Negative electrode sheet, method for manufacturing the same, and battery

Abstract

The embodiment of the present application provides a negative plate, which comprises a current collector, a first negative coating arranged on the surface of the current collector, and a second negative coating arranged on the side of the first negative coating away from the current collector, wherein the first negative active material has a first rate, the second negative active material has a second rate, and the first rate is less than the second rate; the negative plate provides a fast ion transmission channel by arranging the second negative coating as an outer layer, so that lithium ions outside the negative plate can quickly reach the inner layer through the outer layer for layer storage, and fast current receiving and conduction are realized; the first negative coating is arranged as an inner layer, so that the inner layer with large and stable capacity can absorb the lithium ions transmitted by the outer layer. The embodiment of the present application also provides a preparation method of the negative plate and a battery, which have the above beneficial effects.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a negative electrode sheet and its preparation method, and a battery. Background Technology

[0002] In related technologies, the negative electrode of a battery typically includes a current collector and a single-layer, single-rate material layer disposed on the surface of the current collector. Using a high-rate material to form a single-layer material layer on the current collector surface results in less heat and stress within the negative electrode, but also makes it highly susceptible to side reactions that can damage the internal structure of the material, leading to lower cycle life and safety. Conversely, using a low-rate material layer on the current collector surface results in a slow migration rate of lithium ions within the negative electrode, leading to slow charging speeds that cannot meet the fast-charging requirements of modern batteries. Summary of the Invention

[0003] The purpose of this application is to provide a negative electrode sheet and its preparation method, as well as a battery, which can meet the requirements of large capacity and fast charging performance, and also improve the stability and safety of the battery.

[0004] In a first aspect, embodiments of this application provide a negative electrode sheet, comprising:

[0005] current collector;

[0006] A first negative electrode coating is disposed on the surface of the current collector, and the first negative electrode coating includes a first negative electrode active material;

[0007] The second negative electrode coating is disposed on the side of the first negative electrode coating that is away from the current collector, and the second negative electrode coating includes a second negative electrode active material;

[0008] Wherein, the first negative electrode active material has a first rate of increase, the second negative electrode active material has a second rate of increase, and the first rate of increase is less than the second rate of increase.

[0009] In one embodiment, at the same rate and with a capacity retention rate not lower than a set value, the number of cycles X of the first negative electrode active material is less than the number of cycles Y of the second negative electrode active material.

[0010] In one embodiment, YX ≥ 100.

[0011] In one embodiment, the first negative electrode active material maintains a capacity retention rate of not less than 80% for 300 to 400 cycles at a first rate, the second negative electrode active material maintains a capacity retention rate of not less than 80% for 500 to 600 cycles at the first rate, and the second negative electrode active material maintains a capacity retention rate of not less than 80% for 300 to 400 cycles at a second rate.

[0012] In one embodiment, the first multiplier is 3C to 5C, and the second multiplier is 6C to 10C.

[0013] In one embodiment, the mass percentage of the first negative electrode coating to the sum of the masses of the first negative electrode coating and the second negative electrode coating is w1%, and the mass percentage of the second negative electrode coating to the sum of the masses of the first negative electrode coating and the second negative electrode coating is w2%, wherein w1% : w2% = (60% to 80%) : (20% to 40%).

[0014] In one embodiment, the first negative electrode active material comprises primary particulate graphite, and / or the second negative electrode active material comprises secondary particulate graphite.

[0015] In one embodiment, the first negative electrode active material includes first graphite particles, the particle size of which is 11.3 μm to 11.7 μm;

[0016] And / or, the second negative electrode active material includes second graphite particles, the particle size of which is 6.5 μm to 7.5 μm.

[0017] In one embodiment, the orientation degree of the first negative electrode active material is 10.4 to 11.4;

[0018] And / or, the orientation degree of the second negative electrode active material is 8.4 to 8.7.

[0019] Secondly, embodiments of this application provide a method for preparing a negative electrode sheet, comprising the following steps:

[0020] S10 provides a current collector;

[0021] S20, a material with a first rate of increase is selected as the first negative electrode active material, and a material with a second rate of increase is selected as the second negative electrode active material, wherein the first rate of increase is less than the second rate of increase;

[0022] S30, a first negative electrode coating material is made of a first negative electrode active material, and a second negative electrode coating material is made of a second negative electrode active material;

[0023] S40, the first negative electrode coating material is coated on the surface of the current collector to form a first negative electrode coating;

[0024] S50, the second negative electrode coating material is coated on the side of the first negative electrode coating away from the current collector to form the second negative electrode coating.

[0025] In one embodiment, step S20 includes:

[0026] S21, the capacity retention rate and cycle number of the materials are measured sequentially at the same rate. The material with a cycle number of not less than the set capacity retention rate and a cycle number of X is selected as the first negative electrode active material, and the material with a cycle number of not less than the set capacity retention rate and a cycle number of Y is selected as the second negative electrode active material, wherein X is less than Y.

[0027] In one embodiment, step S20 further includes YX ≥ 100.

[0028] In one embodiment, in step S20,

[0029] The first negative electrode active material is selected, which includes first graphite particles, and the particle size of the first graphite particles is 11.3 μm to 11.7 μm;

[0030] And / or, select a second negative electrode active material comprising second graphite particles, wherein the particle size of the second graphite particles is 6.5 μm to 7.5 μm;

[0031] And / or, select the first negative electrode active material with an orientation degree between 10.4 and 11.4;

[0032] And / or, select the second negative electrode active material with an orientation degree between 8.4 and 8.7.

[0033] Thirdly, embodiments of this application provide a battery including the negative electrode sheet described above or the negative electrode sheet prepared by the above preparation method, and also including a positive electrode sheet and a separator. The negative electrode sheet, the separator and the positive electrode sheet are stacked, and the separator is disposed between the positive electrode sheet and the negative electrode sheet.

[0034] The beneficial effects of the negative electrode sheet provided in this application are as follows: Compared with related technologies, the negative electrode sheet of this application includes a current collector, a first negative electrode coating disposed on the surface of the current collector, and a second negative electrode coating disposed on the side of the first negative electrode coating facing away from the current collector. The first negative electrode active material has a first rate capability, the second negative electrode active material has a second rate capability, and the first rate capability is less than the second rate capability. The current collector surface of the negative electrode sheet of this application includes a double-layer coating. By setting the second negative electrode coating with a larger rate capability as the outer layer, a fast ion transport channel is provided, allowing lithium ions outside the negative electrode sheet to quickly reach the inner layer for storage, achieving rapid current reception and conduction, thereby improving the fast-charging performance of the battery. Setting the first negative electrode coating with a smaller rate capability as the inner layer allows the inner layer to have a large and stable capacity to absorb lithium ions transported from the outer layer, thereby increasing the battery capacity. Furthermore, the first negative electrode coating is stable and can mitigate internal structural changes in the material of the second negative electrode coating, reducing the occurrence of side reactions, thereby ensuring the overall stability and safety of the battery. This application also provides a method for preparing a negative electrode sheet and a battery, which have the above-mentioned beneficial effects. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the structure of a negative electrode sheet provided in an embodiment of this application;

[0037] Figure 2 A scanning electron microscope (SEM) image of a negative electrode sheet provided in an embodiment of this application;

[0038] Figure 3 A schematic flowchart illustrating a method for preparing a negative electrode sheet according to another embodiment of this application;

[0039] Figure 4 for Figure 3 A schematic diagram of the structure used in the fabrication of the intermediate negative electrode sheet;

[0040] Figure 5 This is a schematic diagram of the structure of a battery provided in yet another embodiment of this application;

[0041] The following are the labeling elements in the figure:

[0042] Battery 100; negative electrode 10; casing 20; tab 30; current collector 11; first negative electrode coating 12; second negative electrode coating 13. Detailed Implementation

[0043] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0044] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0045] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0046] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0047] Please refer to the following: Figure 1 and Figure 2 The negative electrode 10 provided in one embodiment of this application will now be described. Figure 1 As shown, the negative electrode 10 includes a current collector 11, a first negative electrode coating 12, and a second negative electrode coating 13. Specifically, the first negative electrode coating 12 is disposed on the surface of the current collector 11, and the second negative electrode coating 13 is disposed on the side of the first negative electrode coating 12 facing away from the current collector 11.

[0048] The first negative electrode coating 12 includes a first negative electrode active material, and the second negative electrode coating 13 includes a second negative electrode active material; wherein the first negative electrode active material has a first rate, the second negative electrode active material has a second rate, and the first rate is less than the second rate.

[0049] The current collector 11 surface of the negative electrode 10 provided in this application embodiment includes a double-layer coating. By setting a second negative electrode coating 13 with a larger capacity as the outer layer, a fast ion transport channel is provided, allowing lithium ions outside the negative electrode 10 to quickly reach the inner layer for storage, achieving rapid current reception and conduction, thereby improving the fast charging performance of the battery. A first negative electrode coating 12 with a smaller capacity is set as the inner layer, so that the inner layer has a large and stable capacity to absorb lithium ions transported by the outer layer, thereby increasing the battery capacity. Furthermore, the first negative electrode coating 12 is stable in nature and can alleviate the structural changes inside the material of the second negative electrode coating 13, reducing the occurrence of side reactions, thereby ensuring the overall stability and safety of the battery.

[0050] Specifically, at the same rate and with a capacity retention rate not lower than the set value, the number of cycles X of the first negative electrode active material is less than the number of cycles Y of the second negative electrode active material, i.e., X < Y. At the same rate and with the same capacity retention rate, the number of cycles X of the first negative electrode active material is less than the number of cycles Y of the second negative electrode active material.

[0051] Optionally, the current collector 11 has a first surface and a second surface; a first negative electrode coating 12 is disposed on the first surface of the current collector 11, and a second negative electrode coating 13 is disposed on the side of the first negative electrode coating 12 facing away from the first surface of the current collector 11; or, the first negative electrode coating 12 is disposed on the second surface of the current collector 11, and the second negative electrode coating 13 is disposed on the side of the first negative electrode coating 12 facing away from the second surface of the current collector 11; or, the first negative electrode coating 12 is disposed on both surfaces of the current collector 11, and the two second negative electrode coatings 13 are respectively disposed on the two surfaces of the first negative electrode coating 12 facing away from the current collector 11. In this embodiment, the first negative electrode coating 12 is disposed on both surfaces of the current collector 11, and the two second negative electrode coatings 13 are respectively disposed on the two surfaces of the first negative electrode coating 12 facing away from the current collector 11, thereby making full use of the current collector 11, increasing the content of the first negative electrode active material and the second negative electrode active material, and improving the current carrying capacity of the negative electrode sheet 10.

[0052] Generally, when a certain rate is applied to a material, its capacity retention decreases as the number of cycles increases. It should be noted that C represents the battery charge / discharge rate. 1C represents the current intensity when the battery is fully discharged in one hour. It should also be noted that the first negative electrode active material has a first rate, and the second negative electrode active material has a second rate. This application selects the first and second negative electrode active materials by applying the same rate conditions and maintaining the same capacity retention, and by comparing the number of cycles. However, the specific first rate of the first negative electrode active material and the second rate of the second negative electrode active material still need to be determined by measurement.

[0053] In this application, under the same ambient temperature and with the same multiplier applied, the second negative electrode active material achieves a higher number of cycles while maintaining a certain capacity retention rate than the first negative electrode active material achieves the same number of cycles. Specifically, at room temperature, the capacity retention rate and number of cycles are measured sequentially using the same multiplier. With a capacity retention rate set to 80%, the material that maintains a capacity retention rate of at least 80% for a number of cycles (X) is selected as the first negative electrode active material, and the material that maintains a capacity retention rate of at least 80% for a number of cycles (Y) is selected as the second negative electrode active material, where X < Y. Alternatively, the number of cycles (X) when the first negative electrode active material drops to 80% is less than the number of cycles (Y) when the second negative electrode active material drops to 80%. In this embodiment, a first multiplier is set, meaning the capacity retention rate and number of cycles are measured sequentially using the first multiplier applied to the materials.

[0054] Furthermore, YX ≥ 100. It is understandable that, at the same rate and with the same capacity retention, the greater the difference between the cycle number Y of the second negative electrode active material and the cycle number X of the first negative electrode active material, the greater the difference in rate capability between the second and first negative electrode active materials. This makes ion insertion and extraction in the second negative electrode active material easier, resulting in higher electronic conductivity and ion diffusion rate. The second negative electrode active material can quickly absorb charging current, leading to a higher lithium-ion concentration in the second negative electrode active material compared to the first. This higher lithium-ion concentration in the second negative electrode active material makes it easier for lithium ions to transfer from the second to the first negative electrode active material. Furthermore, the greater the difference in rate capability between the second and first negative electrode active materials, the greater the difference in lithium-ion concentration between them, further accelerating the migration of lithium ions from the second negative electrode coating 13 to the first negative electrode coating 12. Optionally, the difference between Y and X can be between 100 and 200, or between 200 and 300, or between 300 and 400, etc.

[0055] In this embodiment, under the condition of applying a first rate, a material with a cycle count between 300 and 400 that maintains a capacity retention rate of not less than 80% is selected as the first negative electrode active material, and a material with a cycle count between 500 and 600 that maintains a capacity retention rate of not less than 80% is selected as the second negative electrode active material.

[0056] Specifically, the first rate of return refers to the rate at which the first negative electrode active material maintains a capacity retention rate of not less than 80% for 300 to 400 cycles at room temperature. In other words, the first negative electrode active material having a first rate of return means that, at room temperature, when the first rate of return is applied to the first negative electrode active material, the number of cycles when the capacity retention rate drops to 80% is between 300 and 400. Similarly, provided that the second rate of return is greater than the first rate of return and the ambient temperature is room temperature, the second rate of return refers to the rate at which the second negative electrode active material maintains a capacity retention rate of not less than 80% for 300 to 400 cycles. In other words, the second negative electrode active material having a second rate of return means that, at room temperature, when the second rate of return is applied to the second negative electrode active material, the number of cycles when the capacity retention rate drops to 80% is between 300 and 400.

[0057] For example, in this embodiment, the first rate is 3C, and the first negative electrode active material has a 3C rate; the second rate is 10C, and the second negative electrode active material has a 10C rate. At room temperature, the first negative electrode active material is cycled at a 3C rate. After 300 cycles, the capacity retention rate of the first negative electrode active material is greater than 80%, and after 400 cycles, the capacity retention rate is less than 80%; or, the number of cycles required for the capacity retention rate of the first negative electrode active material to drop to 80% is between 300 and 400. Similarly, the second negative electrode active material is cycled at a 10C rate. After 300 cycles, the capacity retention rate of the second negative electrode active material is greater than 80%, and after 400 cycles, the capacity retention rate is less than 80%; or, the number of cycles required for the capacity retention rate of the second negative electrode active material to drop to 80% is between 300 and 400.

[0058] The following description continues using this embodiment. At room temperature, the second negative electrode active material is cycled at a 3C rate. After 400 cycles, the capacity retention rate of the second negative electrode active material is greater than 80%; or, the number of cycles required for the capacity retention rate of the second negative electrode active material to drop to 80% is greater than 400 (greater than the number of cycles required for the first negative electrode active material under the same conditions). The first negative electrode active material is cycled at a 10C rate. After 300 cycles, the capacity retention rate of the first negative electrode active material is less than 80%; or, the number of cycles required for the capacity retention rate of the first negative electrode active material to drop to 80% is less than 300 (less than the number of cycles required for the second negative electrode active material under the same conditions).

[0059] Optionally, the first multiplier is O1, where O1 = 0.5k, and k is an integer greater than 0; the second multiplier is O2, where O2 = 0.5m, and m is an integer greater than k. During the selection of the first and second negative electrode active materials, multiple multipliers from small to large are applied sequentially to screen for materials with a first multiplier that maintains a capacity retention rate of not less than 80% for 300-400 cycles and a second multiplier that maintains a capacity retention rate of not less than 80% for 500-600 cycles. To avoid repeated measurements, the first multiplier O1 is directly applied during material selection, thus determining the first multiplier material with a capacity retention rate of not less than 80% for 300-400 cycles at the first multiplier O1 as the first negative electrode active material, and the second multiplier material with a capacity retention rate of not less than 80% for 500-600 cycles at the first multiplier O1 as the second negative electrode active material. In this selection process, the first rate O1 of the first negative electrode active material has been determined; then the second rate O2 of the second negative electrode active material is measured to determine the second rate O2 of the second negative electrode active material to maintain a cycle number of 300 to 400 with a capacity retention rate of not less than 80%.

[0060] To improve selection efficiency and simplify the selection process, multiple ratios are set as an arithmetic sequence with a tolerance of 0.5C. Therefore, the first negative electrode active material with a first ratio O1 of 0.5 is selected, and the second negative electrode active material with a second ratio O2 of greater than 0.5 of O1 is determined.

[0061] Alternatively, the first multiplier is O1, where O1 = k, and k is an integer greater than 0; the second multiplier is O2, where O2 = m, and m is an integer greater than k, and the specific multiplier is determined based on the tolerance between the multiple multipliers during selection and measurement.

[0062] Understandably, setting multiple magnification tolerances greater than 1C results in excessively large differences in magnification between various materials, leading to a limited selection of materials. Setting multiple magnification tolerances less than 0.5C results in similar results when applying multiple magnifications to the same material, but this leads to too many measurements and low efficiency in material selection and testing.

[0063] Optionally, in some other embodiments, O1 = 0.2k and O2 = 0.2m.

[0064] Optionally, the first rate of charge is 3C to 5C, and the second rate of charge is 6C to 10C. Specifically, the first rate of charge is 3C, 3.5C, 4C, 4.5C, or 5C, etc., and the second rate of charge is 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, or 10C, etc. The first negative electrode active material with a first rate of 3C to 5C has high capacity and stability. During fast charging, the first negative electrode active material located in the inner layer can store a large number of lithium ions transferred from the outer layer, ensuring that the inner layer has sufficient capacity to accommodate the lithium ions rapidly transferred from the outer layer during fast charging. The stability of the first negative electrode active material can improve the cycle life and safety of the battery. During fast charging, a large amount of heat and stress are generated inside the battery. The stability of the first negative electrode active material can reduce the occurrence of side reactions within the negative electrode sheet and the structural damage inside the material, thereby improving the cycle life and safety of the battery. The second negative electrode active material with a second rate of 6C to 10C has good electronic conductivity and ion diffusion rate. The outer second negative electrode active material can rapidly receive and conduct charging current. During fast charging, a large amount of current needs to quickly enter the negative electrode 10. The second negative electrode active material can efficiently receive current to provide current to the first negative electrode active material, reducing current accumulation and polarization on the surface of the negative electrode 10. The second negative electrode active material can rapidly undergo ion insertion and extraction reactions. During fast charging, lithium ions are rapidly inserted into the negative electrode 10 and migrate rapidly within it, thereby accelerating the charging speed.

[0065] Furthermore, the difference between the second and first rates is greater than 3C, i.e., O2-O1>3. Understandably, the higher the second rate of the second negative electrode active material, the easier it is for ions to insert and extract, resulting in greater electronic conductivity and ion diffusion rate. This allows for faster absorption of charging current, leading to a higher lithium-ion concentration in the second negative electrode active material compared to the first. This higher lithium-ion concentration in the second negative electrode active material facilitates lithium-ion transfer from the second to the first negative electrode active material. Moreover, the greater the difference between the second and first rates, the greater the difference in lithium-ion concentration between the second and first negative electrode active materials, further accelerating the migration of lithium ions from the second negative electrode coating 13 to the first negative electrode coating 12.

[0066] Furthermore, the contact area between the negative electrode 10 and the electrolyte affects electrolyte wetting. Low electrolyte wetting reduces the reaction sites for both positive and negative electrode active materials, leading to increased internal resistance and consequently higher battery temperature. The difference in lithium-ion concentration between the second and first negative electrode active materials promotes electrolyte wetting.

[0067] Optionally, the mass percentage of the first negative electrode coating 12 to the sum of the masses of the first negative electrode coating 12 and the second negative electrode coating 13 is w1%, and the mass percentage of the second negative electrode coating 13 to the sum of the masses of the first negative electrode coating 12 and the second negative electrode coating 13 is w2%, where w1%:w2% = (60%~80%):(20%~40%). Specifically, w1%:w2% = 60%:40%, or w1%:w2% = 70%:30%, or w1%:w2% = 80%:20%, etc. It is understandable that the heavier the mass percentage of the first negative electrode coating 12, the greater the current capacity that the first negative electrode coating 12 can store within the negative electrode sheet 10, thus increasing the battery capacity; the heavier the mass percentage of the second negative electrode coating 13, the faster and larger the second negative electrode coating 13 can absorb lithium ions within the negative electrode sheet 10, thereby improving the battery's fast-charging capability.

[0068] In this embodiment, the first negative electrode active material includes first graphite particles, which include primary graphite particles. The second negative electrode active material includes second graphite particles, which include secondary graphite particles. The primary particles have a relatively complete crystal structure and fewer defects; therefore, the electron transport path within the first negative electrode active material is more direct and smooth, resulting in relatively good conductivity. The primary graphite particles in the first negative electrode active material are formed from the raw materials of the first negative electrode active material through granulation, graphitization, coating, and carbonization, which can improve the conductivity of the first negative electrode coating 12. The secondary particles are formed by the agglomeration of primary particles; their morphology and structure allow them to form a high packing density when stacked, thereby increasing the energy density of the negative electrode sheet 10. Furthermore, since the secondary particles are formed by the agglomeration of primary particles, their surface is uneven, thus the secondary particles have a larger surface area, which to some extent increases the contact area between the second negative electrode coating 13 and the electrolyte, promoting ion transport and reaction, thereby improving the electrochemical performance of the negative electrode sheet 10.

[0069] Optionally, the first graphite particle further includes a first coating layer covering the primary particle, the first coating layer being a solid-phase carbon coating layer. The second graphite particle further includes a second coating layer covering the secondary particle, the second coating layer being a liquid resin coating layer. Both the first and second graphite particles include nanoscale first and second coating layers. Both the first and second coating layers are crystalline carbon coating layers with a wavy lattice. Coating the surface of the primary particle with the first coating layer can improve defects such as surface cracks and pores, thereby improving the structural stability of the first graphite particle. Coating the surface of the secondary particle with the second coating layer can improve surface cracks and pores. The first and second coating layers are isotropic, providing more active centers and fast lithium-ion transport channels for lithium-ion intercalation, reducing polarization, and promoting lithium-ion diffusion.

[0070] In this embodiment, the particle size of the first graphite particles is 11.3 micrometers (μm) to 11.7 micrometers, such as 11.3 μm, 11.4 μm, 11.5 μm, 11.6 μm, or 11.7 μm. The particle size of the second graphite particles is 6.5 μm to 7.5 μm, such as 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm, 7.1 μm, 7.2 μm, 7.3 μm, 7.4 μm, or 7.5 μm. It is understood that the smaller the particle size, the better the rate performance of the material.

[0071] Furthermore, the orientation degree of the first negative electrode active material is 10.4–11.4. Optionally, the orientation degree of the first negative electrode active material is 10.4, 10.5, 10.6, 10.8, 11.0, 11.2, or 11.4, etc. And / or, the orientation degree of the second negative electrode active material is 8.4–8.7. Optionally, the orientation degree of the second negative electrode active material is 8.4, 8.5, 8.6, or 8.7. Providing a first negative electrode active material with an orientation degree of 10.4–11.4 and a second negative electrode active material with an orientation degree of 8.4–8.7 makes the crystal structures of the first and second negative electrode active materials more conducive to lithium-ion insertion and extraction during charge and discharge.

[0072] Orientation degree is a measure of the degree of orientation of a polymer, mainly referring to the degree to which various structural units, including microcrystals, such as macromolecules or chain segments, are regularly arranged along the fiber axis. In this application, the orientation degree of the material is determined using X-ray diffraction. X-ray diffraction is a method for analyzing the internal crystal structure of a material by measuring its diffraction pattern under X-ray irradiation. In determining the orientation degree, X-ray diffraction infers the material's orientation degree by analyzing the position and intensity of diffraction peaks in the diffraction pattern.

[0073] Optionally, the first negative electrode coating 12 further includes a first conductive agent, a first suspending agent, a first binder, and a first solvent. The mass ratio of the first negative electrode active material, the first conductive agent, the first suspending agent, and the first binder is (95.8–97.6):(0.2–0.6):(1.0–2.0):(1.5–2.5). The second negative electrode coating 13 further includes a second conductive agent, a second suspending agent, a second binder, and a second solvent. The mass ratio of the second negative electrode active material, the second conductive agent, the second suspending agent, and the second binder is (95.8–97.6):(0.2–0.6):(1.0–2.0):(1.5–2.5).

[0074] Optionally, both the first and second conductive agents can be conductive carbon black (Super P, SP), or other conductive agents. Conductive carbon black SP is a furnace black-like conductive carbon black, which is formed by the aggregation of primary particles with a diameter of about 40 nm into primary aggregates of 150 nm to 200 nm, and then shaped through subsequent processing such as agglomeration and artificial compression.

[0075] Optionally, both the first and second suspending agents are carboxymethyl cellulose lithium (CMC-Li). Optionally, both the first and second solvents are water (H2O).

[0076] Furthermore, the mass percentage of the first negative electrode active material in the first negative electrode coating 12 is less than the mass percentage of the second negative electrode active material in the second negative electrode coating 13, thereby increasing the proportion of the second negative electrode active material in the negative electrode sheet 10 and ensuring the fast-charging capability of the negative electrode sheet 10. For example, the mass percentage of the first negative electrode active material in the first negative electrode coating 12 is 95.8%, and the mass percentage of the second negative electrode active material in the second negative electrode coating 13 is 97.6%, etc. The mass percentage of the second binder in the second negative electrode coating 13 is less than the mass percentage of the first binder in the first negative electrode coating 12. By setting a larger content of the first binder in the first negative electrode coating 12, the adhesion between the first negative electrode coating 12 and the current collector 11 or the second negative electrode coating 13 is enhanced, preventing the negative electrode sheet 10 from shedding material. The second binder is a low-swelling binder, thereby effectively suppressing thickness expansion during battery cycling and improving the battery's cycle life. For example, the proportion of the first binder in the first negative electrode coating 12 is 2%, and the proportion of the second binder in the second negative electrode coating 13 is 1%, etc. In this embodiment, both the first and second adhesives are styrene-butadiene rubber (SBR) adhesives. Optionally, the first adhesive may be Zeon's BTR-102 or BASF's Liofol LA 9522. Optionally, the second adhesive may include carboxylated styrene-butadiene rubber, modified styrene-butadiene rubber, or waterborne styrene-butadiene rubber. The requirement is that the swelling rate of the second adhesive is less than 50%, and the amount of the second adhesive used is less than the amount of the first adhesive. In this application, a low swelling rate adhesive refers to an adhesive with a swelling rate less than 50%, specifically, a swelling rate of 49%, 45%, 30%, 20%, or 15%, etc.

[0077] In this embodiment, the mass ratio of the first negative electrode active material, conductive carbon black, first suspending agent, and first binder is 97.00% : 0.4% : 1.1% : 1.5%. The mass ratio of the second negative electrode active material, conductive carbon black, second suspending agent, and second binder is 97.5% : 0.4% : 1.1% : 1.0%.

[0078] Please see Figure 3 and Figure 4 This application also provides a method for preparing a negative electrode 10, used to prepare the negative electrode 10 provided in this application embodiment. Figure 3 As shown, the preparation method of the negative electrode 10 includes the following steps:

[0079] S10 provides a current collector 11;

[0080] S20, a material with a first rate of increase is selected as the first negative electrode active material, and a material with a second rate of increase is selected as the second negative electrode active material, wherein the first rate of increase is less than the second rate of increase;

[0081] S30, a first negative electrode coating material is made of a first negative electrode active material, and a second negative electrode coating material is made of a second negative electrode active material;

[0082] S40, the first negative electrode coating material is coated on the surface of the current collector 11 to form the first negative electrode coating 12;

[0083] S50, the second negative electrode coating material is coated on the side of the first negative electrode coating 12 that is away from the current collector 11, forming the second negative electrode coating 13.

[0084] The following describes the preparation method of the negative electrode 10 using the negative electrode 10 provided in Example 1 as an example.

[0085] S10 provides a current collector 11, such as Figure 4 As shown.

[0086] The next step, S20, involves selecting the first and second negative electrode active materials.

[0087] Specifically, step S20 includes:

[0088] S21, set the same multiplier and measure the capacity retention rate and cycle number of the materials sequentially. The material with a cycle number of not less than the set capacity retention rate and a cycle number of X is used as the first negative electrode active material; the material with a cycle number of not less than the set capacity retention rate and a cycle number of Y is used as the second negative electrode active material, where X is less than Y.

[0089] In this embodiment, the capacity retention rate and cycle number of the material are measured sequentially at a first multiplier, and the capacity retention rate is set to 80%. The material with a capacity retention rate of not less than 80% and a cycle number X between 300 and 400 at the first multiplier is selected as the first negative electrode active material, and the material with a capacity retention rate of not less than 80% and a cycle number between 500 and 600 at the first multiplier is selected as the second negative electrode active material.

[0090] The following section explains the specific material selection and magnification testing methods.

[0091] The materials selected and rate-tested were performed using Xinwei equipment, and the selection and testing temperatures were at room temperature. In this application, room temperature refers to 20℃~25℃. The materials to be tested included a variety of negative electrode active materials.

[0092] The specific methods for material selection and rate testing include:

[0093] S201, let the material to be tested stand for 10 minutes;

[0094] S202 is discharged to 3.0V with a constant current of 0.5C.

[0095] S203, let the material to be tested stand for 10 minutes;

[0096] S204 was charged to 4.5V under constant current and constant voltage at multiple different currents, and cut off at 0.02C.

[0097] Specifically, the various currents include: 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, 3.0C, 3.5C, 4.0C, 4.5C, 5.0C, 5.5C, 6.0C, 6.5C, 7.0C, 7.5C, and 8.0C.

[0098] That is, multiple differential rates are set with a tolerance of 0.5C, and constant current and constant voltage charging is performed sequentially at these rates from smallest to largest. Understandably, setting differential rates with a tolerance of 0.5C can improve selection efficiency and simplify the selection and measurement steps.

[0099] Optionally, multiple different currents are available, including: 1.0C, 2.0C, 3.0C, 4.0C, 5.0C, 6.0C, 7.0C, and 8.0C. If the tolerance for multiple current settings is greater than 1C, the difference in magnification between various materials will be too large, resulting in a limited selection of materials. If the tolerance for multiple current settings is less than 0.5C, the results of multiple measurements at different magnifications for the same material will be similar, but this leads to too many measurements and low material selection efficiency.

[0100] Since the multiple rate / current settings are based on an arithmetic sequence with a tolerance of 0.5C, the first rate O1 of the first negative electrode active material is selected as a multiple of 0.5. Specifically, the first rate O1 is set and applied to various materials, and the first and second negative electrode active materials are selected. The first rate O1 of the first negative electrode active material has been determined, while the second rate O2 of the second negative electrode active material needs to be determined through further measurement.

[0101] The second negative electrode active material was then measured at multiple rates / currents with a tolerance of 0.5C, which was greater than the first rate O1. The second rate O2 of the second negative electrode active material was determined. Since the multiple rates / currents were set as an arithmetic sequence with a tolerance of 0.5C, the second rate O2 was a multiple of 0.5 greater than O1.

[0102] S205, let the material to be tested stand for 10 minutes;

[0103] S206, Repeat steps S21 to S25 for a total of 3 cycles.

[0104] The above steps are repeated multiple times, recording the applied capacity factor (O1) and the capacity retention rate and cycle number of various test materials. In this embodiment, the first capacity factor (O1) is set to 3C. The first capacity factor (O1) is applied to various materials. The material with a capacity retention rate of not less than 80% and a cycle number (X) between 300 and 400 is selected as the first negative electrode active material; the material with a capacity retention rate of not less than 80% and a cycle number (Y) between 500 and 600 is selected as the second negative electrode active material, where Y > X and YX ≥ 100. In other words, the first negative electrode active material maintains a capacity retention rate of not less than 80% and a cycle number between 300 and 400, and the second negative electrode active material maintains a capacity retention rate of not less than 80% and a cycle number between 500 and 600.

[0105] During the material selection process, the first rate factor O1 of the first negative electrode active material has been determined to be 3C, while the second rate factor O2 of the second negative electrode active material still needs to be determined. Specifically, in this embodiment, the first rate factor O1 is 3C, and the second rate factor O2 is 10C. It is understood that the difference between Y and X is selected to be greater than or equal to 100, i.e., YX≥100, so that the greater the rate factor difference between the second and first negative electrode active materials, the greater the difference in lithium ion concentration between the second and first negative electrode active materials, further accelerating the migration of lithium ions from the second negative electrode coating 13 to the first negative electrode coating 12.

[0106] Furthermore, a first negative electrode active material comprising first graphite particles with a particle size of 11.3 μm to 11.7 μm is selected. And / or, a second negative electrode active material comprising second graphite particles with a particle size of 6.5 μm to 7.5 μm is selected. And / or, a first negative electrode active material with an orientation degree between 10.4 and 11.4 is selected. And / or, a second negative electrode active material with an orientation degree between 8.4 and 8.7 is selected.

[0107] In this embodiment, the particle size of the first graphite particles is 11.3 micrometers (μm) to 11.7 micrometers, such as 11.3 μm, 11.4 μm, 11.5 μm, 11.6 μm, or 11.7 μm. The particle size of the second graphite particles is 6.5 μm to 7.5 μm, such as 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm, 7.1 μm, 7.2 μm, 7.3 μm, 7.4 μm, or 7.5 μm. It is understood that the smaller the particle size, the better the rate performance of the material. Optionally, the orientation degree of the first negative electrode active material is 10.4, 10.5, 10.6, 10.8, 11.0, 11.2, or 11.4. Optionally, the orientation degree of the second negative electrode active material is 8.4, 8.5, 8.6, or 8.7. The first negative electrode active material has an orientation degree of 10.4 to 11.4, and the second negative electrode active material has an orientation degree of 8.4 to 8.7, so that the crystal structures of the first negative electrode active material and the second negative electrode active material are more conducive to lithium ion insertion and extraction during charging and discharging.

[0108] Then, step S30 is performed, in which a first negative electrode active material is used to make a first negative electrode coating material, and a second negative electrode active material is used to make a second negative electrode coating material.

[0109] Specifically, the first negative electrode active material, the first conductive agent, and the first suspending agent are dry-mixed, and then the first binder and the first solvent are added respectively, and mixed and stirred evenly to prepare the first negative electrode coating material slurry.

[0110] The first negative electrode active material, the first conductive agent, the first suspending agent, and the first binder are mixed in a first solvent at a mass ratio of (95.8–97.6):(0.2–0.6):(1.0–2.0):(1.5–2.5) to form a first negative electrode coating material slurry. The viscosity of the first negative electrode coating material slurry is 3000 mPa·s to 5000 mPa·s, and the solid content is 40%–55%.

[0111] The first negative electrode active material includes first graphite particles, which comprise primary graphite particles and a first coating layer covering the primary particles. The first coating layer is a solid-phase carbon coating layer.

[0112] Specifically, the second negative electrode active material, the second conductive agent, and the second suspending agent are dry-mixed, and then the second binder and the second solvent are added respectively, and mixed and stirred evenly to prepare the second negative electrode coating material slurry.

[0113] The second negative electrode active material, the second conductive agent, the second suspending agent, and the second binder are prepared in a second solvent at a mass ratio of (95.8–97.6):(0.2–0.6):(1.0–2.0):(1.5–2.5) to form a second negative electrode coating material slurry. The viscosity of the second negative electrode coating material slurry is 2000 mPa·s to 4000 mPa·s, and the solid content is 40%–45%.

[0114] The second negative electrode active material, the second conductive agent, the second suspending agent, and the second binder are formulated into a second negative electrode coating material in a second solvent at a mass ratio of (95.8–97.6):(0.2–0.6):(1.0–2.0):(1.5–2.5).

[0115] The second negative electrode active material includes second graphite particles, which comprise secondary graphite particles and a second coating layer covering the secondary particles. The second coating layer is a liquid resin coating layer.

[0116] Both the first and second conductive agents are conductive carbon black. Optionally, the first binder may be Zeon's BTR-102 or BASF's Liofol LA 9522, etc. Optionally, the second binder may include one of carboxylated styrene-butadiene rubber, modified styrene-butadiene rubber, or waterborne styrene-butadiene rubber.

[0117] Optionally, both the first and second suspending agents are carboxymethyl cellulose lithium (CMC-Li). Optionally, both the first and second solvents are water (H2O).

[0118] Subsequently, steps S40 and S50 are performed: a first negative electrode coating material is coated onto the surface of the current collector 11 to form a first negative electrode coating 12; a second negative electrode coating material is coated onto the side of the first negative electrode coating 12 facing away from the current collector 11 to form a second negative electrode coating 13, as shown below. Figure 4 As shown.

[0119] The mass ratio of the first negative electrode coating material to the second negative electrode coating material is calculated as (60%–80%):(20%–40%). Using a double-layer coating machine, the first negative electrode coating material is coated on the surface of the current collector 11, and the second negative electrode coating material is coated on the side of the first negative electrode coating 12 facing away from the current collector 11. After drying, the first negative electrode coating material forms the first negative electrode coating 12, and the second negative electrode coating material forms the second negative electrode coating 13, resulting in a negative electrode sheet 10 with a diameter of 200 μm to 300 μm. The mass percentage of the first negative electrode coating 12 to the sum of the masses of the first negative electrode coating 12 and the second negative electrode coating 13 is w1%, and the mass percentage of the second negative electrode coating 13 to the sum of the masses of the first negative electrode coating 12 and the second negative electrode coating 13 is w2%, where w1%:w2% = (60%–80%):(20%–40%).

[0120] Please see Figure 5 This application also provides a battery 100, including a negative electrode 10 provided in this application or a negative electrode 10 prepared using the preparation method provided in this application, and further including a positive electrode and a separator. The negative electrode 10, the separator, and the positive electrode are stacked, with the separator disposed between the positive electrode and the negative electrode 10, forming a core package. Optionally, there are multiple positive electrode, negative electrode 10, and separators, and multiple positive electrode, multiple separators, and multiple negative electrode 10 are sequentially stacked to form a stacked core package. Alternatively, multiple positive electrode, multiple separators, and multiple negative electrode 10 are wound to form a wound core package. Optionally, the core package is square or cylindrical. The battery 100 also includes a housing 20 and tabs 30. The core package is disposed within the housing 20. The tabs 30 include a positive tab and a negative tab. The positive tab is connected to the positive electrode and is also connected to a positive terminal on the housing 20. The negative electrode tab is connected to the negative electrode plate 10, and the negative electrode tab is connected to the negative electrode post on the housing 20.

[0121] Example 1

[0122] The negative electrode sheet 10 in this embodiment includes a current collector 11, a first negative electrode coating 12 disposed on the surface of the current collector 11, and a second negative electrode coating 13 disposed on the side of the first negative electrode coating 12 facing away from the current collector 11.

[0123] The first negative electrode coating 12 includes a first negative electrode active material, a first conductive agent, a first suspending agent, a first binder, and a first solvent. The first negative electrode active material includes primary particulate graphite coated with a solid-phase carbon coating layer; the particle size of the first graphite particles is 11.3 μm to 11.7 μm; the orientation degree of the first negative electrode active material is 10.4 to 11.4; the first conductive agent is conductive carbon black SP; the first suspending agent is CMC-Li; the first binder is BTR-102 from Zeon Corporation of Japan; and the first solvent is water. The mass ratio of the first negative electrode active material, the first conductive agent, the first suspending agent, and the first binder is 97.00% : 0.4% : 1.1% : 1.5%. The first rate factor O1 of the first negative electrode active material is 3C.

[0124] The second negative electrode coating 13 comprises a second negative electrode active material, a second conductive agent, a second suspending agent, a second binder, and a second solvent. The second negative electrode active material comprises secondary particulate graphite coated with a liquid resin coating layer; the particle size of the second graphite particles is 6.5 μm to 7.5 μm; the orientation degree of the second negative electrode active material is 8.4 to 8.7; the second conductive agent is conductive carbon black SP; the second suspending agent is CMC-Li; the second binder is carboxylated styrene-butadiene rubber; and the second solvent is water. The mass ratio of the second negative electrode active material, the second conductive agent, the second suspending agent, and the second binder is 97.50% : 0.4% : 1.1% : 1.0%. The second rate O2 of the second negative electrode active material is 10C.

[0125] The percentage w1% of the mass of the first negative electrode coating 12 to the sum of the masses of the first negative electrode coating 12 and the second negative electrode coating 13 is 70%, and the percentage w2% of the mass of the second negative electrode coating 13 to the sum of the masses of the first negative electrode coating 12 and the second negative electrode coating 13 is 30%, w1%∶w2%=70%∶30%.

[0126] This application tests and records the capacity retention rate and cycle number of the negative electrode 10 of Example 1, the negative electrode of Comparative Example 1, and the negative electrode of Comparative Example 2.

[0127] The negative electrode under test was tested using Xinwei equipment; the test conditions were room temperature (20℃~25℃). The specific test method was as follows:

[0128] P1, let the negative electrode to be tested rest for 10 minutes;

[0129] P2 is discharged to 3.0V with a constant current of 1C;

[0130] P3, let the negative electrode to be tested rest for 10 minutes;

[0131] P4 is charged sequentially with constant current and constant voltage at 4.0C, 3.0C, and 2.0C; charged at 4.0C to 4.20V, then stopped at 3.0C; charged at 3.0C with constant current and constant voltage to 4.33V, then stopped at 2.0C; charged at 2.0C with constant current and constant voltage to 4.50V, then stopped at 0.02C.

[0132] P5, let the negative electrode sheet to be tested rest for 10 minutes;

[0133] P6, repeat steps P2 to P5, repeating 1000 times.

[0134] Please refer to Table 1. The first row shows the battery charge-discharge cycle number, and the first column shows the tested samples. The negative electrode of Comparative Example 1 includes a current collector and a single-layer coating 1 disposed on the surface of the current collector. Coating 1 is prepared using the same material as the first negative electrode coating 12 of Example 1, and the negative electrode active material in coating 1 has a rate of 3C. The negative electrode of Comparative Example 2 includes a current collector and a single-layer coating 2 disposed on the surface of the current collector. Coating 2 is prepared using the same material as the second negative electrode coating 13 of Example 1, and the negative electrode active material in coating 2 has a rate of 10C.

[0135] Table 1

[0136] 100 weeks 200 weeks 300 weeks 400 weeks 500 weeks 600 weeks 700 weeks 800 weeks Comparative Example 1 99.00％ 96.4％ 85.60％ Comparative Example 2 99.56％ 96.76％ 95.34％ 90.61％ 80.35％ Example 1 99.24％ 98.47％ 97.60％ 95.6％ 93.00％ 92.1％ 90.99％ 87.62％

[0137] As shown in Table 1, the negative electrode with only a single-layer coating 1 maintains a capacity retention rate of over 80% for a maximum of 300-400 cycles; the negative electrode with only a single-layer coating 2 maintains a capacity retention rate of over 80% for a maximum of 500-600 cycles; while the negative electrode 10 of Example 1 maintains a capacity retention rate of over 80% for over 700 cycles, with a maximum cycle count even exceeding 800 cycles, demonstrating extremely superior rate performance. The negative electrode 10 of Example 1 exhibits rapid conduction and responsiveness, along with high capacity and stability, resulting in excellent fast-charging performance of the battery.

[0138] Example 2

[0139] The negative electrode sheet 10 in this embodiment includes a current collector 11, a first negative electrode coating 12 disposed on the surface of the current collector 11, and a second negative electrode coating 13 disposed on the side of the first negative electrode coating 12 facing away from the current collector 11.

[0140] The first negative electrode coating 12 includes a first negative electrode active material, a first conductive agent, a first suspending agent, a first binder, and a first solvent. The first negative electrode active material includes primary particulate graphite coated with a solid-phase carbon coating layer; the particle size of the first graphite particles is 11.3 μm to 11.7 μm; the orientation degree of the first negative electrode active material is 10.4 to 11.4; the first conductive agent is conductive carbon black SP; the first suspending agent is CMC-Li; the first binder is BASF's Liofol LA 9522; and the first solvent is water. The mass ratio of the first negative electrode active material, the first conductive agent, the first suspending agent, and the first binder is 97.00% : 0.2% : 1.3% : 1.5%. The first rate factor (O1) of the first negative electrode active material is 5C.

[0141] The second negative electrode coating 13 includes a second negative electrode active material, a second conductive agent, a second suspending agent, a second binder, and a second solvent. The second negative electrode active material includes secondary particulate graphite coated with a liquid resin coating layer; the particle size of the second graphite particles is 6.5 μm to 7.5 μm; the orientation degree of the second negative electrode active material is 8.4 to 8.7; the second conductive agent is conductive carbon black SP; the second suspending agent is CMC-Li; the second binder is water-based styrene-butadiene rubber; and the second solvent is water. The mass ratio of the second negative electrode active material, the second conductive agent, the second suspending agent, and the second binder is 97.50% : 0.2% : 1.3% : 1.0%. The second rate O2 of the second negative electrode active material is 8C.

[0142] The percentage w1% of the mass of the first negative electrode coating 12 to the sum of the masses of the first negative electrode coating 12 and the second negative electrode coating 13 is 60%, and the percentage w2% of the mass of the second negative electrode coating 13 to the sum of the masses of the first negative electrode coating 12 and the second negative electrode coating 13 is 40%, w1%∶w2%=60%∶40%.

[0143] This application tests and records the capacity retention rate and cycle number of the negative electrode 10 of Example 2, the negative electrode of Comparative Example 3, and the negative electrode of Comparative Example 4.

[0144] The negative electrode under test was tested using Xinwei equipment; the test conditions were room temperature (20℃~25℃). The specific test method was as follows:

[0145] P1, let the negative electrode to be tested rest for 10 minutes;

[0146] P2 is discharged to 3.0V with a constant current of 1C;

[0147] P3, let the negative electrode to be tested rest for 10 minutes;

[0148] P4 is charged sequentially with constant current and constant voltage at 4.0C, 3.0C, and 2.0C; charged at 4.0C to 4.20V, then stopped at 3.0C; charged at 3.0C with constant current and constant voltage to 4.33V, then stopped at 2.0C; charged at 2.0C with constant current and constant voltage to 4.50V, then stopped at 0.02C.

[0149] P5, let the negative electrode sheet to be tested rest for 10 minutes;

[0150] P6, repeat steps P2 to P5, repeating 1000 times.

[0151] Please refer to Table 2. The first row shows the number of charge-discharge cycles of the battery, and the first column shows the tested samples. The negative electrode of Comparative Example 3 includes a current collector and a single-layer coating 3 disposed on the surface of the current collector. Coating 3 is prepared using the same material as the first negative electrode coating 12 of Example 2, and the negative electrode active material in coating 3 has a rate of 5C. The negative electrode of Comparative Example 4 includes a current collector and a single-layer coating 4 disposed on the surface of the current collector. Coating 4 is prepared using the same material as the second negative electrode coating 13 of Example 2, and the negative electrode active material in coating 4 has a rate of 8C.

[0152] Table 2

[0153] 100 weeks 200 weeks 300 weeks 400 weeks 500 weeks 600 weeks 700 weeks 800 weeks Comparative Example 3 99.00％ 96.1％ 85.08％ Comparative Example 4 99.23％ 97.1％ 96.61％ 91.31％ 85.33％ Example 2 99.54％ 98.62％ 97.32％ 95.23％ 93.70％ 92.8％ 92.01％ 85.41％

[0154] As shown in Table 1, the negative electrode with only a single-layer coating 3 maintains a capacity retention rate of over 80% for a maximum of 300-400 cycles; the negative electrode with only a single-layer coating 4 maintains a capacity retention rate of over 80% for a maximum of 500-600 cycles; while the negative electrode 10 of Example 2 maintains a capacity retention rate of over 80% for over 700 cycles, with a maximum cycle count even exceeding 800 cycles, demonstrating extremely superior rate performance. The negative electrode 10 of Example 2 exhibits rapid conduction and responsiveness, along with high capacity and stability, resulting in excellent fast-charging performance of the battery.

[0155] The above is a description of the negative electrode 10 and its preparation method, and the battery 100 provided in the embodiments of this application.

[0156] The negative electrode sheet provided in this application includes a current collector, a first negative electrode coating disposed on the surface of the current collector, and a second negative electrode coating disposed on the side of the first negative electrode coating facing away from the current collector. The first negative electrode active material has a first rate capability, and the second negative electrode active material has a second rate capability, with the first rate capability being less than the second rate capability. The current collector surface of the negative electrode sheet in this application includes a double-layer coating. By setting the second negative electrode coating with a larger rate capability as the outer layer, a fast ion transport channel is provided, allowing lithium ions outside the negative electrode sheet to quickly reach the inner layer for storage, achieving rapid current reception and conduction, thereby improving the fast-charging performance of the battery. The first negative electrode coating with a smaller rate capability is set as the inner layer, allowing the inner layer to have a large and stable capacity to absorb lithium ions transported from the outer layer, thereby increasing the battery capacity. Furthermore, the first negative electrode coating is stable and can mitigate internal structural changes in the material of the second negative electrode coating, reducing the occurrence of side reactions, thereby ensuring the overall stability and safety of the battery. This application also provides a method for preparing a negative electrode sheet and a battery, which have the above-mentioned beneficial effects.

[0157] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode sheet, characterized in that, include: current collector; A first negative electrode coating is disposed on the surface of the current collector, and the first negative electrode coating includes a first negative electrode active material; The second negative electrode coating is disposed on the side of the first negative electrode coating that is away from the current collector, and the second negative electrode coating includes a second negative electrode active material; Wherein, the first negative electrode active material has a first rate, the second negative electrode active material has a second rate, and the first rate is less than the second rate; Specifically, at the same rate and with a capacity retention rate not lower than the set value, the number of cycles X of the first negative electrode active material is less than the number of cycles Y of the second negative electrode active material; the number of cycles of the first negative electrode active material with a capacity retention rate of not less than 80% at the first rate is between 300 and 400, the number of cycles of the second negative electrode active material with a capacity retention rate of not less than 80% at the first rate is between 500 and 600, and the number of cycles of the second negative electrode active material with a capacity retention rate of not less than 80% at the second rate is between 300 and 400.

2. The negative electrode sheet according to claim 1, characterized in that, YX≥100.

3. The negative electrode sheet according to claim 2, characterized in that, The first multiplier is 3C~5C, and the second multiplier is 6C~10C.

4. The negative electrode sheet according to claim 1, characterized in that, The mass percentage of the first negative electrode coating to the sum of the masses of the first negative electrode coating and the second negative electrode coating is w1%, and the mass percentage of the second negative electrode coating to the sum of the masses of the first negative electrode coating and the second negative electrode coating is w2%, wherein w1%∶w2%=(60%~80%)∶(20%~40%).

5. The negative electrode sheet according to claim 1, characterized in that, The first negative electrode active material comprises primary particulate graphite, and / or the second negative electrode active material comprises secondary particulate graphite.

6. The negative electrode sheet according to claim 1, characterized in that, The first negative electrode active material includes first graphite particles, the particle size of which is 11.3 μm to 11.7 μm; And / or, the second negative electrode active material includes second graphite particles, the second graphite particles having a particle size of 6.5 μm to 7.5 μm.

7. The negative electrode sheet according to claim 1, characterized in that, The orientation degree of the first negative electrode active material is 10.4~11.4; And / or, the orientation degree of the second negative electrode active material is 8.4~8.

7.

8. A method for preparing a negative electrode sheet, characterized in that, The method for preparing the negative electrode sheet according to any one of claims 1-7 comprises the following steps: S10 provides a current collector; S20, a material with a first rate of increase is selected as the first negative electrode active material, and a material with a second rate of increase is selected as the second negative electrode active material, wherein the first rate of increase is less than the second rate of increase; S30, a first negative electrode coating material is made of a first negative electrode active material, and a second negative electrode coating material is made of a second negative electrode active material; S40, the first negative electrode coating material is coated on the surface of the current collector to form a first negative electrode coating; S50, the second negative electrode coating material is coated on the side of the first negative electrode coating away from the current collector to form the second negative electrode coating.

9. A battery, characterized in that, The negative electrode sheet includes any one of the negative electrode sheets as described in claims 1 to 7, or the negative electrode sheet prepared by the preparation method as described in claim 8, and further includes a positive electrode sheet and a separator, wherein the negative electrode sheet, the separator and the positive electrode sheet are stacked, and the separator is disposed between the positive electrode sheet and the negative electrode sheet.

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