Negative electrode sheet, battery cell, battery and electrical equipment

Abstract

The present application provides a negative electrode sheet, a battery cell, a battery and an electrical device, and relates to the field of batteries. The negative electrode sheet includes a current collector and a negative electrode active layer formed on the current collector, and the negative electrode active layer includes a first negative electrode active material layer, a second negative electrode active material layer and a third negative electrode active material layer arranged in sequence along a preset direction. The median particle size and true density of the negative electrode active materials in the first negative electrode active material layer and the third negative electrode active material layer are respectively greater than the median particle size and true density of the negative electrode active material in the second negative electrode active material layer, the width of the first negative electrode active material layer in the preset direction is D1, the width of the second negative electrode active material layer in the preset direction is D2, and the width of the third negative electrode active material layer in the preset direction is D3, wherein 0.05<D2 / (D2+D1+D3)≤0.45, and the above arrangement can improve the technical problems of lithium deposition in the middle area of ​​the negative electrode sheet and sacrificing energy density.

Description

Technical Field

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

[0002] During the formation or cycle process of current secondary batteries, lithium is easily deposited in the middle of the negative electrode sheet, affecting the safety and cycle performance of the battery cell. The traditional method of increasing the amount of liquid injection can partially improve the lithium deposition in the middle of the negative electrode sheet, but it will sacrifice the energy density and cost of the battery cell. Summary of the invention

[0003] In view of the above problems, the present application provides a negative electrode sheet, a battery cell, a battery and an electrical device, which can improve the technical problems of lithium deposition in the middle area of ​​the negative electrode sheet and sacrifice of energy density.

[0004] In a first aspect, an embodiment of the present application provides a negative electrode sheet, which includes a current collector and a negative electrode active layer formed on the current collector, wherein the current collector is provided with a negative electrode tab on any side of a preset direction, and the negative electrode active layer includes a first negative electrode active material layer, a second negative electrode active material layer, and a third negative electrode active material layer arranged in sequence along the preset direction. Among them, the median particle size of the negative electrode active material in the first negative electrode active material layer and the third negative electrode active material layer is greater than the median particle size of the negative electrode active material in the second negative electrode active material layer, and the true density in the first negative electrode active material layer and the third negative electrode active material layer is greater than the true density of the second negative electrode active material layer. The width of the first negative electrode active material layer in the preset direction is D1, the width of the second negative electrode active material layer in the preset direction is D2, and the width of the third negative electrode active material layer in the preset direction is D3, wherein 0.05<D2 / (D2+D1+D3)≤0.45; the median particle size of the negative electrode active material in the first negative electrode active material layer is C1μm, the median particle size of the negative electrode active material in the second negative electrode active material layer is C2μm, and the median particle size of the negative electrode active material in the third negative electrode active material layer is C3μm, wherein 5≤C1≤25, 0.5≤C2≤15, and 5≤C3≤25.

[0005] In the technical solution of the embodiment of the present application, by controlling the true density of the first negative electrode active material layer, the second negative electrode active material layer and the third negative electrode active material layer arranged in sequence in a preset direction, the median particle size and the width of the contained negative electrode active materials, the electrolyte is effectively promoted to diffuse from the outer edge to the middle of the negative electrode sheet from the preset direction while reducing the sacrificial energy density, thereby improving the wetting performance of the electrolyte on the middle part of the negative electrode sheet, which can not only alleviate the problem of lithium precipitation in the middle part of the negative electrode sheet, but also avoid sacrificing energy density, improve the capacity retention rate of the negative electrode sheet for multiple cycles, and improve the cycle stability and safety performance.

[0006] In some embodiments, the true density of the first negative electrode active material layer is T1 g / cm 3 The true density of the second negative electrode active material layer is T2 g / cm 3 The true density of the third negative electrode active material layer is T3g / cm 3 , 3≥T1>T2≥1.4, 3≥T3>T2≥1.4. Within the above range, it is helpful to maintain the high energy density of the negative electrode sheet and improve the capacity retention rate of the negative electrode sheet for multiple cycles, improve the electrolyte retention ability of the middle part of the negative electrode sheet, improve the wetting effect of the electrolyte on the middle part of the negative electrode sheet, alleviate lithium precipitation in the middle part of the negative electrode sheet, improve the cycle stability and safety performance of the negative electrode sheet, and help it to avoid lithium precipitation when it is cycled 600 times. If the true density of the second negative electrode active material layer is too small, although the ability of the middle part of the negative electrode sheet to be infiltrated by the electrolyte can be improved, the load of active material on the negative electrode sheet will be reduced, which has a negative effect on the improvement of the energy density of the negative electrode sheet and the battery cell.

[0007] In some embodiments, 2.3≥T1≥2.0, 2.2≥T2≥1.9, 2.3≥T3≥2.0. Optionally, 2.26≥T1≥2.18, 2.04≥T2≥1.96, 2.26≥T3≥2.18. Within the above range, the electrolyte retention capacity of the middle part of the negative electrode sheet can be further improved while improving or maintaining the high energy density of the negative electrode sheet, further improving the wetting effect of the electrolyte on the middle part of the negative electrode sheet, avoiding lithium precipitation in the middle part of the negative electrode sheet, and improving the long-term cycle stability of the negative electrode sheet.

[0008] In some embodiments, 10≤C1≤20, 2≤C2≤10, 10≤C3≤20; optionally, 12≤C1≤16, 4≤C2≤6, 12≤C3≤16. Within the above range, it is not only helpful to improve the electrode sheet's wettability to the electrolyte, improve the long-term cycle stability of the negative electrode sheet, and help it to alleviate the lithium decomposition problem when it is cycled for 600 cycles, but also facilitate processing and improve the performance of the battery cell. If the median particle size of the negative electrode active material is too large, it is not conducive to improving the electrode sheet's wettability to the electrolyte. If the median particle size of the active material is too small, it is easy to cause sedimentation / gel problems during the slurry coating process of the negative electrode sheet, which is not conducive to improving the processing cost and will also deteriorate the performance of the battery cell.

[0009] In some embodiments, 0.1≤D2 / (D2+D1+D3)≤0.3, 0.1≤D1 / (D2+D1+D3)≤0.6, 0.1≤D3 / (D2+D1+D3)≤0.6. The limitation of the width of the first negative electrode active material layer, the second negative electrode active material layer and the third negative electrode active material layer in a preset direction not only helps to improve the lithium deposition in the middle of the negative electrode sheet when it is cycled for 600 cycles, effectively improves the long-term cycle stability of the negative electrode sheet, but also avoids the decrease in the energy density of the single battery and improves the capacity cycle retention rate.

[0010] In some embodiments, D2=D3, that is, the first negative electrode active material layer and the third negative electrode active material layer are symmetrically distributed at both ends of the second negative electrode active material layer, which is beneficial to alleviate lithium deposition in the middle of the negative electrode sheet.

[0011] In some embodiments, the negative electrode active material in the first negative electrode active material layer is the same as the negative electrode active material in the third negative electrode active material layer. Under the above settings, the same ratio can be selected to prepare the first negative electrode active material layer and the third negative electrode active material layer with the same true density, effectively reducing the difficulty and cost of preparation.

[0012] In some embodiments, the negative electrode active material of the first negative electrode active material layer is different from the negative electrode active material in the second negative electrode active material layer, and the negative electrode active material in the third negative electrode active material layer is different from the negative electrode active material in the second negative electrode active material layer. Since the true density of each layer is mainly related to the negative electrode active material when the first negative electrode active material layer, the second negative electrode active material layer and the third negative electrode active material layer have the same ratio, the above-mentioned setting can be used to directly control the true density corresponding to each layer by using different negative electrode active materials, and the preparation difficulty is low.

[0013] In some embodiments, the negative electrode active material includes at least one of a carbon-based material, a silicon-based material and a lithium titanate material, and the carbon-based material includes at least one of hard carbon, soft carbon, artificial graphite, natural graphite and expanded graphite. The negative electrode active material is easy to obtain.

[0014] In a second aspect, the present application provides a battery cell, which includes the negative electrode sheet in the above embodiment.

[0015] In a third aspect, the present application provides a battery, which includes the battery cell in the above embodiment.

[0016] In a fourth aspect, the present application provides an electrical device, which includes the battery in the above embodiment, and the battery is used to provide electrical energy.

[0017] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0019] Figure 1 A schematic diagram of the structure of a vehicle according to some embodiments of the present application;

[0020] Figure 2 A schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0021] Figure 3 A schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

[0022] Figure 4 A schematic diagram of the cross-sectional structure of a negative electrode sheet according to some embodiments of the present application;

[0023] Figure 5 This is a schematic diagram of the structure of the negative electrode sheet of some embodiments of the present application;

[0024] Figure 6 This is a schematic diagram of the structure of the negative electrode sheet of some embodiments of the present application;

[0025] Figure 7 This is a schematic diagram of the structure of the negative electrode sheet of some embodiments of the present application;

[0026] Figure 8 This is a schematic diagram of the structure of the negative electrode sheet of some embodiments of the present application;

[0027] Fig. 9 This is a schematic diagram of the structure of the negative electrode sheet of some embodiments of the present application;

[0028] Fig.10 This is a schematic diagram of the structure of the negative electrode sheet of some embodiments of the present application.

[0029] The reference numerals in the specific implementation manner are as follows:

[0030] 1000-Vehicles;

[0031] 100-battery; 200-controller; 300-motor;

[0032] 10-box; 11-first part; 12-second part;

[0033] 20-battery cell; 21-end cover; 21a-electrode terminal; 22-insulating member; 23-current collecting assembly; 24-housing; 25-electrode assembly;

[0034] 24 - negative electrode sheet; 240 - current collector; 241 - negative electrode tab; 243 - negative electrode film layer; 244 - first negative electrode active material layer; 245 - second negative electrode active material layer; 247 - third negative electrode active material layer. DETAILED DESCRIPTION

[0035] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0037] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0038] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0039] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0040] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0041] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0042] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0043] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0044] The inventors have discovered that in order to pursue high energy density, current secondary batteries set a larger compression and higher loading for the negative electrode sheet, resulting in low porosity of the negative electrode sheet and poor wettability to the electrolyte, so that the electrolyte infiltration in the middle area of ​​the negative electrode sheet is insufficient, resulting in the precipitation of metallic lithium during the formation or circulation process due to the large ion diffusion impedance, affecting the safety performance and cycle performance of the battery cell.

[0045] In order to alleviate the problem of lithium deposition in the middle of the negative electrode sheet, the inventors tried to increase the porosity in the middle of the negative electrode sheet in the hope of improving the wettability to the electrolyte to solve the above technical problems. However, the inventors found that if only the porosity in the middle of the negative electrode sheet is increased, the capacity of the negative electrode sheet will be sacrificed, and the cycle retention rate of the negative electrode sheet capacity is poor, and lithium deposition problems will still occur in the middle after long-term cycling, such as 600 cycles.

[0046] In order to solve the problem of easy lithium precipitation in the middle of the negative electrode sheet and poor cycle retention rate, the inventor has designed a negative electrode sheet after in-depth research, which includes a current collector and a negative electrode active layer with uniform thickness formed on the current collector, the current collector is provided with a negative electrode tab on any side of a preset direction, and the negative electrode active layer includes a first negative electrode active material layer, a second negative electrode active material layer and a third negative electrode active material layer arranged in sequence along the preset direction. Among them, the median particle size of the negative electrode active material in the first negative electrode active material layer and the third negative electrode active material layer is greater than the median particle size of the negative electrode active material in the second negative electrode active material layer, and the true density in the first negative electrode active material layer and the third negative electrode active material layer is greater than the true density of the second negative electrode active material layer. The width of the first negative electrode active material layer in the preset direction is D1, the width of the second negative electrode active material layer in the preset direction is D2, and the width of the third negative electrode active material layer in the preset direction is D3, wherein 0.05<D2 / (D2+D1+D3)≤0.45, the median particle size of the negative electrode active material in the first negative electrode active material layer is C1μm, the median particle size of the negative electrode active material in the second negative electrode active material layer is C2μm, and the median particle size of the negative electrode active material in the third negative electrode active material layer is C3μm, wherein 5≤C1≤25, 0.5≤C2≤15, and 5≤C3≤25.

[0047] In such a negative electrode sheet, by controlling the true density of the first negative electrode active material layer, the second negative electrode active material layer and the third negative electrode active material layer arranged in sequence in a preset direction, the median particle size and the width of the negative electrode active material contained therein, the electrolyte is effectively promoted to diffuse from the outer edge to the middle of the negative electrode sheet in a preset direction while reducing the sacrificial energy density, thereby improving the wetting performance of the electrolyte on the middle part of the negative electrode sheet, which can not only alleviate the problem of lithium precipitation in the middle part of the negative electrode sheet, but also avoid sacrificing energy density, improve the capacity retention rate of the negative electrode sheet for multiple cycles, and improve the cycle stability and safety performance.

[0048] The median particle size of the negative electrode active material in the first negative electrode active material layer and the third negative electrode active material layer is greater than the median particle size of the negative electrode active material in the second negative electrode active material layer, so that the diffusion capacity of the second negative electrode active material layer is better than the first negative electrode active material layer and the third negative electrode active material layer at both ends, so as to promote the diffusion of the electrolyte from the two ends to the middle, so as to better infiltrate the second negative electrode active material layer, avoid lithium precipitation in the middle of the negative electrode sheet and improve the cycle stability, and utilize the true density of the first negative electrode active material layer and the third negative electrode active material layer to be greater than the true density of the second negative electrode active material layer, so as to effectively improve the liquid retention capacity of the second negative electrode active material layer, prolong the contact time between the second negative electrode active material layer and the electrolyte, so as to better infiltrate the second negative electrode active material layer, avoid lithium precipitation in the middle of the negative electrode sheet and further improve the cycle stability, and under the above-mentioned setting, the thickness of the negative electrode active layer is uniform, the processing difficulty is low, and it is conducive to the subsequent formation process, so that the surface of the negative electrode sheet tends to form a complete and uniform formation interface, further avoiding lithium precipitation in the middle of the negative electrode sheet.

[0049] In addition, the width of the second negative electrode active material layer is reasonable, which can be further coordinated with the median particle size and true density to solve the problem of lithium deposition in the middle of the negative electrode sheet, and can also improve the capacity retention rate of the negative electrode sheet for multiple cycles, improve the cycle stability and safety performance. If the width of the second negative electrode active material layer is too large, the electrolyte required for the entire single cell will increase significantly, which will reduce the mass energy density of the single cell; if the width of the second negative electrode active material layer area is too small, the area size range for improved electrolyte infiltration is limited, and during the charge and discharge process, the middle of the negative electrode sheet may still not be wetted by the electrolyte and lithium deposition may occur.

[0050] The battery cells disclosed in the embodiments of the present application can be used, but not limited to, in electrical devices such as vehicles, ships or aircraft. A power supply system comprising the battery cells and batteries disclosed in the present application can be used to form the electrical device, which is conducive to alleviating and automatically adjusting the deterioration of the expansion force of the battery cell, replenishing the consumption of the electrolyte, and improving the stability of the battery performance and the battery life.

[0051] The embodiment of the present application provides an electric device using a battery as a power source, and the electric device may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0052] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0053] Please refer to Figure 1 , Figure 1 A schematic diagram of the structure of a vehicle 1000 provided for some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000, and the battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The battery 100 may be used to power the vehicle 1000, for example, the battery 100 may be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, and the controller 200 is used to control the battery 100 to power the motor 300, for example, for starting, navigating and driving the vehicle 1000.

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

[0055] Please refer to Figure 2 , Figure 2 An exploded view of a battery 100 provided in some embodiments of the present application. The battery 100 includes a box 10 and a battery cell 20, and the battery cell 20 is contained in the box 10. Among them, the box 10 is used to provide a storage space for the battery cell 20, and the box 10 can adopt a variety of structures. In some embodiments, the box 10 may include a first part 11 and a second part 12, the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a storage space for accommodating the battery cell 20. The second part 12 may be a hollow structure with one end open, the first part 11 may be a plate-like structure, and the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define a storage space; the first part 11 and the second part 12 may also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12. Of course, the box 10 formed by the first part 11 and the second part 12 may be in a variety of shapes, such as a cylinder, a cuboid, etc.

[0056] In the battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in a mixed connection. A mixed connection means that the multiple battery cells 20 are both connected in series and in parallel. The multiple battery cells 20 may be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the box 10; of course, the battery 100 may also be a battery module formed by connecting multiple battery cells 20 in series, in parallel, or in a mixed connection, and then the multiple battery modules are connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The battery 100 may also include other structures, for example, the battery 100 may also include a busbar component for realizing electrical connection between the multiple battery cells 20.

[0057] Each battery cell 20 may be a secondary battery or a primary battery, or a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 20 may be cylindrical, flat, rectangular, or in other shapes.

[0058] Please refer to Figure 3 , Figure 3 The schematic diagram of the exploded structure of the battery cell 20 provided in some embodiments of the present application. The battery cell 20 refers to the smallest unit that constitutes the battery. Figure 3 The battery cell 20 includes an end cap 21, an insulating member 22, a current collecting assembly 23, a shell 24, an electrode assembly 25, an electrolyte (not shown) and other functional components.

[0059] The end cap 21 refers to a component that covers the opening of the shell 24 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 can be adapted to the shape of the shell 24 to match the shell 24. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the end cap 21 is not easily deformed when squeezed and collided, so that the battery cell 20 can have a higher structural strength and the safety performance can also be improved. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The material of the end cap 21 can also be a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not impose any special restrictions on this.

[0060] Functional components such as electrode terminals 21a are provided on the end cap 21. The electrode terminal 21a can be used to electrically connect to the electrode assembly 25 to output or input the electrical energy of the battery cell 20. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The material of the end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not impose any special restrictions on this.

[0061] The insulating member 22 is located inside the end cap 21, and can be used to isolate the electrical connection components in the housing 24 from the end cap 21 to reduce the risk of short circuit. For example, the insulating member 22 can be made of plastic, rubber, etc.

[0062] The current collecting assembly 23 is located on a side of the insulating member 22 away from the end cover 21 , and is used to electrically connect the electrode terminal 21 a with the electrode assembly 25 to transmit electrical energy from the electrode assembly 25 to the electrode terminal 21 a , and then to the outside of the electrode assembly 25 via the electrode terminal 21 a .

[0063] The shell 24 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20, wherein the formed internal environment can be used to accommodate the electrode assembly 25, the electrolyte and other components. The shell 24 and the end cap 21 can be independent components, and an opening can be set on the shell 24, and the internal environment of the battery cell 20 is formed by covering the opening with the end cap 21 at the opening. Without limitation, the end cap 21 and the shell 24 can also be integrated. Specifically, the end cap 21 and the shell 24 can form a common connection surface before other components are put into the shell, and when the interior of the shell 24 needs to be encapsulated, the end cap 21 covers the shell 24. The shell 24 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 24 can be determined according to the specific shape and size of the electrode assembly 25. The material of the shell 24 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0064] The electrode assembly 25 is a component in the battery cell 20 where an electrochemical reaction occurs. One or more electrode assemblies 25 may be included in the housing 24. The electrode assembly 25 is mainly formed by winding or stacking a positive electrode sheet and a negative electrode sheet, and a separator is usually provided between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet has a portion of a positive electrode active material and a portion of a negative electrode sheet having a negative electrode active material, which together constitute the main body of the electrode assembly 25, and the portion of the positive electrode sheet without a positive electrode active material and the portion of the negative electrode sheet and the negative electrode sheet without a negative electrode active material each constitute a tab. The positive electrode tab and the negative electrode tab 241 may be located together at one end of the main body or at both ends of the main body respectively. During the charge and discharge process of the battery, the positive electrode active material and the negative electrode active material react with the electrolyte, and the positive electrode tab and the negative electrode tab 241 connect the electrode terminal 21a to form a current loop.

[0065] Among them, the active material of the positive electrode sheet includes but is not limited to lithium cobalt oxide, and can also be one or more of lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, olivine-structured lithium phosphate, layered sodium-containing oxide, sodium iron sulfate, and sodium-containing Prussian blue analog materials. Those skilled in the art can choose according to actual needs and are not limited here.

[0066] The material of the diaphragm includes but is not limited to polyethylene diaphragm, polypropylene diaphragm, glass fiber diaphragm and a composite diaphragm composed of at least two of them, which is not limited here, and those skilled in the art can choose according to actual needs.

[0067] The electrolyte may only contain electrolytes and solvents, and may also contain additives. Those skilled in the art may select the type of electrolyte according to actual needs, and the type is not limited here.

[0068] See also Figures 4 to 10 , Figures 5 to 10 In the figure, the X direction represents the preset direction. According to some embodiments of the present application, the negative electrode sheet includes a current collector 240 and a negative electrode active layer formed on the current collector 240, the current collector 240 is provided with a negative electrode tab 241 on any side of the preset direction, and the negative electrode active layer includes a first negative electrode active material layer 244, a second negative electrode active material layer 245, and a third negative electrode active material layer 247 arranged in sequence along the preset direction. The median particle size of the negative electrode active material in the first negative electrode active material layer 244 and the third negative electrode active material layer 247 is greater than the median particle size of the negative electrode active material in the second negative electrode active material layer 245, and the true density in the first negative electrode active material layer 244 and the third negative electrode active material layer 247 is greater than the true density of the second negative electrode active material layer 245. The width of the first negative electrode active material layer 244 in the preset direction is D1, the width of the second negative electrode active material layer 245 in the preset direction is D2, and the width of the third negative electrode active material layer 247 in the preset direction is D3, wherein 0.05<D2 / (D2+D1+D3)≤0.45. The median particle size of the negative electrode active material in the first negative electrode active material layer is C1μm, the median particle size of the negative electrode active material in the second negative electrode active material layer is C2μm, and the median particle size of the negative electrode active material in the third negative electrode active material layer is C3μm, wherein 5≤C1≤25, 0.5≤C2≤15, 5≤C3≤25.

[0069] The negative electrode active layer refers to a coating layer mainly composed of a mixture of a negative electrode active material, a conductive agent and a binder.

[0070] The median particle size is the D50 particle size, which refers to the particle size corresponding to when the cumulative particle size distribution percentage of the negative electrode active material reaches 50%.

[0071] True density refers to the actual mass of solid matter per unit volume in each negative electrode active material layer in an absolutely dense state, that is, the density after removing internal pores or gaps between particles.

[0072] The first negative electrode active material layer 244, the second negative electrode active material layer 245 and the third negative electrode active material layer 247 are arranged in sequence in a preset direction, which means that one side of the second negative electrode active material layer 245 in the preset direction is connected to an edge of the first negative electrode active material layer 244, and the other side is connected to an edge of the third negative electrode active material layer 247, so that the first negative electrode active material layer 244 and the third negative electrode active material layer 247 are respectively located on both sides of the second negative electrode active material layer 245 in the preset direction.

[0073] In the technical solution of the embodiment of the present application, by utilizing the true density of the first negative electrode active material layer 244, the second negative electrode active material layer 245 and the third negative electrode active material layer 247 which are sequentially arranged in a preset direction and the control of the median particle size of the negative electrode active materials contained therein, the electrolyte is effectively promoted to diffuse from the outer edge to the middle of the negative electrode sheet in a preset direction while reducing the sacrificial energy density, thereby improving the wetting performance of the electrolyte on the middle part of the negative electrode sheet, which can not only alleviate the problem of lithium precipitation in the middle part of the negative electrode sheet, but also avoid sacrificing energy density, improve the capacity retention rate of the negative electrode sheet for multiple cycles, and improve the cycle stability and safety performance.

[0074] The median particle size of the negative electrode active material in the first negative electrode active material layer 244 and the third negative electrode active material layer 247 is greater than the median particle size of the negative electrode active material in the second negative electrode active material layer 245, so that the diffusion ability of the second negative electrode active material layer 245 is better than the first negative electrode active material layer 244 and the third negative electrode active material layer 247 at both ends, so as to promote the diffusion of the electrolyte from both ends to the middle, so as to better infiltrate the second negative electrode active material layer 245, avoid lithium precipitation in the middle of the negative electrode sheet and improve the cycle stability, and utilize the fact that the true density of the first negative electrode active material layer 244 and the third negative electrode active material layer 247 is greater than the true density of the second negative electrode active material layer 245, so as to effectively improve the liquid retention capacity of the second negative electrode active material layer 245, prolong the contact time between the second negative electrode active material layer 245 and the electrolyte, so as to better infiltrate the second negative electrode active material layer 245, avoid lithium precipitation in the middle of the negative electrode sheet and further improve the cycle stability. In addition, the width of the second negative electrode active material layer 245 is reasonable, which can be further coordinated with the median particle size and true density to solve the problem of lithium deposition in the middle of the negative electrode sheet, and can also improve the capacity retention rate of the negative electrode sheet for multiple cycles, improve the cycle stability and safety performance. If the width of the second negative electrode active material layer 245 is too large, the electrolyte required for the entire single cell will be greatly increased, which will reduce the mass energy density of the single cell; if the width of the second negative electrode active material layer 245 area is too small, the size range of the area for improving electrolyte infiltration is limited, and during the charge and discharge process, the middle of the negative electrode sheet may still not be infiltrated by the electrolyte and lithium deposition may occur. If the median particle size of the negative electrode active material is too large or too small, lithium deposition in the middle of the negative electrode sheet cannot be alleviated.

[0075] Illustratively, C1 is any value among 5, 7, 10, 12, 15, 17, 18, 20, 22 or 25 or between any two values, C2 is any value among 0.5, 1, 2, 4, 5, 6, 10, 12 or 15 or between any two values, and C3 is any value among 5, 7, 10, 12, 15, 17, 18, 20, 22 or 25 or between any two values.

[0076] like Figure 5 As shown, the first negative electrode active material layer 244 may be located on a side of the third negative electrode active material layer 247 close to the negative electrode tab 241, or may be located on a side of the third negative electrode active material layer 247 close to the negative electrode tab 241. Figure 6 As shown, the first negative electrode active material layer 244 may be located on a side of the third negative electrode active material layer 247 away from the negative electrode tab 241 . Those skilled in the art may make a selection according to actual needs, which is not limited here.

[0077] The negative electrode tab 241 can be Figure 7 The full-pole ear is shown, but it can also be Figure 5 and Figure 6The split tabs shown can be selected by those skilled in the art according to actual needs and are not limited here.

[0078] Among them, each negative electrode active material layer can be locally patterned so that the overall true density and particle size of each negative electrode active material layer meet the above requirements, but the true density of each negative electrode active material layer and / or the particle size of the negative electrode active material can be different. In order to facilitate processing and setting, each negative electrode active material layer can be formed by coating with a negative electrode slurry containing negative electrode active materials with the same median particle size, so that the true density of each negative electrode active material layer is the same.

[0079] Alternatively, if Figure 4 As shown, the thickness of the negative electrode active layer is uniform, that is, the thickness of the negative electrode active layer is basically the same everywhere, and the thickness deviation is controlled within 1%. The negative electrode active layer with uniform thickness is easy to process, and is conducive to forming a complete and uniform formation interface on the surface of the negative electrode sheet in the subsequent formation process, further avoiding lithium deposition on the negative electrode sheet.

[0080] The current collector 240 has an extension direction perpendicular to the preset direction. Figures 5 to 10 The negative electrode tab 241 is arranged on any side of the current collector 240 in a preset direction and extends along the extension direction.

[0081] like Figures 5 to 7 As shown, the width D1 of the first negative electrode active material layer 244 remains unchanged in the extension direction, the width D2 of the second negative electrode active material layer 245 remains unchanged in the extension direction, and the width D3 of the third negative electrode active material layer 247 remains unchanged in the extension direction. At this time, the contact interface between the second negative electrode active material layer 245 and the first negative electrode active material layer 244 is a plane, and the contact interface between the second negative electrode active material layer 245 and the third negative electrode active material layer 247 is also a plane.

[0082] like Figures 8 to 10 As shown in FIG. 1 , the width D1 of the first negative electrode active material layer 244, the width D2 of the second negative electrode active material layer 245, and the width D3 of the third negative electrode active material layer 247 vary in the extension direction, but the variation range meets the above requirements. At this time, the contact interface between the second negative electrode active material layer 245 and the first negative electrode active material layer 244 can be as follows: Figure 8 and Fig. 9 The surface shown can also be Fig.10 As shown in the folded surface, the contact interface between the second negative electrode active material layer 245 and the third negative electrode active material layer 247 can be as follows Fig. 9 The surface shown can also be Fig.10 Folded surface shown.

[0083] Among them, Figures 5 to 7As shown, the width of the first negative electrode active material layer 244 can be the same as the width of the third negative electrode active material layer 247. In this case, the first negative electrode active material layer 244 and the third negative electrode active material layer 247 are symmetrically distributed at both ends of the second negative electrode active material layer 245 in a preset direction. In addition, the width of the first negative electrode active material layer 244 can also be greater than or less than the thickness of the third negative electrode active material layer 247, as long as the above range requirements are met. In this case, the first negative electrode active material layer 244 and the third negative electrode active material layer 247 are located at both ends of the second negative electrode active material layer 245 in an asymmetrical distribution manner. The asymmetrical distribution manner is, for example, Figure 8 shown.

[0084] According to some embodiments of the present application, optionally, the true density of the first negative electrode active material layer 244 is T1 g / cm 3 The true density of the second negative electrode active material layer 245 is T2 g / cm 3 The true density of the third negative electrode active material layer 247 is T3 g / cm 3 , among which, 3≥T1>T2≥1.4, 3≥T3>T2≥1.4.

[0085] Within the above range, it is helpful to maintain the high energy density of the negative electrode sheet and improve the capacity retention rate of the negative electrode sheet for multiple cycles, improve the electrolyte retention capacity of the middle part of the negative electrode sheet, improve the wetting effect of the electrolyte on the middle part of the negative electrode sheet, alleviate the lithium precipitation in the middle part of the negative electrode sheet, improve the cycle stability and safety performance of the negative electrode sheet, and help it to avoid lithium precipitation when it is cycled 600 times. If the true density of the second negative electrode active material layer 245 is too small, although the ability of the middle part of the negative electrode sheet to be infiltrated by the electrolyte can be improved, the load of active material on the negative electrode sheet will be reduced, which has a negative effect on the improvement of the energy density of the negative electrode sheet and the battery cell.

[0086] The true density of the first negative electrode active material layer 244 may be the same as or different from the true density of the third negative electrode active material layer 247. In some embodiments, optionally, 2.3≥T1≥2.0, 2.2≥T2≥1.9, and 2.3≥T3≥2.0.

[0087] Within the above range, the electrolyte retention capacity of the middle part of the negative electrode sheet can be further improved while improving or maintaining the high energy density of the negative electrode sheet, further improving the wetting effect of the electrolyte on the middle part of the negative electrode sheet, avoiding lithium precipitation in the middle part of the negative electrode sheet, and improving the long-term cycle stability of the negative electrode sheet.

[0088] For example, T1 is any value among 2.00, 2.05, 2.10, 2.15, 2.18, 2.20, 2.25, 2.26, 2.28 or 2.30 or between any two values, T2 is any value among 1.90, 1.96, 2.00, 2.04, 2.10 or 2.20 or between any two values, and T1>T2. T3 is any value among 2.00, 2.05, 2.10, 2.15, 2.18, 2.20, 2.25, 2.26, 2.28 or 2.30 or between any two values, and T3>T2.

[0089] Optionally, 2.26≥T1≥2.18, 2.04≥T2≥1.96, 2.26≥T3≥2.18.

[0090] Within the above range, the wetting effect of the electrolyte on the middle part of the negative electrode sheet is further improved, lithium precipitation in the middle part of the negative electrode sheet is avoided, and the long-term cycle stability of the negative electrode sheet is further improved.

[0091] According to some embodiments of the present application, optionally, 10≤C1≤20, 2≤C2≤10, 10≤C3≤20.

[0092] Within the above range, it is not only helpful to improve the electrode sheet's ability to wet the electrolyte, improve the long-term cycle stability of the negative electrode sheet, and help it to relieve the lithium decomposition problem when it is cycled for 600 cycles, but also easy to process and improve the performance of the battery cell. If the median particle size of the negative electrode active material is too large, it is not conducive to improving the electrode sheet's ability to wet the electrolyte. If the median particle size of the active material is too small, it is easy to cause sedimentation / gel problems during the slurry coating process of the negative electrode sheet, which is not conducive to improving the processing cost and will also deteriorate the performance of the battery cell.

[0093] The median particle size of the negative electrode active material in the first negative electrode active material layer 244 may be the same as or different from the median particle size of the negative electrode active material in the third negative electrode active material layer 247 , and may be selected according to actual needs.

[0094] Optionally, 12≤C1≤16, 4≤C2≤6, 12≤C3≤16. Within the above range, the electrode sheet's wettability to the electrolyte is further improved, and the negative electrode sheet's cycle stability and capacity retention rate are further improved.

[0095] According to some embodiments of the present application, optionally, 0.1≤D2 / (D2+D1+D3)≤0.3, 0.1≤D1 / (D2+D1+D3)≤0.6, 0.1≤D3 / (D2+D1+D3)≤0.6.

[0096] By limiting the width of the first negative electrode active material layer 244, the second negative electrode active material layer 245 and the third negative electrode active material layer 247 in a preset direction, it is not only helpful to improve the lithium deposition in the middle of the negative electrode sheet when it is cycled for 600 cycles, effectively improving the long-term cycle stability of the negative electrode sheet, but also avoiding the decrease in the energy density of the single cell and improving the capacity cycle retention rate. If the width of the second negative electrode active material layer 245 is too large, the electrolyte required for the entire single cell will be greatly increased, which will reduce the mass energy density of the single cell.

[0097] According to some embodiments of the present application, optionally, D2=D3.

[0098] That is, the first negative electrode active material layer 244 and the third negative electrode active material layer 247 are symmetrically distributed at both ends of the second negative electrode active material layer 245 , which is helpful to alleviate lithium deposition in the middle of the negative electrode sheet.

[0099] The negative electrode active material in the first negative electrode active material layer 244 and the negative electrode active material in the third negative electrode active material layer 247 may be the same or different, and those skilled in the art may select the one according to actual needs.

[0100] According to some embodiments of the present application, optionally, the negative electrode active material in the first negative electrode active material layer 244 and the negative electrode active material in the third negative electrode active material layer 247 are the same.

[0101] When the negative electrode active material in the first negative electrode active material layer 244 and the negative electrode active material in the third negative electrode active material layer 247 are the same, the same ratio can be selected to prepare the first negative electrode active material layer 244 and the third negative electrode active material layer 247 with the same true density, effectively reducing the difficulty and cost of preparation.

[0102] Moreover, the negative electrode active material of the second negative electrode active material layer 245 may be the same as or different from the negative electrode active material in the first negative electrode active material layer 244, and the negative electrode active material of the second negative electrode active material layer 245 may be the same as or different from the negative electrode active material in the third negative electrode material layer, and those skilled in the art may define it according to actual needs.

[0103] According to some embodiments of the present application, optionally, in some embodiments, the negative electrode active material of the first negative electrode active material layer 244 is different from the negative electrode active material in the second negative electrode active material layer 245 , and the negative electrode active material in the third negative electrode active material layer 247 is different from the negative electrode active material in the second negative electrode active material layer 245 .

[0104] Under the premise that the first negative electrode active material layer 244, the second negative electrode active material layer 245 and the third negative electrode active material layer 247 have the same ratio, the true density of each layer is mainly related to the negative electrode active material. Therefore, by adopting the above setting, different negative electrode active materials can be used to directly control the true density of each layer, and the preparation difficulty is low.

[0105] According to some embodiments of the present application, optionally, the negative electrode active material includes at least one of a carbon-based material, a silicon-based material and a lithium titanate material, and the carbon-based material includes at least one of hard carbon, soft carbon, artificial graphite, natural graphite and expanded graphite. The above negative electrode active material is easy to obtain.

[0106] Among them, when the negative electrode active material of the first negative electrode active material layer 244 and the negative electrode active material of the third negative electrode active material layer 247 are artificial graphite and / or natural graphite respectively, the negative electrode active material of the second negative electrode active material layer 245 can be one or more of hard carbon, soft carbon, and artificial graphite.

[0107] When the negative electrode active material of the first negative electrode active material layer 244 and the negative electrode active material of the third negative electrode active material layer 247 are respectively a mixture of a silicon-based material and graphite (artificial graphite and / or natural graphite), the negative electrode active material of the second negative electrode active material layer 245 may be artificial graphite or natural graphite.

[0108] According to some embodiments of the present application, the present application also provides a battery cell, which includes the negative electrode sheet provided by any of the above solutions.

[0109] According to some embodiments of the present application, the present application also provides a battery, comprising a battery cell provided by any of the above schemes.

[0110] According to some embodiments of the present application, the present application also provides an electrical device, comprising a battery according to any of the above schemes, and the battery is used to provide electrical energy to the electrical device.

[0111] The power-consuming device may be any of the aforementioned devices or systems using batteries.

[0112] Some specific embodiments are listed below to better illustrate the present application.

[0113] Examples and Comparative Examples

[0114]

Full battery production

[0115] 1. Positive electrode: the active material LiNi 0.8 Co 0.1 Mn 0.1 O 2, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96.8:2.2:1, dissolved in N-methylpyrrolidone (NMP), and the positive electrode slurry is prepared after slurrying. It is coated on an aluminum foil with a width of 400 mm, dried, cold pressed, and cut to obtain a positive electrode sheet.

[0116] 2. Separation membrane: Use polyethylene (PE) porous polymer membrane as the separation membrane.

[0117] 3. Negative electrode:

[0118] The preparation method of the negative electrode sheet in [Examples 1-30 and Comparative Examples 3-8] is:

[0119] The negative electrode active material 2 (see Table 1 for details), conductive carbon black (SP), styrene-butadiene rubber emulsion (SBR), and sodium carboxymethyl cellulose are mixed in the dry matter mass ratio shown in Table 1, dissolved in deionized water, and coated on both surfaces of a copper foil with a width of 404 mm after slurry. This coating is a material layer with uniform thickness.

[0120] Next, the negative electrode active material 1 (see Table 1 for details), conductive carbon black (SP), styrene-butadiene rubber emulsion (SBR), and sodium carboxymethyl cellulose are mixed according to the dry matter mass ratio shown in Table 1, and the slurry is applied to both ends of the second negative electrode active material layer in a preset direction to obtain a first negative electrode active material layer and a third negative electrode active material layer having the same thickness as the second negative electrode active material layer. The coated electrode sheet is dried and cold pressed, and cut into negative electrode sheets.

[0121] In Table 1, the true density of hard carbon is 2.06, the true density of porous hard carbon 1 is 1.95, the true density of porous hard carbon 2 is 1.2, the true density of artificial graphite is 2.27, and the true density of natural graphite is 2.24. The true density of silicon oxide is 3.0, and the true density is tested according to GB / T24586.

[0122] The only difference between [Comparative Example 1] and Example 1 is that the second negative electrode active material layer is used to replace the first negative electrode active material layer and the third negative electrode active material layer.

[0123] The preparation method of the negative electrode sheet in [Comparative Example 2] is: replacing the second negative electrode active material layer with the first negative electrode active material layer.

[0124] 4. Electrolyte: Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:6:1, and then add fully dried lithium salt (LiPF 6 ) is dissolved in a mixed organic solvent at a ratio of 1 mol / L to obtain the desired electrolyte.

[0125] 5. Full battery assembly: stack the above positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is between the positive and negative electrodes to play a role of isolation, and wind them to obtain a bare cell. Place the bare cell in an outer aluminum shell, inject the prepared electrolyte into the dry cell after high-temperature drying, and obtain a lithium-ion secondary cylindrical battery after vacuum packaging, standing, formation, shaping and other processes.

[0126]

Performance evaluation of full battery

[0127] The performance evaluation of each embodiment and comparative example was carried out according to the following method, and the test results are shown in Table 2.

[0128] 1. Cycle performance test:

[0129] Under a constant temperature environment of 25°C, the full batteries corresponding to each embodiment and the comparative example were charged and discharged for the first time, and constant current and constant voltage charging (charging to a current of 0.05C) was performed at a charging current of 1.0C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour) until the upper limit voltage reached 4.25V. After standing for 5 minutes, constant current discharge was performed at a discharge current of 1.0C until the final voltage was 2.8V, and the discharge capacity of the first cycle was recorded; and then continuous charge and discharge cycles were performed.

[0130] Capacity retention rate at the nth cycle=(discharge capacity at the nth cycle / discharge capacity at the first cycle)×100%.

[0131] 2. Lithium precipitation test.

[0132] After the corresponding number of cycles, each full battery was charged to a fully charged state (100% SOC), and the battery was disassembled in a dry environment at 20°C and 2% humidity. The negative electrode sheets of each disassembled full battery were unfolded to observe the lithium deposition in the area where the second negative electrode active material layer was located, and photographed and recorded.

[0133] The degree of lithium precipitation is defined as follows:

[0134] 0: Lithium deposition cannot be observed with the naked eye;

[0135] 1: Trace lithium deposition (lithium deposition area is less than 10% of the area of ​​the second negative electrode active material layer);

[0136] 2: Small area lithium deposition (lithium deposition area is 10-30%);

[0137] 3: Large-area lithium deposition (lithium deposition area > 30%).

[0138] Table 1 Preparation parameters of negative electrode sheets of examples and comparative examples

[0139]

[0140]

[0141] In Table 1, the first negative electrode active material layer and the third negative electrode active material layer have the same true density, and the negative electrode active material material and median particle size are the same.

[0142] Table 2 Test results of examples and comparative examples

[0143]

[0144]

[0145] According to Table 1 and Table 2, Examples 1-30 can effectively improve the lithium deposition in the middle of the negative electrode sheet, and the lithium deposition level is 0 after 600 cycles, and Example 1-29 has a cycle retention rate of >90% after 200 cycles.

[0146] Compared with Example 22, Example 30 has a smaller true density T2, resulting in that although it can improve lithium deposition in the middle of the negative electrode sheet, the cycle retention rate after 200 cycles is less than 90%.

[0147] According to Comparative Example 1, if the negative electrode active layer is entirely composed of the second negative electrode active material layer, although the lithium deposition in the middle of the negative electrode sheet can be improved, the energy density will be sacrificed, so that the capacity retention rate of the negative electrode sheet after 200 cycles is only 87.5%, which cannot meet the requirements of high energy density.

[0148] According to Comparative Example 2, if the negative electrode active layer is entirely composed of the first negative electrode active material layer, not only will the lithium plating in the middle of the negative electrode sheet fail to be improved, but the energy density will also be significantly sacrificed, so that the capacity retention rate of the negative electrode sheet after 200 cycles is only 86.4%, which cannot meet the requirements of high energy density.

[0149] The only difference between Comparative Example 3 and Example 1 is that the median particle size C1 of the negative electrode active materials in the first negative electrode active material layer and the third negative electrode active material layer is equal to the median particle size C2 of the negative electrode active material in the second negative electrode active material layer. The above setting not only sacrifices the energy density, so that the capacity retention rate of the negative electrode sheet after 200 cycles is only 89.3%, which cannot meet the requirements of high energy density, but also after the negative electrode sheet is cycled 600 times, lithium is deposited in the middle of the negative electrode sheet, and the cycle stability is poor.

[0150] The difference between Comparative Example 4 and Example 1 is that the true density T1 of the first negative electrode active material layer and the third negative electrode active material layer is equal to the true density T2 of the second negative electrode active material layer. The above setting not only sacrifices the energy density, so that the capacity retention rate of the negative electrode sheet after 200 cycles is only 89.3%, which cannot meet the requirements of high energy density, but also cannot solve the problem of lithium deposition in the middle of the negative electrode sheet.

[0151] In Comparative Example 5, the width ratio of the second negative electrode active material layer on the negative electrode active layer is too small, which makes it unable to improve the problem of lithium deposition in the middle of the negative electrode sheet, and causes the capacity retention rate of the negative electrode sheet after 200 cycles to be only 88.6%. In Comparative Example 6, the width ratio of the second negative electrode active material layer on the negative electrode active layer is too large, which makes it unable to improve the problem of lithium deposition in the middle of the negative electrode sheet, and causes the capacity retention rate of the negative electrode sheet after 200 cycles to be only 84.8%.

[0152] Compared with Example 1, the difference between Comparative Examples 7 and 8 is that the median particle size C1 of the negative electrode active material 1 in Comparative Example 7 is too small, which makes it unable to improve the problem of lithium deposition in the middle of the negative electrode sheet, and the capacity retention rate of the negative electrode sheet after 200 cycles is only 85.1%; the median particle size C2 of the negative electrode active material 2 in Comparative Example 8 is too large, which makes it unable to improve the problem of lithium deposition in the middle of the negative electrode sheet, and the capacity retention rate of the negative electrode sheet after 200 cycles is only 87.7%.

[0153] In summary, the present application utilizes the improvement of the negative electrode sheet to improve lithium deposition in the middle area of ​​the negative electrode sheet, improve cycle stability and safety, and can increase energy density, thereby improving the performance of battery cells, batteries, and electrical equipment containing the above-mentioned negative electrode sheet.

[0154] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A negative electrode sheet, characterized in that: It comprises a current collector and a negative electrode active layer formed on the current collector, wherein the current collector is provided with a negative electrode tab on any side of a preset direction, and the negative electrode active layer comprises a first negative electrode active material layer, a second negative electrode active material layer and a third negative electrode active material layer arranged in sequence along the preset direction; wherein the median particle size of the negative electrode active material in the first negative electrode active material layer and the third negative electrode active material layer is greater than the median particle size of the negative electrode active material in the second negative electrode active material layer, and the true density in the first negative electrode active material layer and the third negative electrode active material layer is greater than the true density of the second negative electrode active material layer; The width of the first negative electrode active material layer in the preset direction is D1, the width of the second negative electrode active material layer in the preset direction is D2, and the width of the third negative electrode active material layer in the preset direction is D3, wherein 0.05<D2 / (D2+D1+D3)≤0.45; The median particle size of the negative electrode active material in the first negative electrode active material layer is C1μm, the median particle size of the negative electrode active material in the second negative electrode active material layer is C2μm, and the median particle size of the negative electrode active material in the third negative electrode active material layer is C3μm, wherein 5≤C1≤25, 0.5≤C2≤15, and 5≤C3≤25.

2. The negative electrode sheet according to claim 1, characterized in that: The true density of the first negative electrode active material layer is T1 g / cm 3 , the true density of the second negative electrode active material layer is T2 g / cm 3 The true density of the third negative electrode active material layer is T3 g / cm 3 , 3≥T1>T2≥1.4, 3≥T3>T2≥1.

4.

3. The negative electrode sheet according to claim 2, characterized in that: 2.3≥T1≥2.0, 2.2≥T2≥1.9, 2.3≥T3≥2.

0.

4. The negative electrode sheet according to claim 2, characterized in that: 2.26≥T1≥2.18, 2.04≥T2≥1.96; 2.26≥T3≥2.

18.

5. The negative electrode sheet according to claim 1, characterized in that: 10≤C1≤20, 2≤C2≤10, 10≤C3≤20.

6. The negative electrode sheet according to claim 1, characterized in that: 12≤C1≤16, 4≤C2≤6, 12≤C3≤16.

7. The negative electrode sheet according to claim 1, characterized in that: 0.1≤D2 / (D2+D1+D3)≤0.3, 0.1≤D1 / (D2+D1+D3)≤0.6, 0.1≤D3 / (D2+D1+D3)≤0.

6.

8. The negative electrode sheet according to claim 7, characterized in that: D2=D3.

9. The negative electrode sheet according to any one of claims 1 to 8, characterized in that: The negative electrode active material in the first negative electrode active material layer and the negative electrode active material in the third negative electrode active material layer are the same.

10. The negative electrode sheet according to any one of claims 1 to 8, characterized in that: The negative electrode active material in the first negative electrode active material layer is different from the negative electrode active material in the second negative electrode active material layer, and the negative electrode active material in the third negative electrode active material layer is different from the negative electrode active material in the second negative electrode active material layer.

11. The negative electrode sheet according to any one of claims 1 to 8, characterized in that: The negative electrode active material includes at least one of a carbon-based material, a silicon-based material and a lithium titanate material, and the carbon-based material includes at least one of hard carbon, soft carbon, artificial graphite, natural graphite and expanded graphite.

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

13. A battery, characterized in that: Comprising the battery cell as claimed in claim 12.

14. The battery according to claim 13, characterized in that The battery is a secondary battery.

15. An electrical equipment, characterized in that: Comprising a battery as claimed in claim 13 or 14.

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