Negative plate, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, in particular to a negative plate, a preparation method thereof and a battery. The negative plate comprises a current collector; the conductive layer is arranged on the surface of at least one side of the current collector along the thickness direction, and the conductive layer comprises a conductive agent; the first active layer is arranged on the surface, far away from the current collector, of the conductive layer, the first active layer comprises a first active substance, and the first active substance comprises a graphite material coated with a conductive material; the second active layer is arranged on the surface, away from the conductive layer, of the first active layer, the second active layer comprises a second active substance, and the second active substance comprises a tin-containing composite material coated with an aromatic conductive polymer; the third active layer is arranged on the surface, away from the first active layer, of the second active layer, and the third active layer comprises a heteroatom-doped porous carbon material. The lithium ion battery comprising the negative plate has the advantages of high energy density, long cycle life and high safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode sheet, a preparation method thereof and a battery. BACKGROUND

[0002] Lithium ion batteries have the advantages of high specific capacity, high working voltage, long service life, no memory effect, etc. as new energy, and the automobile energy storage device with lithium ion battery is also attracting attention. With the continuous development of science and technology and economy, people pay more and more attention to the comprehensive performance of lithium ion secondary batteries, and lithium ion batteries with energy density, long cycle life and high safety become the focus of research and development. At present, the main way to improve the energy density of the battery is: 1. Improve the compaction density of the positive and negative electrode materials, but high compaction will lead to low porosity of the electrode sheet, and the liquid retention capacity will decrease, which will lead to insufficient cycle life of the battery; 2. Improve the specific capacity of the negative electrode material, that is, replace graphite with silicon-based negative electrode material, but the great volume change of the silicon-based material during charging and discharging will cause the material to powder, peel off from the current collector, and lead to rapid capacity attenuation, accompanied by safety problems.

[0003] The existing solutions include, for example, using negative active materials with different compaction densities to improve the liquid retention capacity of the electrode sheet and improve the long cycle life while ensuring high compaction density; or using a method of coating different active material layers to improve the overall capacity of the battery. However, these improvements have limited ability to improve the performance of the battery, so there is an urgent need to develop a lithium ion battery with high energy density, long cycle life and high safety. SUMMARY

[0004] Therefore, the present application aims to at least partially solve one of the problems in the related art. To this end, the present application provides a negative electrode sheet, a preparation method thereof and a battery, and the battery prepared by the negative electrode sheet has high energy density, long cycle life and high safety performance.

[0005] To solve the above technical problems, the present application is implemented as follows: According to one aspect of the present application, the embodiments of the present application provide a negative electrode sheet, which comprises: a current collector; a conductive layer disposed on at least one side surface of the current collector in the thickness direction, the conductive layer comprising a conductive agent; a first active layer disposed on the surface of the conductive layer away from the current collector, the first active layer comprising a first active material, the first active material comprising a graphite material coated with a conductive material; a second active layer disposed on the surface of the first active layer away from the conductive layer, the second active layer comprising a second active material, the second active material comprising a tin-containing composite material coated with an aromatic conductive polymer. a third active layer disposed on a surface of the second active layer distal from the first active layer, the third active layer comprising a third active material; wherein the third active material comprises a heteroatom-doped porous carbon material.

[0006] In some embodiments, the conductive material comprises a conductive polymer.

[0007] In some embodiments, the conductive polymer comprises at least one of polypyrrole, polyaniline, polyacetylene, or poly(3,4-ethylenedioxythiophene).

[0008] In some embodiments, the graphite material comprises artificial graphite and natural graphite, and a mass ratio of the artificial graphite and the natural graphite is (0.1-1):1.

[0009] In some embodiments, a mass ratio of the conductive material and the graphite material is (0.01-0.1):(8-12).

[0010] In some embodiments, the first active layer further comprises a first conductive agent and a first binder.

[0011] In some embodiments, a mass ratio of the first active material, the first conductive agent, and the first binder is (96-98):(0.1-1):(1-3).

[0012] In some embodiments, a thickness of the first active layer is 10-60 μm.

[0013] In some embodiments, the aromatic conductive polymer comprises at least one of polyaniline, a polyaniline derivative, polycarbazole, a polycarbazole derivative, polypyrrole, or a polypyrrole derivative.

[0014] In some embodiments, a mass ratio of the aromatic conductive polymer and the tin-containing composite material is (0.05-1):5.

[0015] In some embodiments, the tin-containing composite material comprises a tin-based material coated with a carbon material and a silicon-based material.

[0016] In some embodiments, the silicon-based material comprises at least one of silicon dioxide and silicon carbide.

[0017] In some embodiments, the tin-based material comprises at least one of tin dioxide and tin diselenide.

[0018] In some embodiments, the carbon material comprises at least one of carbon nanotubes, graphene, and fullerenes.

[0019] In some embodiments, the molar ratio of the silicon-based material to the tin-based material is (1-3):1.

[0020] In some embodiments, the molar ratio of the tin-based material to the carbon material is (1-2):(1-2).

[0021] In some embodiments, the second active layer further comprises a second conductive agent and a second binder.

[0022] In some embodiments, the mass ratio of the second active material, the second conductive agent, and the second binder is (96-98):(0.1-1):(1-3).

[0023] In some embodiments, the thickness of the second active layer is 10-60 μm.

[0024] In some embodiments, the heteroatom comprises a nitrogen atom.

[0025] In some embodiments, the doping rate of the heteroatom is 20-30%.

[0026] In some embodiments, the porosity of the heteroatom-doped porous carbon material is 75-85%.

[0027] In some embodiments, the third active layer further comprises a third conductive agent and a third binder.

[0028] In some embodiments, the mass ratio of the third active material, the third conductive agent, and the third binder is (96-98):(0.1-1):(1-3).

[0029] In some embodiments, the thickness of the third active layer is 10-60 μm.

[0030] According to another aspect of the present application, the embodiments of the present application provide a preparation method of a negative electrode sheet, comprising the following steps: coating a conductive paste on at least one side surface of the current collector to obtain a conductive layer; coating a first active paste on the surface of the conductive layer to obtain a first active layer; coating a second active paste on the surface of the first active layer to obtain a second active layer; coating a third active paste on the surface of the second active layer to obtain a third active layer; rolling the current collector coated with the conductive layer, the first active layer, the second active layer, and the third active layer; In some embodiments, the conductive paste comprises a conductive agent. The first active paste comprises a first active substance; The second active paste comprises a second active substance; The third active paste comprises a third active substance.

[0031] In some embodiments, the preparation of the conductive paste comprises mixing a conductive agent and a binder in a solvent to obtain the conductive paste.

[0032] In some embodiments, the mass ratio of the conductive agent to the binder in the conductive paste is (93-99):(1-7).

[0033] In some embodiments, the preparation of the first active paste comprises mixing a first active substance, a first conductive agent and a first binder in a solvent to obtain the first active paste.

[0034] In some embodiments, the preparation of the second active paste comprises mixing a second active substance, a second conductive agent and a second binder in a solvent to obtain the second active paste.

[0035] In some embodiments, the preparation of the third active paste comprises mixing a third active substance, a third conductive agent and a third binder in a solvent to obtain the third active paste.

[0036] In some embodiments, the compaction density of the rolling is 1.5 g / cm 3 ~1.7 g / cm 3 .

[0037] In some embodiments, the solvent is deionized water.

[0038] In some embodiments, the preparation method of the first active substance comprises: mixing a conductive polymer monomer, an initiator and a graphite material in a solvent, and obtaining the first active substance after stirring, standing and drying.

[0039] In some embodiments, the mass ratio of the conductive polymer monomer, the initiator and the graphite material is (0.01-0.1):(0.001-0.005):(8-12).

[0040] In some embodiments, the conductive polymer monomer comprises at least one of pyrrole, aniline, acetylene or 3,4-ethylenedioxythiophene.

[0041] In some embodiments, the initiator comprises at least one of perchloric acid, potassium dichromate, hydrogen peroxide or ammonium persulfate.

[0042] In some embodiments, the stirring time is 4-6 hours.

[0043] In some embodiments, the stirring temperature is 5-30°C.

[0044] In some embodiments, the standing time is 30-40 hours.

[0045] In some embodiments, the drying temperature is 80-120°C.

[0046] In some embodiments, the preparation method of the second active material comprises: mixing the silicon-based material with the tin-based material, ball-milling to complete coating of the silicon-based material on the tin-based material, then mixing with the carbon material, and sintering to obtain a tin-containing composite material; mixing the tin-containing composite material, the aromatic conductive polymer monomer, and the oxidizing agent in a solvent, and then performing a polymerization reaction to obtain the second active material.

[0047] In some embodiments, the ball-milling speed is 500-600 r / min, and the time is 6-12 hours.

[0048] In some embodiments, the sintering temperature is 600-1200°C, the time is 5-20 hours, and the heating rate is 1-10°C / min.

[0049] In some embodiments, the oxidizing agent comprises at least one of hydrogen peroxide, pyridinium chlorochromate, or pyridinium dichromate.

[0050] In some embodiments, the solvent comprises at least one of N-methylpyrrolidone, N,N-dimethylformamide, or acetone.

[0051] In some embodiments, the polymerization reaction temperature is 20-60°C, and the time is 2-8 hours.

[0052] In some embodiments, the preparation method of the third active material comprises: mixing a carbon source containing a heteroatom with a pore-forming agent, dissolving in water, and pre-carbonizing to obtain a pre-carbonized carbon material; sintering the pre-carbonized carbon material in an inert atmosphere to obtain the third active material.

[0053] In some embodiments, the pore-forming agent is at least one of potassium oxalate or calcium carbonate.

[0054] In some embodiments, the pre-carbonization step is performed under vacuum, and the pre-carbonization temperature is 150-180°C, and the pre-carbonization time is 8-12 hours.

[0055] In some embodiments, the pre-carbonized carbon material has a particle size of 4-25 microns before sintering.

[0056] In some embodiments, the sintering temperature is 700-800°C, the sintering time is 1-3 hours, and the heating rate is 2-4°C / min.

[0057] According to another aspect of the present application, the embodiments of the present application provide a battery comprising a negative electrode sheet, wherein the negative electrode sheet is the aforementioned negative electrode sheet or is prepared according to the aforementioned preparation method.

[0058] The technical solutions of the present application have at least the following beneficial effects: In the negative electrode sheet of the present application, a conductive layer is arranged between the current collector and the first active layer. The presence of the conductive layer can reduce the contact resistance between the first active layer and the current collector, improve the interaction force between the first active layer and the current collector, and avoid the peeling of the first active material. The first active material of the first active layer includes a graphite material coated with a conductive material. The first active layer can improve the capacity of the battery, and the graphite coated with the conductive material can improve the conductivity of the first active layer. The second active material is a tin-containing composite material coated with an aromatic conductive polymer. The tin-based composite material has a low volume expansion rate, a low interfacial resistance, and can improve the transmission performance of lithium ions, thereby improving the cycle stability and capacity retention rate of the battery. Further, the tin-based composite material is coated with an aromatic conductive polymer on the surface, which has conductivity and can contribute to a certain capacity (i.e., has a high energy storage capacity), thereby ensuring the conductivity of the second active material and improving the rate performance of the battery. The third active layer includes a porous carbon material doped with heteroatoms, wherein a large number of pores improve the storage capacity of lithium ions, effectively adapt to the volume change during lithium intercalation / deintercalation; a high specific surface area provides sufficient contact of the electrolyte with the electrode surface and enhances the charge transfer, thereby obtaining a very low transmission resistance; in addition, the doping of heteroatoms produces more defects, providing more active sites for storage, while inhibiting the decomposition of the electrolyte and the side reaction between the electrolyte and the electrode, thereby reducing the formation of SEI film. Furthermore, in the negative electrode sheet of the present application, the aromatic conductive polymer coated on the tin-based composite material in the second active layer can have π-π interaction and hydrogen bond interaction with the benzene ring in the porous carbon material doped with heteroatoms in the third active layer, thereby enhancing the interaction between the second active layer and the third active layer and effectively preventing the peeling of the two active layers. Thus, the lithium ion battery can have high energy density, long cycle life, and high safety.

[0059] Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the attendant drawings herein or can be learned by practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 SEM image of the third active material, nitrogen-doped porous carbon material, provided in Example 1 of the present application.

[0061] Figure 2 SEM image of the third active material, nitrogen-doped porous carbon material, provided in Example 1 of the present application.

[0062] 1 - mesoporous; 2 - microporous. DETAILED DESCRIPTION

[0063] The application will be further described with reference to the following examples. It should be understood that these examples are intended to illustrate the application and are not intended to limit the scope of the application.

[0064] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are provided as approximate descriptions of the ranges and are understood to be open-ended. Each range disclosed herein is to be understood to include individual values, and sub-ranges, falling within the stated range. In other words, any range disclosed herein is a continuum of values, and any value within the continuum can be selected as the endpoint of the range. In addition, any value within the continuum can be selected as the endpoint of a sub-range within the continuum. For example, if a range is disclosed as 1 to 5, it is understood that any number between 1 and 5, e.g., 1.1, 1.2, 1.3, 1.4, 1.5, 2, 3, 4, and 5, is contemplated for use as an endpoint of the range, as well as sub-ranges such as 1 to 3.3, and 3.3 to 5. It will be further understood that the endpoints of the ranges can be combined with one another to form further ranges.

[0065] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, if not specifically stated.

[0066] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, if not specifically stated.

[0067] All steps of the present application can be performed in sequence or randomly, preferably in sequence, if not specifically stated. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0068] As used herein, the terms "comprises", "comprising", "includes", "including" or "contains", "containing" means "including, but not limited to", unless otherwise specified. For example, the "comprises" and "comprising" can mean that it can also include or contain other components not listed, or can only include or contain the listed components.

[0069] Currently, the energy density and charging time of the battery are two important technical indicators, and the common method for improving the fast charging performance of lithium ion batteries in the market is to use modified lithium titanate, such as Chinese patent CN201510116652.6 discloses a composite titanium oxide negative electrode material and a fast-charging lithium ion battery containing the same, which mainly improves the cycle performance and rate performance of the battery by compounding two kinds of titanium oxide. However, when lithium titanate is used as a negative electrode material, the potential platform is as high as 1.55V, the energy density of the single cell is low, which limits the application field of lithium ion batteries of lithium titanate series. Therefore, it is urgent to develop a lithium ion battery with high energy density, long cycle life and high safety.

[0070] [Negative electrode sheet] Therefore, the negative electrode sheet provided by the embodiments of the present application comprises: a current collector; a conductive layer disposed on at least one side surface of the current collector in the thickness direction, the conductive layer comprising a conductive agent; a first active layer disposed on the surface of the conductive layer away from the current collector, the first active layer comprising a first active material, the first active material comprising a graphite material coated with a conductive material; a second active layer disposed on the surface of the first active layer away from the conductive layer, the second active layer comprising a second active material, the second active material comprising a tin-containing composite material coated with an aromatic conductive polymer; a third active layer disposed on the surface of the second active layer away from the first active layer, the third active layer comprising a third active material; wherein the third active material comprises a heteroatom-doped porous carbon material.

[0071] The provided silicon-doped negative electrode sheet has a multilayer structure, which comprises a current collector, a conductive layer, a first active layer, a second active layer and a third active layer stacked in sequence, that is, the conductive layer is disposed on at least one side surface of the current collector, the first active layer is disposed on the surface of the conductive layer, the second active layer is disposed on the surface of the first active layer, and the third active layer is disposed on the surface of the second active layer.

[0072] The "conductive layer is arranged on at least one surface of the current collector in the thickness direction" means that the conductive layer can be arranged on one surface of the current collector in the thickness direction of the current collector, or arranged on two surfaces of the current collector in the thickness direction of the current collector. The "surface" can be the entire area of the current collector, or a partial area of the current collector. In the embodiment, the surface can be the entire area of the current collector, and the application does not have a specific limitation, as long as the purpose of the application can be achieved.

[0073] For example, the current collector has two opposite surfaces in the thickness direction thereof, and the conductive layer is arranged on the two opposite surfaces of the current collector. Further, the first active layer is formed on the surfaces of the conductive layers on both sides. Further, the second active layer is formed on the surfaces of the first active layers on both sides. Further, the third active layer is formed on the surfaces of the second active layers on both sides. It can be understood that in other embodiments, the conductive layer can also be arranged on any one of the two surfaces of the current collector.

[0074] In the application, the material of the current collector in the negative electrode sheet is not specifically limited.

[0075] In the application, the conductive layer is arranged between the current collector and the first active layer in the negative electrode sheet. The presence of the conductive layer can reduce the contact resistance between the first active layer and the current collector, improve the force between the first active layer and the current collector, and avoid the peeling of the first active material.

[0076] In the application, the first active material of the first active layer in the negative electrode sheet includes a graphite material coated with a conductive material. The first active layer can improve the capacity of the battery, and the graphite coated with the conductive material can improve the conductivity of the first active layer.

[0077] In the application, the second active material in the negative electrode sheet is a tin-containing composite material coated with an aromatic conductive polymer. The tin-based composite material has a low volume expansion rate, a low interface resistance, and can improve the transmission performance of lithium ions, thereby improving the cycle stability and capacity retention rate of the battery. Further, the surface of the tin-based composite material is coated with an aromatic conductive polymer, which has conductivity and can contribute to a certain capacity (i.e. has a high energy storage capacity), thereby ensuring the conductivity of the second active material and improving the rate performance of the battery.

[0078] In the application, in the negative electrode sheet, the third active layer comprises a heteroatom-doped porous carbon material, wherein a large number of pores improve the storage capacity of lithium ions and effectively adapt to the volume change in the lithium intercalation / deintercalation process; a high specific surface area provides sufficient contact of the electrolyte with the electrode surface and enhances the charge transfer, thereby obtaining an extremely low transmission resistance; in addition, the doping of the heteroatom produces more defects, thereby providing more active sites for storage, and at the same time, the decomposition of the electrolyte and the side reaction between the electrolyte and the electrode can be inhibited, and the formation of the SEI film is reduced.

[0079] In addition, in the negative electrode sheet of the application, the aromatic conductive polymer coated on the surface of the tin-based composite material in the second active layer can have π-π interaction and hydrogen bond interaction with the benzene ring in the heteroatom-doped porous carbon material in the third active layer, thereby enhancing the interaction between the second active layer and the third active layer and effectively avoiding the peeling between the two active layers.

[0080] Therefore, the negative electrode sheet of the application comprises a current collector, a conductive layer, a first active layer, a second active layer and a third active layer which are sequentially stacked. By providing the conductive layer, the peeling between the negative active material layer and the negative current collector in the traditional double-layer coating mode can be avoided, and by limiting the composition of the second active layer and the third active layer, the accelerated decay of the battery capacity and even the occurrence of safety problems can be fundamentally avoided. At the same time, the lithium ion battery can have high energy density, long cycle life and high safety.

[0081] In some embodiments, the conductive layer further comprises a binder.

[0082] In some embodiments, the mass ratio of the conductive agent and the binder is (93-99):(1-7). For example, the mass ratio of the conductive agent and the binder can be 93:7, 94:6, 95:5, 97:3, etc., and of course can also be a certain ratio within the above range, which is not specifically limited herein.

[0083] In some embodiments, the conductive material comprises a conductive polymer.

[0084] In some embodiments, the conductive polymer comprises at least one of polypyrrole, polyaniline, polyacetylene or poly(3,4-ethylenedioxythiophene). For example, the conductive polymer can be polypyrrole, and can be polyaniline.

[0085] In some embodiments, the thickness of the conductive layer is 1 μm-5 μm. For example, the thickness of the conductive layer can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc., and of course can also be a certain value within the above range, which is not specifically limited herein.

[0086] In some embodiments, the graphite material includes artificial graphite and natural graphite, and the mass ratio of the artificial graphite to the natural graphite is (0.1-1):1. For example, the mass ratio of the artificial graphite to the natural graphite can be 0.1:1, 0.5:1, 1:1, or any ratio within the above range, without being specifically limited herein. In particular, the use of the mixture of the artificial graphite and the natural graphite has the following advantages: 1. synergistic enhancement of conductivity: the conductivities of the natural graphite and the artificial graphite have respective characteristics, the natural graphite has relatively high crystallinity and conductivity, and the artificial graphite has better structural uniformity and stable conductivity. The use of the mixture can take advantage of both and improve the charge-discharge performance of the battery. 2. better cost-effectiveness: the use of the natural graphite or the artificial graphite alone can have trade-off in cost-effectiveness, the natural graphite has relatively low cost but unstable performance, and the artificial graphite has stable performance but relatively high cost. The use of the mixture can optimize the cost while ensuring the performance and improve the economic benefit.

[0087] In some embodiments, the mass ratio of the conductive material to the graphite material is (0.01-0.1):(8-12). For example, the mass ratio of the conductive material to the graphite material can be 0.01:8, 0.05:10, 0.1:12, or any ratio within the above range, without being specifically limited herein.

[0088] In some embodiments, the first active layer further includes a first conductive agent and a first binder.

[0089] In some embodiments, the mass ratio of the first active material, the first conductive agent, and the first binder is (96-98):(0.1-1):(1-3). For example, the mass ratio of the first active material, the first conductive agent, and the first binder can be 96:0.1:1, 97:0.5:2, 98:1:3, or any ratio within the above range, without being specifically limited herein.

[0090] In some embodiments, the thickness of the first active layer is 10-60 μm. For example, the thickness of the first active layer can be 10 μm, 20 μm, 30 μm, 50 μm, 60 μm, or any value within the above range, without being specifically limited herein.

[0091] In some embodiments, the aromatic conductive polymer includes at least one of polyaniline, a polyaniline derivative, polycarbazole, a polycarbazole derivative, polypyrrole, or a polypyrrole derivative. For example, the aromatic conductive polymer can be polyaniline, a polyaniline derivative, or polycarbazole.

[0092] In some embodiments, the mass ratio of the aromatic conductive polymer to the tin-containing composite material is (0.05-1):5. For example, the mass ratio of the aromatic conductive polymer to the tin-containing composite material can be 0.05:5, 0.5:5, 1:5, or any value within the range, without being limited thereto.

[0093] In some embodiments, the tin-containing composite material comprises a tin-based material coated with a carbon material and a silicon-based material. More specifically, the silicon-based material is coated on the surface of the tin-based material, which can reduce the interaction between the tin-based material and the electrolyte, reduce the interfacial resistance, improve the transport performance of lithium ions, and inhibit the volume expansion, thereby improving the cycle stability and capacity retention rate of the battery. The carbon material can improve the conductivity of the tin-based material, thereby improving the rate performance of the battery as a whole.

[0094] In some embodiments, the tin-based material coated with the silicon-based material has a coating thickness of 1-10 nm. For example, the tin-based material coated with the silicon-based material can have a coating thickness of 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, or any value within the range, without being limited thereto.

[0095] In some embodiments, the silicon-based material comprises at least one of silicon dioxide and silicon carbide. For example, the tin-based material can be silicon dioxide, or silicon carbide.

[0096] In some embodiments, the tin-based material comprises at least one of tin dioxide and tin diselenide. For example, the tin-based material can be tin dioxide, or tin diselenide.

[0097] In some embodiments, the carbon material comprises at least one of carbon nanotubes, graphene, and fullerene. For example, the carbon material can be carbon nanotubes, graphene, or fullerene. The carbon material is preferably carbon nanotubes, which have mechanical support and can effectively inhibit the volume expansion of the tin-based material.

[0098] In some embodiments, the molar ratio of the silicon-based material to the tin-based material is (1-3):1. For example, the molar ratio of the silicon-based material to the tin-based material can be 1:1, 2:1, 3:1, or any value within the range, without being limited thereto.

[0099] In some embodiments, the molar ratio of the tin-based material to the carbon material is (1-2):(1-2). For example, the molar ratio of the tin-based material to the carbon material can be 1:1, 1:2, 2:1, or any value within the range, without being limited thereto.

[0100] In some embodiments, the second active layer further comprises a second conductive agent and a second binder.

[0101] In some embodiments, the mass ratio of the second active material, the second conductive agent, and the second binder is (96-98):(0.1-1):(1-3). For example, the mass ratio of the second active material, the second conductive agent, and the second binder can be 96:0.1:1, 97:0.5:2, 98:1:3, or any value within the above range, which is not specifically limited herein.

[0102] In some embodiments, the thickness of the second active layer is 10-60 μm. For example, the thickness of the second active layer can be 10 μm, 20 μm, 30 μm, 50 μm, 60 μm, or any value within the above range, which is not specifically limited herein.

[0103] In some embodiments, the heteroatom includes a nitrogen atom. The doping of the nitrogen atom can cause more defects in the porous carbon, provide more active sites for storing lithium ions, and inhibit the decomposition of the electrolyte and the side reaction between the electrolyte and the electrode, thereby reducing the formation of the SEI film.

[0104] In some embodiments, the doping rate of the heteroatom is 20%-30%. For example, the doping rate of the heteroatom can be 20%, 25%, 30%, or any value within the above range, which is not specifically limited herein.

[0105] In some embodiments, the porosity of the porous carbon material doped with the heteroatom is 75%-85%. For example, the porosity of the porous carbon material doped with the heteroatom can be 75%, 80%, 85%, or any value within the above range, which is not specifically limited herein.

[0106] In some embodiments, the pores of the porous carbon material doped with the heteroatom include micropores and mesopores, and the porous carbon material doped with the heteroatom has a micropore-mesopore crosslinked interpenetrating structure. The micropore-mesopore crosslinked interpenetrating structure allows lithium ion diffusion and electron transmission, and shortens the transmission path of the lithium ions. A large number of interconnected micropores provide a storage layer and improve the storage capacity of the lithium ions, and effectively adapt to the volume change in the lithium intercalation / deintercalation process. The micropore refers to a pore with a pore size of <2 nm, and the micropore usually has a very high specific surface area. The mesopore refers to a pore with a pore size of 2-50 nm, and the mesopore material has a high specific surface area and a three-dimensional pore structure. For specific differences, please refer to the description accompanying drawings. Figure 2 .

[0107] In some embodiments, the third active layer further includes a third conductive agent and a third binder.

[0108] In some embodiments, the mass ratio of the third active material, the third conductive agent, and the third binder is (96-98):(0.1-1):(1-3). For example, the mass ratio of the third active material, the third conductive agent, and the third binder can be 96:0.1:1, 97:0.5:2, 98:1:3, or any value within the above range, without being limited thereto.

[0109] In some embodiments, the thickness of the third active layer is 10-60 μm. For example, the thickness of the third active layer can be 10 μm, 20 μm, 30 μm, 50 μm, 60 μm, or any value within the above range, without being limited thereto.

[0110] It should be noted that the conductive agent, the first conductive agent, the second conductive agent, and the third conductive agent each independently include, but are not limited to, at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube, or graphene. The conductive carbon black includes acetylene black, Ketjen black, etc. The conductive carbon fiber includes vapor grown carbon fiber.

[0111] It should be further noted that the binder, the first binder, the second binder, and the third binder each independently include, but are not limited to, at least one of polyvinylidene fluoride, carboxymethyl cellulose, butadiene-styrene rubber, sodium alginate, or polyacrylic acid. For example, the first binder can be a mixture of carboxymethyl cellulose and butadiene-styrene rubber.

[0112] It can be understood that the mass ratio of the conductive agent and the binder, the mass ratio of the first active material, the first conductive agent, and the first binder, the mass ratio of the second active material, the second conductive agent, and the second binder, and the mass ratio of the third active material, the third conductive agent, and the third binder are related to the electrochemical performance of the corresponding battery, and further affect the structural stability of the negative electrode sheet. By controlling the proportion of each material in the conductive layer, the first negative electrode coating, the second negative electrode coating, and the third negative electrode coating within the above range, the functions among the materials are fully exerted, and the cycle performance, the fast-charging performance, and the structural stability of the negative electrode sheet are effectively improved.

[0113] It can be further understood that the surface thickness of the coating layer affects the electrical performance (such as energy density, cycle performance, and rate performance) of the battery, the preparation cost, and the safety performance. If the thickness of the conductive layer, the first active layer, the second active layer, and the third active layer is too large, the electron transmission distance increases, the electron resistance increases, the rate performance decreases, which adversely affects the electrical performance of the battery, and further increases the difficulty of thermal management of the battery. However, if the thickness of the conductive layer, the first active layer, the second active layer, and the third active layer is too low, the structural stability of the negative electrode sheet is not obviously improved, which adversely affects the safety and long-term cycle stability of the battery.

[0114] In some embodiments, the current collector comprises at least one of a copper foil, a foamed nickel, a nickel mesh, or a composite copper foil. As an example, the current collector can be a copper foil, or a foamed nickel.

[0115] Thus, based on the above scheme, in the negative electrode sheet of the present application, an electrically conductive layer is arranged between the current collector and the first active layer. The presence of the electrically conductive layer can reduce the contact resistance between the first active layer and the current collector, improve the force between the first active layer and the current collector, and avoid peeling of the first active material. The first active material of the first active layer comprises a graphite material coated with an electrically conductive material. The first active layer can improve the capacity of the battery, and the graphite coated with the electrically conductive material can improve the electrical conductivity of the first active layer. The second active material is a tin-containing composite material coated with an aromatic conductive polymer. The tin-based composite material has a low volume expansion rate, a low interfacial resistance, and can improve the transmission performance of lithium ions, thereby improving the cycle stability and capacity retention rate of the battery. Further, the surface of the tin-based composite material is coated with an aromatic conductive polymer, which itself has electrical conductivity and can contribute to a certain capacity (i.e., has a high energy storage capacity), thereby ensuring the electrical conductivity of the second active material and improving the rate performance of the battery. The third active layer comprises a porous carbon material doped with a heteroatom, which has a micro-mesoporous cross-linked interpenetrating structure. The micro-mesoporous cross-linked interpenetrating structure allows lithium ion diffusion and electron transmission, shortening the transmission path of lithium ions. A large number of interconnected micropores provide a storage layer, improve the storage capacity of lithium ions, and effectively adapt to the volume change during the lithium intercalation / deintercalation process; a high specific surface area provides sufficient contact of the electrolyte with the electrode surface and enhances the charge transfer, resulting in extremely low transmission resistance; in addition, the doping of the heteroatom produces more defects, providing more active sites for storage, while inhibiting the decomposition of the electrolyte and the side reactions between the electrolyte and the electrode, reducing the formation of SEI film. Furthermore, in the negative electrode sheet of the present application, the aromatic conductive polymer coated on the surface of the tin-based composite material in the second active layer interacts with the benzene rings in the porous carbon material doped with a heteroatom in the third active layer through π-π interaction and hydrogen bonding, enhancing the interaction between the second active layer and the third active layer and effectively preventing peeling between the two active layers. As a result, the lithium ion battery can have high energy density, long cycle life, and high safety.

[0116] [Method for preparing negative electrode sheet] According to another aspect of the present application, the embodiments of the present application provide a method for preparing a negative electrode sheet, comprising the following steps: coating an electrically conductive paste on at least one side surface of the current collector to obtain an electrically conductive layer; coating a first active paste on the surface of the electrically conductive layer to obtain a first active layer; coating a second active paste on the surface of the first active layer to obtain a second active layer; coating a third active slurry on the surface of the second active layer to obtain a third active layer; rolling the current collector coated with the conductive layer, the first active layer, the second active layer, and the third active layer; The conductive slurry comprises a conductive agent. The first active slurry comprises a first active substance. The second active slurry comprises a second active substance. The third active slurry comprises a third active substance.

[0117] It should be understood that all the features and advantages described above for the “negative electrode sheet” also apply to the “method for manufacturing the negative electrode sheet”, which will not be repeated here.

[0118] In some embodiments, the preparation of the conductive slurry comprises: uniformly mixing the conductive agent and the binder in the solvent to obtain the conductive slurry.

[0119] In some embodiments, the mass ratio of the conductive agent to the binder in the conductive slurry is (93-99):(1-7). For example, the mass ratio of the conductive agent to the binder can be 93:7, 94:6, 95:5, 97:3, etc., and of course can also be a certain ratio within the above range, which is not specifically limited here.

[0120] In some embodiments, the preparation of the first active slurry comprises: uniformly mixing the first active substance, the first conductive agent, and the first binder in the solvent to obtain the first active slurry.

[0121] In some embodiments, the mass ratio of the first active substance to the first conductive agent to the first binder is (96-98):(0.1-1):(1-3). For example, the mass ratio of the first active substance to the first conductive agent to the first binder can be 96:0.1:1, 97:0.5:2, 98:1:3, etc., and of course can also be a certain ratio within the above range, which is not specifically limited here.

[0122] In some embodiments, the preparation of the second active slurry comprises: uniformly mixing the second active substance, the second conductive agent, and the second binder in the solvent to obtain the second active slurry.

[0123] In some embodiments, the mass ratio of the second active substance to the second conductive agent to the second binder is (96-98):(0.1-1):(1-3). For example, the mass ratio of the second active substance to the second conductive agent to the second binder can be 96:0.1:1, 97:0.5:2, 98:1:3, etc., and of course can also be a certain ratio within the above range, which is not specifically limited here.

[0124] In some embodiments, the third active material is prepared by mixing a third active material, a third conductive agent and a third binder in a solvent to obtain a third active slurry.

[0125] In some embodiments, the mass ratio of the third active material, the third conductive agent and the third binder is (96-98):(0.1-1):(1-3). For example, the mass ratio of the third active material, the third conductive agent and the third binder can be 96:0.1:1, 97:0.5:2, 98:1:3, or any value within the above range.

[0126] In some embodiments, the solvent in the conductive slurry, the first active slurry, the second active slurry and the third active slurry can be deionized water.

[0127] In some embodiments, the coating process further includes a drying step. For example, the drying can be performed by using a 5-stage oven, and the temperature of each stage is 60°C, 80°C, 110°C, 110°C and 100°C, respectively.

[0128] In some embodiments, the compaction density of the rolling is 1.5 g / cm 3 -1.7 g / cm 3 . For example, the compaction density of the rolling can be 1.5 g / cm 3 , 1.6 g / cm 3 , 1.7 g / cm 3 , or any value within the above range.

[0129] [Preparation method of the first active material] In some embodiments, the preparation method of the first active material includes: mixing a conductive polymer monomer, an initiator and a graphite material in a solvent, and then stirring, standing and drying to obtain the first active material.

[0130] In some embodiments, the mass ratio of the conductive polymer monomer, the initiator and the graphite material is (0.01-0.1):(0.001-0.005):(8-12). For example, the mass ratio of the conductive polymer monomer, the initiator and the graphite material can be 0.01:0.001:8, 0.05:0.003:10, 0.1:0.005:12, or any value within the above range.

[0131] In some embodiments, the conductive polymer coated graphite material in the first active material has a coating thickness of 1 nm to 10 nm. For example, the coating thickness can be 1 nm, 4 nm, 8 nm, 10 nm, or the like, or any value within the range, without being limited thereto.

[0132] In some embodiments, the conductive polymer monomer includes at least one of pyrrole, aniline, acetylene, or 3,4-ethylenedioxythiophene. For example, the conductive polymer monomer can be pyrrole, can be aniline, or can be acetylene.

[0133] In some embodiments, the initiator includes at least one of perchloric acid, potassium dichromate, hydrogen peroxide, or ammonium persulfate. For example, the initiator can be perchloric acid, can be potassium dichromate, or can be hydrogen peroxide.

[0134] In some embodiments, the solvent includes at least one of water, ethanol, acetone, dimethylpyrrolidone, chloroform, butanol, or tetrahydrofuran. For example, the solvent can be water, can be ethanol, or can be a mixture of the two.

[0135] In some embodiments, the stirring time is 4 h to 6 h. For example, the stirring time can be 4 h, 5 h, 6 h, or the like, or any value within the range, without being limited thereto.

[0136] In some embodiments, the stirring temperature is 5°C to 30°C. For example, the stirring temperature can be 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, or the like, or any value within the range, without being limited thereto.

[0137] In some embodiments, the standing time is 30 h to 40 h. For example, the standing time can be 30 h, 35 h, 40 h, or the like, or any value within the range, without being limited thereto.

[0138] In some embodiments, the drying temperature is 80°C to 120°C. For example, the drying temperature can be 80°C, 100°C, 120°C, or the like, or any value within the range, without being limited thereto.

[0139] [Method for preparing second active material] In some embodiments, the method for preparing the second active material includes: mixing the silicon-based material and the tin-based material, coating the silicon-based material on the tin-based material after ball milling, and then mixing the coated material with a carbon material to obtain a tin-containing composite material after sintering; mixing the tin-containing composite material, the aromatic conductive polymer monomer, and the oxidizing agent in a solvent to perform a polymerization reaction, thereby obtaining the second active material.

[0140] In some embodiments, the molar ratio of silicon in the silicon-based material to tin in the tin-based material is (1-3):1. For example, the molar ratio of silicon in the silicon-based material to tin in the tin-based material can be 1:1, 2:1, 3:1, or any ratio within the above range, without being limited thereto.

[0141] In some embodiments, the rotation speed of the ball milling is 500-600 r / min, and the time is 6-12 h. For example, the rotation speed of the ball milling can be 500 r / min, 550 r / min, 600 r / min, or any value within the above range, without being limited thereto. The time of the ball milling can be 6 h, 9 h, 12 h, or any value within the above range, without being limited thereto.

[0142] In some embodiments, the mixing of the silicon-based material coated tin-based material and the carbon material comprises: after ultrasonic dispersion of the silicon-based material coated tin-based material and the carbon material in an ethanol solution, dissolving in an organic solution containing a binder and an additive, mechanically stirring until viscous, and vacuum drying. The binder comprises at least one of polyvinylidene fluoride, polyacrylic acid, or butadiene styrene rubber; and the additive comprises at least one of carboxymethyl cellulose, polyvinylpyrrolidone, or polyethylene glycol. The use of the additive can improve the dispersibility of the material.

[0143] The mass ratio of the silicon-based material coated tin-based material, the carbon material, the binder, the additive, and the organic solvent is (60-70):(10-20):(5-10):(0-5):(100-200). For example, the mass ratio of the silicon-based material coated tin-based material, the carbon material, the binder, the additive, and the organic solvent can be 60:10:5:0:100, 65:15:7:3:150, 70:20:10:5:200, or any ratio within the above range, without being limited thereto.

[0144] In some embodiments, the sintering temperature is 600-1200℃, the time is 5-20 h, and the heating rate is 1-10℃ / min. For example, the sintering temperature can be 600℃, 900℃, 1200℃, or any value within the above range, without being limited thereto. The sintering time can be 5 h, 10 h, 15 h, 20 h, or any value within the above range, without being limited thereto. The heating rate during sintering can be 1℃ / min, 5℃ / min, 10℃ / min, or any value within the above range, without being limited thereto.

[0145] In some embodiments, after mixing the tin-containing composite, the aromatic conductive polymer monomer, and the oxidizing agent in the solvent, a step of heating is further included, wherein the heating is performed to a temperature corresponding to a temperature at which the initiator initiates polymerization.

[0146] In the present application, via the above-mentioned sintering conditions, the following effects can be brought about: 1. Optimizing crystal structure: within the temperature range of 600-1200°C, the tin-containing composite can be fully crystallized to form a uniform and stable crystal structure, thereby improving the structural stability and electrochemical performance of the material.

[0147] 2. Improving material purity: the moderate sintering temperature helps to remove impurities and organic residues in the material, improving the purity of manganese lithium iron, reducing the occurrence of side reactions, and enhancing the cycle stability of the battery.

[0148] 3. Controlling particle size: the heating rate of 1-10°C / min helps to control the particle growth rate of the material, avoiding excessively large or small particles, thereby optimizing the specific surface area and conductivity of the material.

[0149] 4. Enhancing mechanical strength: the longer sintering time (5-20 hours) can promote the densification of the material, enhance the mechanical strength of the tin-containing composite, and reduce the material breakage and structural damage caused by volume change during charging and discharging.

[0150] 5. Improving electrochemical performance: appropriate sintering temperature and sintering time can optimize the electrochemical performance of the material, improving the charging and discharging efficiency, rate performance, and cycle life of the battery.

[0151] 6. Reducing energy consumption: while ensuring the performance of the material, selecting appropriate heating rate and sintering time can reduce energy consumption and improve the economic benefits of the preparation process.

[0152] In some embodiments, the oxidizing agent includes at least one of hydrogen peroxide, pyridinium chlorochromate, or pyridine dichromate. As an example, the oxidizing agent can be hydrogen peroxide, or pyridinium chlorochromate.

[0153] In some embodiments, the aromatic conductive polymer monomer includes at least one of aniline, aniline derivative, carbazole, carbazole derivative, pyrrole, or pyrrole derivative.

[0154] In some embodiments, the mass ratio of the tin-containing composite, the aromatic conductive polymer monomer, and the oxidizing agent is (10-20):(0.01-0.1):(0.001-0.005). For example, the mass ratio of the tin-containing composite, the aromatic conductive polymer monomer, and the oxidizing agent can be 10:0.01:0.001, 15:0.05:0.002, 20:0.1:0.005, or any ratio within the above range.

[0155] In some embodiments, the solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, or acetone. For example, the solvent can be N-methylpyrrolidone, or N,N-dimethylformamide.

[0156] In some embodiments, the temperature of the polymerization reaction is 20-60°C, and the time is 2-8 hours. For example, the temperature of the polymerization reaction can be 20°C, 40°C, 60°C, or any temperature within the above range. The time of the polymerization reaction can be 2 hours, 4 hours, 6 hours, 8 hours, or any time within the above range. Under the above reaction conditions, the aromatic conductive polymer monomer is polymerized in situ to obtain the aromatic conductive polymer-coated tin-containing composite, i.e., the second active material.

[0157] [Method for preparing the third active material] In some embodiments, the method for preparing the third active material includes: mixing the carbon source containing a heteroatom with a pore-forming agent, dissolving the mixture in water, and pre-carbonizing to obtain a pre-carbonized carbon material; sintering the pre-carbonized carbon material in an inert atmosphere to obtain the third active material.

[0158] In some embodiments, the mass ratio of the carbon source and the pore-forming agent is (1-3):1. For example, the mass ratio of the carbon source and the pore-forming agent can be 1:1, 2:1, 3:1, or any ratio within the above range.

[0159] In some embodiments, the carbon source includes an organic carbon containing a heteroatom, and preferably includes an organic carbon containing an N atom. For example, the carbon source can be D-glucosamine, or chitosan.

[0160] In some embodiments, the pore-forming agent is at least one of potassium oxalate or calcium carbonate. For example, the pore-forming agent can be potassium oxalate, or calcium carbonate; preferably, the pore-forming agent is a mixture of potassium oxalate and calcium carbonate. Further, the mass ratio of potassium oxalate and calcium carbonate is (8-12):1, and preferably 10:1.

[0161] In some embodiments, the carbon source and the pore-forming agent can be ground for 20-40 minutes, then dissolved in water, and then pre-carbonized. For example, the grinding time can be 20 minutes, 30 minutes, 40 minutes, etc., and can also be a value within the above range, which is not specifically limited herein.

[0162] In some embodiments, the pre-carbonization step is performed under vacuum conditions, and the pre-carbonization temperature is 150-180°C, and the pre-carbonization time is 8-12 hours. For example, the pre-carbonization temperature can be 150°C, 160°C, 180°C, etc., and can also be a value within the above range, which is not specifically limited herein. The pre-carbonization time can be 8 hours, 10 hours, 12 hours, etc., and can also be a value within the above range, which is not specifically limited herein.

[0163] In some embodiments, the particle size of the pre-carbonized carbon material before sintering is 4-25 μm. For example, the particle size of the pre-carbonized carbon material before sintering can be 4 μm, 10 μm, 15 μm, 25 μm, etc., and can also be a value within the above range, which is not specifically limited herein.

[0164] In some embodiments, the sintering is performed under an inert atmosphere, the sintering temperature is 700-800°C, the sintering time is 1-3 hours, and the heating rate is 2-4°C / min. For example, the sintering temperature can be 700°C, 750°C, 800°C, etc., and can also be a value within the above range, which is not specifically limited herein. The sintering time can be 1 hour, 2 hours, 3 hours, etc., and can also be a value within the above range, which is not specifically limited herein. The heating rate during sintering can be 2°C / min, 3°C / min, 4°C / min, etc., and can also be a value within the above range, which is not specifically limited herein.

[0165] In some embodiments, the nitrogen atom doping ratio can be controlled by the following methods: 1. Adjusting the sintering temperature: fewer amide bonds are broken at low temperatures, and the nitrogen atom retention rate is high; 2. Selecting the sintering atmosphere: inert atmosphere (Ar, N2) can reduce the reaction of nitrogen atoms with oxygen, and reduce nitrogen loss, which is a common condition for high nitrogen doping; 3. Adjusting the heating rate: slow heating (5-10°C / min) can allow the nitrogen-containing intermediates to fully react and embed in the carbon skeleton, and the nitrogen retention rate is higher.

[0166] In some embodiments, the sintered material further includes an acid washing step, preferably using dilute hydrochloric acid for acid washing to remove excess calcium and potassium salts, then using deionized water for washing, and then filtering after washing, and repeating multiple times until the pH = 7. The water-washed material is placed in a vacuum drying oven for drying treatment, and a heteroatom-doped porous carbon material is obtained.

[0167] Thus, based on the above scheme, in the negative electrode sheet of the present application, the preparation methods of the first active material, the second active material and the third active material are provided respectively, and they are used to prepare the first active layer, the second active layer and the third active layer respectively. The first active material of the first active layer includes a graphite material coated with a conductive material. Among them, the first active layer can improve the capacity of the battery, and at the same time, the graphite coated with the conductive material can improve the conductivity of the first active layer. The second active material is a tin-containing composite material coated with an aromatic conductive polymer. Among them, the tin-based composite material has a lower volume expansion rate, has a lower interfacial resistance, and can also improve the transmission performance of lithium ions, ultimately improving the cycle stability and capacity retention rate of the battery. Further, the surface of the tin-based composite material is also coated with an aromatic conductive polymer, which itself has conductivity and can also contribute to a certain capacity (i.e. has a higher energy storage capacity), thereby ensuring the conductivity of the second active material and improving the rate performance of the battery. The third active layer includes a porous carbon material doped with a heteroatom, which has a micro-mesoporous cross-linked interpenetrating structure. The micro-mesoporous cross-linked interpenetrating structure allows lithium ion diffusion and electron transmission, shortening the transmission path of lithium ions. Among them, a large number of interconnected micropores provide a storage layer, improve the storage capacity of lithium ions, and effectively adapt to the volume change during the lithium intercalation / deintercalation process; the high specific surface area provides sufficient contact of the electrolyte with the electrode surface and enhances the charge transfer, obtaining extremely low transmission resistance; in addition, the doping of the heteroatom will produce more defects, providing more active sites for storage, while inhibiting the decomposition of the electrolyte and the side reaction between the electrolyte and the electrode, reducing the formation of SEI film. In addition, in the negative electrode sheet of the present application, the aromatic conductive polymer coated on the surface of the tin-based composite material in the second active layer will have π-π interaction and hydrogen bond interaction with the benzene ring in the porous carbon material doped with a heteroatom in the third active layer, enhancing the interaction between the second active layer and the third active layer, and effectively avoiding the peeling between the two active layers. Thus, the lithium ion battery can have high energy density, long cycle life and high safety.

[0168] [Battery] Based on the same inventive concept, the embodiments of the present application provide a battery comprising the negative electrode sheet as described above, or prepared by the preparation method as described above.

[0169] The battery comprises the negative electrode sheet provided by the embodiments of the present application, and therefore has high energy density, long cycle life and high safety.

[0170] In some embodiments, the battery can be a lithium ion battery. The battery can be, for example, a winding type or a laminated type battery, and can be, for example, a square shell (aluminum shell, steel shell, etc.) battery, a soft package battery or a cylindrical battery, without limitation.

[0171] In some embodiments, the above battery further comprises a positive electrode sheet, an electrolyte and a separator. That is, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.

[0172] In the present embodiment, for the positive electrode sheet, the positive current collector, the conductive agent, the binder and other materials in the positive active material layer, the structure and the like are not limited, and the positive electrode sheet structure and the components that can be used for the secondary battery known in the art can be selected.

[0173] In the present embodiment, the specific material or type of the separator is not limited, and the separator that can be used for the secondary battery known in the art can be selected.

[0174] It should be further pointed out that the battery of the present application is not limited in terms of the specific material or type of the electrolyte, and the components and types that can be used for the secondary battery known in the art can be selected, as long as the purpose of the present application can be achieved.

[0175] Since the battery provided by the embodiment of the present application adopts all the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described here.

[0176] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not specified in the embodiments, it is carried out according to the technology or condition described in the literature in the art or according to the product instruction. If the reagent, material or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0177] Embodiment 1 S1: Preparation of conductive slurry The conductive carbon black, butadiene styrene rubber and polyvinylidene fluoride were mixed in deionized water at a mass ratio of 97:0.5:1.5 to obtain a conductive slurry; wherein the solid content of the conductive slurry was 40 wt%.

[0178] S2: Preparation of first active slurry The first active material, conductive carbon black, butadiene styrene rubber and carboxymethyl cellulose were mixed in deionized water at a mass ratio of 97:0.5:1.5:1 to obtain a first active slurry; wherein the solid content of the first active slurry was 40 wt%.

[0179] The preparation of the first active material comprises: at room temperature, 3,4-ethylenedioxythiophene is dissolved in anhydrous ethanol, stirred for 5h, then artificial graphite, natural graphite and hydrogen peroxide are added, heated to 50℃ and continue to stir for 5h, then the sample is left to stand for 36h, then the solvent is evaporated and dried at 100℃ to obtain the target product coated graphite composite material; The mass ratio of 3,4-vinyldioxylthiophene, artificial graphite, natural graphite and hydrogen peroxide is 0.05:5:5:0.003. The coating thickness of the conductive polymer graphite material coated on the first active material is 10 nm.

[0180] S3: Preparation of the second active slurry The second active material, conductive carbon black, styrene-butadiene rubber and carboxymethyl cellulose are mixed in deionized water at a mass ratio of 97:0.5:1.5:1 to obtain a second active slurry; wherein the solid content of the second active slurry is 40 wt%.

[0181] The preparation of the second active material includes: mixing SiO2 and SnO2 nanoparticles at a molar ratio of 1:1, and then ball milling at a speed of 500 revolutions / min for 12 h. The prepared modified SnO2 and CNT (carbon nanotube) are respectively placed in an ethanol solution and ultrasonically dispersed for a certain time. Then, the above dispersed solution is poured into an organic solution (organic solvent is methanol) containing polyvinylidene fluoride and carboxymethyl cellulose in proportion. Then mechanically stir until the solution becomes viscous, and dry the sample in a vacuum at 65℃ until the solvent is completely volatilized. Carbonize and sinter the dried solid, wherein the sintering temperature is 1000℃, the heating rate is 4℃ / min, and the sintering time is 8h. Finally, a tin-containing composite material is obtained. The tin-containing composite material, pyrrole and hydrogen peroxide are mixed in N-methyl pyrrolidone, and then reacted at 55℃ for 6h to obtain the second active material.

[0182] The mass ratio of modified SnO2, CNT, polyvinylidene fluoride, carboxymethyl cellulose and methanol is 70:20:5:5:200.

[0183] The mass ratio of the tin-containing composite material, pyrrole and oxidizing agent is 10:0.1:0.005.

[0184] S4: Preparation of the third active slurry The third active material, conductive carbon black, styrene-butadiene rubber and carboxymethyl cellulose are mixed in deionized water at a mass ratio of 97:0.5:1.5:1 to obtain a third active slurry; wherein the solid content of the third active slurry is 40 wt%.

[0185] The preparation of the third active substance involves mixing D-glucosamine (a carbon source) and a pore-forming agent in a mass ratio of 2:1. The mixture is then ground in an agate mortar for 30 minutes. The ground mixture is then transferred to a polytetrafluoroethylene (PTFE) beaker, and an appropriate amount of deionized water is added to dissolve the solid mixture by stirring. The mixture is then pre-carbonized in a vacuum drying oven at 160°C for 10 hours. After pre-carbonization, the solid in the beaker is transferred to a mortar and ground into a powder (to a particle size of 10 μm). The powder is then placed in a porcelain boat, placed in a tube furnace, and purged with argon. Under an argon atmosphere, the temperature is increased at a rate of 3°C / min to 750°C and held for 2 hours to produce a black powder. The fired black powder is then washed in a beaker with dilute hydrochloric acid to remove excess calcium and potassium salts, then washed with deionized water and filtered. This process is repeated multiple times until the pH reaches 7. The washed material is placed in a vacuum drying oven for drying (temperature is 120°C) to obtain the third active substance.

[0186] The pore-forming agent is a mixture of potassium oxalate and calcium carbonate with a mass ratio of 10:1; the nitrogen atom doping rate is 25%; and the porosity is 80%. Figures 1 and 2 It can be seen that the nitrogen-doped porous carbon material has a loose and porous structure, with micropores with a diameter of less than 2 nm and mesopores with a diameter of 2-50 nm distributed, and has a large number of interconnected micropores and interconnected porous structures.

[0187] S5: coating Using a coating machine, the conductive slurry was uniformly coated on the first surface of a 6μm thick copper foil. On the first surface of the negative electrode current collector, the conductive slurry was coated starting from one end of the negative electrode current collector and ending at the other end to form a conductive coating. The first active slurry was coated on the surface of the conductive coating, and the first drying process was carried out. After drying, the second active slurry was coated, and the second drying process was carried out. After drying, the third active slurry was coated, and the third drying process was carried out. The coating speed was 5m / min. After coating, it was dried in a 5-stage oven, and the temperature of each oven was 60℃, 80℃, 110℃, 110℃, and 100℃ respectively. The thickness of the conductive coating was 3μm, the thickness of the first active layer was 60μm, the thickness of the second active layer was 20μm, and the thickness of the third active layer was 20μm. Repeat the coating to complete the coating of the second surface of the copper foil opposite to the first surface, and then use a roller press to pressurize it to obtain a compaction density of 1.65g / cm 3 The negative electrode.

[0188] Example 2 The difference between Example 2 and Example 1 is that the thickness of the second active layer is 40 μm.

[0189] Example 3 Example 3 differs from Example 1 in that the thickness of the third active layer is 40 μm.

[0190] Example 4 Example 4 differs from Example 1 in that the thickness of the conductive layer is 5 μm.

[0191] Example 5 Example 5 differs from Example 1 in that the mass ratio of artificial graphite to natural graphite is 0.5:1 when preparing the first active material.

[0192] Example 6 Example 6 differs from Example 1 in that the carbon material used when preparing the second active material is fullerene.

[0193] Example 7 Example 7 differs from Example 1 in that the third active material is prepared as follows: D-glucosamine (carbon source) is mixed with a pore-forming agent in a mass ratio of 2:1, and then ground in a marver for 30 min. The ground mixture is then transferred to a PTFE beaker, and an appropriate amount of deionized water is added to stir and dissolve the solid mixture. The mixture is then placed in a vacuum drying oven and pre-carbonized at 160°C for 10 h. After the pre-carbonization is complete, the solid in the beaker is transferred to a mortar and ground into a powder (ground to a particle size of 10 μm). Finally, the solid powder material is placed in a porcelain boat, which is then placed in a tube furnace and purged with argon. The temperature is raised to 700°C at a rate of 2°C / min, and then held for 2 h to obtain a black powder. The black powder after firing is placed in a beaker and acid washed with dilute hydrochloric acid to remove excess calcium and potassium salts. The material is then washed with deionized water, filtered, and repeated multiple times until the pH = 7. The water-washed material is then dried in a vacuum drying oven (temperature of 120°C) to obtain the third active material.

[0194] In this example, the pore-forming agent is a mixture of potassium oxalate and calcium carbonate in a mass ratio of 10:1; the doping rate of nitrogen atoms is 30%; and the porosity is 85%.

[0195] Comparative Example 1 Comparative Example 1 differs from Example 2 in that it does not contain a third active layer.

[0196] Comparative Example 2 Comparative Example 2 differs from Example 2 in that it does not contain a second active layer.

[0197] Comparative Example 3 Comparative Example 3 differs from Example 2 in that it does not contain a first active layer.

[0198] Comparative Example 4 Comparative Example 4 differs from Example 2 in that artificial graphite and natural graphite are directly used as the first active material; and a composite of SnO2 and CNT is directly used as the second active material.

[0199] The preparation of the first active material includes: mixing artificial graphite and natural graphite at a mass ratio of 1:1, and then ball milling for 0.5 h at a rotation speed of 600 r / min.

[0200] The preparation of the second active material includes: respectively placing SnO2 and CNT (carbon nanotube) into an ethanol solution for ultrasonic dispersion for a certain time. Subsequently, the above-mentioned solution after the dispersion treatment is poured into an organic solution (organic solvent is methanol) containing polyvinylidene fluoride and carboxymethyl cellulose in proportion. Then, mechanical stirring is performed until the solution becomes viscous, and the sample is dried in a vacuum at 65°C until the solvent is completely volatilized. Carbonization sintering is performed on the dried solid, wherein the sintering temperature is 1000°C, the temperature rising speed is 4°C / min, and the sintering time is 8 h. The mass ratio of SnO2, carbon material, polyvinylidene fluoride, carboxymethyl cellulose and methanol is 70:20:5:5:200.

[0201] Performance test 1. Preparation of the battery Preparation of the positive electrode sheet: LiCoO2, a positive electrode active material, a binder polyvinylidene fluoride (PVDF) and a conductive agent conductive carbon black (SP) are dissolved in N-methyl pyrrolidone (NMP) in a mass ratio of 97%:1.5%:1.5% to uniformly stir and prepare a slurry, which is uniformly coated on the surfaces of both sides of a positive electrode current collector aluminum foil, and then baked at 100-150°C for 4-8 h. After cold pressing and slitting, a positive electrode sheet of a lithium ion battery is prepared, and the compacted density is 4.1 g / cm 3 , and the thickness of the single-sided positive electrode active material layer is 62 μm.

[0202] Separator film: a composite separator film of a polyethylene film (9 μm) + double-sided adhesive coating (single-sided adhesive thickness 3 μm) + single-sided ceramic (3 μm) is selected as the separator film.

[0203] Electrolyte: in an inert gas-filled glove box, ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate and propane lactone are mixed in a mass ratio of 1:1:1:1:1 to obtain an organic solvent, and then lithium salt LiPF6 is dissolved in the organic solvent to obtain an electrolyte, wherein the concentration of the lithium salt is 1.2 mol / L.

[0204] Battery assembly: the positive electrode sheet, the separator film and the negative electrode sheet are arranged in sequence, and then a winding structure of a winding core wrapped by a positive electrode is prepared by using a winding machine. The winding core is packaged with an aluminum plastic film, baked in a vacuum state for 48 h to remove moisture, and then injected with the electrolyte. The battery is subjected to conventional formation and sorting to obtain a square soft package lithium ion battery.

[0205] 2. Electrochemical performance test of the battery The assembled CR2032 button cell was tested by constant current charge / discharge test using LAND CT2001A battery test system, and the charge / discharge voltage window was 2 V ~ 4.3 V.

[0206] (1) Cycle life and battery cycle expansion rate test: the battery was charged to 4.45 V at 1.5C rate, then charged at 4.45 V, the cutoff current was 0.025C, then discharged at 0.5C rate, the cutoff voltage was 3 V, which was one charge-discharge cycle process, and the charge-discharge cycle process was repeated until the capacity retention rate of the battery was less than 80% or the cycle number reached 800 times; at the same time, the battery cycle expansion rate of the battery at a certain cycle number was tested, and the calculation method was: the thickness of the battery at full charge before cycling was tested by a thickness tester as the initial thickness, and the thickness of the battery at full charge after every 100 cycles was tested and recorded, and the cycle expansion rate was (cycle full charge under the platform thickness / initial full charge thickness)*100%.

[0207] (2) Charge capacity (maximum chargeable current): the maximum chargeable current when the negative electrode does not produce metal lithium at 25℃.

[0208] (3) Charge time: the total time when the battery is charged from 3.0 V to 4.35 V at the maximum chargeable current and is fully charged at 4.35 V at 0.025C at 25℃.

[0209] The test results of each example and comparative example are shown in Table 1.

[0210] Table 1 From Examples 1 to 3, it can be seen that the performance of Example 2 is the best, that is, when the coating thickness ratio of the first active material layer, the second active material layer and the third active material layer is 3:2:1, the energy density reaches 728 mWh / L, the battery cycle expansion rate is 6.1% @800 times, the cycle life meets 800 times, and the charge capacity is 1.55C. In addition, the overall electrochemical performance of the battery prepared by the negative electrode sheet of the example is significantly better than that of the comparative example.

[0211] From the test data of Examples 4 to 7, it can be seen that the suitable ratio of artificial graphite and natural graphite in the first layer of active material, the second active material being a tin-containing composite material, and the suitable nitrogen atom doping rate and porosity of the porous carbon material in the third active material layer, together affect the performance of the battery, so that the battery has high energy density, good cycle performance and fast charging capacity.

[0212] From the test results of Example 2 and Comparative Example 1, it can be seen that the battery prepared in Example 2 has a longer cycle life, higher charging capacity, higher charging rate, and lower battery expansion rate. This is because, compared with Comparative Example 1, Example 2 has a third active material coating, i.e., a layer of nitrogen-doped porous carbon material, which can effectively reduce the expansion rate of the battery. The specific reasons are as follows: Improve the conductivity of the electrode material: nitrogen-doped porous carbon material has good conductivity, which can improve the overall conductivity of the positive electrode material, thereby reducing the thermal expansion caused by increased resistance during charging and discharging; active material volume change: porous carbon material can provide additional space to accommodate the volume change of active materials (such as silicon or tin lithium alloy) during charging and discharging, thereby reducing the electrode expansion caused by volume change; enhance interface stability: porous carbon material can improve the interface stability between electrode material and electrolyte through coating and modification technology, reduce side reactions and gas generation, and further reduce the expansion rate of the battery; optimize electrode structure: the introduction of porous carbon material can optimize the microstructure of the electrode, improve the diffusion path of lithium ions, and reduce the stress accumulation during lithium ion intercalation / deintercalation, thereby reducing the expansion of the electrode.

[0213] Further, since the anode sheet of Example 2 has an additional third active layer compared with Comparative Example 1, the nitrogen-doped porous carbon multi-level pore structure in the third active layer allows lithium ion diffusion and electron transport, shortening the lithium ion transport path. Among them, a large number of interconnected micropores provide storage, improve the Li + storage capacity, effectively adapt to the volume change during Li intercalation / deintercalation; high specific surface area provides sufficient contact of electrolyte with electrode surface and enhances charge transfer, obtaining extremely low transport resistance; in addition, the doping of nitrogen element produces more defects, providing more active sites for storage, while inhibiting the decomposition of electrolyte and the side reaction between electrolyte and electrode, reducing the formation of SEI film. Thus, the battery has a longer cycle life, higher charging capacity, and higher charging rate.

[0214] From the test results of Example 2 and Comparative Example 2, it can be seen that the presence of the second active layer can significantly improve the energy density of the battery, and the battery exhibits low cycle expansion rate. This is because the second active layer is a composite material of SnO2 and CNT with a surface coated with conductive polymer, and SnO2 is a modified material with a surface coated with SiO2. The conductivity and mechanical support of CNT material can effectively inhibit the volume expansion of tin-based anode material, and the coating of SiO2 on the surface of SnO2 can reduce its interaction with electrolyte, reduce the interfacial resistance, improve the transport performance of lithium ions, and at the same time inhibit the volume expansion, improve the cycle stability and capacity retention rate.

[0215] From the test results of Example 2 and Comparative Example 3, it can be seen that the role of the graphite layer in the coating of the pole piece is: 1. to improve the energy density and the diffusion rate of lithium ions, promote the rapid embedding and extraction of lithium ions, thereby promoting the rapid embedding and extraction of lithium ions under high-rate charging and discharging conditions, improving the charging capacity of the battery, and shortening the charging time From the test results of Example 2 and Comparative Example 4, it can be seen that the SiO2 contained in the second layer of active material can significantly improve the energy density of the material; at the same time, the silicon-based material can provide channels for lithium ion embedding and extraction from various directions, making the transmission of lithium ions more smooth, thereby greatly shortening the charging time The part of the present application not described in detail is the technology known to those skilled in the art.

[0216] The above describes the basic principles of the present application in combination with specific embodiments, but it should be pointed out that the advantages, advantages, effects, etc. mentioned in the present application are only examples and not limitations, and these advantages, advantages, effects, etc. cannot be considered as the must-have of each embodiment of the present application. In addition, the above specific details disclosed are only for the purpose of example and for the purpose of understanding, and the above details do not limit the present application to the above specific details.

[0217] It should be noted that the term "and / or" or " / " used herein is only to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the existence of A alone, the existence of A and B, and the existence of B alone. The singular form "one", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural form, unless the context clearly indicates otherwise.

[0218] In the detailed description and claims, a list of items connected by the term "at least one of", "at least one", "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0219] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A negative electrode sheet, characterized in that: The negative electrode sheet comprises: current collector; a conductive layer disposed on at least one surface of the current collector along the thickness direction, the conductive layer comprising a conductive agent; a first active layer, disposed on a surface of the conductive layer away from the current collector, the first active layer comprising a first active material, the first active material comprising a graphite material coated with a conductive material; a second active layer disposed on a surface of the first active layer away from the conductive layer, the second active layer comprising a second active material comprising a tin-containing composite material coated with an aromatic conductive polymer; a third active layer, disposed on a surface of the second active layer away from the first active layer, the third active layer comprising a third active material; Wherein, the third active material includes a heteroatom-doped porous carbon material.

2. The negative electrode sheet according to claim 1, characterized in that: The first active layer satisfies at least one of the following characteristics (1) to (5): (1) The conductive material includes a conductive polymer; The conductive polymer includes at least one of polypyrrole, polyaniline, polyacetylene or poly (3,4-ethylenedioxythiophene); (2) The graphite material includes artificial graphite and natural graphite, and the mass ratio of the artificial graphite to the natural graphite is (0.1~1):1; (3) The mass ratio of the conductive material to the graphite material is (0.01-0.1): (8-12); (4) The first active layer further includes a first conductive agent and a first adhesive; The mass ratio of the first active material, the first conductive agent, and the first binder is (96-98): (0.1-1): (1-3); (5) The thickness of the first active layer is 10 μm to 60 μm.

3. The negative electrode sheet according to claim 1, characterized in that: The second active layer satisfies at least one of the following characteristics (1) to (5): (1) The aromatic conductive polymer includes at least one of polyaniline, a polyaniline derivative, polycarbazole, a polycarbazole derivative, polypyrrole, or a polypyrrole derivative; (2) The mass ratio of the aromatic conductive polymer to the tin-containing composite material is (0.05-1):5; (3) The tin-containing composite material includes a tin-based material coated with a carbon material and a silicon-based material; The silicon-based material includes at least one of silicon dioxide and silicon carbide; The tin-based material includes at least one of tin dioxide and tin diselenide; The carbon material includes at least one of carbon nanotubes, graphene, and fullerene; The molar ratio of the silicon-based material to the tin-based material is (1-3):1; The molar ratio of the tin-based material to the carbon material is (1-2): (1-2); (4) The second active layer further includes a second conductive agent and a second adhesive; The mass ratio of the second active material, the second conductive agent, and the second binder is (96-98): (0.1-1): (1-3); (5) The thickness of the second active layer is 10 μm to 60 μm.

4. The negative electrode sheet according to claim 1, characterized in that: The third active layer satisfies at least one of the following characteristics (1) to (5): (1) The heteroatom includes a nitrogen atom; (2) The doping rate of the heteroatom is 20% to 30%; (3) The porosity of the heteroatom-doped porous carbon material is 75% to 85%; (4) The third active layer further includes a third conductive agent and a third binder; The mass ratio of the third active material, the third conductive agent, and the third binder is (96-98): (0.1-1): (1-3); (5) The thickness of the third active layer is 10 μm to 60 μm.

5. The method for preparing a negative electrode sheet according to any one of claims 1 to 4, wherein: The following steps are involved: Coating a conductive slurry on at least one side of the current collector to obtain a conductive layer; Coating a first active slurry on the surface of the conductive layer to obtain a first active layer; Coating a second active slurry on the surface of the first active layer to obtain a second active layer; coating a third active slurry on the surface of the second active layer to obtain a third active layer; Roll-pressing the current collectors coated with the conductive layer, the first active layer, the second active layer, and the third active layer; Wherein, the conductive paste includes a conductive agent; The first active slurry includes a first active material; The second active slurry includes a second active material; The third active slurry includes a third active material.

6. The method for preparing a negative electrode sheet according to claim 5, wherein: The preparation of the conductive paste comprises: uniformly mixing a conductive agent and a binder in a solvent to obtain a conductive paste; The preparation of the first active slurry includes: uniformly mixing a first active material, a first conductive agent and a first binder in a solvent to obtain a first active slurry; The preparation of the second active slurry includes: uniformly mixing a second active material, a second conductive agent, and a second binder in a solvent to obtain a second active slurry; The preparation of the third active slurry includes: uniformly mixing a third active material, a third conductive agent and a third binder in a solvent to obtain a third active slurry; The mass ratio of the conductive agent to the binder in the conductive paste is (93-99): (1-7); The compacted density of the roller is 1.5 g / cm 3 ~1.7 g / cm 3 ; The solvent is deionized water.

7. The method for preparing a negative electrode sheet according to claim 5, wherein: The preparation method of the first active substance comprises: The conductive polymer monomer, the initiator, and the graphite material are mixed in a solvent, and the mixture is stirred, allowed to stand, and dried to obtain a first active material; The mass ratio of the conductive polymer monomer, initiator and graphite material is (0.01-0.1): (0.001-0.005): (8-12); The conductive polymer monomer includes at least one of pyrrole, aniline, acetylene or 3,4-ethylenedioxythiophene; The initiator includes at least one of perchloric acid, potassium dichromate, hydrogen peroxide or ammonium persulfate; The stirring time is 4h~6h; The stirring temperature is 5°C to 30°C; The standing time is 30h~40h; The drying temperature is 80°C to 120°C.

8. The method for preparing a negative electrode sheet according to claim 5, wherein: The preparation method of the second active substance comprises: The silicon-based material and the tin-based material are mixed, ball-milled to coat the tin-based material with the silicon-based material, and then mixed with the carbon material and sintered to obtain a tin-containing composite material; The tin-containing composite material, aromatic conductive polymer monomer, and oxidant are mixed in a solvent and subjected to polymerization reaction to obtain a second active material; The ball milling speed is 500 r / min ~ 600 r / min, and the time is 6h ~ 12h; The sintering temperature is 600°C to 1200°C, the sintering time is 5h to 20h, and the heating rate is 1°C / min to 10°C / min; The oxidant comprises at least one of hydrogen peroxide, pyridinium chlorochromate or pyridinium dichromate; The solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide or acetone; The polymerization reaction temperature is 20° C. to 60° C., and the reaction time is 2 h to 8 h.

9. The method for preparing a negative electrode sheet according to claim 5, wherein: The preparation method of the third active substance includes: A carbon source containing heteroatoms is mixed with a pore-forming agent and dissolved in water for pre-carbonization to obtain a pre-carbonized carbon material; sintering the pre-carbonized carbon material under an inert atmosphere to obtain a third active material; The pore-forming agent is at least one of potassium oxalate or calcium carbonate; The pre-carbonization step is carried out under vacuum conditions, the pre-carbonization temperature is 150° C. to 180° C., and the time is 8 h to 12 h; The particle size of the pre-carbonized carbon material before sintering is 4 μm to 25 μm; The sintering temperature is 700° C. to 800° C., the sintering time is 1 h to 3 h, and the heating rate is 2° C. / min to 4° C. / min.

10. A battery comprising a negative electrode sheet, characterized in that: The negative electrode sheet includes the negative electrode sheet according to any one of claims 1 to 4, or includes the negative electrode sheet prepared by the preparation method according to any one of claims 5 to 9.

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