average weight of active material per unit area at the edge of the first active material layer 112 is 0.12 g / 1540.25 mm 2 .

[0197] Example 3

[0198] The negative electrode slurry is non-uniformly coated on both surfaces of the copper foil, the thickness of the first active material layer 112 gradually increases from the two edges to the middle of the negative electrode sheet 11 in the width direction, the thickness of the active material in the middle of the first active material layer 112 is 137 μm, the thickness of the active material at the edge of the first active material layer 112 is 113 μm, and the average weight of the active material per unit area in the middle of the first active material layer 112 is 0.16 g / 1540.25 mm 2 The average weight of active material per unit area at the edge of the first active material layer 112 is 0.14 g / 1540.25 mm 2 .

[0199] The battery cells 10 prepared in Comparative Example 1 and Examples 1 to 3 were subjected to cycle charge and discharge tests respectively.

[0200] Cyclic charge and discharge test

[0201] The battery cells prepared in each embodiment and comparative example are set to multiple parallel samples, and the battery cells are hung for testing cycles, with a setting ratio of 0.5C, a temperature of 60 degrees Celsius, and a charge and discharge voltage range of [2.5V, 3.65V], and the change of SOH with the number of cycles is recorded. For each 1% SOH, the battery cell is disassembled (it must be in 100% SOC state), and the negative electrode sheet is visually inspected to see if there is obvious abnormal lithium insertion color (such as black, gray, etc.), and the corresponding cycle number of the battery cell when the color abnormality begins to occur is recorded. Please refer to Table 1 for the above test data.

[0202] Table 1

[0203]

[0204] It should be noted that the thickness in Table 1 is in μm and the unit weight is in g / 1540.25 mm 2 .

[0205] From the comparison between comparative example 1 and examples 1 to 3, it can be seen that in examples 1 to 3, the active material on the negative electrode sheet shows a linear change, and the sum of the unit weights of the active materials in the middle area and the edge area of ​​the negative electrode sheet is 0.3g / 1540.25mm 2 The average unit weight of the negative electrode sheets in Examples 1 to 3 is 0.15 g / 1540.25 mm 2 , which is consistent with the average unit weight on the negative electrode sheet in Comparative Example 1, so that the CB values ​​in Examples 1 to 3 are equal to the CB value of Comparative Example 1. Under the premise of the same CB value, the number of cycles in Examples 1 to 3 is greater than that in Comparative Example 1, and when the ratio of the unit weight of the active material in the middle region of the negative electrode sheet to the unit weight of the active material in the edge region is 1.2, the number of cycles is 204 more than that in Comparative Example 1. Therefore, making the average unit area weight of the active material in the middle part of the negative electrode sheet 11 greater than the average unit area weight of the active material on both sides is beneficial to reducing the probability of lithium precipitation and extending the service life of the battery cell 10, wherein the CB value is the ratio of the unit area capacity of the active material in the negative electrode sheet to the unit area capacity of the active material in the positive electrode sheet.

[0206] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0207] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A negative electrode sheet, characterized in that: At least one surface of the negative electrode sheet along its thickness direction comprises a first active material layer (112); The first active material layer (112) comprises a first coating area (11c) and second coating areas (11e) respectively arranged on two opposite sides of the first coating area (11c) along a preset direction (X), and the average weight of active material per unit area in the first coating area (11c) is greater than the average weight of active material per unit area in each of the second coating areas (11e).

2. The negative electrode sheet according to claim 1, characterized in that: The average weight of active material per unit area in the first coating area (11c) is recorded as CW1, and the average weight of active material per unit area in each of the second coating areas (11e) is recorded as CW2, wherein 1<CW1 / CW2≤2.

3. The negative electrode sheet according to claim 2, characterized in that: CW1 / CW2 also satisfies the condition: 1<CW1 / CW2≤1.

5.

4. The negative electrode sheet according to claim 1, characterized in that: In at least one of the second coating areas (11e), the weight per unit area of ​​the active substance tends to increase from a side of the second coating area (11e) away from the first coating area (11c) to a side of the second coating area (11e) close to the first coating area (11c).

5. The negative electrode sheet according to claim 4, characterized in that: In at least one of the second coating regions (11e), the thickness of the active material gradually increases from a side of the second coating region (11e) away from the first coating region (11c) to a side of the second coating region (11e) close to the first coating region (11c).

6. The negative electrode sheet according to claim 1, characterized in that: The first coating area (11c) includes a first line (11d) intersecting the preset direction (X), and the weight per unit area of ​​the active substance tends to increase from at least one side of the first coating area (11c) close to the second coating area (11e) to the first line (11d).

7. The negative electrode sheet according to claim 6, characterized in that: The thickness of the active material gradually increases from at least one side of the first coating area (11c) close to the second coating area (11e) to the first line (11d).

8. The negative electrode sheet according to claim 6, characterized in that: The first line (11d) overlaps with a center line of the first active material layer (112) along the preset direction (X).

9. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The dimension of the first coating area (11c) along the preset direction (X) is recorded as W1, wherein 5mm≤W1≤100mm.

10. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The active material of the first active material layer (112) includes at least one of a carbon material and a silicon material.

11. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The negative electrode sheet further comprises a first current collector (111), and the first active material layer (112) is disposed on at least one surface of the first current collector (111).

12. The negative electrode sheet according to claim 11, characterized in that: The first current collector (111) comprises a main body (11a) and a tab (11b) disposed at at least one end of the main body (11a) along the preset direction (X), and the first active material layer (112) is disposed on at least one surface of the main body (11a).

13. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The average weight of active material per unit area in the first coating area (11c) is 0.1 g / 1540.25 mm 2 ~0.25g / 1540.25mm 2 .

14. A method for preparing a negative electrode sheet, characterized in that: The method comprises: Providing a first current collector (111); A first active material layer (112) is formed on at least one surface of the first current collector (111), and the average weight of active material per unit area in a first coating area (11c) of the first active material layer (112) is controlled to be greater than the average weight of active material per unit area in a second coating area (11e) of the first active material layer (112), wherein the first active material layer (112) comprises a first coating area (11c) and second coating areas (11e) respectively arranged on opposite sides of the first coating area (11c) along a preset direction (X).

15. The method for preparing a negative electrode sheet according to claim 14, characterized in that: The step of forming a first active material layer (112) on at least one surface of the first current collector (111) comprises: On the surface of the first current collector (111), an active material coating operation is performed at preset intervals along the preset direction (X), and the coating parameters in each coating operation are larger as they are closer to the center line of the first active material layer (112), wherein the coating parameters include at least one of the coating time and the flow rate of the active material, and the center line of the first active material layer (112) is located in the first coating area (11c).

16. The method for preparing a negative electrode sheet according to claim 15, characterized in that: The preset spacing is 5mm~100mm.

17. An electrode assembly, characterized in that: The electrode assembly comprises a positive electrode sheet (12), a separator (13), and a negative electrode sheet according to any one of claims 1 to 13, wherein the separator (13) is arranged between the positive electrode sheet (12) and the negative electrode sheet.

18. The electrode assembly according to claim 17, characterized in that At least one surface of the positive electrode sheet (12) along its thickness direction comprises a second active material layer (122); The second active material layer (122) includes a third coating area (12a) opposite to the first coating area (11c) and a fourth coating area (12c) opposite to the second coating area (11e), and the average weight of active material per unit area in the third coating area (12a) is less than the average weight of active material per unit area in each of the fourth coating areas (12c).

19. The electrode assembly according to claim 18, characterized in that The average weight of active material per unit area in the third coating area (12a) is recorded as CW3, and the average weight of active material per unit area in each of the fourth coating areas (12c) is recorded as CW4, wherein 0.5≤CW3 / CW4<1.

20. The electrode assembly according to claim 19, characterized in that CW3 / CW4 also satisfies the condition: 0.7≤CW3 / CW4<1.

21. The electrode assembly according to claim 18, characterized in that In at least one of the fourth coating areas (12c), the weight per unit area of ​​the active substance tends to decrease from a side of the fourth coating area (12c) away from the third coating area (12a) to a side of the fourth coating area (12c) close to the second coating area (11e).

22. The electrode assembly according to claim 21, characterized in that In at least one of the second coating areas (11e), the thickness of the active material gradually decreases from a side of the fourth coating area (12c) away from the third coating area (12a) to a side of the fourth coating area (12c) close to the third coating area (12a).

23. The electrode assembly according to claim 18, characterized in that The third coating area (12a) includes a second line (12b) intersecting the preset direction (X), and the weight per unit area of ​​the active substance tends to decrease from at least one side of the third coating area (12a) close to the fourth coating area (12c) to the second line (12b).

24. The electrode assembly according to any one of claims 18 to 23, characterized in that: The dimension of the third coating area (12a) along the preset direction (X) is recorded as W2, wherein 5mm≤W2≤100mm.

25. A battery cell, characterized in that: The battery cell comprises the electrode assembly according to any one of claims 17-24.

26. A battery device, characterized in that: The battery device comprises the battery cell according to claim 25 .

27. An electrical equipment, characterized in that: The electrical equipment comprises the battery cell according to claim 25 or the battery device according to claim 26.

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