Negative electrode sheet, preparation method thereof, electrode assembly, battery cell, battery device and electrical equipment

Abstract

The present application relates to a negative electrode sheet, a preparation method thereof, an electrode assembly, a battery cell, a battery device and an electrical device. 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, and the average weight of the active material per unit area in the middle first coating area is greater than the average weight of the active material per unit area in the second coating areas on both sides, so that the ability of the first coating area to allow ion insertion is greater than that of the second coating areas on both sides, compensating for the difference in the degree of metal ion insertion at different positions of the negative electrode sheet in the later stage of cycling, effectively reducing the probability of lithium plating in the middle of the negative electrode sheet, and improving the service life of the battery cell.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode sheet and a preparation method thereof, an electrode assembly, a battery cell, a battery device and an electrical equipment. Background Art

[0002] As a component in a battery cell where an electrochemical reaction occurs, the electrode sheet is divided into a negative electrode sheet and a positive electrode sheet. During charge and discharge, the negative active material of the negative electrode sheet and the positive active material of the positive electrode sheet react with the electrolyte respectively to achieve energy storage or energy supply. However, limited by the structural design of the traditional negative electrode sheet, lithium precipitation is likely to occur in the middle of the negative electrode sheet during charge and discharge, reducing 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 an electrical equipment, which can reduce the probability of lithium precipitation and improve the service life of the battery cell.

[0004] In a first aspect, the present application provides a negative electrode sheet, at least one surface of the negative electrode sheet along its 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] For the above negative electrode sheet, 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, and the average weight of the active material per unit area in the middle first coating area is greater than the average weight of the active material per unit area in the second coating areas on both sides, so that the ability of the first coating area to allow ion insertion is larger than that of the second coating areas on both sides, making up for the difference in the degree of metal ion insertion at different positions of the negative electrode sheet in the later stage of cycling, effectively reducing the probability of lithium precipitation in the middle of the negative electrode sheet, and improving the service life of the battery cell.

[0006] In some embodiments, the average weight of the active material per unit area in the first coating area is denoted as CW1, and the average weight of the active material per unit area in each second coating area is denoted as CW2, wherein, 1 < CW1 / CW2 ≤ 2. With such a design, the ratio between the average weight of the active material per unit area in the first coating area and the average weight of the active material per unit area in the second coating area is controlled between 1 and 2, increasing the ability of the first coating area to allow ion insertion, reducing the probability of lithium precipitation in the middle of the negative electrode sheet, and extending the service life of the battery cell.

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

[0008] In some embodiments, in at least one second coating area, the weight per unit area of the active material shows an increasing trend from the side of the second coating area far from the first coating area to the side of the second coating area close to the first coating area. With such a design, it is convenient to effectively make up for the difference in the degree of insertion of metal ions between the middle and the edge of the negative electrode sheet, reduce the probability of lithium plating, and extend 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 far from the first coating area to the side of the second coating area close to the first coating area. With such a design, the thickness of the active material in the second coating area is designed to be larger closer to the first coating area, so that the weight of the active material shows an increasing trend from the edge to the middle of the negative electrode sheet, making up for the difference in the degree of insertion of metal ions at different positions on 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 the preset direction, and the weight per unit area of the active material shows an increasing trend from at least one side of the first coating area close to the second coating area to the first line. With such a design, in the first coating area, the weight per unit area of the active material is designed to be larger closer to the first line, effectively making up for the insufficient degree of insertion at the first line, thereby effectively reducing the probability of lithium plating.

[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. With such a design, the thickness of the active material in the first coating area is designed to be larger closer to the first line, making up for the difference in the degree of insertion of metal ions at different positions on the negative electrode sheet, reducing the probability of lithium plating 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 midline of the first active material layer along the preset direction. With such a design, the first coating area is arranged in the middle of the negative electrode sheet, which is convenient for increasing the ability of the middle of the negative electrode sheet to allow ions to be inserted, reducing the probability of lithium plating in the middle, and improving the service life of the battery cell.

[0013] In some embodiments, the size of the first coating region in the preset direction is denoted as W1, where 5 mm ≤ W1 ≤ 100 mm. With such a design, controlling the size of the first coating region in the preset direction between 5 mm and 100 mm facilitates accurately increasing the embedding ability of the effective region on the negative electrode sheet, and effectively improves the problem of lithium deposition 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. With such a design, it is convenient to effectively improve the problem of lithium deposition in the battery monomer of the carbon-containing or silicon-containing system, and improve the service life of the battery monomer.

[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, introducing the first current collector facilitates forming different active material weights at different positions on the first current collector, making up for the difference in the embedding degree of metal ions at different positions on the negative electrode sheet, and reducing the probability of lithium deposition.

[0016] In some embodiments, the first current collector includes a body portion and a tab disposed at at least one end of the body portion in the preset direction, and the first active material layer is disposed on at least one surface of the body portion. With such a design, designing the first current collector as the body portion and the tab facilitates the power transmission between the negative electrode sheet and the outside; at the same time, designing the preset direction as the distribution direction between the body portion and the tab enables the first coating region and the second coating region in the wound electrode assembly to be sequentially distributed 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 the active material per unit area in the first coating region is 0.1 g / 1540.25 mm 2 ~0.25 g / 1540.25 mm 2 。With such a design, controlling the average weight of the active material per unit area in the first coating region between 0.1 g / 1540.25 mm 2 ~0.25 g / 1540.25 mm 2 can meet the effective embedding of metal ions in the middle of the negative electrode sheet during cyclic charge and discharge, and effectively reduce the probability of lithium deposition.

[0018] In a second aspect, the present application provides a method for preparing a negative electrode sheet, the method including: 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 the active material per unit area in the first coating region of the first active material layer to be greater than the average weight of the active material per unit area in the second coating region of the first active material layer, where the first active material layer includes a first coating region and second coating regions respectively disposed on opposite sides of the first coating region in the preset direction.

[0019] The above method for preparing a negative electrode sheet includes providing a first active material layer on a first current collector, and providing a first coating area and second coating areas on both sides of the first coating area on the first active material layer. Since the average weight of the active material per unit area in the middle first coating area is greater than that in the second coating areas on both sides, the ability of the first coating area to allow ion insertion is greater than that of the second coating areas on both sides, compensating for the difference in the degree of metal ion insertion at different positions on the negative electrode sheet in the later stage of cycling, effectively reducing the probability of lithium plating occurring in the middle of the negative electrode sheet, and extending the service life of the battery cell.

[0020] In some embodiments, the step of forming the first active material layer on at least one surface of the first current collector includes: performing an active material coating operation on the surface of the first current collector at preset intervals along a preset direction, and the coating parameters in each coating operation are larger the closer they are to the center line of the first active material layer, where 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 is located in the first coating area. Designed in this way, with the coating parameters in each coating operation being larger the closer they are to the center line of the first active material layer, 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 metal ion insertion at different positions on the negative electrode sheet, reducing the probability of lithium plating, and effectively extending the service life of the battery cell.

[0021] In some embodiments, the preset interval is 5 mm to 100 mm. Designed in this way, with the preset interval designed to be between 5 mm and 100 mm, it is convenient to control 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, which includes a positive electrode sheet, a separator, and the negative electrode sheet of any one of the above, with a separator disposed between the positive electrode sheet and the negative electrode sheet.

[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 fourth coating areas opposite to the second coating areas, and the average weight of the active material per unit area in the third coating area is less than that in each of the fourth coating areas. Designed in this way, it is beneficial to increase the CB value in the middle of the electrode assembly, facilitate the full insertion of metal ions in the middle of the electrode assembly, and reduce the risk of lithium plating.

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

[0025] In some embodiments, the condition that CW3 / CW4 further satisfies is: 0.7 ≤ CW3 / CW4 < 1. With such a design, the ratio between the average weight of the active material per unit area in the third coating region and the average weight of the active material per unit area in the fourth coating region is further controlled between 0.7 and 1. On the premise of being able to make up for the difference in the embedding degree in the later stage of the cycle, the difference between the active materials in different coating regions 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 region, the weight per unit area of the active material shows a decreasing trend from the side of the fourth coating region far from the third coating region to the side of the fourth coating region close to the second coating region. With such a design, the weight per unit area of the active material in the fourth coating region is designed to decrease closer to the third coating region, so that the weight of the active material shows a decreasing trend from the edge to the middle of the positive electrode plate, the probability of lithium deposition in the middle of the electrode assembly is decreased, and the service life of the battery cell is effectively prolonged.

[0027] In some embodiments, in at least one second coating region, the thickness of the active material gradually decreases from the side of the fourth coating region far from the third coating region to the side of the fourth coating region close to the third coating region. With such a design, the thickness of the active material in the fourth coating region is designed to decrease closer to the third coating region, so that the weight of the active material shows a decreasing trend from the edge to the middle of the positive electrode plate, the aggregation of metal ions in the middle is reduced, the probability of lithium deposition is decreased, and the service life of the battery cell is effectively prolonged.

[0028] In some embodiments, the third coating region includes a second line intersecting with a preset direction, and the weight per unit area of the active material shows a decreasing trend from at least one side of the third coating region close to the fourth coating region to the second line. With such a design, in the third coating region, the weight per unit area of the active material is designed to be smaller closer to the second line, the aggregation of metal ions in the middle is reduced, so as to effectively make up for the insufficient embedding degree at the second line, and thus effectively decrease the probability of lithium deposition.

[0029] In some embodiments, the size of the third coating area along a preset direction is denoted as W2, where 5 mm ≤ W2 ≤ 100 mm. With such a design, the thickness of the active material in the third coating area is designed to be smaller closer to the second line, reducing the central convergence of metal ions and the probability of lithium deposition in the middle of the positive electrode sheet, effectively extending the service life of the battery cell.

[0030] Fourthly, the present application provides a battery cell, which includes the electrode assembly of any one of the above.

[0031] Fifthly, the present application provides a battery device, which includes the battery cell above.

[0032] Sixthly, the present application provides an electrical equipment, which includes the battery cell above or the battery device above. Description of the Drawings

[0033] Figure 1 It is a schematic structural diagram of a vehicle provided by some embodiments of the present application.

[0034] Figure 2 It is an exploded view of a battery device provided by some embodiments of the present application.

[0035] Figure 3 It is a schematic exploded structural diagram of a battery cell provided by some embodiments of the present application.

[0036] Figure 4 It is a perspective view of the structure of a negative electrode sheet provided by some embodiments of the present application.

[0037] Figure 5 It is a sectional view of the structure of a negative electrode sheet provided by some embodiments of the present application Figure 1 .

[0038] Figure 6 It is a sectional view of the structure of a negative electrode sheet provided by some embodiments of the present application Figure 2 .

[0039] Figure 7 It is another perspective view of the structure of a negative electrode sheet provided by some embodiments of the present application.

[0040] Figure 8 It is a schematic diagram of the manufacturing process of a negative electrode sheet provided by some embodiments of the present application.

[0041] Figure 9 It is a schematic diagram of preset interval coating on a negative electrode sheet provided by some embodiments of the present application.

[0042] Figure 10 It is a partial structural sectional view of an electrode assembly provided by some embodiments of the present application.

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

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

[0045] 1000, vehicle; 100, battery device; 200, controller; 300, motor; 10, battery cell; 20, box; 201, first part; 202, second part; 1, electrode assembly; 11, negative electrode sheet; 111, first current collector; 11a, body part; 11b, tab; 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, separator; 2, end cap; 21, electrode terminal; 3, housing; 31, opening. Detailed implementation manners

[0046] To make the above objects, features, and advantages of the present application more apparent and understandable, the following will describe the detailed implementation manners of the present application with reference to the accompanying drawings. Many specific details are set forth in the following description to facilitate a thorough 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 departing from the connotation of the present application. Therefore, 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 terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or positional relationship indicated by these terms is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present application.

[0048] In addition, if the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. 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 specifically defined.

[0049] In this application, unless otherwise clearly defined and limited, if terms such as "installed", "connected", "joined", "fixed", etc. appear, these terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0050] In this application, unless otherwise clearly defined and limited, if there is a description such as a first feature being "on" or "under" a second feature, its meaning can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature can be that the first feature is directly above or obliquely above the second feature, or simply means that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature can be that the first feature is directly below or obliquely below the second feature, or simply means that the first feature has a lower horizontal height than the second feature.

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

[0052] Currently, from the perspective of the development of the market situation, the application of power batteries is becoming more and more extensive. Power batteries are not only applied to energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely applied to electric transportation means such as electric bicycles, electric motorcycles, electric vehicles, as well as multiple fields such as military equipment and aerospace. With the continuous expansion of the application fields of power batteries, the market demand is also constantly increasing.

[0053] As a component where electrochemical reactions occur within a battery cell, the electrode assembly mainly includes a negative electrode sheet and a positive electrode sheet. During the charge and discharge processes, the negative active material of the negative electrode sheet and the positive active material of the positive electrode sheet react with the electrolyte respectively 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, reducing the service life of the battery cell.

[0054] Based on this, in view of the problem that lithium deposition easily occurs in the middle of the negative electrode sheet during the charge and discharge process of traditional battery cells, the present application provides a negative electrode sheet. A first coating area and second coating areas located on both sides of the first coating area are respectively provided on the first active material layer, and the average weight of the active material per unit area in the middle first coating area is greater than that in the second coating areas on both sides. This makes the ability of the first coating area to allow ion intercalation larger than that of the second coating areas on both sides, compensates for the difference in the degree of metal ion intercalation 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.

[0055] The battery cell disclosed in the embodiments of the present application can be but is not limited to being used in power-consuming devices such as vehicles, ships, or aircraft. A power supply system of the power-consuming device can be composed of the battery cell, battery device, etc. disclosed in the present application.

[0056] The embodiments of the present application provide a power-consuming device using a battery device as a power source. The power-consuming device can be but is not limited to mobile phones, tablets, laptop computers, electric toys, electric tools, battery cars, electric vehicles, ships, spacecraft, etc. Among them, the electric toys can include fixed or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys, and electric aircraft toys, etc. The spacecraft can include airplanes, rockets, space shuttles, and spaceships, etc.

[0057] For the convenience of description, the following embodiments take a power-consuming device of a vehicle 1000 in an embodiment of the present application as an example for description.

[0058] Please refer to Figure 1 , Figure 1Schematic structural diagram of vehicle 1000 provided by some embodiments of the present application. Vehicle 1000 can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle, an extended-range vehicle, etc. A battery device 100 is disposed inside vehicle 1000. The battery device 100 can be disposed at the bottom, the head, or the tail of vehicle 1000. The battery device 100 can be used to supply power to vehicle 1000. For example, the battery device 100 can serve as the operating power source of vehicle 1000. Vehicle 1000 may further include a controller 200 and a motor 300. The controller 200 is used to control the battery device 100 to supply power to the motor 300. For example, it is used for the working power requirements during the start-up, navigation, and driving of vehicle 1000.

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

[0060] Please refer to Figure 2 , Figure 2 Explosion diagram of the battery device 100 provided by some embodiments of the present application. The battery device 100 includes a box body 20 and battery cells 10. The battery cells 10 are accommodated in the box body 20. Among them, the box body 20 is used to provide an accommodation space for the battery cells 10, and the box body 20 can adopt various structures. In some embodiments, the box body 20 can include a first part 201 and a second part 202. The first part 201 and the second part 202 are covered with each other, and the first part 201 and the second part 202 jointly define an accommodation space for accommodating the battery cells 10. The second part 202 can be a hollow structure with one end open, and the first part 201 can be a plate-like structure. 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 an accommodation space; the first part 201 and the second part 202 can also both 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 of various shapes, such as a cylinder, a cuboid, etc.

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

[0062] Among them, each battery cell 10 can be a secondary battery or a primary battery; it can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 10 can be in the shape of a cylinder, a flat body, a cuboid, or other shapes, etc.

[0063] Please refer to Figure 3 , Figure 3 which is a schematic exploded view of the battery cell 10 provided in some embodiments of the present application. The battery cell 10 refers to the smallest unit that makes up the battery device 100. As Figure 3 shown, the battery cell 10 includes an end cap 2, a housing 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 housing 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 housing 3 to cooperate with the housing 3. Optionally, the end cap 2 can be made of a material with a certain hardness and strength (such as aluminum alloy). In this way, the end cap 2 is not easily deformed when subjected to extrusion and collision, enabling the battery cell 10 to have 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 terminals 21 can be used for electrically connecting with the electrode assembly 1 to output or input the electrical energy of the battery cell 10. In some embodiments, a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 10 reaches a threshold can also be provided on the end cap 2. The material of the end cap 2 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. The embodiments of the present application do not make special restrictions on this. In some embodiments, an insulating member can also be provided on the inner side of the end cap 2. The insulating member can be used to isolate the electrical connection components in the housing 3 from the end cap 2 to reduce the risk of short circuit. Exemplarily, the insulating member can be plastic, rubber, etc.

[0065] The housing 3 is a component for cooperating 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 housing 3 and the end cap 2 can be independent components. An opening 31 can be provided on the housing 3, and the end cap 2 is covered at the opening 31 to form the internal environment of the battery cell 10. Without limitation, the end cap 2 and the housing 3 can also be integrated. Specifically, the end cap 2 and the housing 3 can first form a common connection surface before other components are put into the housing, and when it is necessary to encapsulate the interior of the housing 3, the end cap 2 is then covered on the housing 3. The housing 3 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 3 can be determined according to the specific shape and size of the electrode assembly 1. The material of the housing 3 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not make special restrictions on this.

[0066] The electrode assembly 1 is a component in the battery cell 10 where an electrochemical reaction occurs. The housing 3 can contain one or more electrode assemblies 1. The electrode assembly 1 is mainly formed by winding or laminating 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 respectively constitute the electrode tabs 11b. The positive electrode tab 11b and the negative electrode tab 11b can be located at one end of the main body together 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 electrode tab 11b is connected to the electrode terminal 21 to form an electric current loop.

[0067] In some embodiments of the present application, please refer to Figure 4 , the present application provides a negative electrode sheet 11, 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 provided 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 of the second coating areas 11e.

[0068] The first active material layer 112 refers to the active material located on the surface of the negative electrode sheet 11, and the materials of its active material can be various. As non-limiting examples, the first active material layer 112 can include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, etc. The silicon-based materials can include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0069] The first active material layer 112 can be located on one surface of the negative electrode sheet 11, or can be respectively disposed on opposite sides of the negative electrode sheet 11. Specifically, in some 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 can be understood that in the first active material layer 112, second coating regions 11e are disposed on both opposite sides of the first coating region 11c, indicating that the first coating region 11c is more likely to be distributed closer to the middle part of the first active material layer 112. During the cyclic charge and discharge of the battery cell 10, some metal ions will converge towards the middle part of the negative electrode sheet 11, resulting in the problem that lithium metal deposition is likely to occur in the middle part of the negative electrode sheet 11. Therefore, in this embodiment, the average weight of the active material per unit area in the first coating region 11c is increased, the ability of the first coating region 11c to allow ion intercalation is increased, and the probability of lithium metal deposition in the middle part of the negative electrode sheet 11 is reduced.

[0071] Among them, the average weight of the active material per unit area can be understood as the average areal density of the active material. To make the average areal density of the first coating region 11c greater than that of the second coating region 11e, there are various methods. For example, when the thickness of the active material in the first coating region 11c is the same as that in the second coating region 11e, the compaction degree in the first coating region 11c is greater than that in the second coating region 11e; or, when the compaction degree of the active material in the first coating region 11c is the same as that in the second coating region 11e, the thickness of the active material in the first coating region 11c is greater than the thickness of the active material in the second coating region 11e.

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

[0073] It should also be noted that the ratio of the dimensions of the first coating area 11c and the second coating area 11e along the preset direction X can be determined according to the dimensions 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 within the first coating area 11c; and one end of the second coating area 11e far 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 or the width direction of the negative electrode sheet 11. If the electrode assembly 1 is a wound structure, the preset direction X can be set as the width direction of the negative electrode sheet 11. In this way, when winding along the length direction, the first coating area 11c and the second coating area 11e can be sequentially distributed along the height direction of the electrode assembly 1, which is convenient for effectively improving the problem of lithium deposition 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 tab 11b.

[0074] With such a design, the ability of the first coating area 11c to allow ion intercalation is larger than that of the second coating areas 11e on both sides, compensating for the difference in the degree of metal ion intercalation at different positions of the negative electrode sheet 11 in the later stage of cycling, 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] In some embodiments of the present application, optionally, please refer to Figure 5 , the average weight of the active material per unit area in the first coating area 11c is denoted as CW1, and the average weight of the active material per unit area in each second coating area 11e is denoted as CW2, where 1 < CW1 / CW2 ≤ 2.

[0076] The ratio between the average weight of the active material per unit area in the first coating area 11c and the average weight of the active material per unit area in the second coating area 11e can take values between 1 and 2. For example, it can be, but is 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 11c along the preset direction X to the weight of the active material at one end of the second coating area 11e far from the first coating area 11c can be 1 to 2.

[0078] With such a design, the ratio between the average weight of the active material per unit area in the first coating area 11c and the average weight of the active material per unit area in the second coating area 11e is controlled between 1 and 2, increasing the ability of the first coating area 11c to allow ion intercalation, 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] In some embodiments of the present application, optionally, the condition that CW1 / CW2 further satisfies is: 1 < CW1 / CW2 ≤ 1.5.

[0080] The ratio between the average weight of the active material per unit area in the first coating area 11c and the average weight of the active material per unit area in the second coating area 11e can further take values between 1 and 1.5. For example, it can be, but is 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 center line of the first coating area 11c along the preset direction X to the weight of the active material at the end of the second coating area 11e far from the first coating area 11c can be 1 to 1.5.

[0082] With such a design, the ratio between the average weight of the active material per unit area in the first coating area 11c and the average weight of the 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 make up for the difference in the degree of insertion in the later stage of the cycle, the difference between the 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] In 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 material shows an increasing trend 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 the active material per unit area in the second coating area 11e refers to the ratio of the weight of all the active materials in the second coating area 11e to the area of the second coating area 11e. The weight per unit area in the second coating area 11e refers to the weight of the active material corresponding to each unit area along the preset direction X in the second coating area 11e. Among them, the average weight of the active material per unit area in the second coating area 11e can be regarded as the average value of the weights of the active materials on each 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 thickness of the active material in the second coating area 11e is greater closer to the first coating area 11c; taking the same thickness as an example, the compaction degree of the active material in the second coating area 11e is greater closer to the first coating area 11c.

[0086] In addition, the weight of the active material at one end of the second coating area 11e close to the first coating area 11c is equal to the weight of the active material at 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 transitionally connected.

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

[0088] Such a design facilitates effectively compensating for the difference in the degree of insertion of metal ions between the middle and the edge of the negative electrode sheet 11, reducing the probability of lithium plating, and extending the service life of the battery cell 10.

[0089] In some embodiments of the present application, optionally, please refer to Figure 5 and Figure 6 , within at least one second coating area 11e, the thickness of the active material gradually increases 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.

[0090] It can be known that within the second coating area 11e, the thickness of the active material gradually increases along the preset direction X and towards the 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 compensate for the difference in the degree of insertion in the middle of the negative electrode sheet 11 and improve the lithium plating problem. In some examples, within the two second coating areas 11e, the thickness of the active material gradually increases 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.

[0091] Such a design makes the thickness of the active material in the second coating area 11e larger closer to the first coating area 11c, so that the weight of the active material shows an increasing trend from the edge to the middle of the negative electrode sheet 11, compensates for the difference in the degree of insertion of metal ions at different positions on the negative electrode sheet 11, reduces the probability of lithium plating, and effectively extends the service life of the battery cell 10.

[0092] In some embodiments of the present application, optionally, please refer to Figure 5 , the first coating area 11c includes a first line 11d intersecting with the preset direction X, and the weight per unit area of the active material shows an increasing trend 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 can be located on the center line of the first coating area 11c along the preset direction X, or on one side of the center line of the first coating area 11c along the preset direction X. Within the first coating area 11c, the weight per unit area of the active material shows an increasing trend 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 make up for the insufficient embedding degree at the first line 11d, thereby effectively reducing the probability of lithium plating.

[0094] In some examples, please refer to Figure 5 , the weight per unit area of the active material shows an increasing trend 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 center line of the first active material layer 112 along the preset direction X. Among them, the increasing trend means that the weight per unit area of the active material in the second coating area 11e can increase linearly or curvilinearly along the preset direction X; of course, it can also show a stepped increase, for example: first gradually increase, then remain unchanged, and then gradually increase, etc.

[0095] It can be understood that the first line 11d of this embodiment is located within the first coating area 11c. Therefore, in addition to intersecting with the preset direction X, the first line 11d 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 pairwise.

[0096] With such a design, within the first coating area 11c, the weight per unit area of the active material is the larger the closer it is to the first line 11d, effectively making up for the insufficient embedding degree at the first line 11d, thereby effectively reducing the probability of lithium plating.

[0097] In 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 within the first coating area 11c, the thickness of the active material gradually increases along the preset direction X and towards the side of the first line 11d, so that the weight of the active material per unit area is the larger the closer it is to the middle of the first coating area 11c, which can effectively make up for the difference in the embedding degree in the middle of the negative electrode sheet 11 and improve the problem of lithium plating. 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] With such a design, the thickness of the active material in the first coating area 11c is designed to be larger closer to the first line 11d, compensating for the difference in the degree of metal ion insertion at different positions on the negative electrode sheet 11, reducing the probability of lithium plating in the middle of the negative electrode sheet 11, and effectively extending the service life of the battery cell 10.

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

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

[0102] With such a design, the first coating area 11c is arranged in the middle of the negative electrode sheet 11, which is convenient for increasing the ion insertion ability in the middle of the negative electrode sheet 11, reducing the probability of lithium plating in the middle, and improving the service life of the battery cell 10.

[0103] In some embodiments of the present application, optionally, the dimension of the first coating area 11c along the preset direction X is denoted as W1, where 5 mm ≤ W1 ≤ 100 mm.

[0104] The dimension of the first coating area 11c along the preset direction X can be between 5 mm and 100 mm. For example, it can be, but is 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, controlling the dimension of the first coating area 11c along the preset direction X between 5 mm and 100 mm is convenient for accurately increasing the insertion ability of the effective area on the negative electrode sheet 11 and effectively improving the lithium plating problem in the middle of the negative electrode sheet 11.

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

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

[0108] With such a design, it is convenient to effectively improve the lithium plating problem of the battery cell 10 with a carbon-containing or silicon-containing system and improve the service life of the battery cell 10.

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

[0110] 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 a 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 opposite surfaces of the first current collector 111.

[0111] With such a design, the introduction of the first current collector 111 facilitates the formation of different weights of active materials at different positions on the first current collector 111, compensates for the difference in the degree of embedding of metal ions at different positions on the negative electrode sheet 11, and reduces the probability of lithium deposition.

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

[0113] The body portion 11a refers to the structure of the first current collector 111 coated with the active material, and the tab 11b refers to the structure of the first current collector 111 not coated with the active material. 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, the structural form of the tab 11b on the first current collector 111 has various forms. For example, the tab 11b on the first current collector 111 can be a full tab 11b, that is, an entire edge of the first current collector 111 along the preset direction X; or the tab 11b on the first current collector 111 is a plurality of protruding structures distributed at intervals.

[0114] In this embodiment, the preset direction X is designed as the distribution direction between the body portion 11a and the tab 11b. In this way, 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 sequentially distributed along the height direction of the electrode assembly 1, which is convenient for effectively reducing the probability of lithium deposition in the middle of the negative electrode sheet 11.

[0115] With such a design, the first current collector 111 is designed as the body part 11a and the tab 11b, which facilitates the power transmission 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 body part 11a and the tab 11b, so that in the wound 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, effectively reducing the probability of lithium deposition in the middle of the negative electrode sheet 11.

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

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

[0118] With such a design, the average weight of the active material per unit area in the first coating area 11c is controlled between 0.1 g / 1540.25 mm 2 ~0.25 g / 1540.25 mm 2 to meet the effective insertion of metal ions in the middle of the negative electrode sheet 11 during cyclic charge and discharge, and effectively reduce the probability of lithium deposition.

[0119] In some embodiments of the present application, please refer to Figure 8 , the present application provides a method for preparing the negative electrode sheet 11, and the method includes:

[0120] S100. Provide the first current collector 111;

[0121] S200. Form a first active material layer 112 on at least one surface of the first current collector 111, and control the average weight of the active material per unit area in the first coating region 11c of the first active material layer 112 to be greater than the average weight of the active material per unit area in the second coating region 11e of the first active material layer 112. The first active material layer 112 includes a first coating region 11c and second coating regions 11e respectively provided on opposite sides of the first coating region 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 a copper metal foil, etc.; or it can be a composite current collector.

[0123] In step S200, there are various ways to form the first active material layer 112 on the first current collector 111. For example, the active material is coated on the first current collector 111 through a coating die. To achieve that the average surface density of the first coating region 11c is greater than that of the second coating region 11e, there are various ways. For example, when the thickness of the active material in the first coating region 11c is the same as that in the second coating region 11e, the degree of compaction in the first coating region 11c is greater than that in the second coating region 11e; or when the degree of compaction of the active material in the first coating region 11c is the same as that in the second coating region 11e, the thickness of the active material in the first coating region 11c is greater than the thickness of the active material in the second coating region 11e.

[0124] With such a design, the ability of the first coating region 11c to allow ion insertion is relatively large compared to the second coating regions 11e on both sides, compensating for the difference in the degree of metal ion insertion at different positions of the negative electrode sheet 11 in the later stage of cycling, effectively reducing the probability of lithium plating in the middle of the negative electrode sheet 11, and improving the service life of the battery cell 10.

[0125] In some embodiments of the present application, optionally, the step of S200 of forming the first active material layer 112 on at least one surface of the first current collector 111 includes: performing an active material coating operation on the surface of the first current collector 111 at preset intervals along a preset direction X, and the coating parameters in each coating operation are larger the closer they are to the midline of the first active material layer 112, where the coating parameters include at least one of the coating time and the flow rate of the active material, and the midline of the first active material layer 112 is located in the first coating region 11c.

[0126] It can be seen that during the coating process, a 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 a preset distance, and the coating of the active material is continued, and such cyclic operations are performed. Among them, the closer the coating device is to the midline of the first active material layer 112, the greater the coating parameters are controlled. For example: the closer to the midline of the first active material layer 112, the longer the coating time for each coating operation; or, the greater the flow rate of the active material for each coating operation, etc. At the same time, the preset distance refers to the control point where the coating device coats 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 distance is equal to the coating width of the coating device, or slightly less than the coating width, etc.

[0127] For ease of understanding the preset distance, reference can be made to Figure 9 , and the preset distance can be Figure 9 the distance represented by D in , during the coating process, after the coating operation is completed at the first coating point, the coating device can move to the next coating point for coating operation, and the distance between two adjacent coating points is the preset distance.

[0128] Of course, in some other embodiments, the coating device can be controlled to move uniformly above the first current collector 111, and the flow rate of the active material is controlled to first increase to the midline of the first active material layer 112 as the first current collector 111 moves, and then, the flow rate of the active material is controlled to gradually decrease.

[0129] With such a design, the design that the coating parameters in each coating operation are larger closer to the midline of the first active material layer 112 makes the weight of the active material show an increasing trend from the edge to the middle of the negative electrode sheet 11, compensates for the difference in the degree of embedding of metal ions at different positions on the negative electrode sheet 11, reduces the probability of lithium deposition, and effectively extends the service life of the battery cell 10.

[0130] In some embodiments according to the present application, the preset distance is 5 mm to 100 mm.

[0131] The preset distance can take values between 5 mm and 100 mm. For example: it can be 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] With such a design, the preset distance 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] In some embodiments according to the present application, please refer to Figure 10, this 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. A separator 13 is disposed between the positive electrode sheet 12 and the negative electrode sheet 11.

[0134] The electrode assembly 1 can be a stacked structure or a wound structure. When the electrode assembly 1 is a wound structure, it can 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 the free passage of lithium ions to form a circuit, while preventing the two electrodes from contacting each other to play an electron insulation role. Its types can be selected as, but are not limited to, polyethylene single-layer film, polypropylene single-layer film, etc.

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

[0137] With such a design, by using the above negative electrode sheet 11, the difference in the degree of insertion of metal ions at different positions on the negative electrode sheet 11 in the later stage of the cycle can be compensated, the probability of lithium deposition in the middle of the negative electrode sheet 11 can be effectively reduced, and the service life of the battery cell 10 can be improved.

[0138] In some embodiments of the present application, optionally, please refer to Figure 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 the active material per unit area in the third coating area 12a is less than the average weight of the active material per unit area in each of the fourth coating areas 12c.

[0139] The second active material layer 122 refers to the active material located on the surface of the positive electrode sheet 12, and there can be various materials for the active material. As a non-limiting example, the first active material layer 112 can include one or more of the following materials: lithium phosphate 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 materials that can be used as the active material of the positive electrode sheet 12 can also be used. Among them, examples of lithium transition metal oxides can 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 (which can also be abbreviated as NCM 333 ), LiNi0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2), and at least one of its modified compounds. Examples of olivine-structured lithium-containing phosphates may include but are not limited to lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), composites of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and composites of lithium manganese iron phosphate and carbon.

[0140] The second active material layer 122 can be located on one surface of the positive electrode sheet 12, or can be respectively 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. Among them, there are various materials for the second current collector 121, such as: the material of the second current collector 121 can be but is not limited to aluminum metal, composite materials, etc.

[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 materials in the third coating area 12a and the first coating area 11c are arranged facing each other, and the active materials in the fourth coating area 12c and the second coating area 11e are arranged facing each other. At this time, the ratio of the capacity per unit area of the active material in the first coating area 11c to the capacity per unit area of the active material in the third coating area 12a is denoted as CB1, and the ratio of the capacity per unit area of the active material in the second coating area 11e to the capacity per unit area of the active material in the fourth coating area 12c is denoted as CB2. CB1 is greater than CB2, that is, the CB value in the middle of the electrode assembly 1 is greater than that on both sides, which is beneficial to the full insertion of metal ions, such as lithium ions, in the middle of the electrode assembly 1 and reduces the risk of lithium precipitation.

[0142] To achieve that the average areal density of the third coating area 12a is less than that of the fourth coating area 12c, there are various ways. For example, 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 degree of compaction in the third coating area 12a is less than that in the fourth coating area 12c; or, when the degree of compaction 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 less than the thickness of the active material in the fourth coating area 12c.

[0143] In addition, the active material in the third coating area 12a may or may not be consistent along the preset direction X. For example, the thickness or degree of compaction 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 or may not be consistent along the preset direction X. For example, the thickness or degree of compaction 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 dimensions 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 within the third coating area 12a; and one end of the fourth coating area 12c far 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 wound structure, the preset direction X can be set as the width direction of the positive electrode sheet 12. In this way, 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, which is conducive to effectively improving the problem of lithium deposition 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 tab 11b.

[0145] Such a design is conducive to increasing the CB value in the middle of the electrode assembly 1, facilitating the full insertion of metal ions in the middle of the electrode assembly 1, and reducing the risk of lithium deposition.

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

[0147] The ratio between the average weight of the active material per unit area in the third coating area 12a and the average weight of the active material per unit area in the fourth coating area 12c can take values between 0.5 and 1. For example, it can be, but is 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 the active material per unit area in the third coating area 12a and the average weight of the active material per unit area in the fourth coating area 12c is controlled between 0.5 and 1, so that the metal ions in the third coating area 12a are relatively reduced, the probability of lithium plating in the middle is decreased, and the service life of the battery cell 10 is prolonged.

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

[0150] The ratio between the average weight of the active material per unit area in the third coating area 12a and the average weight of the active material per unit area in the fourth coating area 12c can further take values between 0.7 and 1, such as: 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 the active material per unit area in the third coating area 12a and the average weight of the active material per unit area in the fourth coating area 12c is further controlled between 0.7 and 1. On the premise of being able to make up for the difference in the embedding degree in the later stage of cycling, the difference between the active materials in different coating areas is controlled as much as possible, so that the performance of the battery cell 10 is more stable.

[0152] In some embodiments of the present application, optionally, please refer to Figure 11 and Figure 12 , in at least one fourth coating area 12c, the weight per unit area of the active material shows a decreasing trend from the side of the fourth coating area 12c far 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 the active material per unit area in the fourth coating area 12c refers to the ratio of the weight of all the active materials 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 the active material corresponding to each unit area along the preset direction X in the fourth coating area 12c. Among them, the average weight of the active material per unit area in the fourth coating area 12c can be regarded as the average value of the weights of the active materials on each 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. Taking the same compaction degree as an example, the thickness of the active material in the fourth coating area 12c is smaller closer to the third coating area 12a; taking the same thickness as an example, the compaction degree of the active material in the fourth coating area 12c is smaller closer to the third coating area 12a.

[0155] In addition, the weight of the active material at one end of the fourth coating area 12c close to the third coating area 12a is equal to the weight of the active material at one 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 transitionally connected.

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

[0157] With such a design, the weight per unit area of the active material in the fourth coating area 12c is designed to decrease closer to 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, reducing the probability of lithium plating in the middle of the electrode assembly 1 and effectively extending the service life of the battery cell 10.

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

[0159] It can be seen that within the fourth coating area 12c, the thickness of the active material gradually decreases along the preset direction X and towards the 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 decreases, which can effectively reduce the concentration of metal ions in the positive electrode sheet 12 and improve the lithium plating problem. In some examples, within the two fourth coating areas 12c, the thickness of the active material gradually decreases from the side of the fourth coating area 12c far from the third coating area 12a to the side of the fourth coating area 12c close to the third coating area 12a.

[0160] With such a design, the thickness of the active material in the fourth coating area 12c is designed to decrease closer to 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, reducing the convergence of metal ions in the middle and decreasing the probability of lithium plating, effectively extending the service life of the battery cell 10.

[0161] In some embodiments of the present application, optionally, please refer to Figure 11 and Figure 12 , the third coating area 12a includes a second line 12b intersecting with the preset direction X, and the weight per unit area of the active material shows a decreasing trend 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 can be located on the center line of the third coating area 12a along the preset direction X, or can be located on one side of the center line of the third coating area 12a along the preset direction X. Within the third coating area 12a, the weight per unit area of the active material shows a decreasing trend 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 convergence of metal ions in the middle, thereby effectively reducing the probability of lithium plating.

[0163] In some examples, the weight per unit area of the active material shows a decreasing trend 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 center line of the first active material layer 112 along the preset direction X. Among them, showing a decreasing trend means that the weight per unit area of the active material in the fourth coating area 12c can decrease linearly or curvilinearly along the preset direction X; of course, it can also show a stepped decrease, for example: first gradually decrease, then remain unchanged, and then gradually decrease, etc.

[0164] It can be understood that the second line 12b of this embodiment is located within the third coating area 12a. Therefore, in addition to intersecting with the preset direction X, the second line 12b will also be 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 in pairs.

[0165] With such a design, within the third coating area 12a, the weight per unit area of the active material is smaller the closer it is to the second line 12b, reducing the convergence 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 plating.

[0166] In some embodiments of the present application, optionally, please refer to Figure 11 and Figure 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 within the third coating area 12a, the thickness of the active material gradually decreases along the preset direction X and towards the side of the second line 12b, so that the closer it is 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 plating 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] With such a design, the thickness of the active material within the third coating area 12a is designed to be smaller the closer it is to the second line 12b, reducing the central convergence of metal ions, reducing the probability of lithium plating in the middle of the positive electrode sheet 12, and effectively extending the service life of the battery cell 10.

[0169] In some embodiments of the present application, optionally, please refer to Figure 11 , the second line 12b overlaps with the midline 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 12a is arranged in the middle of the positive electrode sheet 12, which is convenient for reducing the central convergence of metal ions, reducing the probability of lithium deposition in the middle, and improving the service life of the battery cell 10.

[0172] In some embodiments of the present application, optionally, please refer to Figure 11 , the size of the third coating area 12a along the preset direction X is denoted as W2, where 5 mm ≤ W2 ≤ 100 mm.

[0173] The size of the third coating area 12a along the preset direction X can be between 5 mm and 100 mm. For example: it can be, but is 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, controlling the size of the third coating area 12a along the preset direction X between 5 mm and 100 mm is convenient for accurately reducing the metal ion concentration in the effective area on the positive electrode sheet 12 and improving the lithium deposition problem in the middle.

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

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

[0177] In some embodiments of the present application, the present application provides an electrical equipment, and the electrical equipment includes the battery cell 10 above or the battery device 100 above.

[0178] In some embodiments of the present application, please refer to Figures 4 to 12, this 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. The number of the second coating areas 11e is multiple, 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 of the second coating areas 11e, and in either side of the first coating area 11c along the preset direction X, all the second coating areas 11e are sequentially distributed 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 the active material per unit area in it.

[0179] At least one surface of the positive electrode sheet 12 along its thickness direction 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. The number of the fourth coating areas 12c is multiple, the average weight of the active material per unit area in the third coating area 12a is less than the average weight of the active material per unit area in each of the fourth coating areas 12c, and in either side of the third coating area 12a along the preset direction X, all the 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 the active material per unit area in it.

[0180] In order to make the purpose, technical solution and advantages of this application more concise and clear, this application is described by the following specific embodiments, but this application is by no means limited to these embodiments. The following described embodiments are only the preferred embodiments of this application, which can be used to describe this application and should not be construed as a limitation on the scope of this application. It should be noted that any modifications, equivalent replacements and improvements made within the spirit and principle of this application shall be included in the protection scope of this application.

[0181] To better illustrate this application, the content of this application will be further described below in conjunction with embodiments. The following are specific embodiments.

[0182] Comparative Example 1

[0183] Prepare the 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 evenly according to 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) Coating is carried out using an extrusion coating equipment, which can adjust the slurry flow rate at each nozzle site (with an interval of 25 cm) to make the flow rates at each nozzle site consistent, and continuously coat the negative electrode slurry on the surface of a 6-μm negative electrode current collector (copper foil) to form a film coating. Control the equipment to make the average weight of the solid substance per unit area be 0.150 g / 1540.25 mm 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 prepared into a negative electrode sheet through drying, rolling, die-cutting, and slitting.

[0187] Preparation of the 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). Mix the above materials in a mass ratio of LFP:PVDF:C = 97.5:2:0.5 and stir evenly. The solid content of the positive electrode slurry is 0.65;

[0189] 2) Coating is carried out using an extrusion coating equipment, and the positive electrode slurry is continuously coated on the surface of a 15-μm positive electrode current collector (aluminum foil) to form a film coating with a width of 200 mm. Control the equipment to make the average weight of the solid substance per unit area be 0.240 g / 1540.25 mm 2 , and the thickness of the positive electrode slurry is 160 μm;

[0190] 3) The positive electrode current collector coated with the film coating is prepared into a positive electrode sheet through drying, rolling, die-cutting, and slitting.

[0191] Assembly of the battery cell 10

[0192] The positive electrode sheet, negative electrode sheet, and separator membrane prepared in the above process are wound into an electrode assembly in the order of: negative electrode - separator - positive electrode - separator; the wound battery core is hot-pressed and then assembled and welded with the top cover housing to complete the assembly of the battery core. Finally, the battery is completed through processes such as liquid injection, formation, exhaust, and sealing.

[0193] Example 1

[0194] Basically the same as Comparative Example 1, the difference is that: 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 in the width direction of the negative electrode sheet 11, 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 2, the average weight of the 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] Basically the same as Comparative Example 1, the difference is that: the negative electrode paste 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 in the width direction of the negative electrode sheet 11, 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 the 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] Basically the same as Comparative Example 1, the difference is that: the negative electrode paste 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 in the width direction of the negative electrode sheet 11, 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 the 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 monomers 10 prepared in Comparative Example 1 and Examples 1 to 3 were respectively subjected to cyclic charge and discharge tests.

[0200] Cyclic charge and discharge test

[0201] The battery monomers prepared in each example and comparative example were set as multiple parallel samples, and the battery monomers were tested in a cyclic manner. The rate was set to 0.5C, the temperature was 60 degrees Celsius, and the charge and discharge voltage range was [2.5V, 3.65V]. The change of SOH with the number of cycles was recorded. The battery monomers were disassembled every 1% SOH (the state of 100% SOC was required), and whether there was an obvious abnormal color of lithium intercalation (such as black, gray, etc.) on the negative electrode sheet was visually observed, and the corresponding number of cycles of the battery monomer when the color abnormality started to occur was recorded. Please refer to Table 1 for the above test data.

[0202] Table 1

[0203]

[0204] It should be noted that the unit of thickness in Table 1 is μm, and the unit of unit weight is g / 1540.25mm 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 substances on the negative electrode sheet show a linear change, and the sum of the unit weights of the active substances in the middle area and the edge area of the negative electrode sheet is 0.3 g / 1540.25 mm 2 。It shows that the overall average unit weight on 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 in Comparative Example 1. On the premise that the CB values are the same, 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 substance in the middle area to the unit weight of the active substance in the edge area in the negative electrode sheet is 1.2, the number of cycles is 204 more than that in Comparative Example 1. Therefore, making the average weight per unit area of the active substance in the middle part of the negative electrode sheet 11 greater than the average weight per unit area of the active substances on both sides is beneficial to reducing the probability of lithium deposition and extending the service life of the battery cell 10, where the CB value is the ratio of the capacity per unit area of the active substance in the negative electrode sheet to the capacity per unit area of the active substance in the positive electrode sheet.

[0206] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, 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, it should be considered as the scope described in this specification.

[0207] The above-described embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended 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), and the negative electrode sheet further comprises a first current collector (111), wherein the first active material layer (112) is disposed on at least one surface of the first current collector (111); 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); 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).

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 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).

7. The negative electrode sheet according to claim 1, characterized in that: The first line (11d) overlaps with a center line of the first active material layer (112) along the preset direction (X).

8. 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.

9. 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.

10. The negative electrode sheet according to claim 1, 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).

11. 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 .

12. A method for preparing a negative electrode sheet, used for preparing the negative electrode sheet according to any one of claims 1 to 11, 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).

13. The method for preparing a negative electrode sheet according to claim 12, 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).

14. The method for preparing a negative electrode sheet according to claim 13, characterized in that: The preset spacing is 5mm~100mm.

15. 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 11, wherein the separator (13) is arranged between the positive electrode sheet (12) and the negative electrode sheet.

16. The electrode assembly according to claim 15, 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).

17. The electrode assembly according to claim 16, 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.

18. The electrode assembly according to claim 17, characterized in that CW3 / CW4 also satisfies the condition: 0.7≤CW3 / CW4<1.

19. The electrode assembly according to claim 16, 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).

20. The electrode assembly according to claim 19, 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).

21. The electrode assembly according to claim 16, 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).

22. The electrode assembly according to any one of claims 16 to 21, characterized in that: The dimension of the third coating area (12a) along the preset direction (X) is recorded as W2, wherein 5mm≤W2≤100mm.

23. A battery cell, characterized in that: The battery cell comprises the electrode assembly according to any one of claims 15-22.

24. A battery device, characterized in that: The battery device comprises the battery cell according to claim 23.

25. An electrical equipment, characterized in that: The electrical equipment comprises the battery cell according to claim 23 or the battery device according to claim 24.

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