Negative electrode sheet, battery cell, battery and electrical equipment

Abstract

This application provides a negative electrode sheet, a battery cell, a battery, and an electrical device, relating to the field of batteries. The negative electrode sheet includes a current collector and a negative electrode film layer disposed on at least one side surface of the current collector. The negative electrode film layer includes a composite active layer, which includes at least one first conductive binder layer and at least two negative electrode active material layers along its thickness direction. Adjacent negative electrode active material layers have different rebound rates after full charge, and the first conductive binder layer is located between adjacent negative electrode active material layers. This design can improve the problem of poor battery cycle performance when the negative electrode sheet uses a multi-layered composite active layer.

Description

Technical Field

[0001] This application relates to the field of batteries, and more specifically, to a negative electrode, a battery cell, a battery, and an electrical device. Background Technology

[0002] The depletion of energy resources has led to a significant development in new energy storage devices. Lithium-ion batteries (LIBs) have attracted considerable attention due to their high energy density, high capacity, good cycle stability, and environmental friendliness. However, existing lithium-ion batteries, when using a negative electrode film composed of multiple layers of active materials, suffer from poor cycle performance. Summary of the Invention

[0003] In view of the above problems, this application provides a negative electrode sheet, a battery cell, a battery, and an electrical device that can improve the technical problem of poor battery cycle performance when the negative electrode sheet adopts a negative electrode film layer composed of multiple active material layers.

[0004] In a first aspect, embodiments of this application provide a negative electrode sheet, which includes a current collector and a negative electrode film layer disposed on at least one side surface of the current collector. The negative electrode film layer includes a composite active layer, and the composite active layer includes at least one first conductive adhesive layer and at least two negative electrode active material layers along the thickness direction. The rebound rates of two adjacent negative electrode active material layers after full charge are different, and the first conductive adhesive layer is located between two adjacent negative electrode active material layers.

[0005] In the technical solution of this application embodiment, since the rebound rates of two adjacent negative electrode active material layers after full charge are different, a first conductive adhesive layer is introduced between the two adjacent negative electrode active material layers to increase the adhesion and conductivity between the two adjacent negative electrode active material layers, alleviate the problem of interlayer peeling and poor interlayer conductivity caused by the difference in rebound rates after full charge, and improve the battery cycle performance.

[0006] In some embodiments, among two adjacent negative electrode active material layers, the rebound rate of the negative electrode active material layer on the side closer to the current collector after full charge is A1, and the rebound rate of the negative electrode active material layer on the side away from the current collector after full charge is A2, where A1 > A2. By utilizing the fact that the rebound rate of the negative electrode active material layer on the side away from the current collector after full charge is less than that on the side closer to the current collector, i.e., by placing the layer with the lower rebound rate on the outside and the layer with the higher rebound rate on the inside, the expansion of the negative electrode active material layer with the higher rebound rate can be limited, alleviating the problems of interlayer delamination and poor interlayer conductivity, and improving the cycle performance of the battery.

[0007] In some embodiments, the composite active layer includes a first conductive binder layer and two negative electrode active material layers. The aforementioned composite active layer has a simple structure, is easy to process, and can improve the cycle performance of the battery.

[0008] In some embodiments, two adjacent negative electrode active material layers serve as a first negative electrode active material layer and a second negative electrode active material layer, respectively. The first negative electrode active material layer includes a first negative electrode active material, and the rebound rate of the first negative electrode active material after full charge is B1, 10% ≤ B1 ≤ 30%. The second negative electrode active material layer includes a second negative electrode active material, and the rebound rate of the second negative electrode active material after full charge is B2, 200% ≤ B2 ≤ 300%. For a second negative electrode active material (e.g., silicon-based material) with a rebound rate of 200%-300%, pairing it with a first negative electrode active material with a rebound rate of 10%-30% can significantly improve the problem caused by the high rebound rate of the second negative electrode active material. Furthermore, the stability of the connection between the two can be effectively improved by utilizing the first conductive binder layer, thereby enhancing the cycle performance of the battery.

[0009] In some embodiments, both the first negative electrode active material layer and the second negative electrode active material layer include a binder; wherein the amount of binder added in the first negative electrode active material layer is less than the amount of binder added in the second negative electrode active material layer. Since the rebound rate of the first negative electrode active material layer is less than that of the second negative electrode active material layer, increasing the amount of binder added in the second negative electrode active material layer can limit the expansion of the second negative electrode active material layer, reduce negative electrode rebound, and improve the cycle performance of the battery.

[0010] In some embodiments, the first negative electrode active material includes graphite, and the second negative electrode active material includes a silicon-based active material. The combination of silicon-based active material and graphite can effectively improve the battery's energy density. Furthermore, when the silicon-based active material is located in a layer close to the current collector, side reactions can be reduced, mitigating the pulverization problem during long cycles, effectively improving back-end charging capability, alleviating the problem of the silicon-based active material's volume expansion breaking through the SEI film, and enhancing the battery's cycle performance.

[0011] In some embodiments, both the first negative electrode active material layer and the second negative electrode active material layer include a conductive agent; wherein the conductivity of the conductive agent in the first negative electrode active material layer is lower than the conductivity of the conductive agent in the second negative electrode active material layer, and the amount of conductive agent added in the first negative electrode active material layer is equal to the amount of conductive agent added in the second negative electrode active material layer. The lower conductivity of the conductive agent in the first negative electrode active material layer compared to the second negative electrode active material layer is beneficial because silicon-based active materials have low conductivity, while graphite has high conductivity. Therefore, this method helps to improve the conductivity of the second negative electrode active material layer, alleviate poor interlayer conductivity, and improve the cycle performance of the battery.

[0012] In some embodiments, the thickness of the second negative electrode active material layer is 1-60 μm. Within this thickness range, the battery exhibits better DC resistance and cycle count, resulting in superior cycle performance.

[0013] In some embodiments, the thickness of the first negative electrode active material layer is 140-210 μm. By using a thicker first negative electrode active material layer, the expansion of the second negative electrode active material layer can be suppressed while maintaining a better energy density, thus alleviating interlayer delamination and improving the cycle performance of the battery.

[0014] In some embodiments, the thickness of the first conductive adhesive layer accounts for 0.98%-5.75% of the thickness of the negative electrode film layer, and the thickness of the first conductive adhesive layer is not less than 1 μm; utilizing the above-mentioned thickness of the first conductive adhesive layer within a reasonable range is beneficial to improving the cycle performance of the battery.

[0015] Optionally, the thickness of the first conductive adhesive layer is 1-10 μm.

[0016] In some embodiments, the negative electrode film layer further includes a second conductive binder layer, which is located between the composite active layer and the current collector. The use of the second conductive binder layer improves the stability of the connection between the composite active layer and the current collector, thereby enhancing the cycle performance of the battery.

[0017] In some embodiments, the negative electrode film layer satisfies at least one of (a1)-(a2): (a1) the adhesion force of the second conductive adhesive layer is less than that of the first conductive adhesive layer; (a2) the conductivity of the second conductive adhesive layer is less than that of the first conductive adhesive layer. Since the second and first conductive adhesive layers are positioned differently, this arrangement limits the relative adhesion force and conductivity between the first and second conductive adhesive layers, which helps alleviate interlayer delamination and poor interlayer conductivity, thereby improving the cycle performance of the battery.

[0018] In some embodiments, both the second conductive adhesive layer and the first conductive adhesive layer include a conductive agent and an adhesive, and the negative electrode film layer satisfies at least one of (b1)-(b2): (b1) the adhesive in the second conductive adhesive layer is the same as the adhesive in the first conductive adhesive layer, and the amount of adhesive added in the second conductive adhesive layer is less than the amount of adhesive added in the first conductive adhesive layer;

[0019] (b2) The amount of conductive agent added in the second conductive adhesive layer is the same as that in the first conductive adhesive layer, and the conductivity of the conductive agent in the second conductive adhesive layer is less than that in the first conductive adhesive layer. Using this setting, the adhesion force of the second conductive adhesive layer can be quickly adjusted to be less than that of the first conductive adhesive layer, and the conductivity of the second conductive adhesive layer can be less than that of the first conductive adhesive layer, thus alleviating problems such as interlayer delamination and poor interlayer conductivity, and improving the cycle performance of the battery.

[0020] In some embodiments, the conductive agent in the first conductive binder layer includes at least one of a one-dimensional conductive agent and a two-dimensional conductive agent. Since the first conductive binder layer is located between two adjacent negative electrode active material layers, the introduction of one-dimensional and two-dimensional conductive agents helps to suppress interlayer delamination and poor interlayer conductivity of the negative electrode active material layers, thereby improving the cycle performance of the battery.

[0021] Optionally, the one-dimensional conductive agent includes at least one of carbon nanotubes and carbon fibers.

[0022] Optionally, the two-dimensional conductive agent includes graphene.

[0023] In some embodiments, the thickness of the second conductive binder is 0.98%-5.75% of the negative electrode film layer, and the thickness of the second conductive binder layer is not less than 1 μm. Utilizing the above-mentioned thickness of the second conductive binder layer within a reasonable range helps to prevent the composite active layer from peeling off from the current collector, thereby improving the cycle performance of the battery.

[0024] Optionally, the thickness of the second conductive adhesive layer is 1-10 μm.

[0025] Secondly, this application provides a battery that includes the battery cell described in the above embodiments.

[0026] Thirdly, this application provides an electrical device that includes the battery cell or battery described in the above embodiments, wherein the battery cell and battery are used to provide electrical energy.

[0027] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0028] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0029] Figure 1 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0030] Figure 2 Exploded structural diagrams of batteries according to some embodiments of this application;

[0031] Figure 3 This is an exploded structural diagram of a battery cell according to some embodiments of this application;

[0032] Figure 4 This is a schematic diagram of the structure of the negative electrode sheet in some embodiments of this application.

[0033] The reference numerals in the detailed embodiments are as follows:

[0034] 1000 - Vehicles;

[0035] 100 - Battery; 200 - Controller; 300 - Motor;

[0036] 10-Box body; 11-First part; 12-Second part;

[0037] 20-Battery cell; 21-End cap; 21a-Electrode terminal; 22-Housing casing; 23-Electrode assembly; 23a-Taper;

[0038] 30-Negative electrode sheet; 31-Current collector; 32-Negative electrode film layer; 33-Composite active layer; 331-First negative electrode active material layer; 332-First conductive binder layer; 333-Second negative electrode active material layer; 34-Second conductive binder layer. Detailed Implementation

[0039] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0041] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0042] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0043] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0044] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0045] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0046] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0047] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0048] However, existing lithium-ion batteries, when the negative electrode sheet has a negative electrode film layer formed by multiple layers of negative electrode active material, have poor cycle performance during the lithium insertion / extraction process.

[0049] The main reason for the poor cycle performance of the aforementioned battery during lithium insertion / extraction is that, when multiple negative electrode active material layers are combined, the rebound rates of two adjacent negative electrode active material layers after full charge are different, leading to delamination or poor interlayer conductivity between the two adjacent negative electrode active material layers. Therefore, this application adopts a technical solution that utilizes a first conductive binder layer located between two adjacent negative electrode active material layers, under the premise that the rebound rates of two adjacent negative electrode active material layers after full charge are different. The first conductive binder layer increases the adhesion and conductivity between the two adjacent negative electrode active material layers with different rebound rates, alleviating the problems of delamination and poor interlayer conductivity caused by the difference in rebound rates, thereby improving the cycle performance of the battery.

[0050] The battery cells disclosed in this application can be used, but are not limited to, in electrical equipment such as vehicles, ships, or aircraft. A power system for such equipment can be constructed using battery cells and batteries as disclosed in this application. This helps to alleviate the problem of poor cycle performance during lithium insertion / extraction when the negative electrode is coated with a film formed by multiple layers of negative electrode active material.

[0051] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0052] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0053] Please refer to Figure 1 , Figure 1This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0054] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0055] Please refer to Figure 2 , Figure 2 This is an exploded view of a battery 100 provided in some embodiments of this application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0056] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0057] Each battery cell 20 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 to these. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0058] Please refer to Figure 3 , Figure 3 This is an exploded structural diagram of a battery cell 20 provided in some embodiments of this application. The battery cell 20 refers to the smallest unit that makes up the battery 100. For example... Figure 3 The battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0059] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, giving battery cell 20 higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with electrode assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose any special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0060] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0061] Electrode assembly 23 is the component in the battery cell 20 where electrochemical reactions occur. The casing 22 may contain one or more electrode assemblies 23. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and typically a separator is provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of the electrode assembly 23, while the portions of the positive and negative electrode sheets without active material each constitute a tab 23a. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery 100, the positive and negative active materials react with the electrolyte, and the tabs 23a connect to the electrode terminals 21a to form a current loop.

[0062] According to some embodiments of this application, please refer to Figure 4 This application provides a negative electrode sheet 30, which includes a current collector 31 and a negative electrode film layer 32 disposed on at least one side surface of the current collector 31. The negative electrode film layer 32 includes a composite active layer 33. The composite active layer 33 includes at least one first conductive adhesive layer 332 and at least two negative electrode active material layers along the thickness direction. The rebound rates of two adjacent negative electrode active material layers after full charge are different. The first conductive adhesive layer 332 is located between two adjacent negative electrode active material layers.

[0063] The thickness direction refers to the direction in which the functional layers are stacked.

[0064] The current collector has two opposing surfaces on both sides along its thickness direction. The negative electrode film layer 32 is disposed on at least one surface of the current collector 31, that is, the negative electrode film layer 32 can be disposed on only one surface, or it can be disposed on another surface. Figure 4As shown, negative electrode film layers 32 are provided on both opposite surfaces of the current collector 31 along the thickness direction. The conductive adhesive layer is a film layer formed by curing an adhesive liquid with conductive and adhesive properties. The adhesive liquid is composed of a conductive agent, an adhesive, and optional additives, such as thickeners or calcium hydroxide that promotes adhesion.

[0065] The negative electrode active material layer refers to the film layer containing negative electrode active materials that react with the electrolyte during the charging and discharging process of the battery. In addition to negative electrode active materials, the negative electrode active material layer may also contain binders, conductive agents and thickeners.

[0066] The state of charge (SOC) of a battery indicates the available state of the remaining charge in the battery. SOC = 0 indicates that the battery is fully discharged, and SOC = 1 indicates that the battery is fully charged. The rebound rate after full charge refers to the increase in the thickness of the negative electrode active material layer after full charge compared to before full charge.

[0067] Test method for rebound rate after full charge: CP cross-section test, with the thickness of the test layer in the discharged state as Base, and the thickness of the test layer in the fully charged state as Base+x, X / Base is the full charge rebound rate. CP cross-section test refers to obtaining the thickness of the test layer by using a scanning electron microscope.

[0068] It is understandable that, since the composite active layer 33 includes at least one first conductive adhesive layer 332 and at least two negative electrode active material layers along the thickness direction, and the first conductive adhesive layer 332 is located between two adjacent negative electrode active material layers, the number of negative electrode active material layers in the composite active layer 33 is n, and the number of first conductive adhesive layers 332 is n-1, where n≥2 and is a natural number.

[0069] In the technical solution of this application embodiment, since the rebound rates of two adjacent negative electrode active material layers after full charge are different, a first conductive adhesive layer 332 is introduced between the two adjacent negative electrode active material layers to increase the adhesion and conductivity between the two adjacent negative electrode active material layers, alleviate the problem of interlayer peeling and poor interlayer conductivity caused by the difference in rebound rates after full charge, and improve the battery cycle performance.

[0070] The current collector 31 is a metal foil or a composite current collector. For example, copper foil or aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0071] Among the two adjacent negative electrode active material layers, the rebound rate of the negative electrode active material layer on the side closer to the current collector 31 after full charging can be less than the rebound rate of the negative electrode active material layer on the side away from the current collector 31 after full charging, or it can be greater than the rebound rate of the negative electrode active material layer on the side away from the current collector 31 after full charging.

[0072] According to some embodiments of this application, in two adjacent negative electrode active material layers, the rebound rate of the negative electrode active material layer on the side closer to the current collector after full charging is A1, and the rebound rate of the negative electrode active material layer on the side away from the current collector after full charging is A2, where A1 > A2.

[0073] By utilizing the fact that the negative electrode active material layer on the side away from the current collector has a lower rebound rate after full charge than the negative electrode active material layer on the side closer to the current collector, and placing the layer with a lower rebound rate on the outside and the layer with a higher rebound rate on the inside, the expansion of the negative electrode active material layer with a higher rebound rate can be limited, thereby alleviating the problems of interlayer delamination and poor interlayer conductivity, and improving the cycle performance of the battery.

[0074] Optionally, in any two adjacent negative electrode active material layers, the rebound rate of the negative electrode active material layer closer to the current collector after full charge is A1, and the rebound rate of the negative electrode active material layer away from the current collector after full charge is A2, where A1 > A2. That is, from the side closer to the current collector to the side away from the current collector, the rebound rate of the negative electrode active material layer after full charge gradually decreases with the increase of the number of layers. By using the above arrangement, the cycle performance of the battery can be improved.

[0075] According to some embodiments of this application, please refer to Figure 4 The composite active layer 33 includes a first conductive binder layer 332 and two negative electrode active material layers.

[0076] The aforementioned composite active layer 33 has a simple structure, is easy to process, and can improve the cycle performance of the battery 100.

[0077] According to some embodiments of this application, please refer to Figure 4The two adjacent negative electrode active material layers are respectively designated as the first negative electrode active material layer 331 and the second negative electrode active material layer 333; the first negative electrode active material layer 331 includes a first negative electrode active material, and the rebound rate of the first negative electrode active material after full charging is B1, 10%≤B1≤30%; the second negative electrode active material layer 333 includes a second negative electrode active material, and the rebound rate of the second negative electrode active material after full charging is B2, 200%≤B2≤300%.

[0078] It should be noted that the rebound rate after full charge is a characteristic of the material. Therefore, by using the rebound rate after full charge of different negative electrode active materials, the relative magnitude of the rebound rate after full charge of different negative electrode active material layers can be obtained.

[0079] When the negative electrode active material layer contains two or more negative electrode active materials, the total rebound rate of each negative electrode active material in the negative electrode active material layer is taken as the rebound rate of the negative electrode active material in the negative electrode active material layer.

[0080] The test method for the rebound rate of the negative electrode active material after full charging includes: mixing the negative electrode active material, conductive agent, thickener, and binder in a ratio of 95:1:2:2 to form a slurry, and applying the slurry with a negative electrode coating surface density of 103 g / m³. 2 The negative electrode compaction is 1.60 g / cm³. 3 The positive electrode uses NCM622 material to fabricate a 10A·h stacked battery. The rebound rate of the negative electrode active material is defined as the ratio of the thickness of the negative electrode sheet after full charging to its initial thickness. It is understandable that when measuring the rebound rate of different negative electrode active materials, the only difference in the above-mentioned rebound rate testing method lies in the different negative electrode active materials.

[0081] For a second negative electrode active material (such as silicon-based material) with a rebound rate of 200-300%, pairing it with a first negative electrode active material with a rebound rate of 10-30% can significantly improve the problem caused by the high rebound rate of the second negative electrode active material. Furthermore, the stability of the connection between the two can be effectively improved by utilizing the first conductive binder layer, thereby enhancing the cycle performance of the battery.

[0082] For example, the rebound rate B1 after full charge is any one of 10%, 15%, 20%, 25%, 30% or between any two values, and the rebound rate B2 after full charge is any one of 200%, 230%, 250%, 270%, 300% or between any two values.

[0083] According to some embodiments of this application, both the first negative electrode active material layer and the second negative electrode active material layer include a binder; wherein, the amount of binder added in the first negative electrode active material layer is less than the amount of binder added in the second negative electrode active material layer.

[0084] Since the rebound rate of the first negative electrode active material layer is lower than that of the second negative electrode active material layer, by increasing the amount of binder added to the second negative electrode active material layer, the expansion of the second negative electrode active material layer can be limited, the rebound of the negative electrode sheet can be reduced, and the cycle performance of the battery can be improved.

[0085] The adhesive includes, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyacrylic acid, polyacrylate, polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0086] According to some embodiments of this application, the first negative electrode active material includes graphite, and the second negative electrode active material includes a silicon-based active material.

[0087] By combining silicon-based active materials with graphite, the energy density of the battery can be effectively improved. When the silicon-based active material is located in a layer close to the current collector, side reactions can be reduced, the pulverization problem during long cycles can be improved, the back-end charging capability can be effectively improved, the volume expansion of the silicon-based active material can be alleviated to prevent it from breaking through the SEI film, and the cycle performance of the battery can be enhanced.

[0088] Graphite includes at least one of natural graphite and artificial graphite.

[0089] Silicon-based active materials refer to at least one of elemental silicon and silicon-containing composite materials, wherein the mass percentage of silicon in silicon-containing composite materials is not less than 50%, and silicon-containing composite materials include at least one of silicon oxide and silicon alloy.

[0090] According to some embodiments of this application, both the first negative electrode active material layer and the second negative electrode active material layer include a conductive agent; wherein, the conductivity of the conductive agent in the first negative electrode active material layer is less than the conductivity of the conductive agent in the second negative electrode active material layer, and the amount of conductive agent added in the first negative electrode active material layer is equal to the amount of conductive agent added in the second negative electrode active material layer.

[0091] Since silicon-based active materials have low conductivity while graphite has high conductivity, the above method is beneficial to improve the conductivity of the second negative electrode active material layer, alleviate poor interlayer conductivity, and improve the cycle performance of the battery.

[0092] The conductive agent includes, but is not limited to, at least one of Ketjen black, conductive carbon black (SuperP), carbon fiber (VGCF), carbon nanotubes (CNT), and graphene.

[0093] Since the conductivity of the conductive agent in the first negative electrode active material layer is less than that of the conductive agent in the second negative electrode active material layer, for example, when the conductive agent in the first negative electrode active material layer is carbon black or Ketjen black, the conductive agent in the second negative electrode active material layer is at least one of carbon fiber, carbon nanotube and graphene.

[0094] According to some embodiments of this application, the thickness of the second negative electrode active material layer is 1-60 μm.

[0095] Within the aforementioned thickness range, the battery exhibits superior DC resistance and cycle count, resulting in excellent cycle performance.

[0096] For example, the thickness of the second negative electrode active material layer is any value of 1μm, 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm or between any two values.

[0097] According to some embodiments of this application, the thickness of the first negative electrode active material layer is 140-210 μm.

[0098] By utilizing a thicker first negative electrode active material layer, the expansion of the second negative electrode active material layer can be suppressed while maintaining a better energy density, thus alleviating interlayer delamination and improving the cycle performance of the battery.

[0099] For example, the thickness of the first negative electrode active material layer is any value of 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 199μm, 200μm, 210μm or between any two values.

[0100] According to some embodiments of this application, the thickness of the first conductive adhesive layer accounts for 0.98%-5.75% of the thickness of the negative electrode film layer, and the thickness of the first conductive adhesive layer is not less than 1 μm.

[0101] By utilizing the thickness of the first conductive adhesive layer within a reasonable range, it is beneficial to avoid the delamination between adjacent negative electrode active material layers.

[0102] For example, the thickness of the first conductive adhesive layer is any one of 0.98%, 1.00%, 2.00%, 3.00%, 4.00%, 5.00%, or 5.75% of the thickness of the negative electrode film layer, or between any two values, and the thickness of the first conductive adhesive layer is not less than 1 μm.

[0103] Optionally, the thickness of the first conductive adhesive layer is 1-10 μm.

[0104] According to some embodiments of this application, please refer to Figure 4The negative electrode film layer 32 also includes a second conductive adhesive layer 34, which is located between the composite active layer 33 and the current collector 31.

[0105] The provision of the second conductive adhesive layer 34 facilitates the stable connection between the composite active layer 33 and the current collector 31, thereby improving the cycle performance of the battery 100.

[0106] According to some embodiments of this application, the negative electrode film layer satisfies at least one of (a1)-(a2): (a1) the adhesion force of the second conductive adhesive layer is less than the adhesion force of the first conductive adhesive layer; (a2) the conductivity of the second conductive adhesive layer is less than the conductivity of the first conductive adhesive layer.

[0107] Since the second conductive adhesive layer and the first conductive adhesive layer are positioned differently, the above arrangement limits the relative bonding force and conductivity between the first and second conductive adhesive layers, which helps to alleviate interlayer delamination and poor interlayer conductivity, and improves the cycle performance of the battery.

[0108] According to some embodiments of this application, both the second conductive adhesive layer and the first conductive adhesive layer include a conductive agent and an adhesive. The negative electrode film layer satisfies at least one of (b1)-(b2): (b1) the adhesive in the second conductive adhesive layer is the same as the adhesive in the first conductive adhesive layer, and the amount of adhesive added in the second conductive adhesive layer is less than the amount of adhesive added in the first conductive adhesive layer; (b2) the amount of conductive agent added in the second conductive adhesive layer is the same as the amount of conductive agent added in the first conductive adhesive layer, and the conductivity of the conductive agent in the second conductive adhesive layer is less than the conductivity of the conductive agent in the first conductive adhesive layer. Using the above settings, the adhesion force of the second conductive adhesive layer can be quickly adjusted and made less than that of the first conductive adhesive layer, and the conductivity of the second conductive adhesive layer can be less than that of the first conductive adhesive layer, thus alleviating the problems of interlayer peeling and poor interlayer conductivity, and improving the cycle performance of the battery.

[0109] Optionally, both the second conductive adhesive layer and the first conductive adhesive layer include a conductive agent, an adhesive, and an additive in a mass ratio of 85-92:8-12:0-3, such as a thickener or calcium hydroxide.

[0110] According to some embodiments of this application, the conductive agent in the first conductive adhesive layer includes at least one of a one-dimensional conductive agent and a two-dimensional conductive agent.

[0111] Since the first conductive binder layer is located between two adjacent negative electrode active material layers, the introduction of one-dimensional and two-dimensional conductive agents helps to suppress interlayer delamination and poor interlayer conductivity of the negative electrode active material layers, thereby improving the cycle performance of the battery.

[0112] One-dimensional conductive agents have a one-dimensional fibrous structure, while two-dimensional conductive agents have a two-dimensional planar structure. One-dimensional conductive agents include at least one of carbon fiber and carbon nanotubes, while two-dimensional conductive agents include graphene.

[0113] According to some embodiments of this application, the thickness of the second conductive adhesive is 0.98%-5.75% of the negative electrode film layer, and the thickness of the second conductive adhesive layer is not less than 1 μm.

[0114] By utilizing the thickness of the second conductive adhesive layer within a reasonable range, it is beneficial to prevent the composite active layer from peeling off from the current collector, thereby improving the cycle performance of the battery.

[0115] For example, the thickness of the second conductive adhesive layer is any one of 0.98%, 1.00%, 2.00%, 3.00%, 4.00%, 5.00%, and 5.75% of the thickness of the negative electrode film layer, or between any two values, and the thickness of the second conductive adhesive layer is not less than 1 μm.

[0116] Optionally, the thickness of the second conductive adhesive layer is 1-10 μm.

[0117] For example, the thickness of the second conductive adhesive layer is any value of 1 μm, 3 μm, 5 μm, 8 μm, 10 μm or between any two values.

[0118] According to some embodiments of this application, please refer to Figure 4 The negative electrode 30 includes a current collector 31 and a negative electrode film layer 32 attached to the surface of the current collector 31. From the side closer to the current collector 31 to the side farther away from the current collector 31, the negative electrode film layer 32 includes a second conductive adhesive layer 34, a second negative electrode active material layer 333, a first conductive adhesive layer 332, and a first negative electrode active material layer 331 arranged in sequence. The rebound rate of the first negative electrode active material layer 331 after full charge is less than that of the second negative electrode active material layer 333 after full charge. The negative electrode active material in the first negative electrode active material layer 331 is graphite, and the negative electrode active material in the second negative electrode active material layer 333 is a silicon-based active material. The adhesive force of the second conductive adhesive layer 34 is less than that of the first conductive adhesive layer 332, and the conductivity of the second conductive adhesive layer 34 is less than that of the first conductive adhesive layer 332.

[0119] According to some embodiments of this application, this application also provides a battery, including a battery cell of any of the above solutions.

[0120] According to some embodiments of this application, this application also provides an electrical device, including a battery cell or battery of any of the above schemes, and the battery cell and battery are used to provide electrical energy.

[0121] The electrical equipment can be any of the aforementioned devices or systems that use batteries.

[0122] The following specific embodiments are provided to better illustrate this application.

[0123] Example 1

[0124] [Preparation of the negative electrode]

[0125] Current collector: Aluminum foil

[0126] Styrene-butadiene rubber (SBR), carbon black, and calcium hydroxide were stirred and dispersed in N-methylpyrrolidone at a mass ratio of 10:88:2 as the first slurry.

[0127] The silica (with a rebound rate of 250% after full charge), carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were stirred and dispersed in deionized water at a mass ratio of 94:1:2:3 as the second slurry.

[0128] Styrene-butadiene rubber (SBR), conductive agent, and calcium hydroxide were stirred and dispersed in N-methylpyrrolidone as the third slurry according to the proportions shown in Table 1.

[0129] Artificial graphite (with a rebound rate of 20% after full filling), carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were stirred and dispersed in deionized water at a mass ratio of 95:1:2:2 as the fourth slurry.

[0130] A first slurry is applied to the current collector to form a first coating. A second slurry is then applied over the first coating to form a second coating. A third slurry is then applied over the second coating to form a third coating. Finally, a fourth slurry is applied over the third coating to form a fourth coating. The mixture is then dried at 80°C and compacted using a cold press to obtain the desired result. Figure 4 The negative electrode 30 shown includes a current collector 31 and a negative electrode film 32. The negative electrode film 32 includes a second conductive adhesive layer 34, a second negative electrode active material layer 333, a first conductive adhesive layer 332 and a first negative electrode active material layer 331 arranged in sequence from the side near the current collector 31 to the side away from the current collector 31.

[0131] [Preparation of the positive electrode plate]

[0132] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, conductive agent Super-P, and binder polyvinylidene fluoride are stirred and dispersed in N-methylpyrrolidone at a mass ratio of 96:2:2 to prepare a positive electrode slurry. The slurry is coated on the positive electrode current collector aluminum foil and then compacted by a cold press to obtain the positive electrode sheet.

[0133] Preparation of Electrolyte

[0134] Lithium salt LiPF6 was added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 35:65 and mixed thoroughly to obtain an electrolyte, wherein the molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0135]

Isolation Film

[0136] A 12μm thick polyethylene porous membrane was selected.

[0137] [Preparation of Lithium-ion Batteries]

[0138] The negative electrode sheet, separator, and positive electrode sheet are stacked in sequence, with the separator placed between the positive and negative electrode sheets to provide isolation. The cells are then wound to obtain a bare cell, which is then inserted into the battery casing. After baking, electrolyte injection, settling, encapsulation, formation, and capacity testing, a lithium-ion battery is obtained.

[0139] Examples 2-14 and Comparative Examples 1-2

[0140] The only difference from Example 1 is that the negative electrode parameters are different, as shown in Table 1.

[0141] In both Example 5 and Comparative Example 1, a second conductive adhesive layer was not provided.

[0142] [Performance measurements were performed on the lithium-ion batteries prepared in each embodiment and comparative example]

[0143] (1) Battery cycle performance test

[0144] At 25°C, the lithium-ion batteries prepared in each embodiment and comparative example were charged and discharged at a 1C rate, respectively, and subjected to full charge and discharge cycle tests until the battery capacity decayed to 80% of the initial capacity. The number of cycles was recorded.

[0145] (2) Battery capacity test

[0146] At 25°C, the lithium-ion batteries prepared in each embodiment and comparative example were discharged to the lower voltage limit at a 1C rate, and then charged to the upper voltage limit at 1 / 3C and 1C rates respectively (without CV charging). The 1 / 3C capacity and 1C capacity were recorded.

[0147] (3) Test method for DC resistance (DCR)

[0148] At 25°C, the lithium-ion battery was charged at a constant current of 1.5C to 4.45V, then charged at a constant voltage of 4.45V to 0.05C, and left to stand for 30 minutes. Then, it was discharged at 0.1C for 10 seconds, and the voltage value U1 was recorded; subsequently, it was discharged at 1C for 360 seconds, and the voltage value U2 was recorded. "1C" is the current value at which the battery capacity is completely discharged within one hour. The DC resistance R of the lithium-ion battery was calculated using the following formula: R = (U2 - U1) / (1C - 0.1C). Unless otherwise specified, the DCR of this application is obtained by testing the lithium-ion battery at 10% state of charge (SOC), and the unit is Ω.

[0149] (4) Weight energy density

[0150] At 25℃, lithium-ion batteries were charged and discharged at a rate of 1C / 1C with a voltage range of 2.5-4.25V on a Newway testing machine. The energy released by the cell during the first charge and discharge cycle was recorded and then divided by the weight of the cell to obtain the cell's gravimetric energy density, expressed in Wh / kg.

[0151] Table 1 Negative Electrode

[0152]

[0153]

[0154] Table 2 Performance Measurement Results

[0155]

[0156]

[0157] According to Tables 1 and 2, it can be seen that the negative electrode sheet provided in this application can improve the technical problem of poor battery cycle performance.

[0158] As can be seen from Examples 1 to 3, the selection of the conductive agent in the first conductive binder layer will affect the cycle performance of the battery. When the conductive agent is composed of carbon nanotubes and graphene, compared with carbon black, the DC resistance of the battery is reduced and the number of cycles is increased, and the cycle performance is significantly improved. This indicates that when the conductive agent in the first conductive binder layer is a one-dimensional conductive agent or a two-dimensional conductive agent, the cycle performance of the battery can be effectively improved.

[0159] In Example 4, the raw material ratio of the first conductive adhesive layer is exactly the same as that of the second conductive adhesive layer. That is, the adhesive strength of the second conductive adhesive layer is the same as that of the first conductive adhesive layer, and the conductivity of the second conductive adhesive layer is the same as that of the first conductive adhesive layer. Compared with Example 1, the DC resistance of the battery increases and the number of cycles decreases, indicating that the adhesive strength of the second conductive adhesive layer is less than that of the first conductive adhesive layer. Setting the conductivity of the second conductive adhesive layer to be less than that of the first conductive adhesive layer can improve the cycle performance of the battery.

[0160] The only difference between Example 5 and Example 4 is that Example 5 does not have a second conductive adhesive layer, which leads to an increase in the DC resistance of the battery and a decrease in the number of cycles, indicating that the addition of a second conductive adhesive layer can improve the cycle performance of the battery.

[0161] As shown in Examples 1 and 6-8, the thickness of the first conductive binder layer and the second conductive binder layer affects the battery's capacity, gravimetric energy density, and DC resistance. The capacity and gravimetric energy density decrease with increasing thickness. When the thickness of the first conductive binder layer and the second conductive binder layer is 0.98%-5.75% of the thickness of the negative electrode film layer, the battery can maintain better capacity, gravimetric energy density, and DC resistance, and has better electrochemical cycle performance.

[0162] The difference between Examples 1 and Examples 9-11 lies in the thickness of the second negative electrode active material layer. When the thickness of the second negative electrode active material layer is 1-60μm, the battery has better DC resistance and cycle count, and better cycle performance.

[0163] The difference between Examples 1 and Examples 12-14 is that the thickness of the first negative electrode active material layer is different. When the thickness of the first negative electrode active material layer is 140-210μm, the battery has better DC resistance and cycle count, and better cycle performance.

[0164] According to Example 1 and Comparative Example 1, it can be seen that in Comparative Example 1, the first negative electrode active material layer is directly formed on the surface of the second negative electrode active material layer without the first conductive binder layer. Since the rebound rate of silicon suboxide and artificial graphite after full charge is significantly different, the DC resistance of Comparative Example 1 increases and the number of cycles decreases significantly, resulting in poor cycle performance. This shows that the first conductive binder layer can significantly affect the cycle performance of the battery.

[0165] According to Example 1 and Comparative Example 2, Comparative Example 2 did not have a first conductive adhesive layer and did not have a second conductive adhesive layer. As a result, the DC resistance of Comparative Example 2 was further increased and the number of cycles was further reduced compared to Comparative Example 1, resulting in poor cycle performance. This indicates that the second conductive adhesive layer can affect the cycle performance of the battery.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A negative electrode sheet, characterized in that, The device includes a current collector and a negative electrode film layer disposed on at least one side surface of the current collector. The negative electrode film layer includes a composite active layer and a second conductive binder layer. The second conductive binder layer is located between the composite active layer and the current collector. The composite active layer includes a first conductive binder layer and two negative electrode active material layers along its thickness direction. Among them, the rebound rates of two adjacent negative electrode active material layers after full charging are different. The first conductive adhesive layer is located between two adjacent negative electrode active material layers. Among the two adjacent negative electrode active material layers, the negative electrode active material layer closer to the current collector is the second negative electrode active material layer, and its rebound rate after full charging is A1. The negative electrode active material layer away from the current collector is the first negative electrode active material layer, and its rebound rate after full charging is A2. A1 > A2. The first negative electrode active material layer and the second negative electrode active material layer each include a negative electrode active material. The negative electrode active material in the first negative electrode active material layer is a first negative electrode active material, and the rebound rate of the first negative electrode active material after full charging is B1, 10%≤B1≤30%. The negative electrode active material in the second negative electrode active material layer is a second negative electrode active material, and the rebound rate of the second negative electrode active material after full charging is B2, 200%≤B2≤300%. The adhesive force of the second conductive adhesive layer is less than that of the first conductive adhesive layer; the conductivity of the second conductive adhesive layer is less than that of the first conductive adhesive layer; the thickness of the second negative electrode active material layer is 1-60 μm, and the thickness of the first negative electrode active material layer is 140-210 μm.

2. The negative electrode sheet according to claim 1, characterized in that, Both the first negative electrode active material layer and the second negative electrode active material layer include a binder; The amount of binder added in the first negative electrode active material layer is less than the amount of binder added in the second negative electrode active material layer.

3. The negative electrode sheet according to claim 2, characterized in that, The first negative electrode active material includes graphite, and the second negative electrode active material includes silicon-based active material.

4. The negative electrode sheet according to claim 3, characterized in that, Both the first negative electrode active material layer and the second negative electrode active material layer include a conductive agent; Wherein, the conductivity of the conductive agent in the first negative electrode active material layer is less than the conductivity of the conductive agent in the second negative electrode active material layer, and the amount of conductive agent added in the first negative electrode active material layer is equal to the amount of conductive agent added in the second negative electrode active material layer.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The thickness of the first conductive adhesive layer accounts for 0.98%-5.75% of the thickness of the negative electrode film layer.

6. The negative electrode sheet according to claim 1, characterized in that, Both the second conductive adhesive layer and the first conductive adhesive layer comprise a conductive agent and an adhesive, and the negative electrode film layer satisfies at least one of (b1)-(b2): (b1) The adhesive in the second conductive adhesive layer is the same as the adhesive in the first conductive adhesive layer, and the amount of adhesive added in the second conductive adhesive layer is less than the amount of adhesive added in the first conductive adhesive layer; (b2) The amount of conductive agent added in the second conductive adhesive layer is the same as that in the first conductive adhesive layer, and the conductivity of the conductive agent in the second conductive adhesive layer is less than that of the conductive agent in the first conductive adhesive layer.

7. The negative electrode sheet according to claim 6, characterized in that, The conductive agent in the first conductive adhesive layer includes at least one of a one-dimensional conductive agent and a two-dimensional conductive agent.

8. The negative electrode sheet according to claim 7, characterized in that, The one-dimensional conductive agent includes at least one of carbon nanotubes and carbon fibers.

9. The negative electrode sheet according to claim 7, characterized in that, The two-dimensional conductive agent includes graphene.

10. The negative electrode sheet according to any one of claims 1-4, characterized in that, The thickness of the second conductive adhesive layer is 0.98%-5.75% of that of the negative electrode film layer, and the thickness of the second conductive adhesive layer is not less than 1 μm.

11. The negative electrode sheet according to claim 10, characterized in that, The thickness of the second conductive adhesive layer is 1-10 μm.

12. A single battery cell, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-11.

13. A battery, characterized in that, Includes the battery cell as described in claim 12.

14. An electrical appliance, characterized in that, Includes a battery cell as described in claim 12 or a battery as described in claim 13, wherein the battery cell and the battery are used to provide electrical energy.

Images