A negative electrode sheet, a method for manufacturing the same, and a lithium ion battery

Abstract

The application discloses a negative plate, a preparation method thereof and a lithium ion battery, and relates to the technical field of batteries. The negative plate comprises a current collector, a first active material coating layer coated on a first region of the current collector, and a second active material coating layer coated on a second region of the current collector; the particle size D50 of the first active material is alpha, and the particle size D50 of the second active material is beta; the width of the first active material coating layer is A1, and the width of the second active material coating layer on one side is A2; wherein alpha, beta, A1 and A2 satisfy the relationship: 4.3 <= (alpha / beta) 2 <= 61.3. The application can fully exert the rate performance of the negative plate by setting two different types of active material coating layers, and the two types of active material coating layers can guarantee that the battery has good low-temperature fast-charging performance while not causing lithium precipitation.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a negative electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, with their high energy density, long cycle life, and environmental friendliness, have been widely used in consumer electronics, electric vehicles, and other fields. As lithium-ion battery technology continues to develop and market demand grows, consumers are placing increasingly higher demands on fast charging and low-temperature fast charging. Fast charging and low-temperature fast charging technologies can significantly shorten battery charging time and improve user experience, which is particularly important for applications such as electric vehicles. However, existing lithium-ion batteries still face many challenges in achieving fast charging and low-temperature fast charging.

[0003] Currently, the main methods to improve the fast-charging performance of lithium-ion batteries include using higher-performance anode materials and reducing the areal density of the electrodes. Employing high-performance anode materials such as silicon-carbon composites and lithium titanate can improve the specific capacity and rate performance of the anode, thereby improving the battery's fast-charging capability. Reducing the areal density of the electrodes, i.e., decreasing the coating thickness or amount of the electrode active material, can shorten the diffusion path of lithium ions within the electrode, reduce charge transport resistance, and improve fast-charging performance.

[0004] However, both of the above-mentioned improvement methods also have certain limitations. High-performance anode materials are generally expensive, which may increase the production cost of the battery. While reducing the electrode areal density can improve fast charging performance, it sacrifices the battery's energy density, reducing the battery's capacity per unit volume or per unit mass. Therefore, achieving fast charging while balancing cost and energy density remains a significant challenge.

[0005] Furthermore, even with the aforementioned improvement methods, lithium-ion batteries may still experience edge lithium plating under high-rate charging conditions. Lithium plating refers to the uneven deposition of metallic lithium on the electrode surface during charging and discharging, forming lithium dendrites or dead lithium, leading to battery performance degradation and safety hazards. Edge lithium plating refers to the phenomenon being more severe at the edges of the battery electrodes. There are two main reasons for edge lithium plating: first, the current density distribution at the electrode edges is uneven, with higher current densities at the edges, causing preferential lithium ion deposition; second, the edge areas are in contact with the external environment, resulting in faster heat dissipation and lower temperatures, which exacerbate lithium plating. Edge lithium plating leads to reduced utilization of electrode materials, decreased battery capacity and cycle life, and may cause safety issues.

[0006] Therefore, how to suppress lithium deposition at the electrode edges while ensuring the fast charging and low-temperature fast charging performance of lithium-ion batteries is a major problem that the industry urgently needs to solve. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a negative electrode sheet that can ensure the fast charging and low-temperature fast charging performance of lithium-ion batteries while suppressing edge lithium deposition.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A negative electrode sheet, comprising:

[0010] current collector;

[0011] A first active material coating is applied to the first region of the current collector;

[0012] A second active material coating is applied to the second region of the current collector;

[0013] The particle size D50 of the first active material is α, and the particle size D50 of the second active material is β;

[0014] The width of the first active material coating is A1, and the width of one side of the second active material coating is A2;

[0015] Among them, α, β, A1, and A2 satisfy the following relationship: 4.3 ≤ (α / β) 2 *A1 / A2≤61.3.

[0016] Preferably, the particle size α of the first active material is 8-12 μm, the particle size β of the second active material is 6.5-10.5 μm, the width A1 of the first active material coating is 6-9 cm, and the width A2 of one side of the second active material coating is 0.5-2 cm.

[0017] Preferably, the particle size α of the first active material and the particle size β of the second active material satisfy the relationship: α ≥ β.

[0018] Preferably, the areal density of the first active material coating is B1, and the areal density of the second active material coating is B2; B1 and B2 satisfy the relationship: 0.98 ≤ B2 / B1 ≤ 1.01; wherein B1 is 6-15 mg / cm³. 2 The B2 concentration is 5-15.5 mg / cm³. 2 .

[0019] Preferably, the specific capacity of the negative electrode active material of the first active material coating is C1, and the specific capacity of the negative electrode active material of the second active material coating is C2, and C1 and C2 satisfy the relationship: 1≤C2 / C1≤1.03.

[0020] Preferably, the compaction density of the first active material coating is D1, and the compaction density of the second active material coating is D2, and D1 and D2 satisfy the relationship: 0.98≤D2 / D1≤1.02.

[0021] Preferably, the negative electrode active material of the first active material coating is one or more substances selected from ordinary graphite, fast-charging graphite, hard carbon, soft carbon, silicon carbide, silicon suboxide, tin oxide, and phosphorus negative electrode material.

[0022] Preferably, the negative electrode active material of the second active material coating is one or more substances selected from fast-charging graphite, hard carbon, soft carbon, silicon carbide, and silicon suboxide.

[0023] Furthermore, the present invention also provides a method for preparing the negative electrode sheet, comprising the following steps:

[0024] Step S1: Mix water and thickener to prepare adhesive solution. Mix the first negative electrode active material and conductive agent and add them to the adhesive solution for mixing. After mixing, add water for dispersion and then add binder for dispersion to obtain the first active material coating slurry.

[0025] Step S2: Mix water and thickener to prepare adhesive solution, mix the second negative electrode active material and conductive agent and add to adhesive solution for mixing, add water for dispersion after mixing, and then add binder for dispersion to obtain second active material coating slurry;

[0026] Step S3: After setting the values ​​of A1 and A2, the zebra stripe coating method is used to simultaneously coat the first active material coating slurry and the second active material coating slurry onto the current collector. After coating, the material is cut to obtain the negative electrode sheet.

[0027] In addition, the present invention provides a lithium-ion battery, including a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the negative electrode is the aforementioned negative electrode.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) The negative electrode sheet provided by the present invention has a first active material coating in the first region of the current collector and a second active material coating in the second region of the current collector. The two different types of active material coatings can make the rate performance of the negative electrode fully utilized. The middle part has a low current density and a small charging rate, and is not prone to lithium plating, so a low fast charging type negative electrode material can be used. The edge has a high current density, so a high fast charging type negative electrode is required. The combination of the two negative electrode materials can ensure that the battery has good low temperature fast charging performance without lithium plating.

[0030] (2) In this invention, by setting the particle size D50 of the first active material and the particle size D50 of the second active material, the width of the coating of the first active material and the width of one side of the coating of the second active material satisfy the following relationship: 3≤(α / β) 2 *A1 / A2≤61.3. The particle size of the material is related to the rate performance of the battery. Therefore, the particle size must be matched with the coating width to ensure that the battery can achieve fast charging performance without lithium plating. Since lithium plating at the battery edge is at least 1 / 10 of the width of the negative electrode during low-temperature charging, it is necessary to use as many low-fast-charging type negative electrodes as possible to reduce costs while ensuring no lithium plating. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the negative electrode sheet according to an embodiment of the present invention.

[0032] Wherein, 1-first region; 2-second region. Detailed Implementation

[0033] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below with reference to specific embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0034] 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 invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0035] According to a first aspect of this application, this application aims to provide a negative electrode sheet, the negative electrode sheet comprising:

[0036] current collector;

[0037] A first active material coating is applied to the first region 1 of the current collector;

[0038] A second active material coating is applied to the second region 2 of the current collector;

[0039] The particle size D50 of the first active material is α, and the particle size D50 of the second active material is β.

[0040] The width of the first active material coating is A1, and the width of one side of the second active material coating is A2;

[0041] Among them, α, β, A1, and A2 satisfy the following relationship: 4.3 ≤ (α / β) 2*A1 / A2≤61.3. The particle size D50 of the active material is related to the kinetic properties of the material. The larger the particle size, the worse the kinetics, that is, the worse the rate performance. However, the particle size cannot be too small. If it is too small, that is, the difference between the two is large, it will cause the first coating layer to be over-pressurized due to excessive compaction, which will lead to lithium plating during charging.

[0042] During low-temperature charging, lithium plating at the battery edge is at least 1 / 10 of the width of the negative electrode. Therefore, it is necessary to use as many low-fast-charging type negative electrodes as possible to reduce costs while ensuring that lithium plating does not occur.

[0043] In some embodiments, the particle size α of the first active material is 8-12 μm, for example, it can be 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm.

[0044] In some embodiments, the particle size β of the second active material is 6.5-10.5 μm, for example, it can be 6.5 μm, 7.5 μm, 8.5 μm, 9.5 μm, or 10.5 μm.

[0045] In some embodiments, the width A1 of the first active material coating is 6-9 cm, for example, it can be 6 cm, 7 cm, 8 cm, or 9 cm.

[0046] In some embodiments, the width A2 of one side of the second active material coating is 0.5-2cm, for example, it can be 0.5cm, 1cm, 1.5cm, or 2cm.

[0047] In some embodiments, the particle size α of the first active material and the particle size β of the second active material satisfy the relationship: α ≥ β.

[0048] In some embodiments, the areal density of the first active material coating is B1, and the areal density of the second active material coating is B2; B1 and B2 satisfy the relationship: 0.98 ≤ B2 / B1 ≤ 1.01, for example, it can be 0.98, 0.99, 1, or 1.01; B1 is 6-15 mg / cm³. 2 For example, it could be 6 mg / cm³ 2 7mg / cm 2 8mg / cm 2 9mg / cm 2 10mg / cm 2 11mg / cm 2 12mg / cm 2 13mg / cm 2 14mg / cm 2 15mg / cm 2 B2 is 5-15.5 mg / cm³ 2 For example, it could be 5mg / cm 26mg / cm 2 7mg / cm 2 8mg / cm 2 9mg / cm 2 10mg / cm 2 11mg / cm 2 12mg / cm 2 13mg / cm 2 14mg / cm 2 15.5 mg / cm 2 To prevent lithium plating at the edges, the areal density of the second active material coating needs to be slightly higher than that of the first active material coating, but not too high, otherwise it will affect the processing. If the areal density of the coating is too low, there is a risk of foil leakage, which may cause lithium plating at the negative electrode. If the coating is too thick, there will be insufficient kinetics, which may also cause lithium plating.

[0049] In some embodiments, the specific capacity of the negative electrode active material of the first active material coating is C1, and the specific capacity of the negative electrode active material of the second active material coating is C2. C1 and C2 satisfy the relationship: 1≤C2 / C1≤1.03, for example, it can be 1, 1.01, 1.02, or 1.03. Due to kinetic reasons, lithium deposition is prone to occur at the electrode edges, and thinning is also a problem. Therefore, the specific capacity of the negative electrode active material of the second active material coating needs to be at least the same as or slightly higher than that of the negative electrode active material of the first active material coating. However, the specific capacity of the negative electrode active material of the second active material coating cannot be too high, otherwise it will waste material, or due to design problems, the thickness of the two negative electrodes will be inconsistent, increasing the difficulty of subsequent electrode rolling.

[0050] In some embodiments, the compaction density of the first active material coating is D1, and the compaction density of the second active material coating is D2. D1 and D2 satisfy the relationship: 0.98 ≤ D2 / D1 ≤ 1.02, for example, 0.98, 0.99, 1.00, 1.01, or 1.02. The compaction densities of the first and second active material coatings should be as similar as possible to ensure that the rolling thickness of the two materials is the same during rolling, thus reducing the difficulty of rolling.

[0051] In some embodiments, the width A1 of the first active material coating is 6-9cm, for example, it can be 6cm, 7cm, 8cm, or 9cm; the width A2 of one side of the second active material coating is 0.5-2cm, for example, it can be 0.5cm, 1cm, 1.5cm, or 2cm.

[0052] In some embodiments, the negative electrode active material of the first active material coating is one or more substances selected from ordinary graphite, fast-charging graphite, hard carbon, soft carbon, silicon carbide, silicon suboxide, tin oxide, and phosphorus negative electrode material.

[0053] In some embodiments, the negative electrode active material of the second active material coating is one or more substances selected from fast-charging graphite, hard carbon, soft carbon, silicon carbide, and silicon suboxide.

[0054] According to a second aspect of this application, this application provides a method for preparing a negative electrode sheet, comprising the following steps: Step S1, mixing water and a thickener to prepare a slurry, mixing a first negative electrode active material and a conductive agent and adding them to the slurry for mixing, adding water for dispersion after mixing, and then adding a binder for dispersion to obtain a coating slurry of the first active material;

[0055] Step S2: Mix water and thickener to prepare adhesive solution, mix the second negative electrode active material and conductive agent and add to adhesive solution for mixing, add water for dispersion after mixing, and then add binder for dispersion to obtain second active material coating slurry;

[0056] Step S3: After setting the values ​​of A1 and A2, the zebra stripe coating method is used to simultaneously coat the first active material coating slurry and the second active material coating slurry onto the current collector. After coating, the material is cut to obtain the negative electrode sheet.

[0057] According to a third aspect of this application, this application provides a lithium-ion battery, including a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the negative electrode is the aforementioned negative electrode.

[0058] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material, which may be, but is not limited to, a chemical formula such as Li. a Ni x Co y M z O 2-b N b (where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5The positive electrode active material can be one or more combinations thereof, including O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The positive electrode active material can also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the positive electrode active material. The materials used for modification can be one or more combinations thereof, including but not limited to Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W. The positive electrode current collector is typically a structure or component that collects current. The positive electrode current collector can be any material suitable for use as a positive electrode current collector in lithium-ion batteries. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil.

[0059] The separator can be any material suitable for lithium-ion battery separators in the art, for example, it can be one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0060] The lithium-ion battery also includes an electrolyte, which comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; or it can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include, but are not limited to, at least one of film-forming additives, conductive additives, flame-retardant additives, overcharge-resistant additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0061] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below with reference to specific embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0062] Example 1

[0063] Preparation of positive electrode sheet

[0064] The active material LiCoO2, conductive agent superconducting carbon, conductive carbon nanotubes, and binder polyvinylidene fluoride (PVDF) were fully dispersed and uniformly coated onto an aluminum current collector in an N-methylpyrrolidone solvent system at a weight ratio of 97.6:0.6:0.5:1.3, and then cold-pressed into strips to obtain the positive electrode sheet.

[0065] Negative electrode preparation

[0066] Step S1: Mix water and thickener to prepare a glue solution. Mix the first negative electrode active material and conductive agent and add them to the glue solution for mixing. After mixing, add water for dispersion, and then add binder for dispersion to obtain the first active material coating slurry. The first negative electrode active material is graphite, the conductive agent is SP, the binder is SBR, and the thickener is CMC. The weight ratio is graphite:SBR:CMC:SP = 96:2:1:1.

[0067] Step S2: Mix water and thickener to prepare a glue solution. Mix the second negative electrode active material and conductive agent and add them to the glue solution for mixing. After mixing, add water for dispersion, and then add binder for dispersion to obtain the second active material coating slurry. The second negative electrode active material is fast-charging graphite, the conductive agent is SP, the binder is SBR, and the thickener is CMC. The weight ratio is graphite:SBR:CMC:SP = 96:2:1:1.

[0068] Step S3: After setting the values ​​of A1 and A2, the zebra stripe coating method is used to simultaneously coat the first active material coating slurry and the second active material coating slurry onto the current collector. After coating, the material is cut to obtain the negative electrode sheet.

[0069] The first negative electrode active material has a particle size α of 10 μm, and the second negative electrode active material has a particle size β of 8.5 μm. In the resulting negative electrode sheet, A1 is 8 cm, A2 is 1 cm, and B1 is 12.5 mg / cm³. 2 B2 was 12.6 mg / cm³. 2 C1 is 350 mAh / g, C2 is 353.5 mAh / g; D1 is 1.5 mg / cm³. 3 D2 is 1.5 mg / cm³ 3 .

[0070] Separating membrane

[0071] A ceramic mixture is coated onto the PE surface to serve as a release membrane.

[0072] Electrolyte preparation

[0073] Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a volume ratio of 1:1:4:4. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0074] Battery manufacturing

[0075] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound or stacked to produce a bare cell. Before winding or stacking, the cells are exposed to light three times to remove water, and then packaged and injected with electrolyte to produce a finished lithium-ion battery.

[0076] Examples 2-13 and Comparative Examples 2-6 are prepared in the same steps as Example 1, except that the parameters in the negative electrode are different. The parameters of each example and comparative example are shown in Table 1-2 below.

[0077] Table 1

[0078]

[0079]

[0080] Table 2

[0081]

[0082]

[0083] Performance testing: After placing the batteries at 0℃ and 25℃ for 2 hours, they were charged and discharged. The charging rate was 0.5-5C, with 0.5C intervals for testing, i.e., charging at 0.5C, 1C, 1.5C, 2C, 2.5C, 3C, 3.5C, 4C, 4.5C, and 5C, and discharging at 1C. After 10 weeks of testing, each battery group was disassembled to observe and record the lithium plating on the negative electrode.

[0084] The test results are shown in Table 3 below.

[0085] Table 3

[0086]

[0087]

[0088] As can be seen from the comparison of the results in Table 1 above, compared with the negative electrode sheets in Comparative Examples 1-8, the negative electrode sheet provided by the present invention can ensure the low-temperature fast charging performance of lithium-ion batteries while preventing lithium deposition at the edges.

[0089] Comparing the data from Example 1 and Comparative Examples 1 and 2, it can be seen that in Comparative Example 1, although parameters such as A1 and A2, α and β all meet the requirements, theoretically the low-temperature rate performance should be improved. However, due to the small difference in particle size of α and β, that is, the difference in specific surface area between regions A1 and A2 is too small, the lithium-ion intercalation sites in the two regions are not much different, and the lithium intercalation capacity is comparable. Therefore, the charge and discharge performance is also basically comparable. No lithium plating was observed at 1.5C at room temperature, but the rate performance improvement of region A2 at low temperature did not reach the expected effect, and edge lithium plating appeared at 1C. In Comparative Example 2, due to the larger width of region A1, more lithium ions are extracted during charging. Region A2, being smaller, does not provide enough space to receive more lithium ions extracted from the cathode corresponding to region A1. Furthermore, the difference in particle size between α and β is more than 2 times, meaning that the specific surface area difference between regions A1 and A2 is too large, resulting in a significant difference in the lithium ion insertion sites between the two regions. Consequently, the lithium insertion capacity of region A1 decreases considerably at the same rate. The combination of these two factors leads to the failure of the overall anode performance improvement to achieve the expected effect, resulting in lithium plating at 1.5C at room temperature and edge lithium plating at 1C at low temperature.

[0090] In Comparative Example 5, although (α / β) 2 *A1 / A2 are within the preset range, but due to the low specific capacity of the A2 region, under the same positive electrode conditions, the capacity of the A2 region of the negative electrode is insufficient, and the lithium ions extracted from the positive electrode cannot be fully inserted into the negative electrode, resulting in lithium deposition.

[0091] In Comparative Example 6, the two compaction differences are significant. Excessive compaction of A1 leads to over-compression at the edge of A1, reducing kinetics. At the same rate, lithium ion insertion in the A1 region becomes more difficult, resulting in lithium plating.

[0092] In Comparative Example 7, α < β, meaning that the material particle size in region A2 is larger than that in region A1, and the specific surface area is smaller. As a result, there are fewer sites available for lithium ion insertion compared to region A1. Consequently, under the same charging rate conditions, region A2 is more likely to accumulate lithium ions, leading to lithium plating.

[0093] In Comparative Example 8, the two compaction differences are significant. Excessive compaction of A2 leads to over-compression at the edge of A2, resulting in reduced kinetics. At the same temperature, lithium plating occurs because lithium ion insertion into A2 becomes more difficult. Conversely, excessive compaction of A2 leads to over-compression at the edge of A2 and lithium plating.

[0094] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A negative electrode sheet, characterized in that, include: current collector; A first active material coating is applied to a first region of the current collector, the first region being located in the middle part of the current collector; A second active material coating is applied to a second region of the current collector, the second region being located at both edges of the current collector; The particle size D50 of the first active material is α, and the particle size D50 of the second active material is β; The width of the first active material coating is A1, and the width of one side of the second active material coating is A2; Among them, α, β, A1, and A2 satisfy the following relationship: 4.3 ≤ (α / β) 2 *A1 / A2≤61.3; The particle size α of the first active material is 8-12 μm, and the particle size β of the second active material is 6.5-10.5 μm; The negative electrode active material of the first active material coating is one or more substances selected from ordinary graphite, fast-charging graphite, hard carbon, soft carbon, silicon carbide, silicon suboxide, tin oxide, and phosphorus negative electrode material; The negative electrode active material of the second active material coating is one or more of the following: fast-charging graphite, hard carbon, soft carbon, silicon carbide, and silicon suboxide.

2. The negative electrode sheet according to claim 1, characterized in that, The width A1 of the first active material coating is 6-9 cm, and the width A2 of one side of the second active material coating is 0.5-2 cm.

3. The negative electrode sheet according to claim 1, characterized in that, The particle size α of the first active material and the particle size β of the second active material satisfy the relationship: α ≥ β.

4. The negative electrode sheet according to claim 1, characterized in that, The areal density of the first active material coating is B1, and the areal density of the second active material coating is B2; B1 and B2 satisfy the relationship: 0.98 ≤ B2 / B1 ≤ 1.01; wherein B1 is 6-15 mg / cm³. 2 The B2 concentration is 5-15.5 mg / cm³. 2 .

5. The negative electrode sheet according to claim 1, characterized in that, The specific capacity of the negative electrode active material of the first active material coating is C1, and the specific capacity of the negative electrode active material of the second active material coating is C2. C1 and C2 satisfy the relationship: 1≤C2 / C1≤1.

03.

6. The negative electrode sheet according to claim 1, characterized in that, The compaction density of the first active material coating is D1, and the compaction density of the second active material coating is D2. D1 and D2 satisfy the relationship: 0.98≤D2 / D1≤1.

02.

7. A method for preparing a negative electrode sheet according to any one of claims 1-6, characterized in that, Includes the following steps: Step S1: Mix water and thickener to prepare a slurry, mix the first negative electrode active material with a conductive agent and add it to the slurry, add water to the mixture for dispersion, and then add a binder for dispersion to obtain the first active material coating slurry. Step S2: Mix water and thickener to prepare a slurry, mix the second negative electrode active material with a conductive agent, add the slurry and mix, add water to the mixture for dispersion, and then add a binder for dispersion to obtain a second active material coating slurry. Step S3: After setting the values ​​of A1 and A2, the first active material coating slurry and the second active material coating slurry are simultaneously coated onto the current collector using the zebra stripe coating method. After coating, the material is cut to obtain the negative electrode sheet.

8. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-6.

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