Negative pole piece, battery monomer, battery and electric device

Abstract

The invention provides a negative pole piece, a battery monomer, a battery and a power utilization device, the negative pole piece comprises a negative current collector, and first negative pole film layers and second negative pole film layers arranged on the surface of the negative current collector, and the first negative pole film layers are arranged on two sides of the second negative pole film layer along the width direction of the negative current collector; the thickness of the first negative electrode film layer is smaller than that of the second negative electrode film layer, when the first negative electrode film layer comprises first graphite and the second negative electrode film layer comprises one sub-film layer, one sub-film layer comprises second graphite, the OI1 value of the first graphite is smaller than the OI2 value of the second graphite, or when the second negative electrode film layer comprises multiple sub-film layers, the OI1 value of the second graphite is smaller than the OI2 value of the second graphite. Each sub-film layer in the multiple sub-film layers comprises graphite, at least one sub-film layer comprises second graphite, the OI2 value of the second graphite is the minimum in the OI values of the graphite, and the OI1 value of the first graphite is smaller than or equal to the OI2 value of the second graphite. According to the negative pole piece, the battery monomer, the battery and the electric device provided by the invention, the lithium precipitation problem of the battery can be relieved, and the performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a negative electrode sheet, a battery cell, a battery, and an electrical device. Background Art

[0002] In recent years, with the increasingly wide application range of batteries, batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of batteries, higher requirements are also put forward for their performance, lifespan, etc.

[0003] During the charge and discharge process of the battery, lithium ions are continuously deintercalated and intercalated between the positive electrode and the negative electrode. After multiple charge and discharge cycles, lithium plating may occur. The precipitated lithium accumulates continuously, causing the separator to be punctured, thereby affecting the performance and lifespan of the battery. Summary of the Invention

[0004] The present application is made in view of the above technical problems, and its purpose is to provide a negative electrode sheet, a battery cell, a battery, and an electrical device. When the negative electrode sheet is applied to a battery, it can alleviate the problem of lithium plating, thereby improving the performance and lifespan of the battery.

[0005] In a first aspect, a negative electrode sheet is provided, including: a negative electrode current collector; and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. Among them, the first negative electrode film layer is provided on both sides of the second negative electrode film layer along the width direction of the negative electrode current collector. The size of the first negative electrode film layer in the thickness direction is smaller than the size of the second negative electrode film layer in the thickness direction. The first negative electrode film layer includes first graphite, and the second negative electrode film layer includes one or more sub-film layers. When the second negative electrode film layer includes one sub-film layer, the one sub-film layer includes second graphite, and the OI1 value of the first graphite is less than the OI2 value of the second graphite. Or, when the second negative electrode film layer includes multiple sub-film layers, each sub-film layer in the multiple sub-film layers includes graphite, and at least one sub-film layer includes second graphite. The OI2 value of the second graphite is the smallest among the OI values of the graphite, and the OI1 value of the first graphite is less than or equal to the OI2 value of the second graphite.

[0006] Since there are thinning areas at both side edges of the negative electrode tab along its width direction, the thickness of the thinning area (i.e., the first negative electrode film layer) of the negative electrode tab is less than the thickness of the second negative electrode film layer. Therefore, in the embodiments of the present application, along the width direction of the negative electrode tab, the first negative electrode film layer including the first graphite is disposed on both sides of the second negative electrode film layer including the second graphite, so that the overall OI value of the graphite in the first negative electrode film layer is less than the OI value of the graphite in the second negative electrode film layer. Since the battery is charged from a fully discharged state to a fully charged state, the expansion rate of the low OI value graphite in the negative electrode tab is greater than that of the high OI value graphite, so that the expansion size of the first negative electrode film layer of the negative electrode tab along its thickness direction can be greater than the expansion size of the second negative electrode film layer along its thickness direction, the interlayer gap of the battery tab at the first negative electrode film layer can be reduced, and further the difference between the lithium ion transmission paths at the first negative electrode film layer and the second negative electrode film layer can be reduced, and the generation of lithium deposition at the first negative electrode film layer of the negative electrode tab can be reduced.

[0007] In a possible implementation, the second negative electrode film layer includes one sub-film layer.

[0008] In the embodiments of the present application, along the width direction of the negative electrode tab, the first negative electrode film layer including the low OI value graphite (the first graphite) is disposed on both sides of the second negative electrode film layer including the high OI value graphite (the second graphite). Since the battery is charged from a fully discharged state to a fully charged state, the expansion rate of the low OI value graphite in the negative electrode tab is greater than that of the high OI value graphite, so that the expansion size of the first negative electrode film layer of the negative electrode tab along its thickness direction can be greater than the expansion size of the second negative electrode film layer along its thickness direction, the interlayer gap of the battery tab at the first negative electrode film layer can be reduced, and further the difference between the lithium ion transmission paths at the first negative electrode film layer and the second negative electrode film layer can be reduced, and the generation of lithium deposition at the first negative electrode film layer of the negative electrode tab can be reduced.

[0009] On the other hand, the low OI value graphite disposed in the first negative electrode film layer is beneficial to the insertion of lithium ions, can improve the diffusion rate of lithium ions in the overhang area, and thus alleviate the lithium deposition problem caused by the slow diffusion of lithium ions in the overhang area.

[0010] In a possible implementation, the OI1 value of the first graphite satisfies: 4 ≤ OI1 ≤ 50, optionally, 13 ≤ OI1 ≤ 23.

[0011] In the embodiments of the present application, by controlling the OI1 value of the first graphite within a suitable range, the generation of lithium deposition caused by the thinning of the edge area of the negative electrode tab along its width direction can be better reduced, and at the same time, the lithium deposition problem caused by the slow diffusion of lithium ions in the overhang area can be better alleviated.

[0012] In a possible implementation, the OI2 value of the second graphite satisfies: 8 ≤ OI2 ≤ 55. Optionally, 15 ≤ OI2 ≤ 27.

[0013] In the embodiments of the present application, by controlling the OI2 value of the second graphite within a suitable range, while alleviating the lithium delamination problem, the cost of the negative electrode sheet can be reduced, the life, specific capacity, and compaction density of the negative electrode sheet can be improved, which is beneficial to reducing the cost of the battery and enhancing the performance and life of the battery.

[0014] In a possible implementation, the first graphite includes at least one of natural graphite and artificial graphite, and / or the second graphite includes at least one of natural graphite and artificial graphite.

[0015] In a possible implementation, the second negative electrode film layer includes multiple sub-film layers. The multiple sub-film layers include a first sub-film layer and a second sub-film layer. The first sub-film layer includes the second graphite, and the second sub-film layer includes the third graphite. Wherein, the second sub-film layer is disposed on the surface of the negative electrode current collector, the first sub-film layer is disposed on the surface of the second sub-film layer away from the negative electrode current collector, and the OI2 value of the second graphite is less than the OI3 value of the third graphite.

[0016] In the embodiments of the present application, in the width direction of the negative electrode sheet, by controlling the OI1 value of the first graphite to be less than or equal to the OI2 value of the second graphite and the OI2 value of the second graphite to be less than the OI3 value of the third graphite, the OI value of the graphite in the first negative electrode film layer is generally less than the OI value of the graphite in the second negative electrode film layer. Since the battery is charged from a fully discharged state to a fully charged state, the expansion rate of the graphite with a low OI value in the negative electrode sheet is greater than that of the graphite with a high OI value. Thus, the expansion size of the first negative electrode film layer of the negative electrode sheet in its thickness direction can be made greater than the expansion size of the second negative electrode film layer in its thickness direction, the interlayer gap of the battery electrode sheet at the first negative electrode film layer can be reduced, and further the difference between the lithium ion transmission paths at the first negative electrode film layer and the second negative electrode film layer can be reduced, and the generation of lithium delamination at the first negative electrode film layer of the negative electrode sheet can be reduced.

[0017] On the other hand, by disposing the second graphite with a low OI value on the surface of the negative electrode sheet, that is, on the surface layer of the second sub-film layer, it is beneficial to the diffusion of lithium ions and improves the fast charging ability of the battery; at the same time, by disposing the third graphite with a high OI value between the first sub-film layer and the negative electrode current collector, the life, compaction density, and specific capacity of the negative electrode sheet can be improved, and the cost of the negative electrode sheet can be reduced, thereby improving the comprehensive performance of the negative electrode sheet.

[0018] In a possible implementation, the OI1 value of the first graphite satisfies: 4 ≤ OI1 ≤ 50. Optionally, 13 ≤ OI1 ≤ 23.

[0019] In the embodiments of the present application, by controlling the OI1 value of the first graphite within a suitable range, it is possible to better reduce the generation of lithium plating caused by the thinning of the edge region of the negative electrode sheet along its width direction, and at the same time, it can also better alleviate the lithium plating problem caused by the slow diffusion of lithium ions in the overhang region.

[0020] In a possible implementation, the OI2 value of the second graphite satisfies: 4 ≤ OI2 ≤ 50, optionally, 13 ≤ OI2 ≤ 23.

[0021] In the embodiments of the present application, by controlling the OI2 value of the second graphite within a reasonable range, it is beneficial to obtain a second negative electrode film layer with a reasonable OI value of graphite, thereby effectively improving the lithium plating problem.

[0022] In a possible implementation, the OI3 value of the third graphite satisfies: 11 ≤ OI3 ≤ 60, optionally, 17 ≤ OI3 ≤ 30.

[0023] In the embodiments of the present application, by controlling the OI3 value of the third graphite within a reasonable range, it is beneficial to obtain a second negative electrode film layer with a reasonable OI value of graphite, thereby effectively improving the lithium plating problem.

[0024] In a possible implementation, the first graphite is artificial graphite, and / or the second graphite is artificial graphite, and / or the third graphite is natural graphite.

[0025] In the embodiments of the present application, since the OI value of artificial graphite is generally lower than that of natural graphite as a whole, artificial graphite with a low OI value can be selected as the first graphite, and / or artificial graphite with a low OI value can be selected as the second graphite, and / or natural graphite with a high OI value can be selected as the third graphite. In this way, it is convenient to select graphite for the negative electrode film layer.

[0026] In a possible implementation, the first negative electrode film layer further includes silicon, and the silicon is doped between the particles of the first graphite.

[0027] In the embodiments of the present application, silicon can be added to the first negative electrode film layer to further increase the expansion size of the first negative electrode film layer of the negative electrode sheet along the thickness direction, thereby reducing the migration path length of lithium ions near the first negative electrode film layer during the charge and discharge process of the battery, and effectively improving the lithium plating caused by the thinning area of the negative electrode sheet.

[0028] In a possible implementation, the first negative electrode film layer further includes amorphous carbon, and the amorphous carbon is used to coat at least part of the surface of the particles of the first graphite.

[0029] In the embodiments of the present application, by coating the outer layer of graphite particles with amorphous carbon, when the battery is charged from a fully discharged state to a fully charged state, the expansion size of the first negative electrode film layer of the negative electrode plate in the thickness direction can be further increased, so that the migration path length of lithium ions near the first negative electrode film layer during the charge and discharge process of the battery can be reduced, and the lithium deposition caused by the thinning area of the negative electrode plate can be effectively improved.

[0030] In a second aspect, a battery cell is provided, and the battery cell includes the negative electrode plate in any possible implementation manner of the first aspect of the present application.

[0031] In a third aspect, a battery is provided, and the battery includes the battery cell in any possible implementation manner of the second aspect of the present application.

[0032] In a fourth aspect, an electrical device is provided, and the electrical device includes the battery cell in any possible implementation manner of the second aspect of the present application, and / or the battery in any possible implementation manner of the third aspect of the present application. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of lithium deposition on the negative electrode plate provided by the embodiments of the present application.

[0034] Figure 2 It is a schematic diagram of the principle of lithium deposition at the overhang area of the negative electrode plate provided by the embodiments of the present application.

[0035] Figure 3 It is a schematic diagram of the negative electrode plate provided by the embodiments of the present application.

[0036] Figure 4 It is a schematic diagram of the negative electrode plate provided by the embodiments of the present application.

[0037] Figure 5 It is a schematic structural diagram of the battery cell provided by the embodiments of the present application.

[0038] Figure 6 It is a schematic diagram of the battery module provided by the embodiments of the present application.

[0039] Figure 7 It is a schematic diagram of the battery provided by the embodiments of the present application.

[0040] Figure 8 It is another schematic diagram of the battery provided by the embodiments of the present application.

[0041] Reference Signs:

[0042] 1 - Negative electrode plate;

[0043] 10 - Negative electrode current collector, 11 - Negative electrode film layer;

[0044] 111 - The first negative electrode film layer, 112 - The second negative electrode film layer;

[0045] 1121 - The first sub - film layer, 1122 - The second sub - film layer;

[0046] 500 - Battery cell, 600 - Battery module, 700 - Battery, 701 - Upper box body, 702 - Lower box body. Detailed implementation manners

[0047] Hereinafter, the implementation manners of the negative electrode plate, battery cell, battery, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well - known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0048] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real - number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] In the description of the present application, it should be noted that unless otherwise specified, the meaning of "a plurality" is more than two; the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. 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 therefore should not be construed as a limitation to the present application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range.

[0050] If there is no special indication, the "including" and "comprising" mentioned in the present application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or it can only include or comprise the listed components.

[0051] If there is no special indication, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0052] If there is no special indication, all steps of the present application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or it can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or it can also include steps (a), (c), and (b), or it can include steps (c), (a), and (b), etc.

[0053] If there is no special indication, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0054] If there is no special indication, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0055] If there is no special indication, the following terms have the following meanings. Any undefined terms have their generally recognized meanings in the art.

[0056] Generally, a battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short - circuit between the positive and negative electrodes, and at the same time allows ions to pass through. In some embodiments, the battery described in the present application is also referred to as a secondary battery.

[0057] Taking a lithium - ion battery as an example in the present application, a lithium - ion battery is a typical secondary battery, which relies on the chemical reaction of lithium ions de - intercalating and intercalating between the positive and negative electrodes for charge and discharge. During the charging process of the lithium - ion battery, lithium ions are extracted from the positive electrode, move and are embedded in the negative electrode; while during the discharging process, lithium ions are extracted from the negative electrode, move and are embedded in the positive electrode.

[0058] It should be understood that the processes of "lithium intercalation" and "intercalation" described in the present application refer to the process in which lithium ions are intercalated into the positive electrode plate and the negative electrode plate due to an electrochemical reaction, and the processes of "extraction", "lithium de - intercalation", and "de - intercalation" described in the present application refer to the process in which lithium ions are extracted from the positive electrode plate and the negative electrode plate due to an electrochemical reaction.

[0059] In order to prevent the edge of the negative electrode plate from bulging, there is a thinned area at the edge of the negative electrode plate along its width direction, so that the thickness of the edge area is less than that of other areas. This way increases the inter - layer gap between the negative electrode plate and the positive electrode plate of the assembled battery cell at the thinned area. During the charge and discharge process, the transmission path of lithium ions in the edge area becomes longer, which may cause local lithium deposition at the edge area of the negative electrode plate, as Figure 1 shown.

[0060] On the other hand, after multiple charge or fast - charge cycles, lithium deposition will occur in the overhang area located at the edge of the negative electrode plate along its width direction. The continuously accumulated deposited lithium will cause the separator between the positive and negative electrodes to be punctured, affecting the performance and life of the battery. The following briefly introduces the lithium deposition in the overhang area located at the edge of the negative electrode plate in combination with Figure 2 to briefly introduce the lithium deposition in the overhang area located at the edge of the negative electrode plate.

[0061] Generally, in the width direction of the electrode plate, the negative electrode plate can be divided into an overhang area and a non - overhang area. The overhang area is the area where the negative electrode plate extends beyond the positive electrode plate or the non - overlapping area between the negative electrode plate and the positive electrode plate, and the non - overhang area is the overlapping area between the negative electrode plate and the positive electrode plate.

[0062] As Figure 2 shown in (a) of Figure 2As shown in (b) therein, the lithium ions in the positive electrode move to the negative electrode and are embedded in the negative electrode. On the one hand, a part of the lithium ions in the positive electrode can be embedded in the overhang region of the negative electrode. On the other hand, the lithium ions in the non-overhang region of the negative electrode undergo edge diffusion and move from the non-overhang region to the overhang region. During the discharging process, the lithium ions in the negative electrode are deintercalated and return to the positive electrode. As shown in Figure 2 in (c) therein, due to the existence of the overhang region, the lithium ion concentration in the edge region of the positive electrode close to the overhang region of the negative electrode is higher than that in other regions of the positive electrode. During the next charging process, as shown in Figure 2 in (d) therein, due to the higher lithium ion concentration in the above-mentioned edge region of the positive electrode, after charging, the lithium ion concentration in the negative electrode close to the overhang region is higher, so lithium deposition occurs at the edge of the overhang region or in the overhang region.

[0063] In view of this, the embodiment of the present application provides a negative electrode tab, which includes: a negative electrode current collector; and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. Among them, the first negative electrode film layer is provided on both sides of the second negative electrode film layer along the width direction of the negative electrode current collector. The size of the first negative electrode film layer in the thickness direction is smaller than that of the second negative electrode film layer in the thickness direction. The first negative electrode film layer includes first graphite, and the second negative electrode film layer includes one or more sub-film layers. When the second negative electrode film layer includes one sub-film layer, the one sub-film layer includes second graphite, and the orientation index (OI)1 value of the first graphite is smaller than the OI2 value of the second graphite. Or, when the second negative electrode film layer includes multiple sub-film layers, each sub-film layer in the multiple sub-film layers includes graphite, and at least one sub-film layer includes second graphite. The OI2 value of the second graphite is the smallest among the OI values of graphite, and the OI1 value of the first graphite is less than or equal to the OI2 value of the second graphite.

[0064] In the embodiment of the present application, along the width direction of the negative electrode tab, the first negative electrode film layer including first graphite is provided on both sides of the second negative electrode film layer including second graphite, so that the OI value of the graphite in the first negative electrode film layer is generally smaller than the OI value of the graphite in the second negative electrode film layer. Since the battery is charged from a fully discharged state to a fully charged state, the expansion rate of the low-OI-value graphite in the negative electrode tab is greater than that of the high-OI-value graphite. Therefore, the expansion size of the first negative electrode film layer of the negative electrode tab in its thickness direction can be greater than that of the second negative electrode film layer in its thickness direction, which can reduce the interlayer gap of the electrode tab of the battery at the first negative electrode film layer, and further reduce the difference between the lithium ion transmission paths at the first negative electrode film layer and the second negative electrode film layer, and can reduce the generation of lithium deposition at the first negative electrode film layer of the negative electrode tab.

[0065] The negative electrode sheet provided by the embodiment of the present application is exemplarily introduced as follows.

[0066] [Negative electrode sheet]

[0067] Figure 3 It is a schematic diagram of the negative electrode sheet provided by the embodiment of the present application. As Figure 3 shown, the negative electrode sheet 1 includes a negative electrode current collector 10 and a negative electrode film layer 11 provided on at least one surface of the negative electrode current collector 10.

[0068] The negative electrode film layer 11 may include a first negative electrode film layer 111 and a second negative electrode film layer 112. Among them, the first negative electrode film layer 111 is provided on both sides of the second negative electrode film layer 112 along the width direction of the negative electrode sheet 1. The size of the first negative electrode film layer 111 along the thickness direction of the negative electrode sheet 1 is smaller than the size of the second negative electrode film layer 112 along the thickness direction of the negative electrode sheet 1. The first negative electrode film layer 111 includes first graphite, and the second negative electrode film layer 112 includes one or more sub-film layers.

[0069] When the second negative electrode film layer 112 includes one sub-film layer, this one sub-film layer includes second graphite, and the OI1 value of the first graphite is less than the OI2 value of the second graphite.

[0070] That is, the second negative electrode film layer 112 includes one sub-film layer, and this one sub-film layer includes second graphite. The OI value of the graphite in the first negative electrode film layer 111 is less than the OI value of the graphite in the second negative electrode film layer 112.

[0071] Or, when the second negative electrode film layer 112 includes multiple sub-film layers, each sub-film layer in this multiple sub-film layers includes graphite, and the OI value of the second graphite is the smallest among the OI values of the graphite in the multiple sub-film layers, and the OI1 value of the first graphite is less than or equal to the OI2 value of the second graphite.

[0072] That is, the second negative electrode film layer 112 includes multiple sub-film layers, and there is a sub-film layer including second graphite in this multiple sub-film layers, and the OI value of the graphite in the sub-film layer including second graphite is the smallest among the multiple sub-film layers. Since the OI value of the second graphite is the smallest among the multiple sub-film layers of the second negative electrode film layer 112, the OI value of the graphite in the second negative electrode film layer 112 is greater than the OI value of the graphite in the first negative electrode film layer 111 as a whole.

[0073] The negative electrode sheet 1 generally includes a negative electrode current collector 10 and a negative electrode film layer 11 provided on at least one surface of the negative electrode current collector 10, and the negative electrode film layer 11 includes graphite.

[0074] As an example, the negative electrode current collector 10 has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer 11 is disposed on either one or both of the two opposite surfaces of the negative electrode current collector 10. That is, the negative electrode film layer 11 is surface-connected to the negative electrode current collector 10 along the thickness direction of the negative electrode current collector 10. Among them, the negative electrode film layer 11 can be directly connected to the negative electrode current collector 10, or can also be indirectly connected to the negative electrode current collector 10.

[0075] The negative electrode current collector 10 can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material substrate layer 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 (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver or 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.).

[0076] The OI value of graphite can be obtained by calculating the peak intensity ratio of the diffraction peak of the (004) crystal plane and the diffraction peak of the (110) crystal plane.

[0077] For example, the OI value of graphite can be measured by an X-ray diffraction method using a powder X-ray diffractometer. The graphite sample to be measured is placed horizontally on the sample stage, and continuous mode scanning is used (scanning range 10 - 80°, scanning speed 2° / min) to obtain the corresponding diffraction pattern. According to the diffraction pattern, the diffraction peak intensity of the (004) crystal plane of graphite is determined as I(004), and the diffraction peak intensity of the (110) crystal plane of graphite is determined as I(110). The OI value calculation formula is as follows: OI = I(004) / I(110).

[0078] Generally speaking, the smaller the OI value of graphite, the more favorable it is for the insertion of lithium ions, which can improve the migration rate of lithium ions, making the expansion size of the negative electrode plate 1 along its thickness direction larger when the battery is in a fully charged state compared to a fully discharged state.

[0079] The smaller the OI value of graphite, the more inclined the graphite particles are to be oriented perpendicular to the surface of the negative electrode current collector 10, that is, the (004) crystal plane is more likely to be arranged perpendicular to the surface of the negative electrode current collector 10. In this way, the negative electrode plate 1 can timely accept lithium ions from the positive electrode plate, which is beneficial to the insertion of lithium ions in the negative electrode plate 1 and can improve the migration rate of lithium ions.

[0080] During the charging and discharging processes of the battery, lithium ions are intercalated into and deintercalated from graphite, and the volume of graphite will expand and contract. The smaller the OI value of graphite, the more favorable it is for the intercalation of lithium ions. Then, during the charging process of the battery, such as charging from a fully discharged state to a fully charged state, the intercalation rate of lithium ions in graphite with a low OI value is greater than that of lithium ions with a high OI value, making the expansion rate of graphite with a low OI value greater than that of graphite with a high OI value. Furthermore, the expansion size of the negative electrode sheet 1 including graphite with a low OI value in the thickness direction is greater than that of the negative electrode sheet 1 including graphite with a high OI value in the thickness direction.

[0081] The larger the OI value of graphite, the lower the cost of the negative electrode sheet 1 including this graphite material, and the higher the compaction density, specific capacity, and lifespan.

[0082] The first negative electrode film layer 111 can be the thinned area of the negative electrode sheet 1, and the second negative electrode film layer 112 can be the main body area of the negative electrode sheet 1. Generally, in order to prevent the edges of the negative electrode sheet 1 from bulging, the edges of the negative electrode sheet 1 are thinned, and the thinned area forms the thinned area, and the unthinned area forms the main body area. The thickness of the thinned area (the first negative electrode film layer 111) is less than the thickness of the main body area (the second negative electrode film layer 112). For example, there are two first negative electrode film layers 111 along the width direction, and the size of each first negative electrode film layer 111 along the width direction of the negative electrode sheet 1 can be 10 mm.

[0083] Since there are thinned areas on both sides of the negative electrode sheet 1 along its width direction, the thickness of the thinned area (i.e., the first negative electrode film layer 111) of the negative electrode sheet 1 is less than the thickness of the main body area (the second negative electrode film layer 112). Therefore, in the embodiments of the present application, along the width direction of the negative electrode sheet 1, the first negative electrode film layer 111 including the first graphite is disposed on both sides of the second negative electrode film layer 112 including the second graphite, such that the overall OI value of the graphite in the first negative electrode film layer 111 is less than the OI value of the graphite in the second negative electrode film layer 112. Since the battery is charged from a fully discharged state to a fully charged state, the expansion rate of graphite with a low OI value in the negative electrode sheet 1 is greater than that of graphite with a high OI value. Thus, the expansion size of the first negative electrode film layer 111 of the negative electrode sheet 1 in the thickness direction can be greater than that of the second negative electrode film layer 112 in the thickness direction, which can reduce the interlayer gap of the electrode sheet of the battery at the first negative electrode film layer 111. Furthermore, the difference in the lithium ion transmission paths between the first negative electrode film layer 111 and the second negative electrode film layer 112 can be reduced, and the generation of lithium deposition at the first negative electrode film layer 111 of the negative electrode sheet 1 can be reduced.

[0084] In some embodiments, the second negative electrode film layer 112 includes one sub-film layer.

[0085] In this embodiment, both the first negative electrode film layer 111 and the second negative electrode film layer 112 include a single sub-film layer. The first negative electrode film layer 111 includes first graphite, and the second negative electrode film layer 112 includes second graphite. The OI1 value of the first graphite is less than the OI2 value of the second graphite. That is, the OI value of the graphite in the first negative electrode film layer 111 is less than the OI value of the graphite in the second negative electrode film layer 112.

[0086] In an embodiment of the present application, along the width direction of the negative electrode tab 1, the first negative electrode film layer 111 including low-OI-value graphite (first graphite) is disposed on both sides of the second negative electrode film layer 112 including high-OI-value graphite (second graphite). Since the battery is charged from a fully discharged state to a fully charged state, the expansion rate of the low-OI-value graphite in the negative electrode tab 1 is greater than that of the high-OI-value graphite. As a result, the expansion size of the first negative electrode film layer 111 of the negative electrode tab 1 in its thickness direction can be greater than the expansion size of the second negative electrode film layer 112 in its thickness direction, which can reduce the interlayer gap of the negative electrode tab 1 at the first negative electrode film layer 111. Furthermore, the difference in the lithium ion transmission paths between the first negative electrode film layer 111 and the second negative electrode film layer 112 can be reduced, and the generation of lithium deposition at the first negative electrode film layer 111 of the negative electrode tab 1 can be reduced.

[0087] On the other hand, the low-OI-value graphite disposed in the first negative electrode film layer 111 is beneficial to the insertion of lithium ions, which can improve the diffusion rate of lithium ions in the overhang region, thereby alleviating the lithium deposition problem caused by the slow diffusion of lithium ions in the overhang region.

[0088] In addition, by disposing the low-OI-value graphite in the first negative electrode film layer 111 and the high-OI-value graphite in the second negative electrode film layer 112, the high-OI-value graphite in the second negative electrode film layer 112 has low cost, high life, high specific capacity, and high tap density. Therefore, while alleviating the lithium deposition problem of the negative electrode tab 1, the cost of the negative electrode tab 1 can be reduced, and the life, specific capacity, and tap density of the negative electrode tab 1 can be improved, which is beneficial to reducing the cost of the battery and improving the performance and life of the battery.

[0089] The size of the first negative electrode film layer 111 in the thickness direction of the negative electrode tab 1 can be a single size or multiple sizes.

[0090] In some embodiments, along the width direction of the negative electrode tab 1 and from both sides of the negative electrode tab 1 towards the middle region, the thickness of the negative electrode tab 1 increases gradually.

[0091] As an example, along the width direction, starting from the edge of the negative electrode tab 1, the thickness of the first negative electrode film layer 111 can show a trend of increasing gradually. For example, the thickness of the second negative electrode film layer 112 is 0.32 mm. Along the width direction, within the range of 0 - 5 mm starting from the edge of the negative electrode tab 1, the thickness of the first negative electrode film layer 111 can be 0.27 mm; within the range of 5 mm - 7 mm starting from the edge of the negative electrode tab 1, the thickness of the first negative electrode film layer 111 can be 0.29 mm; within the range of 7 mm - 10 mm starting from the edge of the negative electrode tab 1, the thickness of the first negative electrode film layer 111 can be 0.30 mm.

[0092] The following gives an exemplary introduction to the OI values and material selection of the first graphite and the second graphite when the second negative electrode film layer 112 includes one sub - film layer.

[0093] In some embodiments, the OI1 value of the first graphite satisfies: 4 ≤ OI1 ≤ 50, optionally, 13 ≤ OI1 ≤ 23.

[0094] For example, the OI1 value can be 5, 15, 20, 25, 30, 35, 40, 45 or 50. For another example, the OI1 value can also be within the range obtained by combining any two of the above values.

[0095] In the embodiments of the present application, by controlling the OI1 value of the graphite within a suitable range, it is possible to better reduce the generation of lithium deposition caused by the thinning of the edge region of the negative electrode tab 1 along its width direction, and at the same time, it can also better alleviate the lithium deposition problem caused by the slow diffusion of lithium ions in the overhang region.

[0096] In some embodiments, the OI2 value of the second graphite satisfies: 8 ≤ OI2 ≤ 55, optionally, 15 ≤ OI2 ≤ 27.

[0097] For example, the OI2 value can be 10, 15, 20, 25, 30, 35, 40, 45, 50 or 55. For another example, the OI2 value can also be within the range obtained by combining any two of the above values.

[0098] In the embodiments of the present application, by controlling the OI2 value of the second graphite within a suitable range, while alleviating the lithium deposition problem, it is possible to reduce the cost of the negative electrode tab 1, improve the life, specific capacity and tap density of the negative electrode tab 1, which is beneficial to reducing the cost of the battery and improving the performance and life of the battery.

[0099] In some embodiments, the first graphite can include at least one of natural graphite or artificial graphite, and / or, the second graphite can be at least one of natural graphite or artificial graphite.

[0100] The first graphite and the second graphite can be the same or different. For example, both the first graphite and the second graphite can be natural graphite.

[0101] In some embodiments, as Figure 4 shown, the second negative electrode film layer 112 includes multiple sub-film layers. The multiple sub-film layers include a first sub-film layer 1121 and a second sub-film layer 1122. The first sub-film layer 1121 includes the second graphite, and the second sub-film layer 1122 includes the third graphite. The OI2 value of the second graphite is less than the OI3 value of the third graphite.

[0102] Among them, the second sub-film layer 1122 is disposed on the surface of the negative electrode current collector 10, the first sub-film layer 1121 is disposed on the surface of the second sub-film layer 1122 away from the negative electrode current collector 10, and the OI2 value of the second graphite is less than the OI3 value of the third graphite.

[0103] Along the thickness direction of the negative electrode plate 1, the second sub-film layer 1122 is located between the first sub-film layer 1121 and the negative electrode current collector 10.

[0104] That is to say, in this embodiment, the first negative electrode film layer 111 includes one sub-film layer, and this one sub-film layer includes the first graphite. The second negative electrode film layer 112 includes the first sub-film layer 1121 and the second sub-film layer 1122. The first sub-film layer 1121 can include the second graphite, and the second sub-film layer 1122 can include the third graphite. The OI1 value of the first graphite is less than or equal to the OI2 value of the second graphite, and the OI2 value of the second graphite is less than the OI3 value of the third graphite.

[0105] In this embodiment, if the OI1 value of the first graphite is less than the OI2 value of the second graphite, and the OI2 value of the second graphite is less than the OI3 value of the third graphite, then the OI value of the graphite in the first negative electrode film layer 111 is less than the OI value of the graphite in the second negative electrode film layer 112.

[0106] Or, if the OI1 value of the first graphite is equal to the OI2 value of the second graphite, and the OI2 value of the second graphite is less than the OI3 value of the third graphite, then the overall OI value of the graphite in the first negative electrode film layer 111 is still less than the OI value of the graphite in the second negative electrode film layer 112.

[0107] In the embodiments of the present application, along the width direction of the negative electrode sheet 1, by controlling the OI1 value of the first graphite to be less than or equal to the OI2 value of the second graphite and the OI2 value of the second graphite to be less than the OI3 value of the third graphite, the overall OI value of the graphite in the first negative electrode film layer 111 is less than the OI value of the graphite in the second negative electrode film layer 112. Since the battery is charged from a fully discharged state to a fully charged state, the expansion rate of the graphite with a low OI value in the negative electrode sheet 1 is greater than that of the graphite with a high OI value. Therefore, the expansion size of the first negative electrode film layer 111 of the negative electrode sheet 1 in its thickness direction can be made greater than the expansion size of the second negative electrode film layer 112 in its thickness direction, which can reduce the interlayer gap of the electrode sheet of the battery at the first negative electrode film layer 111, and further reduce the difference between the lithium ion transmission paths at the first negative electrode film layer 111 and the second negative electrode film layer 112, and can reduce the generation of lithium deposition at the first negative electrode film layer 111 of the negative electrode sheet 1.

[0108] On the other hand, by disposing the second graphite with a low OI value on the surface of the negative electrode sheet 1, that is, on the surface layer of the second sub-film layer 1122, it is beneficial to the diffusion of lithium ions and improves the fast charging ability of the battery; at the same time, by disposing the third graphite with a high OI value between the first sub-film layer 1121 and the negative electrode current collector 10, the service life, compaction density, and specific capacity of the negative electrode sheet 1 can be improved, and the cost of the negative electrode sheet 1 can be reduced, thereby improving the comprehensive performance of the negative electrode sheet 1.

[0109] The following gives an exemplary introduction to the value ranges and material selections of the OI values of the first graphite, the second graphite, and the third graphite when the second negative electrode film layer 112 includes the first sub-film layer 1121 and the second sub-film layer 1122.

[0110] In some embodiments, the second graphite may include at least one of natural graphite and artificial graphite, and / or the third graphite may be at least one of natural graphite and artificial graphite.

[0111] The second graphite and the third graphite may be the same or different. For example, both the second graphite and the third graphite may be artificial graphite.

[0112] In some embodiments, the OI1 value of the first graphite satisfies: 4 ≤ OI1 ≤ 50, optionally, 13 ≤ OI1 ≤ 23.

[0113] For example, the OI1 value may be 5, 15, 20, 25, 30, 35, 40, 45, or 50. For another example, the OI1 value may also be within the range obtained by combining any two of the above values.

[0114] In the embodiments of the present application, by controlling the OI1 value of graphite within a suitable range, it is possible to better reduce the generation of lithium deposition caused by the thinning of the edge region of the negative electrode sheet 1 along its width direction, and at the same time, it can also better alleviate the lithium deposition problem caused by the slow diffusion of lithium ions in the overhang region.

[0115] In some embodiments, the OI2 value of the second graphite satisfies: 4 ≤ OI2 ≤ 50, optionally, 13 ≤ OI2 ≤ 23.

[0116] For example, the OI2 value can be 10, 20, 30, 40, or 50. For another example, the OI2 value can also be within the range obtained by combining any two of the above numerical values.

[0117] In the embodiments of the present application, by controlling the OI2 value of the second graphite within a reasonable range, it is beneficial to obtain a second negative electrode film layer 112 with the OI value of graphite within a reasonable range, thereby effectively improving the lithium deposition problem.

[0118] In some embodiments, the OI3 value of the third graphite satisfies: 11 ≤ OI3 ≤ 60, optionally, 17 ≤ OI3 ≤ 30.

[0119] For example, the OI3 value can be 20, 30, 40, 50, or 60. For another example, the OI3 value can also be within the range obtained by combining any two of the above numerical values.

[0120] In the embodiments of the present application, by controlling the OI3 value of the third graphite within a reasonable range, it is beneficial to obtain a second negative electrode film layer 112 with the OI value of graphite within a reasonable range, thereby effectively improving the lithium deposition problem.

[0121] In a possible implementation manner, the first graphite is artificial graphite, and / or, the second graphite is artificial graphite, and / or, the third graphite is natural graphite.

[0122] As an example, the first graphite and the second graphite can select artificial graphite with a low OI (such as an OI value of 4), and the third graphite can select natural graphite with a high OI value (such as an OI value of 15).

[0123] In some embodiments, the thickness ratio of the first sub-film layer 1121 to the second sub-film layer 1122 is (0.2 - 0.8) : (0.8 - 0.2)

[0124] In the embodiments of the present application, since the OI value of artificial graphite is generally lower than that of natural graphite as a whole, artificial graphite with a low OI value can be selected as the first graphite, and / or, artificial graphite with a low OI value can be selected as the second graphite, and / or, natural graphite with a high OI value can be selected as the third graphite. In this way, it is convenient to select graphite for the negative electrode film layer 11.

[0125] In some embodiments, the first negative electrode film layer 111 further includes silicon, and the silicon is doped between the particles of the first graphite.

[0126] In this embodiment, in addition to the expansion of the first graphite in the first negative electrode film layer 111 from the fully discharged state to the fully charged state, the doped silicon also expands, and the expansion rate is generally greater than that of the first graphite.

[0127] As an example, the expansion rate of a certain material from the fully discharged state to the fully charged state can be calculated by (d b2 -d b1 ) / d b1 *100%, where d b1 is the dimension of the material in the thickness direction in the fully discharged state, and d b2 is the dimension of the material in the thickness direction in the fully discharged state.

[0128] When the battery is in the fully charged state, it means that the battery has been fully charged. For example, when the power of the battery system is greater than or equal to a certain threshold (the state of charge (SOC) is greater than or equal to 95%), the battery system is in the fully charged state. For another example, when the voltage of the battery system is equal to or greater than the overvoltage threshold, the battery system is in the fully charged state.

[0129] When the battery is in the fully discharged state, it means that the energy of the battery has been exhausted. For example, when the power of the battery system is less than or equal to a certain threshold (such as SOC is less than or equal to 5%), the battery system is in the fully discharged state. For another example, when the voltage of the battery system is less than or equal to the undervoltage threshold, the battery system is in the fully discharged state.

[0130] In the embodiments of the present application, adding silicon to the first negative electrode film layer 111 can further increase the expansion dimension of the first negative electrode film layer 111 of the negative electrode plate 1 in the thickness direction when the battery goes from the fully discharged state to the fully charged state, so as to reduce the migration path length of lithium ions near the first negative electrode film layer 111 during the charge and discharge process of the battery, and improve the lithium deposition caused by the thinning area of the negative electrode plate 1.

[0131] In a possible implementation manner, the first negative electrode film layer 111 further includes amorphous carbon, and the amorphous carbon is used to coat at least part of the surface of the particles of the first graphite.

[0132] That is, amorphous carbon can be used as a coating layer to coat the particles of the first graphite to form coated secondary graphite particles. Then, the slurry for forming the first negative electrode film layer 111 can be prepared by using the particles.

[0133] In this embodiment, in addition to the expansion of the first graphite in the first negative electrode film layer 111 from the fully discharged state to the fully charged state, the amorphous carbon also expands, and the expansion rate is generally greater than that of the first graphite.

[0134] In the embodiment of the present application, by coating amorphous carbon on the graphite particles, when the battery goes from the fully discharged state to the fully charged state, the expansion size of the first negative electrode film layer 111 of the negative electrode sheet 1 in the thickness direction can be further increased, so that the migration path length of lithium ions near the first negative electrode film layer 111 during the charge and discharge process of the battery can be reduced, effectively improving the lithium deposition caused by the thinning area of the negative electrode sheet 1.

[0135] In some embodiments, the negative electrode film layer 11 further includes a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), or carboxymethyl chitosan (CMCS).

[0136] In some embodiments, the negative electrode film layer 11 further includes a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0137] In some embodiments, the negative electrode film layer 11 further includes other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0138] The embodiment of the present application also provides a battery cell, a battery, and an electrical device. The battery cell, the battery, and the electrical device provided by the embodiment of the present application are described below.

[0139] The battery cell may include a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator.

[0140] The content of the negative electrode sheet may refer to the relevant description above, and the present application will not elaborate here.

[0141] [Positive Electrode Sheet]

[0142] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

[0143] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0144] In some embodiments, the ratio of the lithium intercalation capacity per unit area of the first negative electrode film layer of the negative electrode sheet to the lithium deintercalation capacity per unit area of the positive electrode sheet is greater than 1.

[0145] As an example, the ratio of the above-mentioned lithium intercalation capacity to the lithium deintercalation capacity can be obtained by calculating (the weight of the coating slurry of the first negative electrode film layer per unit area * the weight ratio of the negative electrode active material in the coating slurry of the first negative electrode film layer * the gram capacity of the negative electrode active material * the cold pressing elongation rate of the positive electrode sheet) / (the weight of the coating slurry of the positive electrode sheet per unit area * the weight ratio of the positive electrode active material in the coating slurry of the positive electrode sheet * the gram capacity of the positive electrode active material * the cold pressing elongation rate of the negative electrode sheet).

[0146] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or 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.).

[0147] In some embodiments, the positive electrode active material can include at least one of the following materials: lithium-containing phosphate with an olivine structure, lithium transition metal oxide, or their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide 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 LiNi1 / 3Co1 / 3Mn1 / 3O2 (which can also be abbreviated as NCM333), LiNi0.5Co0.2Mn0.3O2 (which can also be abbreviated as NCM523), LiNi0.5Co0.25Mn0.25O2 (which can also be abbreviated as NCM211), LiNi0.6Co0.2Mn0.2O2 (which can also be abbreviated as NCM622), LiNi0.8Co0.1Mn0.1O2 (which can also be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi0.85Co0.15Al0.05O2), or modified compounds, etc.). Examples of the lithium-containing phosphate with an olivine structure can include but are not limited to lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, or a composite material of lithium manganese iron phosphate and carbon.

[0148] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0149] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0150] In some embodiments, the positive electrode plate can be prepared in the following manner: Dispersing the above-mentioned components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; Coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0151] [Electrolyte]

[0152] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0153] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0154] In some embodiments, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate.

[0155] In some embodiments, the solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, or diethyl sulfone.

[0156] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, and the like.

[0157] [Separator film]

[0158] The present application does not particularly limit the type of the separator film. For example, it may be a porous structure separator film with good chemical stability and mechanical stability.

[0159] In some embodiments, the material of the separator film may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator film may be a single-layer thin film or a multi-layer composite thin film, without particular limitation. When the separator film is a multi-layer composite thin film, the materials of each layer may be the same or different, without particular limitation.

[0160] In some embodiments, the outer package of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic. As plastics, polypropylene, polybutylene terephthalate, or polybutylene succinate, etc. may be listed.

[0161] The present application does not particularly limit the shape of the battery cell, which may be cylindrical, square, or any other arbitrary shape. For example, Figure 5 is a battery cell 500 with a square structure as an example.

[0162] Figure 6 is a battery module 600 as an example. Referring to Figure 6 , in the battery module 600, a plurality of battery cells 500 may be arranged in sequence along the length direction of the battery module 600. Of course, they may also be arranged in any other arbitrary manner. Further, the plurality of battery cells 500 may be fixed by fasteners.

[0163] In one embodiment, the battery module 600 may further include a housing having an accommodation space, and a plurality of battery cells 500 are accommodated in the accommodation space.

[0164] In one embodiment, the above battery module 600 may also be assembled into a battery. The number of battery modules 600 included in the battery may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery.

[0165] Figure 7 and Figure 8 is a battery 700 as an example. Referring to Figure 7 and Figure 8, in the battery 700, a battery case and a plurality of battery modules 600 disposed in the battery case can be included. The battery case includes an upper case 701 and a lower case 702. The upper case 701 can cover the lower case 702 and form a closed space for accommodating the battery modules 600. The plurality of battery modules 600 can be arranged in the battery case in any manner.

[0166] It should be understood that in some other embodiments, the above battery 700 is also referred to as a battery pack. The battery cells 500 can first form battery modules 600, and the battery 700 is composed of the battery modules 600. It is also possible to directly form the battery 700 from the battery cells 500, omitting the intermediate form of the battery modules 600.

[0167] In addition, the present application also provides an electrical device. The electrical device includes at least one of the battery cell 500, the battery module 600, or the battery 700 provided by the present application. The battery cell 500, the battery module 600, or the battery 700 can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, or energy storage systems, etc., but is not limited thereto.

[0168] The electrical device can select the battery cell 500, the battery module 600, or the battery 700 according to its usage requirements.

[0169] As an example, the electrical device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for secondary batteries, a battery pack or a battery module can be adopted.

[0170] As another example, the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thin and light design, and a secondary battery can be used as the power source.

[0171] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those without specific technical or conditions noted in the embodiments, the techniques or conditions described in the literature in the art or according to the product specifications are followed. Those reagents or instruments without the manufacturer noted are all conventional products that can be obtained through commercial procurement.

[0172] [Examples 1 - 11 and Comparative Examples 1 - 3]

[0173] Example 1

[0174] (1) Preparation of the positive electrode sheet

[0175] The positive electrode active material lithium iron phosphate, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are dissolved in the solvent N-methylpyrrolidone (NMP), and the positive electrode slurry is obtained after being fully stirred and mixed. The positive electrode slurry is then evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain the positive electrode sheet. Among them, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 96:2:2.

[0176] (2) Test of graphite OI value

[0177] Conduct OI value test on graphite to determine and select graphite with OI value that meets the requirements.

[0178] The OI value of graphite can be obtained by testing a polycrystalline X-ray diffractometer using an X-ray diffraction method. Place the graphite sample to be tested horizontally on the sample stage and scan in continuous mode (scanning interval 10-80°, scanning speed 2° / min) to obtain the corresponding diffraction spectrum. According to the diffraction spectrum, the diffraction peak intensity of the graphite (004) crystal plane is determined to be I(004), and the diffraction peak intensity of the graphite (110) crystal plane is determined to be I(110). The OI value calculation formula is as follows: OI = I(004) / I(110).

[0179] (3) Preparation of negative electrode sheet

[0180] Artificial graphite with an OI value of 4, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose were weighed and dissolved in deionized water solvent in a mass ratio of 96:2:1:1, and mixed evenly to obtain the first slurry. Artificial graphite with an OI value of 8, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose were weighed and dissolved in deionized water solvent in a mass ratio of 96:2:1:1, and mixed evenly to obtain the second slurry.

[0181] The first slurry and the second slurry are coated on an 8 μm thick common copper foil (current collector) by an extrusion coater, wherein the first slurry is coated on both sides of the second slurry along the width direction of the common copper foil. After coating, drying, cold pressing, cutting, etc. are performed to obtain the negative electrode sheet.

[0182] The first slurry forms the first negative electrode film layer of the negative electrode sheet, and the second slurry forms the second negative electrode film layer of the negative electrode sheet. On each side in the width direction, the dimension d of the first negative electrode film layer in the width direction is 10 mm.

[0183] In the width direction of the negative electrode plate, within the range of 0 - 2 mm from the edge of the negative electrode plate, the thickness of the first negative electrode film layer is 0.126 mm; within the range of 2 mm - 5 mm from the edge of the negative electrode plate, the thickness of the first negative electrode film layer is 0.130 mm; within the range of 5 mm - 7 mm from the edge of the negative electrode plate, the thickness of the first negative electrode film layer is 0.134 mm; within the range of 7 - 10 mm from the edge of the negative electrode plate, the thickness of the first negative electrode film layer is 0.139 mm. The thickness of the second negative electrode film layer is 0.140 mm.

[0184] (4) Assembly of the battery cell

[0185] Stack the positive electrode plate, separator, and negative electrode plate in sequence such that the separator is between the positive electrode plate and the negative electrode plate and can isolate the positive electrode plate from the negative electrode plate; then wind the above-stacked components to obtain an electrode assembly; place the electrode assembly in a housing, inject a LiPF6 electrolyte with a mass fraction of 11% after drying, wherein the volume ratio of the organic solvent ethylene carbonate (EC) to ethyl methyl carbonate (EMC) in the electrolyte is 3:7; obtain the battery cell after processes such as formation and standing.

[0186] Example 2

[0187] Compared with Example 1, Example 2 only changes the OI values of artificial graphite in the first slurry and the second slurry, that is, the OI value of artificial graphite in the first slurry is 13, and the OI value of artificial graphite in the second slurry is 15.

[0188] Example 3

[0189] Compared with Example 1, Example 3 only changes the OI values of artificial graphite in the first slurry and the second slurry, that is, the OI value of artificial graphite in the first slurry is 23, and the OI value of artificial graphite in the second slurry is 27.

[0190] Example 4

[0191] Compared with Example 1, Example 4 only changes the OI values of artificial graphite in the first slurry and the second slurry, that is, the OI value of artificial graphite in the first slurry is 50, and the OI value of artificial graphite in the second slurry is 55.

[0192] Example 5

[0193] Compared with Example 1, the second negative electrode film layer in Example 5 is prepared from a third slurry and a fourth slurry, forming a first sub-film layer and a second sub-film layer respectively. Among them, the first sub-film layer is disposed on the surface of the second sub-film layer, and the second sub-film layer is disposed on the surface of the negative electrode current collector. Weigh artificial graphite with an OI value of 4, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethylcellulose in a mass ratio of 96:2:1:1, dissolve them in deionized water as the solvent, and obtain the third slurry after mixing evenly. Weigh natural graphite with an OI value of 11, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethylcellulose in a mass ratio of 96:2:1:1, dissolve them in deionized water as the solvent, and obtain the fourth slurry after mixing evenly.

[0194] Among them, the mass ratio of the third slurry and the fourth slurry coated in the second negative electrode film layer is 0.50:0.50, and the thickness ratio of the obtained first sub-film layer and the second sub-film layer is 0.50:0.50.

[0195] Example 6

[0196] Compared with Example 2, the second negative electrode film layer in Example 6 is prepared from two slurries, namely a third slurry and a fourth slurry, to form a first sub-film layer and a second sub-film layer respectively. Among them, the first sub-film layer is disposed on the surface of the second sub-film layer, and the second sub-film layer is disposed on the surface of the negative electrode current collector. Weigh artificial graphite with an OI value of 13, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethylcellulose in a mass ratio of 96:2:1:1, dissolve them in deionized water as the solvent, and obtain the third slurry after mixing evenly. Weigh natural graphite with an OI value of 17, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethylcellulose in a mass ratio of 96:2:1:1, dissolve them in deionized water as the solvent, and obtain the fourth slurry after mixing evenly.

[0197] Among them, the mass ratio of the third slurry and the fourth slurry coated in the second negative electrode film layer is 0.50:0.50, and the thickness ratio of the obtained first sub-film layer and the second sub-film layer is 0.50:0.50.

[0198] Example 7

[0199] Compared with Example 3, in Example 7, the second negative electrode film layer is prepared from two kinds of slurries, namely the third slurry and the fourth slurry, to form a first sub-film layer and a second sub-film layer respectively. Among them, the first sub-film layer is disposed on the surface of the second sub-film layer, and the second sub-film layer is disposed on the surface of the negative electrode current collector. Artificial graphite with an OI value of 23, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are weighed according to a mass ratio of 96:2:1:1 and dissolved in deionized water as the solvent. After mixing evenly, the third slurry is obtained. Natural graphite with an OI value of 30, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are weighed according to a mass ratio of 96:2:1:1 and dissolved in deionized water as the solvent. After mixing evenly, the fourth slurry is obtained.

[0200] Among them, the mass ratio of the third slurry and the fourth slurry coated in the second negative electrode film layer is 0.50:0.05, and the thickness ratio of the obtained first sub-film layer and the second sub-film layer is 0.50:0.50.

[0201] Example 8

[0202] Compared with Example 4, in Example 8, the second negative electrode film layer is prepared from two kinds of slurries, namely the third slurry and the fourth slurry, to form a first sub-film layer and a second sub-film layer respectively. Among them, the first sub-film layer is disposed on the surface of the second sub-film layer, and the second sub-film layer is disposed on the surface of the negative electrode current collector. Artificial graphite with an OI value of 50, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are weighed according to a mass ratio of 96:2:1:1 and dissolved in deionized water as the solvent. After mixing evenly, the third slurry is obtained. Natural graphite with an OI value of 60, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are weighed according to a mass ratio of 96:2:1:1 and dissolved in deionized water as the solvent. After mixing evenly, the fourth slurry is obtained.

[0203] Among them, the mass ratio of the third slurry and the fourth slurry coated in the second negative electrode film layer is 0.50:0.50, and the thickness ratio of the obtained first sub-film layer and the second sub-film layer is 0.50:0.50.

[0204] Example 9

[0205] Compared with Example 7, in Example 9, the mass ratio in the two slurries of the second negative electrode film layer is changed, that is, the mass ratio of the third slurry and the fourth slurry coated in the second negative electrode film layer is 0.7:0.3, and the thickness ratio of the obtained first sub-film layer and the second sub-film layer is 0.7:0.3.

[0206] Example 10

[0207] Compared with Example 1, the first negative electrode film layer in Example 10 further includes amorphous carbon. That is, artificial graphite is coated with amorphous carbon. Weigh amorphous carbon-coated artificial graphite with an OI value of 4, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 96:2:1:1 (where the mass ratio of amorphous carbon to artificial graphite is 1:99), and dissolve them in the solvent deionized water. After mixing evenly, the first slurry is obtained.

[0208] Example 11

[0209] Compared with Example 1, the material of the first negative electrode film layer in Example 11 further includes silicon. That is, weigh silicon-doped artificial graphite with an OI value of 4, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 96:2:1:1 (silicon is doped in artificial graphite, and the mass ratio of silicon to artificial graphite is 1:9), and dissolve them in the solvent deionized water. After mixing evenly, the first slurry is obtained.

[0210] Comparative Example 1

[0211] Compared with Example 1, the OI value of the artificial graphite in the first slurry in Comparative Example 1 is 4, and the OI value of the artificial graphite in the second slurry is 4.

[0212] Comparative Example 2

[0213] Compared with Example 1, the OI value of the artificial graphite in the first slurry in Comparative Example 2 is 8, and the OI value of the artificial graphite in the second slurry is 8.

[0214] Comparative Example 3

[0215] Compared with Example 1, the OI value of the artificial graphite in the first slurry in Comparative Example 3 is 8, and the OI value of the artificial graphite in the second slurry is 4.

[0216] For specific parameter settings of examples and comparative examples, please refer to Table 1.

[0217] Table 1 Parameter Settings of Examples and Comparative Examples

[0218]

[0219] In Table 1, OI1 is the OI value of the first graphite in the first negative electrode film layer of the negative electrode sheet. When the second negative electrode film layer includes one sub-film layer, OI2 is the OI value of the second graphite in this one sub-film layer. When the second negative electrode film layer includes two sub-film layers, namely the first sub-film layer and the second sub-film layer, OI2 is the OI value of the second graphite in the first sub-film layer, OI3 is the OI value of the third graphite in the second sub-film layer, and A and B are the mass ratios of the third slurry and the fourth slurry coated in the second negative electrode film layer, respectively.

[0220] In Table 1, in Examples 1 to 4 and Examples 10 to 11, the first negative electrode film layer is prepared from a kind of slurry including first graphite; the second negative electrode film layer is prepared from a kind of slurry including second graphite.

[0221] In Examples 5 to 9, the first negative electrode film layer is prepared from a kind of slurry including first graphite; the second negative electrode film layer is prepared from two kinds of slurries, namely the third slurry and the fourth slurry, which respectively form the first sub-film layer and the second sub-film layer, and the OI values of the graphite in the two kinds of slurries are different, that is, in the second negative electrode film layer, the OI value of the second graphite in the first sub-film layer is less than the OI value of the third graphite in the second sub-film layer.

[0222] In Comparative Examples 1 and 2, both the first slurry and the second slurry of the negative electrode sheet are prepared from the same kind of slurry. In Comparative Example 3, the first negative electrode film layer and the second negative electrode film layer are respectively prepared from two kinds of slurries, and the OI value of the graphite in the first negative electrode film layer is greater than the OI value of the graphite in the second negative electrode film layer.

[0223] The battery monomers obtained in Examples 1 to 11 and Comparative Examples 1 to 3 are subjected to lithium plating tests.

[0224] Lithium plating test: The prepared battery monomer is subjected to charge and discharge cycles at 25°C. After 70 cycles, the battery monomer is disassembled and the lithium plating situation of the negative electrode sheet is observed, and the area ratio of lithium plating within 10 mm from the edge along the width direction of the outermost negative electrode sheet is calculated. When the lithium plating area ratio is 0, it means no lithium plating; when the lithium plating area ratio is 0 - 50%, it means slight lithium plating; when the lithium plating area ratio is greater than 50%, it means severe lithium plating.

[0225] Among them, during each charge and discharge cycle, it is charged at a constant current of 1C to 20% of the rated capacity of the battery monomer, then continued to be charged at a constant current of 1.3C to 55% of the rated capacity, and then continued to be charged at a constant current of 1C to 80% of the rated capacity; it is discharged at a constant current of 1C to 5% of the rated capacity of the battery monomer. Among them, when charging, the charging capacity of the first full charge of the battery monomer can be used as the rated capacity of the battery monomer, and when discharging, the discharging capacity of the first full discharge can be used as the rated capacity of the battery monomer.

[0226] Cycling performance test: During the 70 charge and discharge cycles of the above battery monomer, the actual discharge amounts at the first discharge and the 70th discharge are measured, and the ratio of the actual discharge amount at the 70th discharge to the actual discharge amount at the first discharge is calculated, and this ratio is used as the capacity retention rate of the cycling performance test of the battery monomer.

[0227] The performance test results of the battery monomers in the above Examples 1 to 11 and Comparative Examples 1 to 3 are shown in Table 2 in detail.

[0228] Table 2 Performance test results of battery cells in different examples and comparative examples

[0229]

[0230]

[0231] The negative electrode sheets prepared in Examples 1 to 9 were respectively applied to lithium-ion batteries, and a slight lithium plating phenomenon occurred. The negative electrode sheets prepared in Examples 10 and 11 were respectively applied to lithium-ion batteries, and basically no lithium plating occurred.

[0232] Comparing Examples 1 to 4 with Comparative Examples 1 to 3, the lithium plating problem was alleviated, and a higher cycle capacity retention rate was obtained. Since there are thinning areas on both sides of the negative electrode sheet along its width direction, the thickness of the thinning area (i.e., the first negative electrode film layer) of the negative electrode sheet is smaller than that of other areas (the second negative electrode film layer). Therefore, in the examples of the present application, along the width direction of the negative electrode sheet, the first graphite with a low OI value is arranged on both sides of the area where the second graphite with a high OI value is located. Since the battery discharges from a fully discharged state to a fully charged state, the expansion rate of the graphite with a low OI value in the negative electrode sheet is greater than that of the graphite with a high OI value. Thus, the expansion size of the first negative electrode film layer of the negative electrode sheet along its thickness direction can be made larger than the expansion size of the second negative electrode film layer along its thickness direction, which can reduce the interlayer gap of the battery electrode sheet at the first negative electrode film layer, and further reduce the difference in the lithium ion transmission paths between the first negative electrode film layer and the second negative electrode film layer, and can reduce the generation of lithium plating at the first negative electrode film layer of the negative electrode sheet.

[0233] Comparing Examples 5 to 9 with Comparative Examples 1 to 3, the lithium plating situation was improved. The OI value of the graphite in the first negative electrode film layer in Examples 5 to 9 is equal to the OI value of the second graphite (the first sub-film layer of the second negative electrode film layer), and the OI value of the second graphite is less than the OI value of the third graphite (the second sub-film layer of the second negative electrode film layer), so that the OI value of the graphite in the first negative electrode film layer 111 is generally less than the OI value of the graphite in the second negative electrode film layer 112. Since the battery charges from a fully discharged state to a fully charged state, the expansion rate of the graphite with a low OI value in the negative electrode sheet 1 is greater than that of the graphite with a high OI value. Thus, the expansion size of the first negative electrode film layer 111 of the negative electrode sheet 1 along its thickness direction can be made larger than the expansion size of the second negative electrode film layer 112 along its thickness direction, which can reduce the interlayer gap of the battery electrode sheet at the first negative electrode film layer 111, and further reduce the difference in the lithium ion transmission paths between the first negative electrode film layer 111 and the second negative electrode film layer 112, and can reduce the generation of lithium plating at the first negative electrode film layer 111 of the negative electrode sheet 1.

[0234] In Examples 10 to 11, lithium plating hardly occurs. When the battery is in a fully charged state as compared to a fully discharged state, the amorphous carbon or silicon can further increase the swelling of the first negative electrode film layer of the negative electrode sheet in the thickness direction, and can further reduce the difference between the lithium ion diffusion paths in the thinned area of the negative electrode sheet and other areas, thereby further improving the lithium plating problem.

[0235] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same constitution and the same effect as the technical idea within the technical solution scope of the present application are all included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other modes constructed by combining some constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode plate, characterized in that, Comprising: A negative electrode current collector; And A negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a first negative electrode film layer and a second negative electrode film layer, wherein the first negative electrode film layer is disposed on both sides of the second negative electrode film layer along the width direction of the negative electrode current collector, and the dimension of the first negative electrode film layer in the thickness direction is smaller than the dimension of the second negative electrode film layer in the thickness direction, the first negative electrode film layer includes a first graphite, and the second negative electrode film layer includes one or more sub-film layers. When the second negative electrode film layer includes one sub-film layer, the one sub-film layer includes a second graphite, and the OI1 value of the first graphite is less than the OI2 value of the second graphite, or When the second negative electrode film layer includes multiple sub-film layers, each sub-film layer in the multiple sub-film layers includes graphite, and at least one sub-film layer includes a second graphite, and the OI2 value of the second graphite is the smallest among the OI values of the graphite, and the OI1 value of the first graphite is less than or equal to the OI2 value of the second graphite.

2. The negative electrode sheet according to claim 1, characterized in that, The second negative electrode film layer includes the one sub-film layer.

3. The negative electrode sheet according to claim 2, characterized in that, The OI1 value of the first graphite satisfies: 4 ≤ OI1 ≤ 50, optionally, 13 ≤ OI1 ≤ 23.

4. The negative electrode sheet according to claim 2 or 3, characterized in that, The OI2 value of the second graphite satisfies: 8 ≤ OI2 ≤ 55, optionally, 15 ≤ OI2 ≤ 27.

5. The negative electrode sheet according to any one of claims 2 to 4, characterized in that, The first graphite includes at least one of natural graphite or artificial graphite, and / or the second graphite includes at least one of natural graphite or artificial graphite.

6. The negative electrode sheet according to claim 1, wherein The second negative electrode film layer includes the multiple sub-film layers, the multiple sub-film layers include a first sub-film layer and a second sub-film layer, the first sub-film layer includes the second graphite, and the second sub-film layer includes a third graphite, wherein the second sub-film layer is disposed on the surface of the negative electrode current collector, and the first sub-film layer is disposed on the surface of the second sub-film layer away from the negative electrode current collector, and the OI2 value of the second graphite is less than the OI3 value of the third graphite.

7. The negative electrode plate according to claim 6, characterized in that, The OI1 value of the first graphite satisfies: 4 ≤ OI1 ≤ 50, optionally, 13 ≤ OI1 ≤ 23.

8. The negative electrode sheet according to claim 6 or 7, characterized in that, The OI2 value of the second graphite satisfies: 4 ≤ OI2 ≤ 50, optionally, 13 ≤ OI2 ≤ 23.

9. The negative electrode plate according to any one of claims 6 to 8, characterized in that, The OI3 value of the third graphite satisfies: 11 ≤ OI3 ≤ 60, optionally, 17 ≤ OI3 ≤ 30.

10. The negative electrode sheet according to any one of claims 6 to 9, characterized in that, The first graphite is artificial graphite, and / or the second graphite is artificial graphite, and / or the third graphite is natural graphite.

11. The negative electrode sheet according to any one of claims 1 to 10, characterized in that, The first negative electrode film layer further includes silicon, and the silicon is doped between the particles of the first graphite.

12. The negative electrode sheet according to any one of claims 1 to 10, characterized in that, The first negative electrode film layer further includes amorphous carbon, and the amorphous carbon coats at least part of the surface of the particles of the first graphite.

13. The negative electrode sheet according to any one of claims 1 to 12, characterized in that, Along the width direction of the negative electrode plate and from both sides of the negative electrode plate to the middle region, the thickness of the first negative electrode film layer increases gradiently.

14. A battery cell, characterized in that, The battery cell includes the negative electrode plate according to any one of claims 1 to 13.

15. A battery, characterized in that, The battery includes the battery cell according to claim 14.

16. An electrical device, characterized in that, The electrical device includes the battery cell according to claim 14, and / or the battery according to claim 15.

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