Silicon-doped negative plate, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, in particular to a silicon-doped negative plate, a preparation method thereof and a battery. The silicon-doped negative plate comprises a current collector; the first negative electrode coating is arranged on the surface of at least one side of the current collector in the thickness direction, and the first negative electrode coating comprises a first polymerization unit and a silicon-based active material; the second negative electrode coating is arranged on the surface, far away from the current collector, of the first negative electrode coating, and the second negative electrode coating comprises a second polymerization unit; the third negative electrode coating is arranged on the surface, far away from the first negative electrode coating, of the second negative electrode coating, and the third negative electrode coating comprises a third polymerization unit and a carbon-based active material. The polymer composed of the three polymerization units can improve the bonding effect between particles and layers, so that the structural stability of the silicon-doped negative electrode plate in the circulation process is improved, and the ion transmission efficiency in the circulation process can be improved; and meanwhile, the fast charging capability and the service life of the silicon-doped negative plate can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a silicon-doped negative electrode sheet, a preparation method thereof, and a battery. Background Art

[0002] In recent years, with the continuous improvement of the performance of electric vehicles and portable electronic products, a high-energy-density lithium-ion battery is urgently needed. The current effective means to improve the energy density of batteries is to use silicon-based materials with higher capacity in combination with graphite negative electrodes. However, the low conductivity and large expansion of silicon-based materials greatly reduce the cycle life and power performance of silicon-doped negative electrodes. Therefore, it is necessary to take effective measures to limit the deterioration of battery performance caused by defects in silicon-based materials.

[0003] The patent technology CN116230867A has been published. It sets a double-layer coating on the negative electrode, and the main material of the lower layer is SiO x The upper layer is mainly graphite material, making SiO x More distributed in the inner layer, the surface graphite can effectively inhibit SiO x However, the upper layer of graphite alone cannot completely suppress the volume expansion of SiO x As the expansion deepens, the interface contact between the upper and lower layers will deteriorate significantly, and the ion and electron transmission efficiency will decay, which will seriously affect the performance of the battery cell.

[0004] Therefore, it is necessary to take effective measures to improve the stability of the upper and lower layer interfaces and reduce the upper and lower layer interface impedance in order to increase the service life of the silicon-based negative electrode. Summary of the invention

[0005] In view of this, the present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the present invention provides a silicon-doped negative electrode sheet and a preparation method thereof and a battery, which can improve the stability of the upper and lower layer interfaces and reduce the upper and lower layer interface impedance, thereby increasing the service life of the silicon-based negative electrode.

[0006] In order to solve the above technical problems, this application is implemented as follows:

[0007] According to one aspect of the present application, an embodiment of the present application provides a silicon-doped negative electrode sheet, the silicon-doped negative electrode sheet comprising:

[0008] current collector;

[0009] A first negative electrode coating is disposed on at least one side of the current collector along the thickness direction, wherein the first negative electrode coating comprises a first polymer unit and a silicon-based active material;

[0010] A second negative electrode coating is disposed on a surface of the first negative electrode coating away from the current collector, wherein the second negative electrode coating comprises a second polymer unit; and

[0011] a third negative electrode coating, disposed on a surface of the second negative electrode coating away from the first negative electrode coating, the third negative electrode coating comprising a third polymerized unit and a carbon-based active material;

[0012] The first polymer unit contains halogen, the number of branches of the second polymer unit is greater than or equal to the number of branches of the first polymer unit or the third polymer unit, and the main chain length of the third polymer unit is greater than the main chain length of the first polymer unit or the second polymer unit.

[0013] In some embodiments, the first polymerized unit includes a structure derived from a halogen-containing acrylic ester monomer, and the halogen is selected from at least one of fluorine, chlorine, or bromine.

[0014] In some embodiments, the halogen-containing acrylic ester monomer has 2-10 carbon atoms.

[0015] In some embodiments, the halogen-containing acrylic ester monomer includes at least one of trifluoroethyl methacrylate, pentafluoropropyl methacrylate, or hexafluorobutyl methacrylate.

[0016] In some embodiments, the second polymerized unit includes a structure derived from a multi-branched acrylic ester monomer, and the number of the branches is 3-8.

[0017] In some embodiments, the multi-branched acrylic ester monomer has 8-30 carbon atoms.

[0018] In some embodiments, the multi-branched acrylate monomer includes at least one of pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate or dipentaerythritol hexaacrylate.

[0019] In some embodiments, the third polymerized unit includes a structure derived from a long-chain alkene ester monomer, and the number of carbon atoms in the main chain is ≥50.

[0020] In some embodiments, the long-chain alkene ester monomer has ≥60 carbon atoms.

[0021] In some embodiments, the long-chain alkene ester monomer includes at least one of polyethylene glycol dimethacrylate, polyethylene glycol diacrylate or polyethylene glycol methacrylate.

[0022] In some embodiments, the silicon-based active material includes at least one of a silicon-oxygen composite material, a silicon-carbon composite material, or pure silicon.

[0023] In some embodiments, the first negative electrode coating further includes a first conductive agent and a first binder.

[0024] In some embodiments, the first conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene.

[0025] In some embodiments, the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate or polyacrylic acid.

[0026] In some embodiments, the mass ratio of the first polymer unit, the silicon-based active material, the first conductive agent and the first binder is (0.2-0.5): (90-95): (1-5): (3-6).

[0027] In some embodiments, the surface density of the first negative electrode coating is 30-50 g / m 2 .

[0028] In some embodiments, the thickness of the first negative electrode coating is 20-33 μm.

[0029] In some embodiments, the second negative electrode coating further includes a composite conductive agent.

[0030] In some embodiments, the composite conductive agent includes a one-dimensional conductive agent and a two-dimensional conductive agent, and the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is (1-1.5):1.

[0031] In some embodiments, the one-dimensional conductive agent includes at least one of carbon fiber or carbon nanotube.

[0032] In some embodiments, the two-dimensional conductive agent includes at least one of graphene or Mxene.

[0033] In some embodiments, the mass ratio of the second polymer unit to the composite conductive agent is (80-90): (10-20).

[0034] In some embodiments, the surface density of the second negative electrode coating is 5-10 g / m 2 .

[0035] In some embodiments, the second negative electrode coating has a thickness of 3-7 μm.

[0036] In some of the embodiments, the carbon-based active material includes at least one of natural graphite or artificial graphite.

[0037] In some embodiments, the third negative electrode coating further includes a second conductive agent and a second binder.

[0038] In some embodiments, the second conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene.

[0039] In some embodiments, the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate or polyacrylic acid.

[0040] In some of the embodiments, the mass ratio of the third polymer unit, the carbon-based active material, the second conductive agent and the second binder is (0.2-0.5): (94-97): (1-4): (2-4).

[0041] In some embodiments, the surface density of the third negative electrode coating is 40-80 g / m 2 .

[0042] In some embodiments, the thickness of the third negative electrode coating is 27-53 μm.

[0043] In some embodiments, the current collector includes at least one of copper foil, copper foam, nickel foam, nickel mesh or composite copper foil.

[0044] According to another aspect of the present application, an embodiment of the present application provides a method for preparing a silicon-doped negative electrode sheet, comprising the following steps:

[0045] Coating a first negative electrode slurry on at least one side of the current collector to obtain a first negative electrode coating;

[0046] Coating a second negative electrode slurry on the surface of the first negative electrode coating to obtain a second negative electrode coating;

[0047] coating a third negative electrode slurry on the surface of the second negative electrode coating to obtain a third negative electrode coating;

[0048] Rolling, soaking and drying the current collector coated with the first negative electrode coating, the second negative electrode coating and the third negative electrode coating;

[0049] Wherein, the first negative electrode slurry comprises a halogen-containing acrylic ester polymer monomer and a silicon-based active material;

[0050] The second negative electrode slurry includes a multi-branched acrylic acid ester polymer monomer;

[0051] The third negative electrode slurry includes a long-chain alkenoate polymerized monomer and a carbon-based active material.

[0052] In some embodiments, the second negative electrode slurry further includes a composite conductive agent and an initiator.

[0053] In some embodiments, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile or dibenzoyl peroxide.

[0054] In some embodiments, in the second negative electrode slurry, the mass ratio of the multi-branched olefin acid ester polymer monomer, the composite conductive agent and the initiator is (80-90): (10-20): (0.1-0.2).

[0055] In some embodiments, the preparation of the first negative electrode slurry includes: uniformly mixing a silicon-based active material, a first conductive agent, a first binder, and a halogen-containing acrylate polymerizable monomer in a solvent to obtain the first negative electrode slurry.

[0056] In some embodiments, the preparation of the second negative electrode slurry includes: uniformly mixing an initiator, a composite conductive agent and a multi-branched alkenoate polymerized monomer in a solvent to obtain the second negative electrode slurry.

[0057] In some embodiments, the preparation of the third negative electrode slurry includes: uniformly mixing the carbon-based active material, the second conductive agent, the second binder and the long-chain alkene ester polymerized monomer in a solvent to obtain the third negative electrode slurry.

[0058] In some embodiments, the compaction density of the roller is 1.3-1.6 g / cm 3 .

[0059] In some embodiments, the soaking step includes soaking the rolled pole piece in a solvent at 55-65° C. for 2-3 hours.

[0060] In some embodiments, the solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or ethylene carbonate.

[0061] In some embodiments, the first negative electrode slurry is coated on the surface of the current collector, and after drying, a first negative electrode coating is formed on the surface of the current collector; the second negative electrode slurry is coated on the first negative electrode coating, and after drying, a second negative electrode coating is formed on the surface of the first negative electrode coating; the third negative electrode slurry is coated on the second negative electrode coating and dried; the current collector coated with the first negative electrode coating, the second negative electrode coating, and the third negative electrode coating is rolled, soaked, and dried to obtain a silicon-doped negative electrode sheet.

[0062] According to another aspect of the present application, an embodiment of the present application provides a battery, including a negative electrode sheet, wherein the negative electrode sheet is the aforementioned silicon-doped negative electrode sheet or a silicon-doped negative electrode sheet prepared according to the aforementioned preparation method.

[0063] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0064] In the silicon-doped negative electrode sheet of the present application, by setting the first polymerization unit in the first negative electrode coating, setting the second polymerization unit in the second negative electrode coating, and setting the third polymerization unit in the third negative electrode coating; and further defining that the first polymerization unit contains halogen, the number of branches of the second polymerization unit is greater than or equal to the number of branches of the first polymerization unit or the third polymerization unit, and the main chain length of the third polymerization unit is greater than the main chain length of the first polymerization unit or the second polymerization unit. In this way, the use of a polymer composed of three polymerization units can improve the bonding effect between particles (between silicon-based active materials or between carbon-based active materials) and between layers (between the first negative electrode coating and the second negative electrode coating or between the second negative electrode coating and the third negative electrode coating), thereby improving the structural stability of the silicon-doped negative electrode sheet during the cycle process, and can also improve the ion transmission efficiency during the cycle process; at the same time, it can also improve the fast charging capability and service life of the silicon-doped negative electrode sheet.

[0065] Additional aspects and advantages of the present application will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 Shown is a schematic diagram of the structure of a silicon-doped negative electrode sheet provided in an embodiment of the present invention.

[0067] 1 current collector;

[0068] 2 first negative electrode coating;

[0069] 3. Second negative electrode coating;

[0070] 4. The third negative electrode coating. DETAILED DESCRIPTION

[0071] The present application is further described below in conjunction with specific embodiments. It should be understood that these embodiments of the present application are only used to illustrate the present application and are not used to limit the scope of the present application.

[0072] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0073] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0074] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0075] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0076] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0077] In the related technology, surface graphite is used to suppress SiO x However, the upper layer of graphite alone cannot completely suppress the volume expansion of SiO x As the expansion deepens, the interface contact between the upper and lower layers will deteriorate significantly, and the ion and electron transmission efficiency will decay, which will seriously affect the performance of the battery cell.

[0078] In view of this, if Figure 1 As shown, the embodiment of the present application provides a silicon-doped negative electrode sheet, and the silicon-doped negative electrode sheet includes:

[0079] current collector 1;

[0080] A first negative electrode coating 2, disposed on at least one side surface of the current collector along the thickness direction, the first negative electrode coating comprising a first polymer unit and a silicon-based active material;

[0081] A second negative electrode coating 3, disposed on a surface of the first negative electrode coating away from the current collector, the second negative electrode coating comprising a second polymer unit; and

[0082] The third negative electrode coating 4 is arranged on a surface of the second negative electrode coating away from the first negative electrode coating, and the third negative electrode coating comprises a third polymer unit and a carbon-based active material.

[0083] The provided silicon-doped negative electrode sheet has a multilayer structure, which includes a current collector 1, a first negative electrode coating 2, a second negative electrode coating 3 and a third negative electrode coating 4 which are stacked in sequence, that is, the first negative electrode coating 2 is arranged on at least one side surface of the current collector 1, the second negative electrode coating 3 is arranged on the surface of the first negative electrode coating 2, and the third negative electrode coating 4 is arranged on the surface of the second negative electrode coating 3. Among them, the first negative electrode coating 2 can be used as a silicon-based layer, the second negative electrode coating 3 can be used as an interface enhancement layer, and the third negative electrode coating 4 can be used as a carbon-based material layer, such as a graphite layer.

[0084] The above “the first negative electrode coating 2 is disposed on at least one side surface of the current collector 1 along the thickness direction” means that the first negative electrode coating 2 can be disposed on one surface of the current collector 1 along its own thickness direction, or on two surfaces of the current collector 1 along its own thickness direction. The “surface” here can be the entire area of ​​the current collector 1, or a partial area of ​​the current collector 1. For example, in this embodiment, the surface can be the entire area of ​​the current collector 1. This application has no particular limitation on this, as long as the purpose of this application can be achieved.

[0085] As an example, the current collector 1 has two surfaces opposite to each other in its own thickness direction, and the first negative electrode coating 2 is arranged on the two opposite surfaces of the current collector 1. Further, a second negative electrode coating 3 is formed on the surface of the first negative electrode coating 2 on both sides. Further, a third negative electrode coating 4 is formed on the surface of the second negative electrode coating 3 on both sides. It can be understood that in other embodiments, the first negative electrode coating 2 can also be stacked on any one of the two surfaces of the current collector 1.

[0086] In the present application, in the silicon-doped negative electrode sheet, the material of the current collector 1 is not specifically limited.

[0087] In the present application, in the silicon-doped negative electrode sheet, the first polymerization unit in the first negative electrode coating 2 contains halogen, wherein the halogen-containing functional group such as the fluorine-containing functional group -CF3 surrounds the Si particles after polymerization, and reacts with the Li + The reaction generates a large amount of LiF on the Si surface. This component is the main inorganic component in the SEI film and has high strength and stability. It can not only limit the expansion of Si particles but also inhibit the side reaction of Si with the electrolyte to cause SEI thickening, thereby improving the comprehensive performance of the first negative electrode coating 2.

[0088] In the present application, in the silicon-doped negative electrode sheet, the number of branches of the second polymer unit is greater than or equal to the number of branches of the first polymer unit or the third polymer unit, wherein a large number of branches in the second polymer unit have good stability and matching in the electrolyte, and can absorb sufficient electrolyte to ensure efficient ion transport.

[0089] In the present application, in the silicon-doped negative electrode sheet, the main chain length of the third polymer unit is greater than the main chain length of the first polymer unit or the second polymer unit, wherein lithium ions can be efficiently transmitted on the main chain of the third polymer unit, so that the third polymer unit has a longer main chain, which can further improve the fast charging capability of the carbon-based material layer and quickly conduct lithium ions to the silicon-based layer.

[0090] Thus, in the silicon-doped negative electrode sheet of the present application, by setting the first polymerization unit in the first negative electrode coating 2, setting the second polymerization unit in the second negative electrode coating 3, and setting the third polymerization unit in the third negative electrode coating 4; and further defining that the first polymerization unit contains halogen, the number of branches of the second polymerization unit is greater than or equal to the number of branches of the first polymerization unit or the third polymerization unit, and the main chain length of the third polymerization unit is greater than the main chain length of the first polymerization unit or the second polymerization unit. The polymer composed of the three polymerization units can improve the bonding effect between particles (between silicon-based active materials or between carbon-based active materials) and between layers (between the first negative electrode coating 2 and the second negative electrode coating 3 or between the second negative electrode coating 3 and the third negative electrode coating 4), thereby improving the structural stability of the silicon-doped negative electrode sheet during the cycle; the three polymerization units can also improve the ion transmission efficiency during the cycle through synergistic action, as well as improve the fast charging capability and service life of the silicon-doped negative electrode sheet.

[0091] In some embodiments, the first polymerized unit includes a structure derived from a halogen-containing acrylic ester monomer, and the halogen is selected from at least one of fluorine, chlorine, or bromine. As an example, the halogen can be fluorine, chlorine, or bromine.

[0092] In some embodiments, the number of carbon atoms in the halogen-containing acrylate monomer is 2-10. As an example, the number of carbon atoms in the halogen-containing acrylate monomer can be 2, 3, 4, 5, 6, 7, 8, 9, 10. If the number of carbon atoms in the halogen-containing acrylate monomer is less than 2, its interfacial stabilization effect on the surface of silicon particles will be greatly weakened, the surface side reaction will be aggravated, and the cycle performance will be deteriorated; if the number of carbon atoms in the halogen-containing acrylate monomer is higher than 10, the effect of improving the interfacial stability will not be significantly improved compared with less than 10, and the polymerization effect will be affected.

[0093] Preferably, the first polymerized unit includes a structure derived from a fluorinated acrylate monomer. In some embodiments, the halogen-containing acrylate monomer includes, but is not limited to, at least one of trifluoroethyl methacrylate, pentafluoropropyl methacrylate, or hexafluorobutyl methacrylate. As an example, the halogen-containing acrylate monomer can be trifluoroethyl methacrylate, pentafluoropropyl methacrylate, hexafluorobutyl methacrylate, or a mixture of trifluoroethyl methacrylate and pentafluoropropyl methacrylate. In addition to the C=C bond that can be polymerized, the fluorinated functional group -CF3 of the fluorinated acrylate monomer surrounds the Si particles after polymerization, and reacts with Li during the charging process. + The reaction generates a large amount of LiF on the Si surface. This component is the main inorganic component in the SEI film and has high strength and stability. It can not only limit the expansion of Si particles but also inhibit the side reaction of Si with the electrolyte to cause SEI thickening, thereby improving the comprehensive performance of the silicon base layer (the first negative electrode coating 2).

[0094] In some embodiments, the second polymer unit includes a structure derived from a multi-branched acrylate monomer, and the number of branches is 3-8. As an example, the number of branches of the multi-branched acrylate monomer can be 3, 4, 5, 6, 7, or 8. If the number of branches of the multi-branched acrylate monomer is less than 3, its adsorption effect on the electrolyte is poor, which affects the transmission of lithium ions and the bonding effect on the upper and lower layers is insufficient; if the number of branches of the multi-branched acrylate monomer is higher than 8, the tensile strength and modulus of the polymer itself will deteriorate, affecting the overall mechanical strength of the pole piece.

[0095] In some embodiments, the number of carbon atoms in the multi-branched acrylate monomer is 8-30. As an example, the number of carbon atoms in the multi-branched acrylate monomer can be 8, 10, 15, 18, 20, 25, 28, 29, 30, etc., and of course it can also be a point value within the above range, which is not specifically limited here. If the number of carbon atoms in the halogen-containing acrylate monomer is less than 8, the overall toughness is poor and it is easy to crack; if the number of carbon atoms in the halogen-containing acrylate monomer is higher than 30, the polymer uniformity is poor and the local bonding strength is low.

[0096] In some embodiments, the multi-branched acrylate monomer includes, but is not limited to at least one of pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate or dipentaerythritol hexaacrylate. As an example, the multi-branched acrylate monomer can be pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, or a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate. In addition to the C=C bond that can be polymerized, the multi-branched olefin ester monomer has rich C=O bonds in the ester group branch chain, which has good stability and compatibility in ester electrolytes, and can adsorb sufficient electrolyte around the polymer to ensure efficient ion transmission.

[0097] In some embodiments, the third polymerized unit includes a structure derived from a long-chain alkenoate monomer, and the number of main chain carbon atoms is ≥50. As an example, the number of main chain carbon atoms of the long-chain alkenoate monomer can be 50, 55, 60, 65, 70, 80, etc., and of course it can also be a point value within the above range, which is not specifically limited here. Preferably, the number of main chain carbon atoms of the long-chain alkenoate monomer is ≥50. If the number of main chain carbon atoms of the long-chain alkenoate monomer is less than 50, the bonding effect and strength of the polymer will be reduced.

[0098] In some embodiments, the number of carbon atoms in the long-chain alkenoic acid ester monomer is ≥ 60. As an example, the number of carbon atoms in the long-chain alkenoic acid ester monomer can be 60, 65, 70, 75, 80, 90, etc., and of course, it can also be a point value within the above range, which is not specifically limited here. Preferably, the number of carbon atoms in the long-chain alkenoic acid ester monomer is ≥ 60.

[0099] In some embodiments, the long-chain alkenoate monomer includes, but is not limited to at least one of polyethylene glycol dimethacrylate, polyethylene glycol diacrylate or polyethylene glycol methacrylate. As an example, the long-chain alkenoate monomer can be polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol methacrylate, or a mixture of polyethylene glycol dimethacrylate and polyethylene glycol methacrylate. Among them, the -O-CH2-CH2- in the long-chain alkenoate monomer has a high-efficiency lithium ion transmission capability, so it can further improve the fast charging capability of the carbon-based material layer and quickly conduct lithium ions to the silicon-based layer.

[0100] It should be noted that in the silicon-doped negative electrode sheet, the specific type of silicon-based active material is not limited and can be set according to conventional selection in the art.

[0101] As an example, in some embodiments, the silicon-based active material includes, but is not limited to, at least one of a silicon-oxygen composite material, a silicon-carbon composite material, or pure silicon. For example, the silicon-based active material may be a silicon-oxygen composite material, a silicon-carbon composite material, pure silicon, or a mixture of a silicon-oxygen composite material and a silicon-carbon composite material.

[0102] In some embodiments, the first negative electrode coating 2 further includes a first conductive agent and a first binder. That is, the first negative electrode coating 2 includes a first polymer unit, a silicon-based active material, a first conductive agent and a first binder.

[0103] In some embodiments, the first conductive agent includes, but is not limited to, at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube, or graphene.

[0104] The conductive carbon black includes acetylene black, Ketjen black, etc. The conductive carbon fiber includes vapor-grown carbon fiber.

[0105] In some embodiments, the first binder includes, but is not limited to, at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, or polyacrylic acid.

[0106] In some embodiments, the mass ratio of the first polymer unit, the silicon-based active material, the first conductive agent, and the first binder is (0.2-0.5): (90-95): (1-5): (3-6). As an example, the mass ratio of the first polymer unit, the silicon-based active material, the first conductive agent, and the first binder can be 0.2:90:1:3, 0.3:92:2:4, 0.4:94:4:5, 0.5:95:5:6, 0.3:95:2:4, 0.4:90:1:3, etc. Of course, it can also be other ratios within the above range, which are not limited here. In addition, if the mass of the first polymer unit is lower than the above range, the overall bonding effect of the lower layer will be reduced and the stability of the silicon surface will also deteriorate; if the mass of the first polymer unit is higher than the above range, it will affect the electron conduction and increase the polarization.

[0107] In some embodiments, the surface density of the first negative electrode coating 2 is 30-50 g / m 2 As an example, the surface density of the first negative electrode coating 2 may be 30 g / m 2 , 35g / m 2 , 40g / m 2 , 45g / m 2 , 38g / m 2 , 50g / m 2 Of course, it can also be other values ​​within the above range and is not limited here.

[0108] In some embodiments, the thickness of the first negative electrode coating 2 is 20-33 μm. As an example, the thickness of the first negative electrode coating 2 can be 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0109] In some embodiments, the second negative electrode coating 3 further includes a composite conductive agent, that is, the second negative electrode coating 3 includes the second polymer unit and the composite conductive agent.

[0110] In some embodiments, the composite conductive agent includes a one-dimensional conductive agent and a two-dimensional conductive agent, and the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is (1-1.5):1. As an example, the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc., and of course it can also be other values ​​within the above range, which are not limited here. A high-strength and high-conductivity conductive network can be constructed by a one-dimensional + two-dimensional composite conductive agent, the conductivity and mechanical strength of the interface enhancement layer (the second negative electrode coating 3) can be improved, and the overall performance of the silicon-doped negative electrode sheet can be improved. However, if only one kind of conductive agent is used, a high-strength conductive network cannot be formed. At this time, it can only rely on the polymer as a strength support, and it is difficult to effectively suppress the expansion of the silicon-based layer, resulting in a low structural stability of the silicon-doped negative electrode sheet, which in turn affects the cycle life of the lithium-ion battery and its fast charging performance.

[0111] Furthermore, the one-dimensional conductive agent is filled between the two-dimensional conductive agent sheets, supporting and isolating the two-dimensional conductive agent sheets to form a porous 3D conductive network. If the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is lower than 1:1, the one-dimensional conductive agent will be difficult to effectively support and isolate the sheets between the two-dimensional conductive agents, resulting in agglomeration between the two-dimensional conductive agents, blocking the transmission channel of lithium ions; if the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is higher than 1.5:1, the one-dimensional conductive agent will become redundant, and the one-dimensional conductive agents will also agglomerate, blocking the transmission channel of lithium ions, thereby having an adverse effect on the lithium battery.

[0112] It should be noted that the one-dimensional conductive agent mentioned above can be any one-dimensional conductive agent, and the two-dimensional conductive agent can be any two-dimensional conductive agent, as long as the above-mentioned effects can be achieved.

[0113] As an example, in some embodiments, the one-dimensional conductive agent includes, but is not limited to, at least one of carbon fiber or carbon nanotube.

[0114] As an example, in some embodiments, the two-dimensional conductive agent includes, but is not limited to, at least one of graphene or Mxene.

[0115] In some embodiments, the mass ratio of the second polymer unit to the compound conductive agent is (80-90): (10-20). As an example, the mass ratio of the second polymer unit to the compound conductive agent can be 80:10, 80:12, 84:15, 88:18, 90:10, 90:20, 85:15, 82:18, etc., and of course it can also be other ratios within the above range, which are not limited here. In addition, if the mass of the second polymer unit is lower than the above range, its adsorption effect on the electrolyte is reduced, and the bonding effect on the upper and lower layers is deteriorated; if the mass of the first polymer unit is higher than the above range, it will affect the electronic conduction and increase the polarization.

[0116] In some embodiments, the surface density of the second negative electrode coating 3 is 5-10 g / m 2 As an example, the surface density of the second negative electrode coating 3 may be 5 g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 , 9g / m 2 , 10g / m 2 Of course, it can also be other values ​​within the above range and is not limited here.

[0117] In some embodiments, the thickness of the second negative electrode coating 3 is 3-7 μm. As an example, the thickness of the second negative electrode coating 3 can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, etc., and of course can be other values ​​within the above range, which is not limited here.

[0118] It should be noted that in the silicon-doped negative electrode sheet, the specific type of carbon-based active material is not limited and can be set according to conventional selection in the art.

[0119] As an example, in some embodiments, the carbon-based active material includes, but is not limited to, at least one of natural graphite or artificial graphite. For example, the carbon-based active material can be natural graphite, artificial graphite, or a mixture of natural graphite and artificial graphite.

[0120] In some embodiments, the third negative electrode coating 4 further includes a second conductive agent and a second binder. That is, the third negative electrode coating 4 includes a third polymerized unit, a carbon-based active material, a second conductive agent and a second binder.

[0121] In some embodiments, the second conductive agent includes, but is not limited to, at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube, or graphene.

[0122] The conductive carbon black includes acetylene black, Ketjen black, etc. The conductive carbon fiber includes vapor-grown carbon fiber.

[0123] In some embodiments, the second binder includes, but is not limited to, at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, or polyacrylic acid.

[0124] In some embodiments, the mass ratio of the third polymer unit, the carbon-based active material, the second conductive agent, and the second binder is (0.2-0.5): (94-97): (1-4): (2-4). As an example, the mass ratio of the third polymer unit, the carbon-based active material, the second conductive agent, and the second binder can be 0.2:94:1:2, 0.3:95:2:3, 0.4:97:3:4, 0.5:95:3:3, 0.4:94:1:4, 0.5:97:4:4, etc., and of course it can also be other ratios within the above range, which are not limited here. In addition, if the mass of the first polymer unit is lower than the above range, the mechanical strength of the pole piece is reduced and the lithium ion conductivity is insufficient; if the mass of the first polymer unit is higher than the above range, it will affect the electronic conduction and increase the polarization.

[0125] In some embodiments, the surface density of the third negative electrode coating 4 is 40-80 g / m 2 As an example, the surface density of the third negative electrode coating 4 may be 40 g / m 2 , 50g / m 2 , 60g / m 2 , 70g / m 2 , 75g / m 2 , 80g / m 2 Of course, it can also be other values ​​within the above range and is not limited here.

[0126] In some embodiments, the thickness of the third negative electrode coating 4 is 27-53 μm. As an example, the thickness of the third negative electrode coating 4 can be 27 μm, 29 μm, 30 μm, 33 μm, 35 μm, 40 μm, 42 μm, 47 μm, 50 μm, 53 μm, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0127] It is understandable that the mass ratio of the first polymer unit, the silicon-based active material, the first conductive agent and the first binder, the mass ratio of the second polymer unit and the composite conductive agent, and the mass ratio of the third polymer unit, the carbon-based active material, the second conductive agent and the second 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 substance in the first negative electrode coating 2, the second negative electrode coating 3 and the third negative electrode coating 4 within the above range, the role of each active material and each polymer unit is fully utilized, and the cycle performance, fast charging performance and structural stability of the silicon-doped negative electrode sheet are effectively improved.

[0128] It can also be understood that the surface density and thickness of the coating will affect the electrical properties of the battery (such as energy density, cycle performance and rate performance), preparation cost and safety performance. If the surface density and thickness of the first negative electrode coating 2, the second negative electrode coating 3 and the third negative electrode coating 4 are too large, the electron transmission distance increases, the electronic resistance increases, and the rate performance decreases, which has an adverse effect on the electrical properties of the battery and further increases the difficulty of thermal management of the battery. However, if the surface density and thickness of the first negative electrode coating 2, the second negative electrode coating 3 and the third negative electrode coating 4 are too low, the structural stability of the silicon-doped negative electrode sheet will not be significantly improved, which will have an adverse effect on the safety and long-term cycle stability of the battery.

[0129] In some embodiments, the current collector 1 includes, but is not limited to, at least one of copper foil, copper foam, nickel foam, nickel mesh, or composite copper foil. As an example, the current collector 1 can be copper foil, copper foam, or composite copper foil.

[0130] Thus, based on the above, a silicon-doped negative electrode sheet is provided. By setting a first polymerization unit in the first negative electrode coating 2, setting a second polymerization unit in the second negative electrode coating 3, and setting a third polymerization unit in the third negative electrode coating 4; and further defining that the first polymerization unit contains halogen, the number of branches of the second polymerization unit is greater than or equal to the number of branches of the first polymerization unit or the third polymerization unit, and the main chain length of the third polymerization unit is greater than the main chain length of the first polymerization unit or the second polymerization unit. The polymer composed of the three polymerization units can improve the bonding effect between particles (between silicon-based active materials or between carbon-based active materials) and between layers (between the first negative electrode coating 2 and the second negative electrode coating 3 or between the second negative electrode coating 3 and the third negative electrode coating 4), thereby improving the structural stability of the silicon-doped negative electrode sheet during the cycle process; the three polymerization units can also improve the ion transmission efficiency during the cycle process through synergistic action, and improve the fast charging ability and service life of the silicon-doped negative electrode sheet. Secondly, a composite conductive agent is also used in the second negative electrode coating 3. Through the one-dimensional + two-dimensional composite conductive agent, a high-strength and high-conductivity conductive network can be constructed, the conductivity and mechanical strength of the interface enhancement layer (the second negative electrode coating 3) can be improved, and the overall performance of the silicon-doped negative electrode sheet can be improved. However, if only one conductive agent is used, a high-strength conductive network cannot be formed. At this time, only the polymer can be relied on as a strength support, and it is difficult to effectively inhibit the expansion of the silicon-based layer, resulting in low structural stability of the silicon-doped negative electrode sheet, which in turn affects the cycle life of the lithium-ion battery and its fast charging performance.

[0131] Based on the same inventive concept, the embodiment of the present application also provides a method for preparing a silicon-doped negative electrode sheet, comprising the following steps:

[0132] Coating a first negative electrode slurry on at least one side of the current collector 1 to obtain a first negative electrode coating 2;

[0133] Coating a second negative electrode slurry on the surface of the first negative electrode coating 2 to obtain a second negative electrode coating 3;

[0134] Coating a third negative electrode slurry on the surface of the second negative electrode coating 3 to obtain a third negative electrode coating 4;

[0135] Rolling, soaking and drying the current collector 1 coated with the first negative electrode coating 2, the second negative electrode coating 3 and the third negative electrode coating 4;

[0136] Wherein, the first negative electrode slurry includes a halogen-containing acrylic ester polymer monomer and a silicon-based active material;

[0137] The second negative electrode slurry includes a multi-branched acrylic ester polymer monomer;

[0138] The third negative electrode slurry includes a long-chain alkenoate polymerized monomer and a carbon-based active material.

[0139] It should be understood that all the features and advantages described above for the “silicon-doped negative electrode sheet” are also applicable to the “method for preparing silicon-doped negative electrode sheet” and will not be described in detail here.

[0140] In some embodiments, the second negative electrode slurry further includes a compound conductive agent and an initiator. That is, the second negative electrode slurry includes a multi-branched acrylic ester polymer monomer, a compound conductive agent and an initiator.

[0141] In some embodiments, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, or dibenzoyl peroxide.

[0142] In some specific embodiments, the method for preparing the diaphragm specifically includes the following steps S1 to S6:

[0143] S1: preparing a first negative electrode coating layer 2.

[0144] In step S1, preparing the first negative electrode coating 2 includes: mixing the silicon-based active material, the first conductive agent, the first binder and the halogen-containing acrylate polymer monomer in a solvent to obtain a first negative electrode slurry, coating the slurry on the surface of the current collector 1, and drying to complete the coating of the silicon-based layer (the first negative electrode coating 2).

[0145] In some embodiments, the mass ratio of the halogen-containing acrylate polymerized monomer, the silicon-based active material, the first conductive agent, and the first binder is (0.2-0.5): (90-95): (1-5): (3-6). As an example, the mass ratio of the halogen-containing acrylate polymerized monomer, the silicon-based active material, the first conductive agent, and the first binder can be 0.2:90:1:3, 0.3:92:2:4, 0.4:94:4:5, 0.5:95:5:6, 0.3:95:2:4, 0.4:90:1:3, etc.

[0146] In some embodiments, the drying temperature in step S1 is ≤ 54° C. As an example, the drying temperature in step S1 can be 54° C., 50° C., 45° C., 40° C., 35° C., etc.

[0147] S2: preparing a second negative electrode coating 3.

[0148] In step S2, preparing the second negative electrode coating 3 includes: mixing the initiator, the composite conductive agent and the multi-branched olefin ester polymerization monomer in a solvent to obtain a second negative electrode slurry, coating the slurry on the surface of the silicon base layer, and drying to complete the coating of the interface enhancement layer (the second negative electrode coating 3).

[0149] In some embodiments, in the second negative electrode slurry, the mass ratio of the multi-branched olefin acid ester polymerized monomer, the compound conductive agent and the initiator is (80-90): (10-20): (0.1-0.2). As an example, the mass ratio of the multi-branched olefin acid ester polymerized monomer, the compound conductive agent and the initiator can be 80:10:0.1, 81:12:0.11, 84:15:0.15, 80:17:0.2, 88:18:0.18, 89:17:0.16, 86:16:0.11, 87:11:0.14, 90:20:0.2, etc.

[0150] In some embodiments, the drying temperature in step S2 is ≤54° C. As an example, the drying temperature in step S2 can be 54° C., 50° C., 45° C., 40° C., 35° C., etc.

[0151] S3: preparing a third negative electrode coating layer 4.

[0152] In step S3, preparing the third negative electrode coating 4 includes: mixing the carbon-based active material, the second conductive agent, the second binder and the long-chain olefinic acid ester polymerization monomer in a solvent to obtain a third negative electrode slurry, coating the slurry on the surface of the interface reinforcement layer, and drying to complete the coating of the carbon-based material layer (the third negative electrode coating 4).

[0153] In some embodiments, the mass ratio of the long-chain olefin ester polymerized monomer, the carbon-based active material, the second conductive agent, and the second binder is (0.2-0.5): (94-97): (1-4): (2-4). As an example, the mass ratio of the long-chain olefin ester polymerized monomer, the carbon-based active material, the second conductive agent, and the second binder can be 0.2:94:1:2, 0.3:95:2:3, 0.4:97:3:4, 0.5:95:3:3, 0.4:94:1:4, 0.5:97:4:4, etc.

[0154] In some embodiments, the drying temperature in step S3 is ≤ 54° C. As an example, the drying temperature in step S3 may be 54° C., 50° C., 45° C., 40° C., 35° C., etc.

[0155] S4 roller pressing.

[0156] In step S4, the coated electrode is rolled.

[0157] In some embodiments, the compacted density of the roller is 1.3-1.6 g / cm 3 As an example, the compacted density of the roller can be 1.3 g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 Of course, it can also be other values ​​within the above range and is not limited here.

[0158] S5 soak.

[0159] In step S5, the electrode is immersed in a solvent and stored at 55-65° C. for 2-3 hours.

[0160] In some embodiments, the solvent includes, but is not limited to, at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or ethylene carbonate.

[0161] As an example, the soaking temperature may be 55°C, 57°C, 59°C, 60°C, 63°C, 65°C, etc., and of course may be other values ​​within the above range, which is not limited here.

[0162] As an example, the soaking time may be 2 h, 2.4 h, 2.8 h, 3 h, etc., and of course may be other values ​​within the above range, which is not limited here.

[0163] It should be noted that the initiation mechanism mainly includes three steps: chain initiation, chain growth and chain termination.

[0164] Chain initiation: The initiator decomposes when heated above 60°C to generate two free radicals, which can initiate the polymerization of the monomers. In this reaction, the initiator decomposes to generate two free radicals, which can further react with the monomers to start the polymerization process.

[0165] Chain growth: The free radicals generated during the chain initiation stage react with the monomers to form longer polymer chains. This process is repeated until all monomers are consumed or a certain degree of polymerization is reached.

[0166] Chain termination: The polymerization reaction ultimately needs to be terminated by chain termination. There are two main termination methods: single-radical termination and double-radical termination. Single-radical termination refers to the combination of two free radicals with different charges into a stable molecule; double-radical termination refers to the combination of two free radicals with the same charge to form a covalent bond.

[0167] Through these steps, the initiator can effectively initiate the polymerization reaction of the monomers to form a high molecular weight polymer.

[0168] In the immersion stage S5 of the present invention, the initiator in the interface enhancement layer decomposes to generate free radicals, which diffuse in the solvent and open the C=C bonds in the polymerized monomers in the first negative electrode coating 2, the second negative electrode coating 3, and the third negative electrode coating 4 to initiate a polymerization reaction. In addition, after the initiator decomposes, a large number of pores are left to accommodate the electrolyte in the later stage to increase the ion migration rate, thereby improving the electrical performance of the silicon-doped negative electrode sheet.

[0169] S6 Dry.

[0170] In step S6, the electrode sheet is dried at 60-80° C. for 2-3 hours to complete the preparation of the silicon-doped negative electrode sheet.

[0171] As an example, the drying temperature may be 60°C, 65°C, 70°C, 75°C, 80°C, etc., and of course may be other values ​​within the above range, which is not limited here.

[0172] As an example, the drying time may be 2 h, 2.4 h, 2.8 h, 3 h, etc., and of course may be other values ​​within the above range, which is not limited here.

[0173] Thus, based on the above scheme, the present invention adds a long-chain olefin monomer to the upper carbon-based material layer (third negative electrode coating 4) on the basis of double-layer coating of the silicon-based negative electrode sheet, adds a fluorinated olefin monomer to the lower silicon-based layer (first negative electrode coating 2), and sets an interface enhancement layer (second negative electrode coating 3) in the middle to add multi-branched olefin, one-dimensional + two-dimensional composite conductive agent and initiator. First, the one-dimensional + two-dimensional composite conductive agent in the middle layer can construct a conductive network with high strength and high conductivity. Secondly, the initiator will decompose at a temperature of 55-65°C in S5, leaving a large number of pores to accommodate electrolytes in the later stage to increase the ion migration rate. The free radicals generated after the initiator decomposes will open the C=C bond in the polymerized monomer to initiate the polymerization reaction, improve the bonding effect between particles and layers, and improve the structural stability. Thirdly, in addition to improving the structural stability through polymerization, the polymerized monomers also have their own advantages. The -O-CH2-CH2- in the long-chain olefin monomer in the upper layer has a high efficiency lithium ion transmission capacity, so it can further improve the fast charging capacity of the carbon-based material layer and quickly conduct lithium ions to the silicon-based layer. Furthermore, the interface enhancement layer is a multi-branched acrylate monomer. In addition to the C=C bond that can be polymerized, the ester branch contains abundant C=O bonds, which have good stability and compatibility in ester electrolytes and can absorb sufficient electrolyte around the polymer to ensure efficient ion transmission. In addition, the silicon-based layer is a fluorinated acrylate. In addition to the C=C bond that can be polymerized, the fluorinated functional group -CF3 surrounds the Si particles after polymerization, which reacts with Li during the charging process. +The reaction generates a large amount of LiF on the Si surface. This component is the main inorganic component in the SEI film. It has high strength and stability, which can not only limit the expansion of Si particles but also inhibit the side reaction between Si and electrolyte to cause SEI thickening, thereby improving the overall performance of the lower layer. Finally, the synergistic effect of the three polymer monomers can greatly improve the structural stability and ion transmission efficiency of the silicon-based negative electrode during the cycle process, and improve the fast charging capability and service life of the electrode.

[0174] Based on the same inventive concept, an embodiment of the present application provides a battery, including a negative electrode sheet, wherein the negative electrode sheet is the aforementioned silicon-doped negative electrode sheet or a silicon-doped negative electrode sheet prepared according to the aforementioned preparation method.

[0175] Since the battery includes the silicon-doped negative electrode sheet provided in the embodiment of the present application, it has relatively excellent structural stability and electrical performance.

[0176] In some embodiments, the battery may be a lithium-ion battery. The battery stacking type may be, for example, a wound or laminated battery, and the structure type may be, for example, a square shell (aluminum shell, steel shell, etc.) battery, a soft pack battery, or a cylindrical battery, etc., without specific limitation, and the battery has excellent high temperature performance and electrical performance.

[0177] 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 silicon-doped negative electrode sheet, an electrolyte and a separator.

[0178] In this embodiment, there is no limitation on the materials and structures of the positive electrode sheet, the positive current collector 1, the conductive agent, the binder, etc. in the positive electrode active material layer, and any positive electrode sheet structure and composition known in the art that can be used for secondary batteries can be selected.

[0179] In this embodiment, there is no limitation on the specific material or type of the separator, and any separator known in the art that can be used for secondary batteries can be selected.

[0180] It should also be noted that the battery of the present application is not limited to the specific material or type of the electrolyte, and the components and types that are known in the art and can be used for secondary batteries can be selected as long as the purpose of the present application can be achieved.

[0181] Since the battery provided in the embodiment of the present invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0182] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in this area or the product instructions are used. If the manufacturer of the reagents, materials or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0183] Example 1

[0184] Preparation of silicon-doped negative electrode

[0185] S1: adding the first negative electrode slurry material into solvent water in proportion and stirring to obtain slurry, coating the slurry on the surface of a copper foil with a thickness of 8 μm, and drying (drying temperature 50° C.) to complete the coating of the silicon-based layer (first negative electrode coating);

[0186] In the first negative electrode slurry, based on the total mass of the solute: the mass proportions of silicon-oxygen composite material, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and trifluoroethyl methacrylate are 92%, 3.5%, 1.6%, 2.5%, and 0.4%, respectively;

[0187] Silicone layer density 40g / m 2 , thickness 27 μm;

[0188] S2: adding the second negative electrode slurry material into the solvent water in proportion and stirring to obtain a slurry, coating the slurry on the surface of the silicon base layer, and drying (drying temperature 50° C.) to complete the coating of the interface enhancement layer (second negative electrode coating);

[0189] In the second negative electrode slurry, based on the total mass of the solute: pentaerythritol triacrylate, carbon fiber, graphene, and azobisisobutyronitrile (AIBN) account for 84.85%, 7.5%, 7.5%, and 0.15% by mass, respectively;

[0190] Interface reinforcement layer density 8g / m 2 , thickness 5 μm;

[0191] S3: adding the third negative electrode slurry material into the solvent water in proportion and stirring to obtain a slurry, coating the slurry on the surface of the interface enhancement layer, and drying (drying temperature 50° C.) to complete the coating of the graphite layer (third negative electrode coating);

[0192] In the third negative electrode slurry, based on the total mass of the solute: artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene glycol dimethacrylate account for 95.8%, 1%, 1.1%, 1.8%, and 0.15% by mass, respectively;

[0193] Graphite layer density 60g / m 2 , thickness 40 μm;

[0194] S4: Roll the coated pole piece to a compaction density of 1.5 g / cm 3

[0195] S5: Soak the electrode in a solvent (diethyl carbonate:ethylene carbonate=1:1) and store at 60°C for 2h;

[0196] S6: Dry the electrode at 60° C. for 2 h to complete the preparation of the silicon-doped negative electrode.

[0197] Example 2

[0198] The only difference between Example 2 and Example 1 is that the polymerizable monomer in the first negative electrode slurry of Example 2 is pentafluoropropyl methacrylate, the polymerizable monomer in the third negative electrode slurry is polyethylene glycol methacrylate, and the polymerizable monomer in the second negative electrode slurry is pentaerythritol tetraacrylate.

[0199] Example 3

[0200] The only difference between Example 3 and Example 1 is that the polymerizable monomer in the first negative electrode slurry of Example 3 is hexafluorobutyl methacrylate, the polymerizable monomer in the third negative electrode slurry is polyethylene glycol methacrylate, and the polymerizable monomer in the second negative electrode slurry is dipentaerythritol hexaacrylate.

[0201] Example 4

[0202] The only difference between Example 4 and Example 1 is that in the second negative electrode slurry of Example 4, based on the total mass of the solute: the mass proportions of pentaerythritol triacrylate, carbon fiber, graphene, and azobisisobutyronitrile (AIBN) are 80%, 9.9%, 9.9%, and 0.2%, respectively.

[0203] Example 5

[0204] The only difference between Example 5 and Example 1 is that in the second negative electrode slurry of Example 5, based on the total mass of the solute: the mass proportions of pentaerythritol triacrylate, carbon fiber, graphene, and azobisisobutyronitrile (AIBN) are 90%, 4.95%, 4.95%, and 0.1%, respectively.

[0205] Example 6

[0206] The only difference between Example 6 and Example 1 is that in the second negative electrode slurry of Example 6, based on the total mass of the solute: the mass proportions of pentaerythritol triacrylate, carbon fiber, graphene, and azobisisobutyronitrile (AIBN) are 90%, 4.7%, 5.2%, and 0.1%, respectively.

[0207] Example 7

[0208] The only difference between Example 7 and Example 1 is that in the first negative electrode slurry of Example 7, based on the total mass of the solute: the mass proportions of the silicon-oxygen composite material, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and trifluoroethyl methacrylate are 92.2%, 3.5%, 1.6%, 2.5%, and 0.2%, respectively.

[0209] Example 8

[0210] The only difference between Example 8 and Example 1 is that in the first negative electrode slurry of Example 8, based on the total mass of the solute: the mass proportions of the silicon-oxygen composite material, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and trifluoroethyl methacrylate are 91.9%, 3.5%, 1.6%, 2.5%, and 0.5%, respectively.

[0211] Example 9

[0212] The only difference between Example 9 and Example 1 is that in the third negative electrode slurry of Example 9, based on the total mass of the solute: the mass proportions of artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene glycol dimethacrylate are 95.9%, 1%, 1.1%, 1.8%, and 0.2%, respectively.

[0213] Example 10

[0214] The only difference between Example 10 and Example 1 is that in the third negative electrode slurry of Example 10, based on the total mass of the solute: the mass proportions of artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene glycol dimethacrylate are 95.6%, 1%, 1.1%, 1.8%, and 0.5%, respectively.

[0215] Embodiment 11

[0216] The only difference between Example 11 and Example 1 is that the initiator of Example 11 is dibenzoyl peroxide (BPO).

[0217] Example 12

[0218] The difference between Example 12 and Example 1 is that the interface reinforcement layer density of Example 12 is 10 g / cm 2 .

[0219] Example 13

[0220] The difference between Example 13 and Example 1 is that the silicon base layer of Example 13 is 30 g / m 2 , thickness 20 μm;

[0221] Graphite layer density 40g / m 2 , thickness 27 μm;

[0222] Interface reinforcement layer density 5g / m 2 , thickness 3μm.

[0223] Embodiment 14

[0224] The difference between Example 14 and Example 1 is that the silicon-based layer of Example 14 is 50 g / m 2 , thickness 33μm;

[0225] Graphite layer density 80g / m 2 , thickness 53μm;

[0226] Interface reinforcement layer density 10g / m 2 , thickness 7μm.

[0227] Comparative Example 1

[0228] The only difference between Comparative Example 1 and Example 1 is that the third negative electrode slurry of Comparative Example 1 does not contain polyethylene glycol dimethacrylate.

[0229] Comparative Example 2

[0230] The only difference between Comparative Example 2 and Example 1 is that the first negative electrode slurry of Comparative Example 2 does not contain trifluoroethyl methacrylate.

[0231] Comparative Example 3

[0232] The only difference between Comparative Example 3 and Example 1 is that the second negative electrode slurry of Comparative Example 3 does not contain pentaerythritol triacrylate.

[0233] Comparative Example 4

[0234] The only difference between Comparative Example 4 and Example 1 is that the conductive agent in the second negative electrode slurry of Comparative Example 4 is conductive carbon black.

[0235] Comparative Example 5

[0236] The only difference between Comparative Example 5 and Example 1 is that in the second negative electrode slurry of Comparative Example 5, based on the total mass of the solute: the mass proportions of pentaerythritol triacrylate, carbon fiber, graphene, and azobisisobutyronitrile (AIBN) are 84.85%, 5%, 10%, and 0.15%, respectively.

[0237] Performance Testing

[0238] 1. Battery preparation

[0239] Preparation of positive electrode sheet: LiNi 0.8 Co 0.1 Mn 0.1O2, conductive carbon black (SP), carbon nanotubes, and binder polyvinylidene fluoride (PVDF5130) are mixed in a mass ratio of 97:1.5:0.5:1, and then N-methylpyrrolidone (NMP) is added, stirred and mixed uniformly to form a stable positive electrode slurry with a solid content of 75%; the positive electrode slurry is evenly coated on a 10μm aluminum foil of the positive electrode current collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0240] Separator: A polyethylene (PE) separator with a thickness of 12 μm is selected as the separator.

[0241] Electrolyte: In a glove box filled with inert gas, ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate are mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then lithium salt LiPF6 is dissolved in the organic solvent. The concentration of the lithium salt is 1.2 mol / L to obtain an electrolyte.

[0242] Battery assembly: Arrange the positive electrode sheet, separator, and negative electrode sheet in order, and assemble them by winding. Inject the electrolyte into the dry battery cell, and obtain the lithium battery after formation and aging.

[0243] 2. Test the electrochemical performance of the battery

[0244] (1) Constant current ratio test: The batteries prepared in each embodiment and comparative example were discharged and charged to 4.25 V at 0.05C and 5C respectively, and the 5C capacity / 0.05C capacity was recorded as the charging constant current ratio (Note: the larger the charging constant current ratio, the higher the fast charging capability of the electrode).

[0245] (2) Capacity retention test after 500 cycles: Take the batteries made in each embodiment and comparative example, let them stand at 25°C for 30 minutes; charge at 2C constant current to 4.25V + charge at constant voltage to 0.05C; let them stand for 30 minutes; then discharge at 2C constant current to 2.5V (the capacity at this step is recorded as the discharge capacity); let them stand for 30 minutes. Repeat the above steps 500 times, and record the ratio of the 500th cycle discharge capacity to the first cycle discharge capacity as the capacity retention rate (Note: the higher the capacity retention rate, the longer the service life of the electrode).

[0246] (3) Electrode rebound rate test after 500 cycles: Disassemble the fully charged battery and fresh fully charged battery after 500 cycles, and record the anode thickness after 500 cycles / fresh anode thickness as the electrode rebound rate (Note: the lower the electrode rebound rate, the higher the stability of the electrode structure).

[0247] The test results are shown in Table 1 below.

[0248] Table 1

[0249]

[0250] From the test results, it can be seen that all the parameters of the examples are within the specifications, and the constant current ratio, capacity retention rate, and electrode rebound rate are all excellent. 2- It has efficient lithium ion transmission capability and polymer fixation on the graphite layer, but its fast charging performance and cycle life are greatly reduced, and the pole piece rebound rate is also increased to a certain extent compared with Example 1, proving that the stability of the graphite layer structure is also deteriorated. In Comparative Example 2, the silicon-based polymerization unit is cancelled, and the silicon negative electrode expansion has no effective inhibition of the pole piece rebound, which is much higher than in Example 1, and the lack of LiF generated by fluoroacrylate on the surface of the material leads to aggravated side reactions and a significant deterioration in capacity retention. In Comparative Example 3, the interface enhancement layer polymerization unit is cancelled. There is no adsorption and stabilization effect of a large number of C=O bonds in the multi-branched acrylate on the electrolyte. The ion conduction rate in this area is greatly attenuated, and the strength is greatly deteriorated. It cannot effectively restrain the expansion of the silicon-based layer, resulting in a much higher pole piece rebound than in Example 1. In Comparative Example 4, the one-dimensional + two-dimensional conductive network is cancelled, and only point-shaped conductive carbon black is used. The particles are small and it is impossible to build a network with high spacing strength and high conductivity. The strength support is provided by the polymer alone, which greatly attenuates the conductivity and mechanical strength of the interface enhancement layer, and deteriorates the overall performance of the pole piece.

[0251] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0252] The basic principle of the present invention is described above in conjunction with specific embodiments. However, it should be pointed out that the advantages, strengths, effects, etc. mentioned in the present invention are only examples and not limitations, and it cannot be considered that these advantages, strengths, effects, etc. must be possessed by each embodiment of the present invention. In addition, the specific details disclosed above are only for the purpose of illustration and facilitation of understanding, rather than limitation, and the above details do not limit the present invention to being implemented by adopting the above specific details.

[0253] It should be noted that the term "and / or" or " / " used in this document is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The singular forms of "a", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0254] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0255] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-doped negative electrode sheet, characterized in that: The silicon-doped negative electrode sheet comprises: current collector; A first negative electrode coating is disposed on at least one side of the current collector along the thickness direction, wherein the first negative electrode coating comprises a first polymer unit and a silicon-based active material; A second negative electrode coating is disposed on a surface of the first negative electrode coating away from the current collector, wherein the second negative electrode coating comprises a second polymer unit; and a third negative electrode coating, disposed on a surface of the second negative electrode coating away from the first negative electrode coating, the third negative electrode coating comprising a third polymerized unit and a carbon-based active material; The first polymer unit contains halogen, the number of branches of the second polymer unit is greater than or equal to the number of branches of the first polymer unit or the third polymer unit, and the main chain length of the third polymer unit is greater than the main chain length of the first polymer unit or the second polymer unit.

2. The silicon-doped negative electrode sheet according to claim 1, characterized in that: The first polymerized unit, the second polymerized unit and the third polymerized unit satisfy at least one of the following characteristics (1) to (3): (1) The first polymerized unit comprises a structure derived from a halogen-containing acrylic ester monomer, wherein the halogen is selected from at least one of fluorine, chlorine or bromine; Preferably, the number of carbon atoms in the halogen-containing acrylate monomer is 2-10; Preferably, the halogen-containing acrylic ester monomer includes at least one of trifluoroethyl methacrylate, pentafluoropropyl methacrylate or hexafluorobutyl methacrylate; (2) The second polymerized unit comprises a structure derived from a multi-branched acrylic ester monomer, and the number of the branches is 3-8; Preferably, the multi-branched acrylic ester monomer has 8 to 30 carbon atoms; Preferably, the multi-branched acrylate monomer includes at least one of pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate or dipentaerythritol hexaacrylate; (3) The third polymerized unit comprises a structure derived from a long-chain alkene ester monomer, and the number of carbon atoms in the main chain is ≥50; Preferably, the number of carbon atoms in the long-chain alkene ester monomer is ≥ 60; Preferably, the long-chain alkene ester monomer includes at least one of polyethylene glycol dimethacrylate, polyethylene glycol diacrylate or polyethylene glycol methacrylate.

3. The silicon-doped negative electrode sheet according to claim 1, characterized in that: The first negative electrode coating satisfies at least one of the following characteristics (1) to (5): (1) The silicon-based active material comprises at least one of a silicon-oxygen composite material, a silicon-carbon composite material or pure silicon; (2) The first negative electrode coating further includes a first conductive agent and a first binder; Preferably, the first conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene; Preferably, the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate or polyacrylic acid; (3) The mass ratio of the first polymer unit, the silicon-based active material, the first conductive agent and the first binder is (0.2-0.5): (90-95): (1-5): (3-6); (4) The surface density of the first negative electrode coating is 30-50 g / m 2 ; (5) The thickness of the first negative electrode coating is 20-33 μm.

4. The silicon-doped negative electrode sheet according to claim 1, characterized in that: The second negative electrode coating satisfies at least one of the following characteristics (1) to (4): (1) The second negative electrode coating further includes a composite conductive agent; Preferably, the composite conductive agent comprises a one-dimensional conductive agent and a two-dimensional conductive agent, and the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is (1-1.5):1; Preferably, the one-dimensional conductive agent includes at least one of carbon fiber or carbon nanotube; Preferably, the two-dimensional conductive agent comprises at least one of graphene or Mxene; (2) The mass ratio of the second polymer unit to the composite conductive agent is (80-90): (10-20); (3) The surface density of the second negative electrode coating is 5-10 g / m 2 ; (4) The thickness of the second negative electrode coating is 3-7 μm.

5. The silicon-doped negative electrode sheet according to claim 1, characterized in that: The third negative electrode coating satisfies at least one of the following characteristics (1) to (5): (1) The carbon-based active material includes at least one of natural graphite or artificial graphite; (2) The third negative electrode coating further includes a second conductive agent and a second binder; Preferably, the second conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene; Preferably, the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate or polyacrylic acid; (3) The mass ratio of the third polymer unit, the carbon-based active material, the second conductive agent and the second binder is (0.2-0.5): (94-97): (1-4): (2-4); (4) The surface density of the third negative electrode coating is 40-80 g / m 2 ; (5) The thickness of the third negative electrode coating is 27-53 μm.

6. The silicon-doped negative electrode sheet according to any one of claims 1 to 5, characterized in that: The current collector includes at least one of copper foil, foam copper, foam nickel, nickel mesh or composite copper foil.

7. The method for preparing a silicon-doped negative electrode sheet according to any one of claims 1 to 6, characterized in that: The following steps are involved: Coating a first negative electrode slurry on at least one side of the current collector to obtain a first negative electrode coating; Coating a second negative electrode slurry on the surface of the first negative electrode coating to obtain a second negative electrode coating; coating a third negative electrode slurry on the surface of the second negative electrode coating to obtain a third negative electrode coating; Rolling, soaking and drying the current collector coated with the first negative electrode coating, the second negative electrode coating and the third negative electrode coating; Wherein, the first negative electrode slurry comprises a halogen-containing acrylic ester polymer monomer and a silicon-based active material; The second negative electrode slurry includes a multi-branched acrylic acid ester polymer monomer; The third negative electrode slurry includes a long-chain alkenoate polymerized monomer and a carbon-based active material.

8. The method for preparing a silicon-doped negative electrode sheet according to claim 7, characterized in that: The second negative electrode slurry also includes a composite conductive agent and an initiator; Preferably, the initiator comprises at least one of azobisisobutyronitrile, azobisisoheptanenitrile or dibenzoyl peroxide; Preferably, in the second negative electrode slurry, the mass ratio of the multi-branched olefin acid ester polymer monomer, the composite conductive agent and the initiator is (80-90): (10-20): (0.1-0.2).

9. The method for preparing a silicon-doped negative electrode sheet according to claim 7 or 8, characterized in that: The preparation of the first negative electrode slurry includes: uniformly mixing the silicon-based active material, the first conductive agent, the first binder and the halogen-containing acrylate polymer monomer in a solvent to obtain the first negative electrode slurry; The preparation of the second negative electrode slurry comprises: uniformly mixing an initiator, a composite conductive agent and a multi-branched alkenoate polymerized monomer in a solvent to obtain a second negative electrode slurry; The preparation of the third negative electrode slurry comprises: uniformly mixing the carbon-based active material, the second conductive agent, the second binder and the long-chain alkene ester polymerized monomer in a solvent to obtain the third negative electrode slurry; Preferably, the compaction density of the roller is 1.3-1.6 g / cm 3 ; Preferably, the soaking step comprises: soaking the rolled pole piece in a solvent at 55-65° C. for 2-3 hours; Preferably, the solvent comprises at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or ethylene carbonate; Preferably, the first negative electrode slurry is coated on the surface of the current collector, and after drying, a first negative electrode coating is formed on the surface of the current collector; the second negative electrode slurry is coated on the first negative electrode coating, and after drying, a second negative electrode coating is formed on the surface of the first negative electrode coating; the third negative electrode slurry is coated on the second negative electrode coating, and dried; the current collector coated with the first negative electrode coating, the second negative electrode coating, and the third negative electrode coating is rolled, soaked, and dried to obtain a silicon-doped negative electrode sheet.

10. A battery comprising a negative electrode sheet, characterized in that: The negative electrode sheet comprises the silicon-doped negative electrode sheet according to any one of claims 1 to 6, or comprises the silicon-doped negative electrode sheet prepared by the preparation method according to any one of claims 7 to 9.

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