A negative electrode sheet, a method for manufacturing the same, and an application thereof

Abstract

The application relates to a negative electrode sheet and a preparation method and application thereof, the negative electrode sheet comprising a current collector and a negative active layer arranged on at least one surface of the current collector along the thickness direction, the negative active layer comprising a first active layer, a second active layer and a third active layer, the first active layer being attached to the surface of the current collector, the second active layer being arranged on the surface of the first active layer away from the current collector, and the third active layer being arranged on the surface of the second active layer away from the first active layer; the first active layer comprising carbon-coated secondary particle graphite, the second active layer comprising heteroatom-doped hard carbon, and the third active layer comprising porous carbon nanofibers. The application simultaneously arranges the multilayer active layer comprising different active materials on the surface of the current collector, and controls the thickness of each active layer and optimizes the preparation process, so that the lithium ion battery comprising the above negative electrode sheet has high energy density, fast charging capacity and excellent cycle life.

Description

Technical Field

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

[0002] Lithium-ion batteries have become a core energy source for electric vehicles, consumer electronics, and energy storage systems due to their high energy density, long cycle life, and environmental friendliness. The negative electrode, as a key component of lithium-ion batteries, directly affects the battery's energy density, fast-charging capability, and cycle stability.

[0003] Traditional negative electrode sheets typically employ a single active layer structure, composed of active materials such as graphite and silicon-based materials, conductive agents, and binders. However, this homogeneous design cannot simultaneously achieve battery energy density, fast charging capability, and cycle stability, resulting in the following problems: (1) The contradiction between energy density and fast charging performance: High active material content can increase energy density, but it will lead to increased lithium-ion diffusion resistance, limiting fast charging capability. On the other hand, reducing the active material content improves rate performance but sacrifices energy density. Therefore, it is difficult to achieve both high energy density and fast charging capability. (2) Limited cycle life: Under fast charging or high load conditions, the single active layer structure is prone to lithium dendrite growth, particle pulverization, or interface side reactions, leading to capacity decay. (3) Insufficient interface stability: In order to improve battery energy density, the negative electrode active material contains silicon-based materials with high theoretical capacity. However, these materials expand greatly in volume during charging and discharging. During long-term cycle charging and discharging, mechanical stress is easily generated between the current collector and the active layer due to the difference in expansion coefficient, resulting in delamination and increased internal resistance.

[0004] Therefore, there is an urgent need to provide a negative electrode that can balance battery energy density, fast charging capability, and cycle stability to meet the high performance requirements of lithium-ion batteries in terms of fast charging, long range, and long life. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a negative electrode sheet, its preparation method, and its application. Through the design of a multi-layer active layer structure and the selection of negative electrode active materials in each active layer, the lithium-ion battery containing this negative electrode sheet can simultaneously possess high energy density, fast charging capability, and excellent cycle performance under the synergistic effect of both.

[0006] Specifically, the following technical solutions are provided:

[0007] The first aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on at least one side of the current collector along the thickness direction, the negative electrode active layer comprising a first active layer, a second active layer and a third active layer;

[0008] The first active layer is attached to the surface of the current collector, the second active layer is disposed on the surface of the first active layer away from the current collector, and the third active layer is disposed on the surface of the second active layer away from the first active layer;

[0009] The first active layer comprises carbon-coated secondary particulate graphite; the second active layer comprises heteroatom-doped hard carbon, wherein the heteroatom includes one or more of B, N, O, P, S, F, and Cl; and the third active layer comprises porous carbon nanofibers.

[0010] Furthermore, the thickness ratio of the first active layer, the second active layer, and the third active layer is (6-8):(1-2):(1-2), for example, 6:2:2, 7:2:1, 7:1:2, or 8:1:1; that is, the thickness of the first active layer accounts for 60%-80% of the total thickness of the negative electrode active layer, the thickness of the second active layer accounts for 10%-20% of the total thickness of the negative electrode active layer, and the thickness of the third active layer accounts for 10%-20% of the total thickness of the negative electrode active layer.

[0011] Furthermore, the length of the porous carbon nanofiber is preferably 3-8 μm, and the diameter is preferably 100-500 nm.

[0012] Furthermore, the mass fraction of heteroatoms in the heteroatom-doped hard carbon is preferably 0.1%-1%.

[0013] Furthermore, the particle size D50 of the carbon-coated secondary particulate graphite is preferably 10-18 μm.

[0014] A second aspect of the present invention provides a method for preparing the negative electrode sheet described in the first aspect, comprising the following steps:

[0015] S1. Carbon-coated secondary granular graphite is mixed evenly with a first conductive agent, a first binder, a first thickener, and a first solvent to obtain a first negative electrode active slurry.

[0016] The heteroatom-doped hard carbon is mixed evenly with a second conductive agent, a second binder, a second thickener, and a second solvent to obtain a second negative electrode active slurry.

[0017] Porous carbon nanofibers are mixed evenly with a third conductive agent, a third binder, a third thickener, and a third solvent to obtain a third negative electrode active slurry.

[0018] S2. Coat the surface of the current collector with the first negative electrode active slurry, the second negative electrode active slurry and the third negative electrode active slurry in sequence, and dry them to obtain the negative electrode sheet.

[0019] Further, in step S1, the mass percentage of the carbon-coated secondary particulate graphite in the first negative electrode active slurry is less than the mass percentage of the heteroatom-doped hard carbon in the second negative electrode active slurry, which in turn is less than the mass percentage of the porous carbon nanofibers in the third negative electrode active slurry; the mass percentage of the carbon-coated secondary particulate graphite in the first negative electrode active slurry is 96.0%-97.0%; the mass percentage of the heteroatom-doped hard carbon in the second negative electrode active slurry is 96.5%-97.5%; and the mass percentage of the porous carbon nanofibers in the third negative electrode active slurry is 97.5%-98%.

[0020] Further, in step S1, the mass percentage of the first binder in the first negative electrode active slurry is greater than the mass percentage of the second binder in the second negative electrode active slurry, which in turn is greater than the mass percentage of the third binder in the third negative electrode active slurry. More preferably, the mass percentage of the first binder in the first negative electrode active slurry is 0.8%-2%; the mass percentage of the second binder in the second negative electrode active slurry is 0.5%-1.5%; and the mass percentage of the third binder in the third negative electrode active slurry is 0.2%-1.0%.

[0021] Further, in step S1, the viscosity of the first negative electrode active slurry > the viscosity of the second negative electrode active slurry > the viscosity of the third negative electrode active slurry; more preferably, the viscosity of the first negative electrode active slurry is 4000-5000 mPa·s; the viscosity of the second negative electrode active slurry is 3000-4000 mPa·s; and the viscosity of the third negative electrode active slurry is 2500-3500 mPa·s.

[0022] Furthermore, in step S1, the solid content of the first negative electrode active slurry, the second negative electrode active slurry, and the third negative electrode active slurry is all 45%-55%.

[0023] Further, in step S1, the carbon-coated secondary particulate graphite is obtained by granulation and carbon coating of primary particulate graphite; specifically: the primary particulate graphite is granulated to obtain secondary particulate graphite, then mixed evenly with a carbon precursor, and carbonized under an inert atmosphere to obtain the carbon-coated secondary particulate graphite.

[0024] Wherein, the primary particulate graphite includes primary particulate artificial graphite and / or primary particulate natural graphite; preferably, the primary particulate artificial graphite includes one or more of needle coke, petroleum coke, pitch coke and mesophase carbon microspheres, and the primary particulate natural graphite includes flake graphite and / or microcrystalline graphite.

[0025] The carbon precursor (the precursor used for carbon coating) includes one or more of the following: coal tar pitch, petroleum pitch, coal liquefaction pitch, ethylene tar pitch, natural pitch, anthracite, mesophase carbon microspheres, coconut shell, cotton, wood, glucose, lignin, cellulose, phenolic resin, polyaniline, and polyacrylonitrile.

[0026] Further, in step S1, the preparation of the heteroatom-doped hard carbon includes the following steps: mixing the hard carbon source with the heteroatom dopant uniformly, and then performing carbonization treatment under an inert atmosphere to obtain the heteroatom-doped hard carbon.

[0027] The hard carbon source includes one or more of coconut shell, cotton, wood, glucose, lignin, cellulose, phenolic resin, polyaniline, and polyacrylonitrile.

[0028] The heteroatom dopant includes one or more of the following: borane, borax, boron tetrachloride, urea, ammonium chloride, ammonium sulfate, ammonium dihydrogen phosphate, elemental sulfur, thiourea, polyvinylidene fluoride, ammonium hexafluorophosphate, and potassium hexafluorophosphate.

[0029] The mass ratio of the hard carbon source to the dopant is preferably 10:(1-5);

[0030] The preferred carbonization temperature is 1200-1800℃, and the preferred carbonization time is 1-5h.

[0031] Further, in step S1, the porous carbon nanowire fibers are first pulverized, and then mixed with a third conductive agent, a third binder, a third thickener, and a third solvent to prepare a third negative electrode active slurry.

[0032] Furthermore, the preparation of the porous carbon nanofibers includes the following steps:

[0033] (1) Phenolic resin, polyacrylonitrile, zinc salt and solvent are mixed to obtain spinning solution;

[0034] (2) Electrospinning treatment is performed on the spinning solution prepared in step (1) to obtain the raw fiber material;

[0035] (3) The precursor fiber material prepared in step (2) is carbonized in an inert atmosphere to obtain the porous carbon nanofiber.

[0036] Further, in step (1), the zinc salt includes one or more of zinc nitrate, zinc chloride, zinc oxide, and zinc phytate; the solvent is N,N-dimethylformamide.

[0037] Further, in step (1), the mixing process is carried out under oil bath heating conditions, wherein the oil bath heating temperature is 40-80℃ and the oil bath heating time is 1-10h.

[0038] Furthermore, in step (1), the mass percentage of zinc salt in the spinning solution is preferably 0.5%-1.5%.

[0039] Further, in step (2), the electrospinning process is characterized by the following: the injection rate is preferably 0.5-1.2 mL / min, the voltage is preferably 16-20 KV, the temperature is preferably 20-25℃, and the humidity is preferably 20%-40%.

[0040] Furthermore, in step (3), the carbonization temperature is preferably 1000-1500℃, and the carbonization time is preferably 1-5h.

[0041] A third aspect of the present invention provides a lithium-ion battery comprising the negative electrode sheet described in the first aspect or the negative electrode sheet prepared by the preparation method described in the second aspect.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] This invention provides a negative electrode with a three-layer active layer structure. The first active layer near the current collector uses carbon-coated secondary graphite particles as the active material, the second active layer uses heteroatom-doped hard carbon as the active material, and the third active layer away from the current collector uses porous carbon nanofibers as the active material. This results in a gradual decrease in the diffusion rate of lithium ions in the negative electrode from the end near the separator to the end near the current collector. Furthermore, by selecting specific negative electrode active materials for each layer, a suitable gradient change in the lithium ion diffusion rate can be achieved within the negative electrode active layers. This not only enables rapid diffusion and transport of lithium ions, improving fast-charging performance, but also helps suppress lithium dendrite growth and improve battery cycle stability. In addition, the above-mentioned multi-layer gradient design, by optimizing the transport path, allows for an increase in the loading of active materials without significantly sacrificing rate performance, thereby improving energy density. This allows lithium-ion batteries to possess high energy density, fast-charging capability, and excellent cycle performance. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of a negative electrode sheet according to the present invention;

[0045] In the figure: 1 is the current collector, 21 is the first active layer, 22 is the second active layer, and 23 is the third active layer. Detailed Implementation

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. "Comprising" or "containing" as used herein means that it may include or contain other components in addition to the stated components. "Comprising" or "containing" as used herein may also be replaced with the closed form "is" or "consisting of".

[0047] As described in the background section, current negative electrode sheets typically employ a single active layer structure, composed of active materials such as graphite and silicon-based materials, conductive agents, and binders. However, this homogeneous design cannot simultaneously address battery energy density, fast charging capability, and cycle stability, failing to meet the high-performance requirements of lithium-ion batteries in terms of fast charging, long range, and long lifespan.

[0048] To address the aforementioned problems, embodiments of the present invention provide a negative electrode sheet, which includes a current collector and a negative electrode active layer disposed on at least one side of the current collector along its thickness direction. The negative electrode active layer comprises a first active layer, a second active layer, and a third active layer; wherein,

[0049] The first active layer is attached to the surface of the current collector, and the first active layer contains carbon-coated secondary particulate graphite; using carbon-coated secondary particulate graphite as the active material of the first active layer (bottom layer) can greatly improve the diffusion rate of lithium ions and reduce the charging time of lithium-ion batteries. Specifically: (1) Secondary particulate graphite has high isotropy, which is beneficial for the insertion and extraction of lithium ions in all directions; (2) The carbon coating modification treatment can improve the diffusion rate of lithium ions in the coating layer.

[0050] The second active layer is disposed on the surface of the first active layer away from the current collector. The first active layer contains carbon-coated secondary particulate graphite. The second active layer contains heteroatom-doped hard carbon, wherein the heteroatom includes one or more of B, N, O, P, S, F, and Cl. Using heteroatom-doped hard carbon material as the active material of the second active layer (intermediate layer) has at least the following advantages: (1) Hard carbon material has a large interlayer spacing, which can greatly improve the diffusion rate of lithium ions in the material; (2) By using heteroatom doping, the interlayer spacing of hard carbon material will be further improved; at the same time, the doping of heteroatom will introduce some pore structure into the material. The existence of pore structure can serve as a channel for rapid lithium ion transport. The significant increase in the lithium ion diffusion rate will shorten the charging time of lithium ion battery; (3) As a connection between the bottom layer and the top layer, the diffusion rate of lithium ions in the intermediate layer is between the top layer and the bottom layer, playing a transitional role, reducing the lithium ion diffusion rate gradient, which is beneficial to reduce the generation of lithium ion diffusion stress and reduce the risk of each coating layer falling off.

[0051] The third active layer is disposed on the surface of the second active layer away from the first active layer; the third active layer comprises porous carbon nanofibers; using porous carbon nanofibers as the active material of the third active layer (upper layer) has the following advantages: (1) Carbon nanofibers have excellent conductivity, which can effectively improve the charge and discharge rate and overall performance of the battery; (2) The large specific surface area of ​​carbon nanofibers helps to increase the contact area between the electrode and the electrolyte, improve the lithium ion transport efficiency, thereby improving the battery capacity and rate performance; (3) The unique nanostructure of carbon nanofibers provides a fast transport channel for lithium ions, which helps to improve the rate performance of the battery; (4) The unique pore structure in porous carbon nanofibers can serve as a channel for the rapid transport of lithium ions, greatly improving the diffusion rate of lithium ions.

[0052] The existing homogenized design of negative electrode sheets cannot simultaneously achieve optimal battery energy density, fast charging capability, and cycle stability. This invention addresses this by designing a multi-layer active layer structure and selecting appropriate negative electrode active materials for each layer. Through the synergistic effect of structure and materials, a lithium-ion battery containing the aforementioned negative electrode sheet can achieve a balance between energy density, fast charging capability, and cycle performance. Specifically, this invention provides a negative electrode sheet with a three-layer active layer structure. The first active layer near the current collector uses carbon-coated secondary graphite particles as the active material; the second active layer uses heteroatom-doped hard carbon as the active material; and the third active layer away from the current collector uses porous carbon nanofibers as the active material. The diffusion rate of lithium ions among these active materials is: porous carbon nanofibers > heteroatom-doped hard carbon > carbon-coated secondary graphite particles. That is, the diffusion rate of lithium ions in the negative electrode sheet gradually decreases from the end near the separator to the end near the current collector. Furthermore, by selecting specific negative electrode active materials for each layer, a suitable gradient change in the lithium ion diffusion rate can be achieved within the negative electrode active layer. Through the synergistic effect of the above structural design and material selection, the prepared negative electrode sheet has at least the following advantages:

[0053] (1) Optimize lithium-ion transport dynamics, reduce concentration polarization, and improve fast charging performance: The diffusion rate is high in the area near the separator, which can quickly respond to the lithium-ion demand in the electrolyte and reduce ion accumulation at the interface; while the diffusion rate is slow in the area near the current collector, which matches the electron conduction speed and avoids local lithium-ion shortage; thus, concentration polarization can be reduced and rate performance can be improved.

[0054] (2) It helps to suppress lithium dendrite growth and improve battery cycle stability and safety: The high diffusion rate region (separator side) can quickly replenish lithium ions, avoiding excessive local lithium ion deposition to form lithium dendrites, and preventing lithium dendrites from piercing the separator and causing thermal runaway. In addition, a suitable gradient distribution of diffusion rate can guide lithium ions to be inserted / extracted more uniformly. For example, using heteroatom-doped hard carbon as the intermediate active material, the heteroatom doping will increase the interlayer spacing of hard carbon and introduce a porous structure. The expansion of the interlayer spacing and the existence of the porous structure make the diffusion rate of lithium ions in heteroatom-doped hard carbon materials second only to porous carbon nanofibers. With this intermediate layer as the connection between the bottom and top layers, the diffusion rate gradient of lithium ions can be reduced, which helps to reduce the generation of lithium ion diffusion stress, thereby reducing the risk of coating layer peeling off and further improving battery cycle stability.

[0055] (3) High energy density compatibility: Gradient design improves the fast charging performance of the electrode by optimizing the transmission path, allowing for increased active material loading without significantly sacrificing battery energy density.

[0056] In this invention, in order to maintain the specific capacity of the electrode and effectively improve the overall fast charging performance of the electrode, the thickness ratio of the first active layer, the second active layer and the third active layer is preferably (6-8):(1-2):(1-2), such as 6:2:2, 7:2:1, 7:1:2, 8:1:1, etc., including but not limited to the thickness ratios listed above; that is, the thickness of the first active layer accounts for 60%-80% of the total thickness of the negative electrode active layer, the thickness of the second active layer accounts for 10%-20% of the total thickness of the negative electrode active layer, and the thickness of the third active layer accounts for 10%-20% of the total thickness of the negative electrode active layer.

[0057] In this invention, the length of the porous carbon nanofibers is preferably 3-8 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc., and the diameter is preferably 100-500 nm, such as 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc., including but not limited to the values ​​listed above. By controlling the length and diameter of the porous carbon nanofibers within the above range, this invention is beneficial to further promote the rapid migration of lithium ions and improve the fast charging capability of lithium-ion batteries.

[0058] In this invention, heteroatom doping of hard carbon can increase the interlayer spacing of the hard carbon, and a larger interlayer spacing is beneficial for the rapid diffusion of lithium ions. Simultaneously, heteroatom doping can improve the conductivity of the material, enhancing the rapid transport of electrons / ions. Furthermore, heteroatom doping can create a porous structure in the material, which can serve as a channel for the rapid transport of lithium ions, accelerating lithium ion transport. However, heteroatom doping also introduces some defects. The formation of the porous structure increases the specific surface area of ​​the material. These defects and the increased specific surface area lead to increased lithium ion consumption and reduced battery cycle life. Therefore, to improve the lithium ion migration rate and thus enhance the fast-charging capability of lithium-ion batteries while minimizing the loss of cycle life, it is preferable to control the mass fraction of heteroatoms in the heteroatom-doped hard carbon within the range of 0.1%-1%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., including but not limited to the mass fractions listed above.

[0059] In this invention, the particle size D50 of the carbon-coated secondary graphite particles is preferably 10-18 μm, such as 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, etc., including but not limited to the particle sizes listed above. Controlling the particle size D50 of the carbon-coated secondary graphite particles within the range of 10-18 μm can ensure that the secondary particles have a high degree of granulation, making them highly isotropic, which is beneficial for the insertion and extraction of lithium ions in all directions.

[0060] The present invention also provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps:

[0061] S1. Carbon-coated secondary granular graphite is mixed evenly with a first conductive agent, a first binder, a first thickener, and a first solvent to obtain a first negative electrode active slurry.

[0062] The heteroatom-doped hard carbon is mixed evenly with a second conductive agent, a second binder, a second thickener, and a second solvent to obtain a second negative electrode active slurry.

[0063] Porous carbon nanofibers are mixed evenly with a third conductive agent, a third binder, a third thickener, and a third solvent to obtain a third negative electrode active slurry.

[0064] S2. Coat the surface of the current collector with the first negative electrode active slurry, the second negative electrode active slurry and the third negative electrode active slurry in sequence, and dry them to obtain the negative electrode sheet.

[0065] In step S1 of this invention, the mass percentage of the carbon-coated secondary particulate graphite in the first negative electrode active slurry is less than the mass percentage of the heteroatom-doped hard carbon in the second negative electrode active slurry, which is less than the mass percentage of the porous carbon nanofibers in the third negative electrode active slurry; the mass percentage of the first binder in the first negative electrode active slurry is greater than the mass percentage of the second binder in the second negative electrode active slurry, which is greater than the mass percentage of the third binder in the third negative electrode active slurry.

[0066] Because the binder floats to the surface during the electrode drying process, the proportion of active material gradually decreases and the proportion of binder gradually increases in the first to third negative electrode active slurries prepared in this invention. This allows the binder to be evenly distributed in each layer of the electrode after drying, preventing the active material from falling off and improving the cycle performance of lithium-ion batteries.

[0067] More preferably, the carbon-coated secondary particulate graphite accounts for 96.0%-97.0% of the mass of the first negative electrode active slurry, for example, 96.0%, 96.5%, 97%, etc.; the heteroatom-doped hard carbon accounts for 96.5%-97.5% of the mass of the second negative electrode active slurry, for example, 96.5%, 97%, 97.5%, etc.; the porous carbon nanofibers account for 97.5%-98% of the mass of the third negative electrode active slurry, for example, 97.5%, 98%, etc.; and the first binder accounts for 0.8%-2% of the mass of the first negative electrode active slurry, for example, 0.8%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9 ... The second binder has a mass percentage of 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc. in the second negative electrode active slurry, such as 0.5%-1.5%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc. in the third negative electrode active slurry, such as 0.2%-1.0%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., including but not limited to the mass percentages listed above.

[0068] In some preferred embodiments of the present invention, in step S1, the mass ratio of carbon-coated secondary particulate graphite to the first conductive agent, the first binder, and the first thickener is (96.0-97.0):(0.7-1.5):(0.8-2):(0.6-1.5); the mass ratio of heteroatom-doped hard carbon to the second conductive agent, the second binder, and the second thickener is (96.5-97.5):(0.7-1.5):(0.5-1.5):(0.4-1.0); and the mass ratio of porous carbon nanofibers to the third conductive agent, the third binder, and the third thickener is (97.5-98.0):(0.7-1.5):(0.2-1.0):(0.2-0.8).

[0069] In step S1 of this invention, the viscosity of the first negative electrode active slurry is greater than that of the second negative electrode active slurry and the viscosity of the third negative electrode active slurry. Because the bottom film surface absorbs the solvent of the slurry during multiple coating processes, the slurry is not easy to level, which leads to the phenomenon of leakage of the bottom film surface. By adjusting the discharge viscosity of the slurry to decrease sequentially, the above-mentioned adverse phenomenon can be avoided.

[0070] More preferably, the viscosity of the first negative electrode active slurry is 4000-5000 mPa·s, such as 4000 mPa·s, 4200 mPa·s, 4400 mPa·s, 4600 mPa·s, 4800 mPa·s, 5000 mPa·s, etc.; and the viscosity of the second negative electrode active slurry is 3000-4000 mPa·s, such as 3000 mPa·s, 3200 mPa·s, 3400 mPa·s, 3600 mPa·s, 3800 mPa·s, etc. Pa·s, 4000 mPa·s, etc.; the viscosity of the third negative electrode active slurry is 2500-3500 mPa·s, such as 2500 mPa·s, 2600 mPa·s, 2700 mPa·s, 2800 mPa·s, 2900 mPa·s, 3000 mPa·s, 3100 mPa·s, 3300 mPa·s, 3300 mPa·s, 3400 mPa·s, 3500 mPa·s, etc., including but not limited to the viscosity values ​​listed above.

[0071] In step S1 of the present invention, the solid content of the first negative electrode active slurry, the second negative electrode active slurry and the third negative electrode active slurry is 45%-55%, for example 45%, 50%, 55% etc.

[0072] In some preferred embodiments of the present invention, in step S1, the carbon-coated secondary particulate graphite is obtained by granulation and carbon coating of primary particulate graphite; specifically: the primary particulate graphite is granulated to obtain secondary particulate graphite, which is then mixed evenly with a carbon precursor and carbonized under an inert atmosphere to obtain the carbon-coated secondary particulate graphite.

[0073] Preferably, the primary particulate graphite includes primary particulate artificial graphite and / or primary particulate natural graphite; the primary particulate artificial graphite includes one or more of needle coke, petroleum coke, pitch coke and mesophase carbon microspheres, and the primary particulate natural graphite includes flake graphite and / or microcrystalline graphite.

[0074] Preferably, the carbon precursor (the precursor used for carbon coating) includes one or more of the following: coal tar pitch, petroleum pitch, coal liquefaction pitch, ethylene tar pitch, natural pitch, anthracite, mesophase carbon microspheres, coconut shell, cotton, wood, glucose, lignin, cellulose, phenolic resin, polyaniline, and polyacrylonitrile.

[0075] In some preferred embodiments of the present invention, step S1, the preparation of the heteroatom-doped hard carbon includes the following steps: mixing the hard carbon source with the heteroatom dopant uniformly, and then performing carbonization treatment under an inert atmosphere to obtain the heteroatom-doped hard carbon.

[0076] Preferably, the hard carbon source includes one or more of coconut shell, cotton, wood, glucose, lignin, cellulose, phenolic resin, polyaniline, and polyacrylonitrile; the heteroatom dopant includes one or more of borane, borax, boron tetrachloride, urea, ammonium chloride, ammonium sulfate, ammonium dihydrogen phosphate, elemental sulfur, thiourea, polyvinylidene fluoride, ammonium hexafluorophosphate, and potassium hexafluorophosphate.

[0077] Preferably, the mass ratio of the hard carbon source to the dopant is 10:(1-5), such as 10:1, 10:2, 10:3, 10:4, 10:5, etc., including but not limited to the mass ratios listed above.

[0078] Preferably, the carbonization temperature is 1200-1800℃, such as 1200℃, 1300℃, 1400℃, 1500℃, 1600℃, 1700℃, 1800℃, etc., and the carbonization time is preferably 1-5h, such as 1h, 2h, 3h, 4h, 5h, etc.

[0079] In some preferred embodiments of the present invention, in step S1, the porous carbon nanowire fibers are first pulverized and then mixed with a third conductive agent, a third binder, a third thickener, and a third solvent to prepare a third negative electrode active slurry.

[0080] In some preferred embodiments of the present invention, step S1, the preparation of the porous carbon nanofibers includes the following steps:

[0081] (1) Phenolic resin, polyacrylonitrile, zinc salt and solvent are mixed to obtain spinning solution;

[0082] (2) Electrospinning treatment is performed on the spinning solution prepared in step (1) to obtain the raw fiber material;

[0083] (3) The precursor fiber material prepared in step (2) is carbonized in an inert atmosphere to obtain the porous carbon nanofiber.

[0084] Preferably, in step (1), the zinc salt includes one or more of zinc nitrate, zinc chloride, zinc oxide, and zinc phytate; the solvent includes, but is not limited to, N,N-dimethylformamide.

[0085] Preferably, in step (1), the mixing process is carried out under oil bath heating conditions, wherein the oil bath heating temperature is 40-80℃ and the oil bath heating time is 1-10h, for example, oil bath heating at 60℃ for 5h.

[0086] Preferably, in step (1), the mass percentage of zinc salt in the spinning solution is 0.5%-1.5%, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc., including but not limited to the mass percentages listed above; in some preferred embodiments of the present invention, the mass ratio of phenolic resin to polyacrylonitrile, zinc salt, and solvent is 4.5%:10.5%:1%:84%.

[0087] Preferably, in step (2), the electrospinning treatment step has the following characteristics: the injection rate is preferably 0.5-1.2 mL / min, the voltage is preferably 16-20 KV, the temperature is preferably 20-25℃, and the humidity is preferably 20%-40%.

[0088] Preferably, in step (3), the carbonization temperature is preferably 1000-1500℃, such as 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, etc., and the carbonization time is preferably 1-5h, such as 1h, 2h, 3h, 4h, 5h, etc.

[0089] In addition, the present invention also provides a lithium-ion battery comprising a negative electrode sheet prepared by the above method. When charged and discharged at high rate, it can not only effectively suppress lithium plating, but also has high energy density and excellent cycle performance.

[0090] Example 1

[0091] This embodiment relates to the preparation of a negative electrode sheet, and the specific operation is as follows:

[0092] Preparation of carbon-coated secondary particulate graphite: Microcrystalline graphite was used as raw material and granulated to obtain secondary particulate graphite; coal tar pitch was used as a coating agent to carbon-coat the secondary particulate graphite (the mass ratio of coating agent to secondary particulate graphite was 1:20) (temperature was 1100℃, holding time was 3h) to obtain carbon-coated secondary particulate graphite material with D50 of 14μm;

[0093] Preparation of heteroatom-doped hard carbon: 10g of a mixture of phenolic resin and polyacrylonitrile (mass ratio of phenolic resin to polyacrylonitrile is 6:4) was ground and mixed with 4g of elemental sulfur. Then, under an inert atmosphere, the mixture was heated to 1600℃ at a heating rate of 3℃ / min and held for 3h. After cooling, sulfur-doped hard carbon material was obtained with a sulfur doping amount of 0.4%.

[0094] Preparation of porous carbon nanofibers:

[0095] The solvent DMF (N,N-dimethylacetamide), the spinning aid PAN (polyacrylonitrile), phenolic resin and zinc chloride were mixed in a ratio of 84%:10.5%:4.5%:1%, and then heated in an oil bath at 60°C for 5 hours to obtain the spinning solution.

[0096] The prepared spinning solution is drawn into a syringe, connected to a needle, and then connected to an electrospinning device. The injection speed is adjusted to 0.8 mL / min, the voltage to 18 KV, the temperature to 23℃, and the humidity to 30%, and electrospinning is performed to obtain the precursor fiber material.

[0097] The raw fiber material was heated to 1300℃ at a heating rate of 3℃ / min under an inert protective atmosphere, held at that temperature for 3 hours to carbonize, and then automatically cooled to obtain porous carbon nanofibers.

[0098] Preparation of negative electrode active slurry:

[0099] The carbon-coated secondary granular graphite obtained above was dry-mixed with conductive carbon black, and then CMCC (sodium carboxymethyl cellulose), SBR (styrene-butadiene rubber), and deionized water were added respectively. The mixture was stirred until homogeneous to prepare the first negative electrode active slurry. The weight ratio of carbon-coated secondary granular graphite, conductive carbon black, binder, and thickener was 96.3:1.0:1.2:1.5. The viscosity of the first negative electrode active slurry was 4400 mPa·s, and the solid content was 50.1%.

[0100] The heteroatom-doped hard carbon material prepared above was dry-mixed with conductive carbon black, and then CMCC binder, SBR thickener, and deionized water were added respectively. The mixture was stirred evenly to prepare the second negative electrode active slurry. The weight ratio of heteroatom-doped hard carbon, conductive carbon black, binder, and thickener was 96.9:1.0:1.3:0.8. The viscosity of the second negative electrode active slurry was 3250 mPa·s, and the solid content was 50.5%.

[0101] The porous carbon nanofibers prepared above were pulverized, and then dry-mixed with conductive carbon black. CMCC binder, SBR thickener, and deionized water were then added and mixed thoroughly to prepare the third anode active slurry. The weight ratio of heteroatom-doped hard carbon, conductive carbon black, binder, and thickener was 97.6:1.2:0.7:0.5. The viscosity of the third anode active slurry was 3240 mPa·s, and the solid content was 50.3%.

[0102] Coating: Using a three-layer coating machine, a first negative electrode active slurry is coated on the surface of the current collector, a second negative electrode active slurry is coated on the surface of the first negative electrode active slurry, and a third negative electrode active slurry is coated on the surface of the second negative electrode active slurry. The coating is then dried to obtain a three-layer coated negative electrode sheet. The thickness ratio of the first active layer, the second active layer, and the third active layer is 6:2:2.

[0103] The active layer of the negative electrode sheet prepared in this embodiment consists of, from the inside out, a carbon-coated secondary particulate graphite layer (first active layer), a heteroatom-doped hard carbon layer (second active layer), and a porous carbon nanofiber layer (third active layer).

[0104] Examples 2-6

[0105] Examples 2-6 all involve the preparation of a negative electrode sheet. The difference from Example 1 lies in the preparation of carbon-coated secondary particulate graphite, heteroatom-doped hard carbon, and porous carbon nanofibers, as well as the formulation of the first, second, and third negative electrode active slurries. The remaining operations are the same; as shown in Tables 1-6 below:

[0106] Table 1

[0107]

[0108] Table 2

[0109]

[0110] Table 3

[0111]

[0112] Table 4

[0113]

[0114] Table 5

[0115]

[0116] Table 6

[0117]

[0118] Example 7

[0119] Example 7 relates to the preparation of a negative electrode sheet. The difference from Example 1 is that the active layer thickness ratio is as follows: the active layer of the negative electrode sheet prepared in this example consists of a carbon-coated secondary particulate graphite layer, a heteroatom-doped hard carbon layer, and a porous carbon nanofiber layer from the inside to the outside. The coating thickness ratio of the carbon-coated secondary particulate graphite layer to the heteroatom-doped hard carbon layer and the porous carbon nanofiber layer is 2:4:4.

[0120] Comparative Example 1

[0121] Comparative Example 1 relates to the preparation of a negative electrode sheet. The difference from Example 1 is that the coating sequence is as follows: Specifically, a third negative electrode active slurry is coated on the surface of the current collector using a three-layer coating machine, a second negative electrode active slurry is coated on the surface of the third negative electrode active slurry, and a first negative electrode active slurry is coated on the surface of the second negative electrode active slurry. The slurry is then dried to obtain a three-layer coated negative electrode sheet.

[0122] The active layer of the negative electrode prepared in this comparative example consists of a porous carbon nanofiber layer, a heteroatom-doped hard carbon layer, and a carbon-coated secondary particle graphite layer from the inside out. The coating thickness ratio of the porous carbon nanofiber layer to the heteroatom-doped hard carbon layer and the carbon-coated secondary particle graphite layer is 2:2:6.

[0123] Comparative Example 2

[0124] Comparative Example 2 relates to the preparation of a negative electrode sheet. The difference from Example 1 is that the coating sequence is as follows: Specifically, a third negative electrode active slurry is coated on the surface of the current collector using a three-layer coating machine, a first negative electrode active slurry is coated on the surface of the third negative electrode active slurry, and a second negative electrode active slurry is coated on the surface of the first negative electrode active slurry. The coating is then dried to obtain a three-layer coated negative electrode sheet.

[0125] The active layer of the negative electrode prepared in this comparative example consists of a porous carbon nanofiber layer, a carbon-coated secondary particulate graphite layer, and a heteroatom-doped hard carbon layer from the inside out. The coating thickness ratio of the porous carbon nanofiber layer to the carbon-coated secondary particulate graphite layer and the heteroatom-doped hard carbon layer is 2:6:2.

[0126] Comparative Example 3

[0127] Comparative Example 3 relates to the preparation of a negative electrode sheet. The difference from Example 1 is that the second negative electrode active material is a heteroatom-doped soft carbon material. The carbon source precursor is changed from a mixture of 10g phenolic resin and polyacrylonitrile (6:4) to 10g coal tar pitch. The other materials are not changed.

[0128] The active layer of the negative electrode prepared in this comparative example consists of a carbon-coated secondary particulate graphite layer, a heteroatom-doped soft carbon layer, and a porous carbon nanofiber layer, from the inside out. The coating thickness ratio of the carbon-coated secondary particulate graphite layer to the heteroatom-doped soft carbon layer and the porous carbon nanofiber layer is 6:2:2.

[0129] Application and performance testing

[0130] The negative electrode sheets prepared in the above embodiments and comparative examples were used to construct lithium-ion pouch batteries, as detailed below:

[0131] Preparation of positive electrode sheet: The positive electrode active material lithium iron phosphate, conductive agent SP and binder polyvinylidene fluoride are mixed in an appropriate amount of N-methylpyrrolidone solvent at a weight ratio of 96.7:1.5:1.8 to form a uniform positive electrode slurry; this slurry is coated on the positive electrode current collector Al foil, dried and cold pressed to obtain the positive electrode sheet.

[0132] Separator: Commercially available ceramic separator membrane is used.

[0133] Electrolyte: Ethyl carbonate EC, diethyl carbonate DEC, and methyl ethyl carbonate EMC are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, solute LiPF6 is added to the organic solvent to dissolve and mix evenly to obtain the electrolyte; wherein the concentration of LiPF6 is 1M.

[0134] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound up and placed in the outer packaging foil. After the cell is baked, the moisture content of both the positive and negative electrodes is less than 200 ppm, and then the electrolyte injection and wetting process can be carried out to prepare a 2.8Ah soft pack battery.

[0135] The following electrochemical performance tests were performed on the pouch cells prepared with different negative electrode sheets:

[0136] Lithium plating test (10C direct charge to 80% SOC): The 2.8Ah soft pack battery was discharged at a constant current of 1C to 2.5V, and then charged at a constant current of 10C for 4.8 minutes, that is, charged to 80% SOC. Then the battery was disassembled and the presence of lithium plating on the negative electrode was observed.

[0137] Cyclic testing: The 2.8Ah pouch battery was discharged at a constant current of 1C to 2.5V, and then charged and discharged at a current of 4C. The upper limit of charging voltage was 3.65V, and the lower limit of discharging voltage was 2.5V. When the capacity retention rate dropped to 80%, the battery was removed from the production line, and the number of cycles at the time of removal was recorded. The removed pouch battery was then disassembled, and the phenomenon of active material shedding from the anode electrode was observed.

[0138] Capacity test (button electrode): The negative electrode sheets of the above embodiments and comparative examples were cut into 14.5mm electrode sheets using a punching machine. Then, a lithium sheet was used as the counter electrode. The above electrolyte and separator were used to conduct a constant current charge-discharge capacity test at a current density of 0.01C. The charge-discharge voltage range was 0.01-2.5V, and its specific capacity was measured.

[0139] The test results are shown in Table 7 below:

[0140] Table 7

[0141]

[0142]

[0143] As shown in Table 7, the lithium-ion batteries constructed from the negative electrode sheets prepared in Examples 1-7, when charged to 80% SOC at 10C, did not exhibit lithium plating. Furthermore, under high-rate (4C) charge-discharge conditions, they maintained a long cycle life, with the number of cycles corresponding to a capacity drop to 80% not less than 1192. In contrast, Comparative Examples 1 and 2, which only adjusted the order of the coatings without changing the content of each active material in the electrode sheet, showed severe lithium plating under the same conditions. Moreover, under high-rate conditions, the battery capacity dropped below 80% in less than 100 charge-discharge cycles (due to polarization during cycling, lithium plating occurred, causing a rapid capacity drop, and the capacity retention rate quickly fell below 80%). Therefore, it can be seen that the coating sequence of each active layer not only has a great influence on the fast charging performance of the battery, but also affects the cycle life under high rate conditions. When the diffusion rate of lithium ions in the negative electrode sheet shows a gradual decreasing trend from the end near the separator to the end of the current collector, the lithium-ion battery not only has fast charging performance, but also has excellent cycle stability.

[0144] As shown in Example 1 and Comparative Example 3, when the heteroatom-doped hard carbon material in the negative electrode of Example 1 is replaced with heteroatom-doped soft carbon material, lithium-ion batteries exhibit lithium plating, and the cycle life at 4C charge-discharge is significantly reduced. Furthermore, compared to Example 1 and Comparative Example 1, the negative electrode sheets prepared in Comparative Examples 2 and 3 all showed active material detachment after cycle testing. This is because the lithium-ion diffusion rate varies significantly between the coatings in the negative electrode sheet, generating substantial stress, which in turn leads to active material detachment. Therefore, it can be concluded that achieving a suitable gradient change in the lithium-ion diffusion rate within the negative electrode active layer through the selection of specific negative electrode active materials in each layer is beneficial for improving battery cycle performance.

[0145] Furthermore, as can be seen from Examples 1 and 7, the specific capacity of the battery is significantly reduced when the graphite content, which is the main capacity support, is only 20%. Therefore, in order to ensure that the battery has high specific capacity while also having fast charging capability and excellent cycle performance, it is preferable to control the thickness of each active layer in the negative electrode sheet within a suitable range, for example, the layer thickness ratio of the first active layer to the second and third active layers is 6:2:2.

[0146] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode active layer disposed on at least one side of the current collector along the thickness direction, the negative electrode active layer comprising a first active layer, a second active layer and a third active layer; The first active layer is attached to the surface of the current collector, the second active layer is disposed on the surface of the first active layer away from the current collector, and the third active layer is disposed on the surface of the second active layer away from the first active layer; The first active layer includes a first active material, which is carbon-coated secondary particulate graphite; the second active layer includes a second active material, which is heteroatom-doped hard carbon, wherein the heteroatoms include one or more of B, N, O, P, S, F, and Cl; the third active layer includes a third active material, which is porous carbon nanofibers; the porous carbon nanofibers have a length of 3-8 μm and a diameter of 100-500 nm; the heteroatom-doped hard carbon has a heteroatom mass fraction of 0.1%-1%; and the carbon-coated secondary particulate graphite has a particle size D50 of 10-18 μm. The diffusion rates of lithium ions in these active materials are in the following order: porous carbon nanofibers > heteroatom-doped hard carbon > carbon-coated secondary particulate graphite.

2. The negative electrode sheet according to claim 1, characterized in that, The thickness of the first active layer accounts for 60%-80% of the total thickness of the negative electrode active layer; the thickness of the second active layer accounts for 10%-20% of the total thickness of the negative electrode active layer; and the thickness of the third active layer accounts for 10%-20% of the total thickness of the negative electrode active layer.

3. A method for preparing the negative electrode sheet according to claim 1 or 2, characterized in that, Includes the following steps: S1. Carbon-coated secondary granular graphite is mixed evenly with a first conductive agent, a first binder, a first thickener, and a first solvent to obtain a first negative electrode active slurry. The heteroatom-doped hard carbon is mixed evenly with a second conductive agent, a second binder, a second thickener, and a second solvent to obtain a second negative electrode active slurry. Porous carbon nanofibers are mixed evenly with a third conductive agent, a third binder, a third thickener, and a third solvent to obtain a third negative electrode active slurry. S2. Coat the surface of the current collector with the first negative electrode active slurry, the second negative electrode active slurry and the third negative electrode active slurry in sequence, and dry them to obtain the negative electrode sheet.

4. The preparation method according to claim 3, characterized in that, Step S1 includes at least one of the following features: (1) The mass percentage of carbon-coated secondary particulate graphite in the first negative electrode active slurry is < the mass percentage of heteroatom-doped hard carbon in the second negative electrode active slurry < the mass percentage of porous carbon nanofibers in the third negative electrode active slurry; the mass percentage of carbon-coated secondary particulate graphite in the first negative electrode active slurry is 96.0%-97.0%; the mass percentage of heteroatom-doped hard carbon in the second negative electrode active slurry is 96.5%-97.5%; and the mass percentage of porous carbon nanofibers in the third negative electrode active slurry is 97.5%-98%. (2) The mass percentage of the first binder in the first negative electrode active slurry > the mass percentage of the second binder in the second negative electrode active slurry > the mass percentage of the third binder in the third negative electrode active slurry; (3) The viscosity of the first negative electrode active slurry > the viscosity of the second negative electrode active slurry > the viscosity of the third negative electrode active slurry; (4) The solid content of the first negative electrode active slurry, the second negative electrode active slurry and the third negative electrode active slurry is 45%-55%.

5. The preparation method according to claim 4, characterized in that, The first binder accounts for 0.8%-2% of the mass of the first negative electrode active slurry; the second binder accounts for 0.5%-1.5% of the mass of the second negative electrode active slurry; and the third binder accounts for 0.2%-1.0% of the mass of the third negative electrode active slurry.

6. The preparation method according to claim 4, characterized in that, The viscosity of the first negative electrode active slurry is 4000-5000 mPa·s; the viscosity of the second negative electrode active slurry is 3000-4000 mPa·s; and the viscosity of the third negative electrode active slurry is 2500-3500 mPa·s.

7. The preparation method according to claim 3, characterized in that, In step S1, the carbon-coated secondary granular graphite is obtained by granulation and carbon coating of primary granular graphite. The primary granular graphite includes primary granular artificial graphite and / or primary granular natural graphite; wherein, the primary granular artificial graphite includes one or more of needle coke, petroleum coke, pitch coke and mesophase carbon microspheres, and the primary granular natural graphite includes flake graphite and / or microcrystalline graphite. The precursors used for carbon coating include one or more of the following: coal tar pitch, petroleum pitch, coal liquefaction pitch, ethylene tar pitch, natural pitch, anthracite, mesophase carbon microspheres, coconut shell, cotton, wood, glucose, lignin, phenolic resin, polyaniline, and polyacrylonitrile.

8. The preparation method according to claim 3, characterized in that, In step S1, the preparation of the heteroatom-doped hard carbon includes the following steps: uniformly mixing a hard carbon source with a heteroatom dopant, and then performing a carbonization treatment under an inert atmosphere to obtain the heteroatom-doped hard carbon; wherein, The hard carbon source includes one or more of coconut shell, cotton, wood, glucose, lignin, phenolic resin, polyaniline, and polyacrylonitrile; The heteroatom dopant includes one or more of the following: borane, borax, boron tetrachloride, urea, ammonium chloride, ammonium sulfate, ammonium dihydrogen phosphate, elemental sulfur, thiourea, polyvinylidene fluoride, ammonium hexafluorophosphate, and potassium hexafluorophosphate. The mass ratio of the hard carbon source to the dopant is 10:(1-5); The carbonization temperature is 1200-1800 ℃, and the carbonization time is 1-5 h.

9. The preparation method according to claim 3, characterized in that, In step S1, the porous carbon nanofibers are first pulverized, and then mixed with a third conductive agent, a third binder, a third thickener, and a third solvent to prepare a third negative electrode active slurry. The preparation of the porous carbon nanofibers includes the following steps: (1) Phenolic resin, polyacrylonitrile, zinc salt and solvent are mixed to obtain spinning solution; (2) The spinning solution prepared in step (1) is subjected to electrospinning treatment to obtain the raw fiber material; (3) The precursor fiber material prepared in step (2) is carbonized in an inert atmosphere to obtain the porous carbon nanofiber.

10. The preparation method according to claim 9, characterized in that, It must contain at least one of the following characteristics: (1) In step (1), the mass percentage of zinc salt in the spinning solution is 0.5%-1.5%; (2) In step (1), the zinc salt includes one or more of zinc nitrate, zinc chloride, and zinc phytate; (3) In step (2), the electrospinning process involves the following steps: the injection rate is 0.5-1.2 mL / min, the voltage is 16-20 KV, the temperature is 20-25 ℃, and the humidity is 20%-40%. (4) In step (3), the carbonization temperature is 1000-1500 ℃ and the carbonization time is 1-5 h.

11. A lithium-ion battery, characterized in that, It includes the negative electrode sheet as described in claim 1 or 2, or the negative electrode sheet prepared by the preparation method described in any one of claims 3-10.

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