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

Abstract

The application relates to the technical field of batteries, in particular to a negative electrode sheet, a preparation method thereof and a battery. The negative electrode sheet comprises: a current collector; a conductive layer arranged on at least one side surface of the current collector in the thickness direction, wherein the conductive layer comprises a conductive agent; a first active layer arranged on the surface of the conductive layer away from the current collector, wherein the first active layer comprises a first active substance, and the first active substance comprises graphite material coated with conductive material; a second active layer arranged on the surface of the first active layer away from the conductive layer, wherein the second active layer comprises a second active substance, and the second active substance comprises tin-containing composite material coated with aromatic conductive polymer; and a third active layer arranged on the surface of the second active layer away from the first active layer, wherein the third active layer comprises heteroatom-doped porous carbon material. The lithium ion battery comprising the negative electrode sheet has 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 advantages of high specific capacity, high working voltage, long service life, no memory effect, etc. as new energy, and automobile energy storage devices with lithium ion batteries are 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 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 cause the capacity to sharply decrease, accompanied by safety problems.

[0003] Existing solutions include, for example, using negative active materials with different compaction densities to improve the liquid retention 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 battery performance, 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:

[0006] According to one aspect of the present application, the embodiments of the present application provide a negative electrode sheet, which comprises:

[0007] a current collector;

[0008] 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;

[0009] 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;

[0010] a second active layer disposed on a surface of the first active layer distal from the conductive layer, the second active layer comprising a second active material, the second active material comprising an aromatic conductive polymer-coated tin-containing composite material;

[0011] 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;

[0012] wherein the third active material comprises a heteroatom-doped porous carbon material.

[0013] In some embodiments thereof, the conductive material comprises a conductive polymer.

[0014] In some embodiments thereof, the conductive polymer comprises at least one of polypyrrole, polyaniline, polyacetylene, or poly(3,4-ethylenedioxythiophene).

[0015] In some embodiments thereof, the graphite material comprises artificial graphite and natural graphite, a mass ratio of the artificial graphite and the natural graphite being (0.1-1):1.

[0016] In some embodiments thereof, a mass ratio of the conductive material and the graphite material is (0.01-0.1):(8-12).

[0017] In some embodiments thereof, the first active layer further comprises a first conductive agent and a first binder.

[0018] In some embodiments thereof, a mass ratio of the first active material, the first conductive agent, and the first binder is (96-98):(0.1-1):(1-3).

[0019] In some embodiments thereof, a thickness of the first active layer is 10-60 μm.

[0020] In some embodiments thereof, the aromatic conductive polymer comprises at least one of polyaniline, a polyaniline derivative, polycarbazole, a polycarbazole derivative, polypyrrole, or a polypyrrole derivative.

[0021] In some embodiments thereof, a mass ratio of the aromatic conductive polymer and the tin-containing composite material is (0.05-1):5.

[0022] In some embodiments thereof, the tin-containing composite material comprises a tin-based material coated with a carbon material and a silicon-based material.

[0023] In some embodiments thereof, the silicon-based material comprises at least one of silicon dioxide and silicon carbide.

[0024] In some embodiments, the tin-based material includes at least one of tin dioxide and tin diselenide.

[0025] In some embodiments, the carbon material includes at least one of carbon nanotubes, graphene, and fullerenes.

[0026] In some embodiments, the molar ratio of the silicon-based material to the tin-based material is (1-3): 1.

[0027] In some embodiments, the molar ratio of the tin-based material to the carbon material is (1-2):(1-2).

[0028] In some embodiments, the second active layer further includes a second conductive agent and a second binder.

[0029] 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).

[0030] In some embodiments, the thickness of the second active layer is 10 μm-60 μm.

[0031] In some embodiments, the heteroatom includes a nitrogen atom.

[0032] In some embodiments, the doping rate of the heteroatom is 20%-30%.

[0033] In some embodiments, the porosity of the heteroatom-doped porous carbon material is 75%-85%.

[0034] In some embodiments, the third active layer further includes a third conductive agent and a third binder.

[0035] 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).

[0036] In some embodiments, the thickness of the third active layer is 10 μm-60 μm.

[0037] According to another aspect of the present application, the embodiments of the present application provide a preparation method of a negative electrode sheet, including the following steps:

[0038] coating a conductive paste on at least one side surface of the current collector to obtain a conductive layer;

[0039] coating a first active paste on a surface of the conductive layer to obtain a first active layer;

[0040] coating a second active paste on the surface of the first active layer to obtain a second active layer;

[0041] coating a third active paste on the surface of the second active layer to obtain a third active layer;

[0042] rolling the current collector coated with the conductive layer, the first active layer, the second active layer and the third active layer;

[0043] wherein the conductive paste comprises a conductive agent;

[0044] the first active paste comprises a first active substance;

[0045] the second active paste comprises a second active substance;

[0046] the third active paste comprises a third active substance.

[0047] In some embodiments, the preparation of the conductive paste comprises: uniformly mixing a conductive agent and a binder in a solvent to obtain the conductive paste.

[0048] In some embodiments, the mass ratio of the conductive agent to the binder in the conductive paste is (93-99):(1-7).

[0049] In some embodiments, the preparation of the first active paste comprises: uniformly mixing a first active substance, a first conductive agent and a first binder in a solvent to obtain the first active paste.

[0050] In some embodiments, the preparation of the second active paste comprises: uniformly mixing a second active substance, a second conductive agent and a second binder in a solvent to obtain the second active paste.

[0051] In some embodiments, the preparation of the third active paste comprises: uniformly mixing a third active substance, a third conductive agent and a third binder in a solvent to obtain the third active paste.

[0052] In some embodiments, the compaction density of the rolling is 1.5 g / cm 3 ~1.7 g / cm 3 .

[0053] In some embodiments, the solvent is deionized water.

[0054] In some embodiments, the preparation method of the first active substance comprises:

[0055] 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.

[0056] 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).

[0057] In some embodiments, the conductive polymer monomer includes at least one of pyrrole, aniline, acetylene, or 3,4-ethylenedioxythiophene.

[0058] In some embodiments, the initiator includes at least one of perchloric acid, potassium dichromate, hydrogen peroxide, or ammonium persulfate.

[0059] In some embodiments, the stirring time is 4-6 hours.

[0060] In some embodiments, the stirring temperature is 5-30°C.

[0061] In some embodiments, the standing time is 30-40 hours.

[0062] In some embodiments, the drying temperature is 80-120°C.

[0063] In some embodiments, the method for preparing the second active material includes:

[0064] Mixing the silicon-based material with the tin-based material, coating the silicon-based material on the tin-based material after ball milling, then mixing with the carbon material, and sintering to obtain a tin-containing composite material;

[0065] 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.

[0066] In some embodiments, the ball milling speed is 500-600 r / min, and the time is 6-12 hours.

[0067] 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.

[0068] In some embodiments, the oxidizing agent includes at least one of hydrogen peroxide, pyridinium chlorochromate, or pyridine dichromate.

[0069] In some embodiments, the solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, or acetone.

[0070] In some embodiments, the temperature of the polymerization reaction is 20-60℃, and the time is 2-8h.

[0071] In some embodiments, the method for preparing the third active material comprises:

[0072] The carbon source containing a heteroatom is mixed with a pore-forming agent and dissolved in water, pre-carbonization is performed, and a pre-carbonized carbon material is obtained;

[0073] The pre-carbonized carbon material is sintered under an inert atmosphere, and the third active material is obtained.

[0074] In some embodiments, the pore-forming agent is at least one of potassium oxalate or calcium carbonate.

[0075] In some embodiments, the pre-carbonization is performed under vacuum, the temperature of the pre-carbonization is 150-180℃, and the time is 8-12h.

[0076] In some embodiments, the particle size of the pre-carbonized carbon material before sintering is 4-25μm.

[0077] In some embodiments, the sintering temperature is 700-800℃, the time is 1-3h, and the heating rate is 2-4℃ / min.

[0078] 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.

[0079] The technical solutions of the present application have at least the following beneficial effects:

[0080] In the negative electrode sheet provided in the embodiments of the present application, the 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 peeling of the first active material. The first active material of the first active layer comprises graphite material coated with conductive material. The first active layer can improve the capacity of the battery, and the graphite coated with conductive material can improve the conductivity of the first active layer. The second active material is tin-containing composite material coated with 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 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 comprises 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 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 heteroatoms produces more defects, providing more active sites for storage, and can inhibit the decomposition of the electrolyte and the side reaction between the electrolyte and the electrode, thereby reducing the formation of SEI film. In addition, 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 avoiding peeling between the two active layers. Thus, the lithium ion battery can have high energy density, long cycle life and high safety.

[0081] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0082] Figure 1 The scanning electron microscope image of the third active material, nitrogen-doped porous carbon material, provided in Example 1 of the present application is shown.

[0083] Figure 2 The three-dimensional structure schematic diagram of the third active material, nitrogen-doped porous carbon material, provided in Example 1 of the present application is shown.

[0084] 1-mesoporous;

[0085] 2-microporous. DETAILED DESCRIPTION

[0086] The application will be further described in conjunction with specific embodiments. It should be understood that these embodiments of the application are only used to illustrate but not to limit the scope of the application.

[0087] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not considered critical for the application. The endpoints of the ranges and any values are only approximate, and they are provided as a convenience to the skilled artisan. The exact values will depend on many factors. This includes that depending on the desired properties of the application the exact values will vary within the range.

[0088] If not specifically explained, all the embodiments and optional embodiments of the application can be combined with each other to form new technical solutions.

[0089] If not specifically explained, all the technical features and optional technical features of the application can be combined with each other to form new technical solutions.

[0090] If not specifically explained, all the steps of the application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises 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.

[0091] If not specifically explained, the "includes" and "contains" mentioned in the application means open, and can also be closed. For example, the "includes" and "contains" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0092] At present, the energy density and charging time of the battery are two important technical indicators, and the common method to improve the fast charging performance of lithium ion battery 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 type 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 battery with lithium titanate. Therefore, it is urgent to develop a lithium ion battery with high energy density, long cycle life and high safety.

[0093] [Negative electrode sheet]

[0094] Therefore, the negative electrode sheet provided by the embodiments of the present application comprises:

[0095] a current collector;

[0096] 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;

[0097] 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;

[0098] 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;

[0099] 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;

[0100] wherein the third active material comprises a heteroatom-doped porous carbon material.

[0101] 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, i.e., 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.

[0102] The above "the conductive layer is disposed on at least one side surface of the current collector in the thickness direction" means that the conductive layer can be disposed on one surface of the current collector in the thickness direction of the current collector, or can be disposed on both surfaces of the current collector in the thickness direction of the current collector. Here, the "surface" can be the entire region of the current collector, or can be a partial region of the current collector. In the embodiments, the surface can be the entire region of the current collector, and the present application does not have a particular limitation as long as the purpose of the present application can be achieved.

[0103] For example, the current collector has two opposite surfaces in the thickness direction thereof, and the conductive layer is disposed 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 stacked on any one of the two surfaces of the current collector.

[0104] In the present application, the material of the current collector in the negative electrode sheet is not particularly limited.

[0105] In the present 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 peeling of the first active material.

[0106] In the present 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 conductive material coated graphite can improve the conductivity of the first active layer.

[0107] In the present 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 interfacial resistance, and can 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 coated with an aromatic conductive polymer, which itself 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.

[0108] In the present application, the third active layer in the negative electrode sheet includes a porous carbon material doped with a heteroatom, wherein a large number of pores improve the storage capacity of lithium ions and effectively adapt to the volume change during lithium insertion / extraction; a high specific surface area provides sufficient contact of the electrolyte with the electrode surface and enhances 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 reaction between the electrolyte and the electrode, reducing the formation of SEI film.

[0109] 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 preventing peeling between the two active layers.

[0110] Therefore, the negative electrode sheet of the present application includes a current collector, a conductive layer, a first active layer, a second active layer, and a third active layer arranged in sequence. By arranging the conductive layer, peeling between the negative active material layer and the negative current collector in the traditional double-layer coating method can be avoided. By limiting the composition of the second active layer and the third active layer, the accelerated decay of battery capacity and 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.

[0111] In some embodiments, the conductive layer further comprises a binder.

[0112] 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 be a ratio within the above range, which is not specifically limited herein.

[0113] In some embodiments, the conductive material comprises a conductive polymer.

[0114] 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.

[0115] In some embodiments, the thickness of the conductive layer is 1-5 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 be a value within the above range, which is not specifically limited herein.

[0116] In some embodiments, the graphite material comprises artificial graphite and natural graphite, and the mass ratio of the artificial graphite and the natural graphite is (0.1-1):1. For example, the mass ratio of the artificial graphite and the natural graphite can be 0.1:1, 0.5:1, 1:1, etc., and of course can be a ratio within the above range, which is not specifically limited herein. In particular, the use of a mixture of artificial graphite and natural graphite in the present application has the following advantages: 1. Synergistic enhancement of conductivity: the respective conductivities of natural graphite and artificial graphite each have their own characteristics, natural graphite has higher crystallinity and conductivity, while artificial graphite has better structural uniformity and conductivity stability. The use of both can take advantage of both, thereby improving the charge and discharge performance of the battery. 2. Better cost-effectiveness: single natural graphite or artificial graphite may have trade-offs in terms of cost-effectiveness, natural graphite is lower in cost but the performance can be unstable, artificial graphite is stable in performance but higher in cost. The use of a mixture can optimize the cost while ensuring performance, thereby improving economic efficiency.

[0117] In some embodiments, the mass ratio of the conductive material and the graphite material is (0.01-0.1):(8-12). For example, the mass ratio of the conductive material and the graphite material can be 0.01:8, 0.05:10, 0.1:12, etc., and of course can be a ratio within the above range, which is not specifically limited herein.

[0118] In some embodiments, the first active layer further comprises a first conductive agent and a first binder.

[0119] 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 value within the above range, without being limited thereto.

[0120] In some embodiments, the first active layer has a thickness of 10-60 μm. For example, the first active layer can have a thickness of 10 μm, 20 μm, 30 μm, 50 μm, 60 μm, or any value within the above range, without being limited thereto.

[0121] 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.

[0122] In some embodiments, the mass ratio of the aromatic conductive polymer and the tin-containing composite material is (0.05-1):5. For example, the mass ratio of the aromatic conductive polymer and the tin-containing composite material can be 0.05:5, 0.5:5, 1:5, or any value within the above range, without being limited thereto.

[0123] In some embodiments, the tin-containing composite material includes 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, lower 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.

[0124] 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 above range, without being limited thereto.

[0125] In some embodiments, the silicon-based material includes at least one of silicon dioxide and silicon carbide. For example, the tin-based material can be silicon dioxide or silicon carbide.

[0126] In some embodiments, the tin-based material includes at least one of tin dioxide and tin diselenide. For example, the tin-based material can be tin dioxide or tin diselenide.

[0127] In some embodiments, the carbon material includes at least one of carbon nanotubes, graphene, and fullerenes. As an example, the carbon material can be carbon nanotubes, can be graphene, or can be fullerenes. The carbon material is preferably carbon nanotubes, which have mechanical support properties and can effectively inhibit the volume expansion of the tin-based material.

[0128] In some embodiments, the molar ratio of the silicon-based material to the tin-based material is (1-3):1. As an example, the molar ratio of the silicon-based material to the tin-based material can be 1:1, 2:1, 3:1, or the like, and can also be a ratio within the above range, which is not specifically limited herein.

[0129] In some embodiments, the molar ratio of the tin-based material to the carbon material is (1-2):(1-2). As an example, the molar ratio of the tin-based material to the carbon material can be 1:1, 1:2, 2:1, or the like, and can also be a ratio within the above range, which is not specifically limited herein.

[0130] In some embodiments, the second active layer further includes a second conductive agent and a second binder.

[0131] 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). As an 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 the like, and can also be a ratio within the above range, which is not specifically limited herein.

[0132] In some embodiments, the thickness of the second active layer is 10 μm-60 μm. As an example, the thickness of the second active layer can be 10 μm, 20 μm, 30 μm, 50 μm, 60 μm, or the like, and can also be a value within the above range, which is not specifically limited herein.

[0133] In some embodiments, the heteroatom includes a nitrogen atom. The doping of the nitrogen atom can cause the porous carbon to have more defects, providing more active sites for storing lithium ions, while inhibiting the decomposition of the electrolyte and the side reaction between the electrolyte and the electrode, reducing the formation of the SEI film.

[0134] In some embodiments, the doping rate of the heteroatom is 20%-30%. As an example, the doping rate of the heteroatom can be 20%, 25%, 30%, or the like, and can also be a value within the above range, which is not specifically limited herein.

[0135] In some embodiments, the porosity of the heteroatom-doped porous carbon material is 75% to 85%. As an example, the porosity of the heteroatom-doped porous carbon material can be 75%, 80%, 85%, etc., or it can be any value within the above range, and no specific limitation is made here.

[0136] In some embodiments, the pores in the heteroatom-doped porous carbon material include micropores and mesopores. This heteroatom-doped porous carbon material possesses a cross-linked, interconnected micro- and mesopore structure, which allows lithium-ion diffusion and electron transport, shortening the lithium-ion transport path. The numerous interconnected micropores provide a reservoir, improving lithium-ion storage capacity and effectively accommodating volume changes during lithium insertion / extraction. Micropores refer to pores with a diameter <2 nm, typically possessing extremely high specific surface area; mesopores refer to pores with a diameter between 2 nm and 50 nm, exhibiting high specific surface area and a three-dimensional channel structure. For specific distinctions, please refer to the appendix to the specification. Figure 2 .

[0137] In some embodiments, the third active layer further includes a third conductive agent and a third binder.

[0138] 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). As an 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, etc., or any ratio within the above range, without specific limitation here.

[0139] In some embodiments, the thickness of the third active layer is 10 μm to 60 μm. As an example, the thickness of the third active layer can be 10 μm, 20 μm, 30 μm, 50 μm, 60 μm, etc., or any value within the above range, and is not specifically limited here.

[0140] 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 nanotubes, or graphene. Among them, the aforementioned conductive carbon black includes acetylene black, Ketjen black, etc. The aforementioned conductive carbon fiber includes vapor-grown carbon fiber.

[0141] It should also be noted that the adhesive, the first adhesive, the second adhesive, and the third adhesive each independently include, but are not limited to, at least one of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, or polyacrylic acid. For example, the first adhesive may be a mixture of carboxymethyl cellulose and styrene-butadiene rubber.

[0142] 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 between each material are fully exerted, and the cycle performance, fast charging performance, and structural stability of the negative electrode sheet are effectively improved.

[0143] It can also be 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 heat 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 improvement of the structural stability of the negative electrode sheet is not obvious, and the safety and long-term cycle stability of the battery are adversely affected.

[0144] In some embodiments, the current collector includes 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, and can be a foamed nickel.

[0145] Thus, based on the above scheme, in the negative electrode sheet of the present application, the 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 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 includes graphite material coated with conductive material. The first active layer can improve the capacity of the battery, and the conductive material coated graphite 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 surface of the tin-based composite material is also coated with an aromatic conductive polymer, which itself 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 heteroatom-doped porous carbon material having 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 lithium intercalation / deintercalation; a high specific surface area provides sufficient contact of the electrolyte with the electrode surface and enhances charge transfer, resulting in extremely 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, 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 can interact with the benzene ring in the heteroatom-doped porous carbon material 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. Thus, the lithium ion battery can have high energy density, long cycle life and high safety.

[0146] [Preparation method of negative electrode sheet]

[0147] 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:

[0148] coating a conductive paste on at least one side surface of the current collector to obtain a conductive layer;

[0149] coating a first active paste on the surface of the conductive layer to obtain a first active layer;

[0150] coating a second active paste on the surface of the first active layer to obtain a second active layer;

[0151] coating a third active paste on the surface of the second active layer to obtain a third active layer;

[0152] rolling the current collector coated with the conductive layer, the first active layer, the second active layer and the third active layer;

[0153] The conductive paste comprises a conductive agent.

[0154] The first active paste comprises a first active substance.

[0155] The second active paste comprises a second active substance.

[0156] The third active paste comprises a third active substance.

[0157] 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.

[0158] In some embodiments, the preparation of the conductive paste comprises: uniformly mixing the conductive agent and the binder in the solvent to obtain the conductive paste.

[0159] In some embodiments, the mass ratio of the conductive agent to the binder in the conductive paste 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.

[0160] In some embodiments, the preparation of the first active paste comprises: uniformly mixing the first active substance, the first conductive agent and the first binder in the solvent to obtain the first active paste.

[0161] 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.

[0162] In some embodiments, the preparation of the second active paste comprises: uniformly mixing the second active substance, the second conductive agent and the second binder in the solvent to obtain the second active paste.

[0163] 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, without being specifically limited herein.

[0164] In some embodiments, the third active material, the third conductive agent, and the third binder are mixed in a solvent to obtain the third active slurry.

[0165] 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 specifically limited herein.

[0166] 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.

[0167] 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.

[0168] 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, without being specifically limited herein.

[0169] [Preparation method of the first active material]

[0170] In some embodiments, the preparation method of the first active material includes:

[0171] The conductive polymer monomer, the initiator, and the graphite material are mixed in a solvent, and after stirring, standing, and drying, the first active material is obtained.

[0172] 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, without being limited thereto.

[0173] In some embodiments, the coated thickness of the conductive polymer graphite material coated in the first active substance is 1 nm-10 nm. For example, the coated thickness can be 1 nm, 4 nm, 8 nm, 10 nm, or any value within the above range, without being limited thereto.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] In some embodiments, the stirring time is 4 h-6 h. For example, the stirring time can be 4 h, 5 h, 6 h, or any value within the above range, without being limited thereto.

[0178] In some embodiments, the stirring temperature is 5℃-30℃. For example, the stirring temperature can be 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, or any value within the above range, without being limited thereto.

[0179] In some embodiments, the standing time is 30 h-40 h. For example, the standing time can be 30 h, 35 h, 40 h, or any value within the above range, without being limited thereto.

[0180] In some embodiments, the drying temperature is 80℃-120℃. For example, the drying temperature can be 80℃, 100℃, 120℃, or any value within the above range, without being limited thereto.

[0181] [Preparation method of second active material]

[0182] In some embodiments, the preparation method of the second active material comprises:

[0183] 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 tin-based material with the carbon material, and sintering to obtain the tin-containing composite material;

[0184] mixing the tin-containing composite material, the aromatic conductive polymer monomer, and the oxidizing agent in a solvent, and then performing polymerization to obtain the second active material.

[0185] 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 value within the above range, which is not specifically limited herein.

[0186] In some embodiments, the rotation speed of ball milling is 500 r / min-600 r / min, and the time is 6 h-12 h. For example, the rotation speed of ball milling can be 500 r / min, 550 r / min, 600 r / min, or any value within the above range, which is not specifically limited herein. The time of ball milling can be 6 h, 9 h, 12 h, or any value within the above range, which is not specifically limited herein.

[0187] In some embodiments, the step of mixing the silicon-based material-coated tin-based material and the carbon material specifically comprises: ultrasonic dispersion of the silicon-based material-coated tin-based material and the carbon material in an ethanol solution, dissolution in an organic solution containing a binder and an additive, mechanical stirring until the mixture becomes 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.

[0188] 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 value within the above range, which is not specifically limited herein.

[0189] In some embodiments, the sintering temperature is 600-1200°C, the sintering time is 5-20 hours, and the heating rate is 1-10°C / min. For example, the sintering temperature can be 600°C, 900°C, 1200°C, etc., and can also be a value within the above range, which is not specifically limited herein. The sintering time can be 5 hours, 10 hours, 15 hours, 20 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 1°C / min, 5°C / min, 10°C / min, etc., and can also be a value within the above range, which is not specifically limited herein.

[0190] In some embodiments, after mixing the tin-containing composite material, the aromatic conductive polymer monomer, and the oxidizing agent in the solvent, a step of heating is further included, and the temperature is raised to a temperature corresponding to the initiation temperature of the initiator to initiate polymerization.

[0191] In the present application, the above-mentioned sintering conditions can bring the following effects:

[0192] 1. Optimizing the crystal structure: within the temperature range of 600-1200°C, the tin-containing composite material can be fully crystallized to form a uniform and stable crystal structure, thereby improving the structural stability and electrochemical performance of the material.

[0193] 2. Improving the purity of the material: a moderate sintering temperature helps to remove impurities and organic residues in the material, improve the purity of manganese lithium iron, reduce the occurrence of side reactions, and enhance the cycle stability of the battery.

[0194] 3. Controlling the particle size: a heating rate of 1-10°C / min helps to control the growth rate of the material particles, avoiding excessively large or small particles, thereby optimizing the specific surface area and electrical conductivity of the material.

[0195] 4. Enhancing the mechanical strength: a longer sintering time (5-20 hours) can promote the densification of the material, enhance the mechanical strength of the tin-containing composite material, and reduce the material breakage and structural damage caused by volume changes during charging and discharging.

[0196] 5. Improving the electrochemical performance: appropriate sintering temperature and sintering time can optimize the electrochemical performance of the material, improve the charging and discharging efficiency, rate performance, and cycle life of the battery.

[0197] 6. Reducing energy consumption: while ensuring the performance of the material, selecting an appropriate heating rate and sintering time can reduce energy consumption and improve the economic benefits of the preparation process.

[0198] In some embodiments, the oxidizing agent includes at least one of hydrogen peroxide, pyridinium chlorochromate, or pyridinium dichromate. For example, the oxidizing agent can be hydrogen peroxide, or pyridinium chlorochromate.

[0199] In some embodiments, the aromatic conductive polymer monomer comprises at least one of aniline, aniline derivative, carbazole, carbazole derivative, pyrrole or pyrrole derivative.

[0200] In some embodiments, the mass ratio of the tin-containing composite, the aromatic conductive polymer monomer and the oxidant 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 oxidant can be 10:0.01:0.001, 15:0.05:0.002, 20:0.1:0.005, or any ratio within the above range, which is not specifically limited herein.

[0201] In some embodiments, the solvent comprises at least one of N-methylpyrrolidone, N,N-dimethylformamide or acetone. For example, the solvent can be N-methylpyrrolidone, or N,N-dimethylformamide.

[0202] In some embodiments, the temperature of the polymerization reaction is 20-60°C, and the time is 2-8h. For example, the temperature of the polymerization reaction can be 20°C, 40°C, 60°C, or any temperature within the above range, which is not specifically limited herein. The time of the polymerization reaction can be 2h, 4h, 6h, 8h, or any time within the above range, which is not specifically limited herein. 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.

[0203] [Preparation method of the third active material]

[0204] In some embodiments, the preparation method of the third active material comprises:

[0205] mixing the carbon source containing heteroatoms with the pore-forming agent and dissolving in water to obtain a pre-carbonized carbon material;

[0206] sintering the pre-carbonized carbon material under an inert atmosphere to obtain the third active material.

[0207] 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, which is not specifically limited herein.

[0208] In some embodiments, the carbon source comprises organic carbon containing heteroatoms, preferably comprises organic carbon containing N atoms. For example, the carbon source can be D-glucosamine, or chitosan.

[0209] In some embodiments, the pore-forming agent is at least one of potassium oxalate or calcium carbonate. As an example, the pore-forming agent can be potassium oxalate, can be calcium carbonate; preferably, the pore-forming agent is a mixture of potassium oxalate and calcium carbonate. Further, the mass ratio of potassium oxalate to calcium carbonate is (8-12): 1, preferably 10: 1.

[0210] 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. As an example, the grinding time can be 20 minutes, 30 minutes, 40 minutes, etc., and of course can also be a certain numerical value within the above range, which is not specifically limited here.

[0211] In some embodiments, the pre-carbonization step is carried out under vacuum conditions, and the pre-carbonization temperature is 150-180°C, and the time is 8-12 hours. As an example, the pre-carbonization temperature can be 150°C, 160°C, 180°C, etc., and of course can also be a certain numerical value within the above range, which is not specifically limited here. The pre-carbonization time can be 8h, 10h, 12h, etc., and of course can also be a certain numerical value within the above range, which is not specifically limited here.

[0212] In some embodiments, the particle size of the pre-carbonized carbon material before sintering is 4-25 μm. As an example, the particle size of the pre-carbonized carbon material before sintering can be 4 μm, 10 μm, 15 μm, 25 μm, etc., and of course can also be a certain numerical value within the above range, which is not specifically limited here.

[0213] In some embodiments, the sintering is carried out under an inert atmosphere, the sintering temperature is 700-800°C, the time is 1-3 hours, and the heating rate is 2-4°C / min. As an example, the sintering temperature can be 700°C, 750°C, 800°C, etc., and of course can also be a certain numerical value within the above range, which is not specifically limited here. The sintering time can be 1h, 2h, 3h, etc., and of course can also be a certain numerical value within the above range, which is not specifically limited here. The heating rate during sintering can be 2°C / min, 3°C / min, 4°C / min, etc., and of course can also be a certain numerical value within the above range, which is not specifically limited here.

[0214] 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 temperature, 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 intermediate to fully react and embed in the carbon skeleton, and the nitrogen retention rate is higher.

[0215] In some embodiments, the sintered material further comprises a step of acid washing, preferably using dilute hydrochloric acid to remove excess calcium and potassium salts, and then using deionized water to wash, after washing, filtering, repeating multiple times until pH = 7. The water-washed material is placed in a vacuum drying oven for drying treatment, thereby obtaining a heteroatom-doped porous carbon material.

[0216] Therefore, 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 comprises a graphite material coated with a conductive material. The first active layer can improve the capacity of the battery, and the conductive material coated graphite 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 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. The third active layer comprises a heteroatom-doped porous carbon material, 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, obtaining an extremely 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, 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 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, 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.

[0217] [Battery]

[0218] Based on the same inventive concept, the embodiments of the present application provide a battery comprising a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode sheet described above, or is prepared by the preparation method described above.

[0219] The battery has high energy density, long cycle life and high safety due to containing the negative electrode sheet provided in the application.

[0220] In some embodiments, the battery can be a lithium ion battery. The battery can be a stacked type such as a winding type or a laminated type, and can be a structure type such as a square can (aluminum can, steel can, etc.) battery, a soft pack battery or a cylindrical battery, without limitation.

[0221] In some embodiments, the 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.

[0222] In the present embodiment, the positive electrode sheet is not limited in terms of the materials, structure, etc. of the positive electrode current collector, the conductive agent, the binder, etc. in the positive electrode active material layer, and the like, and any positive electrode sheet structure and composition known in the art that can be used in a secondary battery can be used.

[0223] In the present embodiment, the separator is not limited in terms of the specific material or type, and the like, and any separator known in the art that can be used in a secondary battery can be used.

[0224] It should be further noted that the battery of the present application is not limited in terms of the specific material or type of the electrolyte, and the like, and any composition and type known in the art that can be used in a secondary battery can be used, as long as the purpose of the present application can be achieved.

[0225] The battery provided in the present embodiment has all the beneficial effects brought by the technical solutions of the above embodiments, and thus will not be described here.

[0226] The following describes the embodiments of the present application. 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 a specific technique or condition is not specified in the embodiments, the technique or condition described in the literature in the art or according to the product manual is used. If the reagent, material or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained from the market.

[0227] Example 1

[0228] S1: Preparation of conductive slurry

[0229] 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%.

[0230] S2: Preparation of first active slurry

[0231] The first 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 first active slurry; wherein the solid content of the first active slurry is 40 wt%.

[0232] The preparation of the first active material includes: dissolving 3,4-ethylenedioxythiophene in anhydrous ethanol at room temperature, stirring for 5 h, then adding artificial graphite, natural graphite, and hydrogen peroxide, heating to 50°C and continuing to stir for 5 h, then placing the sample for 36 h, then evaporating the solvent and drying at 100°C to obtain the target product coated graphite composite material;

[0233] The mass ratio of 3,4-ethylenedioxythiophene, artificial graphite, natural graphite, and hydrogen peroxide is 0.05:5:5:0.003.

[0234] The coating thickness of the conductive polymer graphite material after coating in the first active material is 10 nm.

[0235] S3: Preparation of the second active slurry

[0236] 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%.

[0237] The preparation of the second active material includes: mixing SiO2 and SnO2 nanoparticles at a molar ratio of 1:1, then ball milling at a speed of 500 rpm for 12 h. The prepared modified SnO2 and CNT (carbon nanotubes) 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 containing polyvinylidene fluoride and carboxymethyl cellulose (organic solvent is methanol) in proportion. Then mechanically stir until the solution becomes viscous, and dry the sample in a vacuum at 65°C until the solvent is completely volatilized. Carbonize and sinter the dried solid, wherein the sintering temperature is 1000°C, the heating rate is 4°C / min, and the sintering time is 8 h. 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°C for 6 h to obtain the second active material.

[0238] The mass ratio of modified SnO2, CNT, polyvinylidene fluoride, carboxymethyl cellulose, and methanol is 70:20:5:5:200.

[0239] The mass ratio of the tin-containing composite material, pyrrole, and oxidizing agent is 10:0.1:0.005.

[0240] S4: Preparation of the third active slurry

[0241] The third active material, conductive carbon black, styrene-butadiene rubber, and carboxymethyl cellulose were mixed in deionized water at a mass ratio of 97:0.5:1.5:1 to obtain the third active slurry; the solid content of the third active slurry was 40 wt%.

[0242] The preparation of the third active substance includes: mixing D-glucosamine (carbon source) and a pore-forming agent at a mass ratio of 2:1, grinding in an agate mortar for 30 min, transferring the ground mixture to a polytetrafluoroethylene (PTFE) beaker, adding an appropriate amount of deionized water to dissolve the solid mixture, and then placing it in a vacuum drying oven for pre-carbonization at 160℃ for 10 h. After pre-carbonization, the solid in the beaker is transferred to a mortar and ground into powder (grinding to a particle size of 10 μm). Finally, the solid powder material is placed in a porcelain boat, and the porcelain boat is placed in a tube furnace and argon gas is introduced. Under the protective atmosphere of argon, the temperature is raised to 750℃ at a heating rate of 3℃ / min and held for 2 h to obtain a black powder. The calcined black powder is placed in a beaker and acid-washed with dilute hydrochloric acid to remove excess calcium and potassium salts, then washed with deionized water, and filtered repeatedly until pH = 7. The washed material is placed in a vacuum drying oven for drying (temperature 120 ℃) ​​to obtain the third active substance.

[0243] The pore-forming agent is a mixture of potassium oxalate and calcium carbonate in a mass ratio of 10:1; the nitrogen doping rate is 25%; and the porosity is 80%. Figures 1-2 It can be seen that nitrogen-doped porous carbon materials have 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 have a large number of interconnected micropores and interconnected porous structures.

[0244] S5: Coating

[0245] Using a coating machine, conductive paste is uniformly coated sequentially on the first surface of a 6μm thick copper foil. On the first surface of the negative current collector, the conductive paste is coated from one end to the other, forming a conductive coating. A first active paste is coated onto the surface of the conductive coating, followed by a first drying process. After drying, a second active paste is coated, followed by a second drying process. A third active paste is then coated, followed by a third drying process. The coating speed is 5 m / min. After coating, the foil is dried in a five-stage oven at temperatures of 60℃, 80℃, 110℃, 110℃, and 100℃. The thickness of the conductive coating is 3μm, the thickness of the first active layer is 60μm, the thickness of the second active layer is 20μm, and the thickness of the third active layer is 20μm. The coating process is repeated on the second surface of the copper foil opposite the first surface. Finally, a roller press is used to apply pressure, resulting in a compaction density of 1.65 g / cm³.3 The negative electrode.

[0246] Example 2

[0247] The difference between Example 2 and Example 1 is that the thickness of the second active layer is 40 μm.

[0248] Example 3

[0249] The difference between Example 3 and Example 1 is that the thickness of the third active layer is 40 μm.

[0250] Example 4

[0251] The difference between Example 4 and Example 1 is that the thickness of the conductive layer is 5 μm.

[0252] Example 5

[0253] The difference between Example 5 and Example 1 is that the mass ratio of artificial graphite to natural graphite is 0.5:1 when preparing the first active material.

[0254] Example 6

[0255] The difference between Example 6 and Example 1 is that the carbon material used in the preparation of the second active material is fullerene.

[0256] Example 7

[0257] The difference between Example 7 and Example 1 lies in the preparation of the third active material: D-glucosamine (carbon source) and pore-forming agent were mixed at a mass ratio of 2:1 and ground in an agate mortar for 30 min. The ground mixture was then transferred to a polytetrafluoroethylene (PTFE) beaker, and an appropriate amount of deionized water was added to dissolve the solid mixture. The mixture was then placed in a vacuum drying oven and pre-carbonized at 160°C for 10 h. After pre-carbonization, the solid in the beaker was transferred to a mortar and ground into powder (to a particle size of 10 μm). Finally, the solid powder was placed in a porcelain boat, which was then placed in a tube furnace and purged with argon gas. Under the protective atmosphere of argon, the temperature was increased to 700°C at a rate of 2°C / min and held for 2 h to obtain a black powder. The calcined black powder was placed in a beaker and acid-washed with dilute hydrochloric acid to remove excess calcium and potassium salts. It was then washed with deionized water and filtered repeatedly until the pH reached 7. The washed material is placed in a vacuum drying oven for drying (temperature 120 ℃) ​​to obtain the third active substance.

[0258] The pore-forming agent is a mixture of potassium oxalate and calcium carbonate in a mass ratio of 10:1; the nitrogen atom doping rate is 30%; and the porosity is 85%.

[0259] Comparative Example 1

[0260] The difference between Comparative Example 1 and Example 2 is that the third active layer is not contained.

[0261] Comparative Example 2

[0262] The difference between Comparative Example 2 and Example 2 is that the second active layer is not contained.

[0263] Comparative Example 3

[0264] The difference between Comparative Example 3 and Example 2 is that the first active layer is not contained.

[0265] Comparative Example 4

[0266] The difference between Comparative Example 4 and Example 2 is that the artificial graphite and the natural graphite are directly used as the first active material; and the composite material of SnO2 and CNT is directly used as the second active material.

[0267] The preparation of the first active material includes: mixing the artificial graphite and the natural graphite in a mass ratio of 1:1, and then ball milling for 0.5 h at a rotating speed of 600 r / min.

[0268] 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 (the 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 heating 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.

[0269] Performance test

[0270] 1. Preparation of the battery

[0271] Preparation of the positive electrode sheet: the positive electrode active material LiCoO2, the binder polyvinylidene fluoride (PVDF) and the conductive agent conductive carbon black (SP) are dissolved in N-methyl pyrrolidone (NMP) in a mass ratio of 97%:1.5%:1.5% to be stirred uniformly to form a slurry, which is uniformly coated on the surfaces of the two sides of the positive electrode current collector aluminum foil, and then baked at 100-150°C for 4-8 h, followed by cold pressing, slitting and then the preparation of the positive electrode sheet of the lithium ion battery, with a compacted density of 4.1 g / cm 3 , and the thickness of the single-sided positive electrode active material layer is 62 μm.

[0272] Separating membrane: a composite separating membrane of a polyethylene membrane (9 μm) + double-sided adhesive coating (the adhesive thickness of a single side is 3 μm) + single-sided ceramic (3 μm) is selected as the separating membrane.

[0273] Electrolyte: In an inert gas-filled glove box, ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, propane lactone were mixed in a mass ratio of 1:1:1:1:1 to obtain an organic solvent, and then lithium salt LiPF6 was dissolved in the organic solvent to obtain an electrolyte. The concentration of the lithium salt was 1.2 mol / L.

[0274] Battery assembly: The positive electrode sheet, the separator, and the negative electrode sheet were arranged in sequence, and then a winding machine was used to wind the positive electrode to obtain a winding structure of the winding core, which was packaged with an aluminum plastic film. After baking for 48 h in a vacuum state to remove moisture, the electrolyte was injected, and the battery was subjected to conventional formation and sorting to obtain a square soft-pack lithium ion battery.

[0275] 2. Electrochemical performance test of the battery

[0276] The assembled CR2032 button cell was subjected to constant current charge / discharge test using a LAND CT2001A battery test system, and the charge / discharge voltage window was 2 V ~4.3V.

[0277] (1) Cycle life and battery cycle expansion rate test: the battery was charged at 1.5C rate to 4.45V at 25℃, and then charged at 4.45V, with a cutoff current of 0.025C. Then it was discharged at 0.5C rate, and the cutoff voltage was 3V. This was one charge-discharge cycle process. 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 with a thickness tester as the initial thickness, and the thickness of the battery at full charge after every 100 cycles was tested and recorded. The cycle expansion rate was (cycle full charge under platform thickness / initial full charge thickness)*100%.

[0278] (2) Charge capacity (maximum chargeable current): the maximum chargeable current when the negative electrode does not produce metal lithium at 25℃.

[0279] (3) Charge time: the total time when the battery is charged from 3.0V to 4.35V at the maximum chargeable current, and then fully charged at 4.35V with a constant voltage of 0.025C at 25℃.

[0280] The test results of each example and comparative example are shown in Table 1.

[0281] Table 1

[0282]

[0283] From Examples 1-3, it can be seen that the performance in Example 2 is the best, i.e. 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% at 800 times, the cycle life meets 800 times, and the charging 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.

[0284] From the test data of Examples 4-7, it can be seen that the appropriate 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 appropriate 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.

[0285] 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 nitrogen-doped porous carbon material layer, which can effectively reduce the expansion rate of the battery. The specific reasons are as follows:

[0286] Improving 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 inhibition 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.

[0287] Further, since the negative electrode sheet of Example 2 has an additional third active layer compared to 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 a reservoir, improve the Li +The storage capacity of the second active layer can effectively adapt to the volume change during the lithium insertion / extraction process; the high specific surface area can provide sufficient contact of the electrolyte with the electrode surface and enhance the charge transfer, so that a very low transmission resistance is obtained; in addition, the doping of nitrogen element can produce more defects to provide more active sites for storage, and can also inhibit the decomposition of the electrolyte and the side reaction between the electrolyte and the electrode, and reduce the formation of SEI film. Therefore, the battery has a longer cycle life, higher charging capacity and higher charging rate.

[0288] As can be seen from the test results of Example 2 and Comparative Example 2, the presence of the second active layer can significantly improve the energy density of the battery, and the battery exhibits a low cycle expansion rate. This is because the second active layer is a composite material of SnO2 coated with a conductive polymer layer and CNT, wherein SnO2 is a modified material coated with SiO2. The conductivity and mechanical support of the CNT material can effectively inhibit the volume expansion of the tin-based negative electrode material, the coating of SiO2 on the surface of SnO2 can reduce the interaction with the 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.

[0289] As can be seen from the test results of Example 2 and Comparative Example 3, the role of the graphite layer in the coating of the electrode sheet is: 1. improving the energy density and lithium ion diffusion rate, promoting the rapid insertion and extraction of lithium ions, thereby promoting the rapid insertion and extraction of lithium ions under high-rate charge and discharge conditions, improving the charging capacity of the battery, and shortening the charging time

[0290] As can be seen from the test results of Example 2 and Comparative Example 4, the presence of SiO2 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 insertion and extraction from all directions, so that the transport of lithium ions is more smooth, thereby greatly shortening the charging time

[0291] The part of the application not described in detail is the technology known to those skilled in the art.

[0292] The above describes the basic principles of the application in combination with specific embodiments, but it should be pointed out that the advantages, advantages, effects and the like mentioned in the application are only examples and not limitations, and these advantages, advantages, effects and the like cannot be considered as the must-have of each embodiment of the application. In addition, the above specific details are only for the purpose of example and for the purpose of understanding, and are not limited to the above specific details to realize the application.

[0293] It should be noted that the terms "and / or" or " / " as used herein merely describes an associated relationship among associated objects, and indicates that there can be three relationships, for example, A and / or B, which can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0294] In the detailed description and in the claims, a list of items connected by the term "at least one of" or "one or more of" can mean any combination of the items in the list. For example, if the list contains A, B, and C, the phrase "at least one of A, B, and C" can mean A alone; B alone; C alone; A and B together; A and C together; B and C together; or A, B, and C together. The item A can include a single element or multiple elements. The item B can include a single element or multiple elements. The item C can include a single element or multiple elements.

[0295] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some technical features; 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 includes: current collector; A conductive layer is disposed on at least one side surface of the current collector along the thickness direction, the conductive layer comprising a conductive agent; A first active layer is disposed on the surface of the conductive layer away from the current collector. The first active layer includes a first active material, which includes graphite material coated with a conductive material. A second active layer is disposed on the surface of the first active layer away from the conductive layer. The second active layer includes a second active material, which includes a tin-containing composite material coated with an aromatic conductive polymer. A third active layer is disposed on the surface of the second active layer away from the first active layer, and the third active layer includes a third active substance; The conductive material in the first active substance includes a conductive polymer; The structure of the tin-containing composite material is as follows: a tin-based material is the core, a silicon-based material is the intermediate coating layer, and a carbon material is the outer coating layer; The third active material includes heteroatom-doped porous carbon material, which has a micro-mesoporous cross-linked interconnected structure.

2. The negative electrode sheet according to claim 1, characterized in that, The first active layer satisfies at least one of the following features (1) to (5): (1) 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 artificial graphite to 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 ~ 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 features (1) to (5): (1) The aromatic conductive polymer includes at least one of polyaniline, polyaniline derivatives, polycarbazole, polycarbazole derivatives, polypyrrole, or polypyrrole derivatives; (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 tin-based materials coated with carbon and silicon-based materials; 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 ~ 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 features (1) to (5): (1) The heteroatoms include nitrogen atoms; (2) The doping rate of the heteroatoms is 20%~30%; (3) The porosity of the heteroatom-doped porous carbon material is 75%~85%; (4) The third active layer further includes a third conductive agent and a third adhesive; 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 ~ 60 μm.

5. The method for preparing the negative electrode sheet according to any one of claims 1 to 4, characterized in that, Includes the following steps: A conductive paste is coated on at least one side of the current collector to obtain a conductive layer; A first active slurry is coated on the surface of the conductive layer to obtain a first active layer; A second active slurry is coated onto the surface of the first active layer to obtain a second active layer; A third active slurry is coated onto the surface of the second active layer to obtain the third active layer; The current collector coated with a conductive layer, a first active layer, a second active layer, and a third active layer is rolled; The conductive paste includes a conductive agent; The first active slurry includes a first active substance; The second active slurry includes a second active substance; The third active slurry includes a third active substance.

6. The method for preparing the negative electrode sheet according to claim 5, characterized in that, The preparation of the conductive paste includes: mixing the conductive agent and the binder evenly in a solvent to obtain the conductive paste; The preparation of the first active slurry includes: mixing the first active substance, the first conductive agent and the first binder uniformly in a solvent to obtain the first active slurry; The preparation of the second active slurry includes: mixing the second active substance, the second conductive agent, and the second binder uniformly in a solvent to obtain the second active slurry; The preparation of the third active slurry includes: mixing the third active substance, the third conductive agent and the third binder uniformly in a solvent to obtain the third active slurry; The mass ratio of conductive agent to binder in the conductive slurry is (93~99):(1~7); The compaction density of the roller press is 1.5 g / cm³. 3 ~1.7 g / cm 3 ; The solvent is deionized water.

7. The method for preparing the negative electrode sheet according to claim 5, characterized in that, The preparation method of the first active substance includes: The conductive polymer monomer, initiator, and graphite material are mixed in a solvent, and the mixture is stirred, allowed to stand, and dried to obtain the 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℃~30℃; The settling time is 30h~40h; The drying temperature is 80℃~120℃.

8. The method for preparing the negative electrode sheet according to claim 5, characterized in that, The preparation method of the second active substance includes: Silicon-based materials and tin-based materials are mixed, ball-milled to coat the tin-based materials with silicon, and then mixed with carbon materials 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 then subjected to a polymerization reaction to obtain the second active substance. The ball mill operates at a speed of 500 r / min to 600 r / min for 6 h to 12 h. The sintering temperature is 600℃~1200℃, the time is 5h~20h, and the heating rate is 1℃ / min~10℃ / min; The oxidant includes 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 is carried out at a temperature of 20℃ to 60℃ for a duration of 2 hours to 8 hours.

9. The method for preparing the negative electrode sheet according to claim 5, characterized in that, 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. The pre-carbonized carbon material is sintered under an inert atmosphere to obtain the 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, and the pre-carbonization temperature is 150℃~180℃, and the time is 8h~12h. The pre-carbonized carbon material has a particle size of 4μm~25μm before sintering; The sintering temperature is 700℃~800℃, the time is 1h~3h, and the heating rate is 2℃ / min~4℃ / min.

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

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