Silicon-based negative pole piece, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, in particular to a silicon-based negative pole piece, a preparation method thereof and a battery. The silicon-based negative electrode plate comprises a current collector, a first negative electrode coating, a second negative electrode coating and a third negative electrode coating; wherein the second negative electrode coating is a porous coating with a porous structure. The second negative electrode coating is arranged as a functional layer, the functional layer has a relatively large pore diameter and a pore structure, and the functional layer also contains a flexible polymer and a binder, so that on one hand, the slurry of the negative electrode coating in the third negative electrode coating can flow into the second negative electrode coating due to the existence of pores; further, the effect of inhibiting the expansion of the silicon-based material in the slurry of the third negative electrode coating is achieved, the interface contact effect is improved, and the risk that the third negative electrode coating falls off is reduced; and on the other hand, the existence of the flexible polymer and the binder can further improve the inhibition effect of the pore structure of the functional layer on the expansion of the silicon-based material.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a silicon-based negative electrode plate and a preparation method thereof, and a battery. Background Art

[0002] In recent years, the market demand for electric vehicle range has been increasing, and the range is proportional to the energy density of lithium batteries, so high energy density battery products have received more and more attention and research. Traditional negative electrode materials only have a gram capacity of 350-370mAh / g, and their energy density has reached a bottleneck. Silicon-carbon and silicon-oxygen materials are widely used in high energy density battery applications because of their theoretical capacity of up to 1600mAh / g.

[0003] However, silicon-carbon and silicon-oxygen materials have a large volume rebound, generally with a volume rebound rate of 100-300%, which is much greater than that of graphite materials. Due to their large volume expansion, the force between the binder and the current collector is weakened after expansion, causing the pole piece and the current collector to separate, deteriorating the electrochemical performance and safety performance of lithium batteries.

[0004] Therefore, when using silicon-based materials as negative electrode materials for lithium batteries, how to reduce the expansion rebound of silicon-based materials and improve their interface conditions has become a technical problem that needs to be urgently solved by technicians in this field. 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-based negative electrode plate and a preparation method thereof and a battery, which can reduce the expansion rebound of silicon-based materials, improve their interface conditions, and enhance the electrochemical performance and safety performance of the battery.

[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-based negative electrode plate, wherein the silicon-based negative electrode plate comprises:

[0008] current collector;

[0009] A first negative electrode coating is disposed on at least one side of the current collector along the thickness direction, and the first negative electrode coating includes a first carbon-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 flexible polymer and a binder; and

[0011] The third negative electrode coating is disposed on the surface of the second negative electrode coating away from the first negative electrode coating, and the third negative electrode coating includes a silicon-based active material and a second carbon-based active material;

[0012] Wherein, the second negative electrode coating is a porous coating with a porous structure.

[0013] In some embodiments, the porosity of the second negative electrode coating is 40 - 60%, and the pore diameter is 1 - 3 μm.

[0014] In some embodiments, the first carbon-based active material includes at least one of natural graphite or artificial graphite.

[0015] In some embodiments, the average particle size D50 of the first carbon-based active material is 6 - 12 μm.

[0016] In some embodiments, the first negative electrode coating further includes a first binder and a first conductive agent.

[0017] In some embodiments, the first binder includes at least one of carboxymethyl cellulose or styrene-butadiene rubber; preferably, the first binder is a mixture of carboxymethyl cellulose and styrene-butadiene rubber.

[0018] In some embodiments, the first conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene.

[0019] In some embodiments, the mass ratio of the carbon-based active material, the first binder, and the first conductive agent is 90 - 98:1.5 - 5:0.5 - 2.

[0020] In some embodiments, the thickness of the first negative electrode coating is 12 - 100 μm.

[0021] In some embodiments, the flexible polymer includes at least one of polystyrene, polyamide or polypropylene.

[0022] In some embodiments, the binder includes at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid or polyacrylonitrile.

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

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

[0025] In some of these embodiments, the mass ratio of the flexible polymer, binder, and second conductive agent is 20-40:40-60:10-20.

[0026] In some of these embodiments, the thickness of the second negative electrode coating is 5-10 μm.

[0027] In some of these embodiments, the silicon-based active material includes at least one of silicon-oxygen composite material, silicon-carbon composite material, or pure silicon.

[0028] In some of these embodiments, the average particle size D50 of the silicon-based active material is 6-12 μm.

[0029] In some of these embodiments, the second carbon-based active material includes at least one of natural graphite or artificial graphite.

[0030] In some of these embodiments, the average particle size D50 of the second carbon-based active material is 12-20 μm.

[0031] In some of these embodiments, the third negative electrode coating further includes a second binder and a third conductive agent.

[0032] In some of these embodiments, the second binder includes at least one of polyacrylic acid or styrene-butadiene rubber; preferably, the second binder is a mixture of polyacrylic acid and styrene-butadiene rubber.

[0033] In some of these embodiments, the third conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube, or graphene.

[0034] In some of these embodiments, the mass ratio of the silicon-based active material, second carbon-based active material, second binder, and third conductive agent is 20-60:40-80:3-15:1-5.

[0035] In some of these embodiments, the thickness of the third negative electrode coating is 12-100 μm.

[0036] In some of these embodiments, the current collector includes at least one of copper foil, copper foam, nickel foam, nickel mesh, or composite copper foil.

[0037] According to another aspect of the present application, an embodiment of the present application provides a method for preparing a silicon-based negative electrode sheet, including the following steps:

[0038] Coat a first negative electrode slurry on at least one surface of the current collector to obtain a first negative electrode coating;

[0039] Coat a second negative electrode paste on the surface of the first negative electrode coating to obtain a second negative electrode coating;

[0040] Coat a third negative electrode paste on the surface of the second negative electrode coating to obtain a third negative electrode coating;

[0041] Wherein, the first negative electrode paste includes a first carbon-based active material;

[0042] The second negative electrode paste includes a flexible polymer and a binder;

[0043] The third negative electrode paste includes a silicon-based active material and a second carbon-based active material.

[0044] In some embodiments, the second negative electrode paste further includes a pore-forming agent.

[0045] In some embodiments, the pore-forming agent includes at least one of an ammonium salt or a carbonate.

[0046] In some embodiments, the mass ratio of the flexible polymer, binder, second conductive agent, and pore-forming agent is 20-40:40-60:10-20:10-30.

[0047] In some embodiments, the preparation of the first negative electrode paste includes: mixing the first carbon-based active material, the first conductive agent, and the first binder uniformly in a solvent to obtain the first negative electrode paste.

[0048] In some embodiments, the preparation of the second negative electrode paste includes: mixing the flexible polymer, binder, second conductive agent, and pore-forming agent uniformly in a solvent to obtain the second negative electrode paste.

[0049] In some embodiments, the preparation of the third negative electrode paste includes: mixing the silicon-based active material, the second carbon-based active material, the second binder, and the third conductive agent uniformly in a solvent to obtain the third negative electrode paste.

[0050] In some embodiments, the solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or ethylene carbonate.

[0051] In some embodiments, coat the first negative electrode paste on the surface of the current collector, and after drying, form a first negative electrode coating on the surface of the current collector; coat the second negative electrode paste on the first negative electrode coating, and after drying, form a second negative electrode coating on the surface of the first negative electrode coating; coat the third negative electrode paste on the second negative electrode coating and dry to obtain the silicon-based negative electrode sheet.

[0052] According to another aspect of the present application, an embodiment of the present application provides a battery, including a negative electrode tab, and the negative electrode tab includes the aforementioned silicon-based negative electrode tab, or a silicon-based negative electrode tab prepared by the aforementioned preparation method.

[0053] Implementing the technical solutions of the present invention has at least the following beneficial effects:

[0054] In the embodiment of the present application, for the provided negative electrode tab, by setting the first negative electrode coating as a carbon-based active material layer, the carbon-based active material has an expansion rate property and has a better adhesion with the current collector. At the same time, the carbon-based active material itself has good electrical conductivity, which can reduce the resistance in the electron transmission path and improve the overall electrical conductivity of the battery. Furthermore, since the carbon-based active material layer is adjacent to the current collector, it can also make the current evenly distributed on a larger surface, avoiding problems caused by too high local current density, and thus improving the safety and stability of the battery. Further, by setting the second negative electrode coating as a functional layer, the functional layer has a larger pore size and pore structure, and the functional layer also has a flexible polymer and a binder. On the one hand, the presence of pores will cause the slurry of the negative electrode coating in the third negative electrode coating to flow into the second negative electrode coating, thereby achieving the effect of suppressing the expansion of the silicon-based material in the slurry of the third negative electrode coating, improving the interface contact effect, and reducing the risk of peeling off of the third negative electrode coating. On the other hand, the presence of the flexible polymer and the binder can further enhance the inhibitory effect of the pore structure of the functional layer on the expansion of the silicon-based material. Even further, by simultaneously providing a carbon-based active material and a silicon-based active material in the third negative electrode coating, the fast charging ability of the battery can be improved.

[0055] Additional aspects and advantages of the present application will be partially given in the following description, partially become apparent from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0056] Figure 1 The figure shows a schematic structural diagram of a silicon-based negative electrode tab provided by Embodiment 1 of the present invention.

[0057] Description of the Reference Numerals in the Drawings

[0058] 10 - Current collector;

[0059] 20 - First negative electrode coating;

[0060] 30 - Second negative electrode coating;

[0061] 40 - Third negative electrode coating;

[0062] 1 - Pore. Detailed Embodiments

[0063] The present application will be 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 not to limit the scope of the present application.

[0064] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values or individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0065] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0066] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0067] If there is no special instruction, all steps of the present application can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can 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 also include steps (c), (a) and (b), etc.

[0068] If there is no special instruction, the "including" and "comprising" mentioned in the present application mean open-ended or may also be closed-ended. For example, the "including" and "comprising" may mean that other components not listed may also be included or comprised, or may only include or comprise the listed components.

[0069] In order to solve the problem of expansion rebound and poor interface condition of silicon-based materials when using silicon-based materials as negative electrode materials of lithium batteries, Chinese patent CN114400312A discloses a method for inhibiting the expansion of silicon-based materials, which adopts the method of depositing a flexible organic polymer layer to inhibit the rebound of silicon oxygen. Although the invention can reduce the rebound of silicon-based negative electrode to a certain extent through the flexibility of the polymer, on the one hand, the method is difficult to prepare and has a high application cost. In addition, although the flexible polymer material has limited ability to suppress the rebound of silicon-based materials, it still cannot effectively solve the problem of interface peeling between the current collector and the silicon-based pole piece. Another Chinese patent CN116544376A discloses a surface deposited amorphous carbon layer to inhibit the expansion of silicon-based negative electrode. Although amorphous carbon can provide greater conductivity and can inhibit the expansion of silicon-based materials to a certain extent, amorphous carbon is brittle and cannot withstand high pressure compaction, resulting in the amorphous carbon layer being easily broken and unable to avoid the shedding of the amorphous carbon layer.

[0070] In view of this, an embodiment of the present application provides a silicon-based negative electrode plate, and the silicon-based negative electrode plate includes:

[0071] Current collector 10;

[0072] A first negative electrode coating 20, disposed on at least one side surface of the current collector 10 along the thickness direction, and the first negative electrode coating 20 includes a first carbon-based active material;

[0073] A second negative electrode coating 30 is disposed on a surface of the first negative electrode coating 20 away from the current collector 10 , and the second negative electrode coating 30 includes a flexible polymer and a binder; and

[0074] The third negative electrode coating 40 is disposed on a surface of the second negative electrode coating 30 away from the first negative electrode coating 20 . The third negative electrode coating 40 includes a silicon-based active material and a second carbon-based active material.

[0075] The provided silicon-based negative electrode sheet has a multilayer structure, which includes a current collector 10, a first negative electrode coating 20, a second negative electrode coating 30 and a third negative electrode coating 40 stacked in sequence, that is, the first negative electrode coating 20 is arranged on at least one side surface of the current collector 10, the second negative electrode coating 30 is arranged on the surface of the first negative electrode coating 20, and the third negative electrode coating 40 is arranged on the surface of the second negative electrode coating 30. Among them, the first negative electrode coating 20 can be used as a carbon-based material layer, such as a graphite layer, the second negative electrode coating 30 is used as a functional layer, and the third negative electrode coating 40 is used as a composite layer of silicon-based material and carbon-based material.

[0076] The statement "the first negative electrode coating 20 is disposed on at least one surface of the current collector 10 in the thickness direction" means that the first negative electrode coating 20 can be disposed on one surface of the current collector 10 in its own thickness direction, or can be disposed on two surfaces of the current collector 10 in its own thickness direction. The "surface" here can be the entire area of the current collector 10 or a partial area of the current collector 10. For example, in this embodiment, the surface can be the entire area of the current collector 10. The present application has no special limitation on this, as long as the purpose of the present application can be achieved.

[0077] As an example, the current collector 10 has two surfaces opposite to each other in its own thickness direction, and the first negative electrode coating 20 is disposed on the two opposite surfaces of the current collector 10. Further, a second negative electrode coating 30 is formed on the surfaces of the first negative electrode coatings 20 on both sides. Still further, a third negative electrode coating 40 is formed on the surfaces of the second negative electrode coatings 30 on both sides. It can be understood that in other embodiments, the first negative electrode coating 20 can also be stacked on any one of the two surfaces of the current collector 10.

[0078] In the present application, in the silicon-doped negative electrode sheet, the material of the current collector 10 is not particularly limited.

[0079] In the present application, the second negative electrode coating 30 is a porous coating having a porous structure. The presence of the pore structure causes the slurry of the third negative electrode coating 40 to flow into the second negative electrode coating 30, and combines with the flexible polymer in the second negative electrode coating 30, achieving the effect of suppressing the expansion of the silicon-based material in the slurry of the third negative electrode coating 40, improving the interfacial contact, and reducing the risk of peeling off of the third negative electrode coating 40.

[0080] Thus, for the negative electrode sheet of the present application, by setting the first negative electrode coating 20 as a carbon-based active material layer, the carbon-based active material has an expansion rate property and has a better adhesion with the current collector 10. At the same time, the carbon-based active material itself has good electrical conductivity, which can reduce the resistance in the electron transmission path and improve the overall electrical conductivity of the battery. Moreover, the carbon-based active material layer is adjacent to the current collector 10, which can also make the current evenly distributed on a larger surface, avoiding problems caused by too high local current density, and thus improving the safety and stability of the battery. Further, by setting the second negative electrode coating 30 as a functional layer, the functional layer has a larger pore size and pore structure, and the functional layer also has a flexible polymer and a binder. On the one hand, the presence of pores will cause the slurry of the negative electrode coating in the third negative electrode coating 40 to flow into the second negative electrode coating 30, thereby achieving the effect of suppressing the expansion of the silicon-based material in the slurry of the third negative electrode coating 40, improving the interface contact effect, and reducing the risk of peeling off of the third negative electrode coating 40. On the other hand, the presence of the flexible polymer and the binder can further enhance the inhibitory effect of the pore structure of the functional layer on the expansion of the silicon-based material. Furthermore, by simultaneously setting a carbon-based active material and a silicon-based active material in the third negative electrode coating 40, the fast charging ability of the battery can be improved.

[0081] In some embodiments, the porosity of the second negative electrode coating 30 is 40-60%, and the pore size is 1-3 μm. As an example, the porosity of the second negative electrode coating 30 can be 40%, 45%, 50%, 55%, 60%, etc. Of course, it can also be a certain point value within the above range, and no specific limitation is made here. As an example, the second negative electrode coating 30 can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, etc. Of course, it can also be a certain point value within the above range, and no specific limitation is made here.

[0082] Among them, when the porosity of the second negative electrode coating 30 is too large and the pore size is too large, the structural strength of the functional layer will be reduced. During the charge and discharge process, the negative electrode material on the negative electrode sheet is likely to fall off, reducing the effective electrode area, and the overall capacity of the battery will be reduced. If the porosity is too low, it is difficult to achieve the effect of suppressing the expansion of the silicon-based material.

[0083] In some embodiments, the first carbon-based active material includes at least one of natural graphite and artificial graphite. As an example, the first carbon-based active material can be natural graphite, can be artificial graphite, or can be a mixture of natural graphite and artificial graphite.

[0084] In some embodiments, the average particle size D50 of the first carbon-based active material is 6-12 μm. As an example, the average particle size D50 of the first carbon-based active material can be 6 μm, 8 μm, 10 μm, 12 μm, etc. Of course, it can also be a certain point value within the above range, and no specific limitation is made here.

[0085] In some embodiments, the first negative electrode coating 20 further includes a first binder and a first conductive agent. That is, the first negative electrode coating 20 includes a carbon-based active material, a first binder, and a first conductive agent.

[0086] In some embodiments, the first binder includes, but is not limited to, at least one of carboxymethyl cellulose or styrene-butadiene rubber. As an example, the first binder can be carboxymethyl cellulose or styrene-butadiene rubber.

[0087] Preferably, the first binder is a mixture of carboxymethyl cellulose and styrene-butadiene rubber, and the mass ratio of carboxymethyl cellulose to styrene-butadiene rubber is 0.5-2:1-3. As an example, the mass ratio of carboxymethyl cellulose to styrene-butadiene rubber can be 0.5:1, 1:1.5, 1.5:2, 2:2.5, 2.3:3, etc. Of course, it can also be a certain ratio within the above range, and no specific limitation is made here. Among them, the combined use of carboxymethyl cellulose and styrene-butadiene rubber can enhance the mechanical strength and structural stability of the negative electrode sheet and also optimize the electrical properties of the electrode.

[0088] 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. As an example, the first conductive agent can be conductive graphite, conductive carbon black, or conductive carbon fiber.

[0089] Among them, the above-mentioned conductive carbon black includes acetylene black, Ketjen black, etc. The above-mentioned conductive carbon fiber includes vapor-grown carbon fiber.

[0090] In some embodiments, the mass ratio of the carbon-based active material, the first binder, and the first conductive agent is 90-98:1.5-5:0.5-2. As an example, the mass ratio of the carbon-based active material, the first binder, and the first conductive agent can be 90:1.5:0.5, 91:2:1, 93:3:1.5, 96:4:1.6, 98:5:2, etc. Of course, it can also be a certain ratio within the above range, and no specific limitation is made here.

[0091] In some embodiments, the thickness of the first negative electrode coating 20 is 12-100 μm. As an example, the thickness of the first negative electrode coating 20 can be 12 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc. Of course, it can also be other values within the above range, and no limitation is made here.

[0092] In some embodiments, the flexible polymer includes, but is not limited to, at least one of polystyrene, polyamide, or polypropylene. As an example, the flexible polymer can be polystyrene, can be polyamide, or can be a mixture of polyamide and polypropylene. The presence of the flexible polymer can offset the stress generated by the expansion and deformation of the silicon-based material, improve the interface contact effect, and reduce the risk of peeling off of the third negative electrode coating 40.

[0093] In some embodiments, the binder includes, but is not limited to, at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, or polyacrylonitrile. As an example, the binder can be carboxymethyl cellulose, can be styrene-butadiene rubber, or can be polyacrylic acid.

[0094] In some embodiments, the second negative electrode coating 30 further includes a second conductive agent.

[0095] 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. As an example, the second conductive agent can be conductive graphite, can be conductive carbon black, or can be conductive carbon fiber.

[0096] Among them, the above-mentioned conductive carbon black includes acetylene black, Ketjen black, etc. The above-mentioned conductive carbon fiber includes vapor-grown carbon fiber.

[0097] In some embodiments, the mass ratio of the flexible polymer, the binder, and the second conductive agent is 20-40:40-60:10-20. As an example, the mass ratio of the flexible polymer, the binder, and the second conductive agent can be 20:40:10, 25:43:12, 30:50:15, 40:60:20, etc. Of course, it can also be a certain ratio within the above range, and no specific limitation is made here.

[0098] In some embodiments, the thickness of the second negative electrode coating 30 is 5-10 μm. As an example, the thickness of the second negative electrode coating 30 can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. Of course, it can also be other values within the above range, and no limitation is made here. If the thickness of the second negative electrode coating 30 is less than 5 μm, if the thickness of the second coating layer is too low, it is equivalent to that the upper slurry penetrates shallowly, then the inhibition effect is weakened, and the interface contact effect between the upper and lower layers is reduced; if the thickness of the second negative electrode coating 30 is greater than 10 μm, it is easy to cause pores in the second coating that are not filled with slurry. On the one hand, it causes loss of energy density, and on the other hand, the electrode sheet is not pressure-resistant and is easy to break.

[0099] In some embodiments, the silicon-based active material includes, but is not limited to, at least one of silicon-oxygen composite material, silicon-carbon composite material, or pure silicon. As an example, the silicon-based active material can be a silicon-oxygen composite material or a silicon-carbon composite material.

[0100] In some embodiments, the average particle size D50 of the silicon-based active material is 6-12 μm. As an example, the average particle size D50 of the silicon-based active material can be 6 μm, 8 μm, 10 μm, 12 μm, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0101] In some embodiments, the second carbon-based active material includes, but is not limited to, at least one of natural graphite or artificial graphite. As an example, the second carbon-based active material can be natural graphite or can be artificial graphite.

[0102] In some embodiments, the average particle size D50 of the second carbon-based active material is 12-20 μm. As an example, the average particle size D50 of the second carbon-based active material can be 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0103] In some embodiments, the third negative electrode coating 40 further includes a second binder and a third conductive agent.

[0104] In some embodiments, the second binder includes, but is not limited to, at least one of polyacrylic acid or styrene-butadiene rubber. As an example, the second binder can be polyacrylic acid, can be styrene-butadiene rubber, or can be a mixture of polyacrylic acid and styrene-butadiene rubber.

[0105] Preferably, the second binder is a mixture of polyacrylic acid and styrene-butadiene rubber. The mass ratio of polyacrylic acid to styrene-butadiene rubber is 2-10:1-5. As an example, the mass ratio of polyacrylic acid to styrene-butadiene rubber can be 2:1, 3:2, 4:1, 5:5, 10:4, etc. Of course, it can also be a certain ratio within the above range, which is not specifically limited herein. Among them, the combined use of polyacrylic acid and styrene-butadiene rubber can enhance the mechanical strength and structural stability of the negative electrode sheet and can also optimize the electrical properties of the electrode.

[0106] In some embodiments, the third conductive agent includes, but is not limited to, at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene. As an example, the third conductive agent can be conductive graphite, can be conductive carbon black, can be conductive carbon fiber.

[0107] Among them, the above-mentioned conductive carbon black includes acetylene black, Ketjen black, etc. The above-mentioned conductive carbon fiber includes vapor-grown carbon fiber.

[0108] In some embodiments, the mass ratio of the silicon-based active material, the second carbon-based active material, the second binder, and the third conductive agent is 20-60:40-80:3-15:1-5. As an example, the mass ratio of the silicon-based active material, the second carbon-based active material, the second binder, and the third conductive agent can be 20:40:3:1, 30:50:5:3, 50:60:10:2, 40:70:10:4, 60:80:15:5, etc. Of course, it can also be a certain ratio within the above range, and no specific limitation is made here.

[0109] In some embodiments, the thickness of the third negative electrode coating 40 is 12-100 μm. As an example, the thickness of the third negative electrode coating 40 can be 12 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc. Of course, it can also be other values within the above range, and no limitation is made here.

[0110] It can be understood that the mass ratios of the carbon-based active material, the first binder, and the first conductive agent, the flexible polymer, the binder, and the second conductive agent, and the silicon-based active material, the second carbon-based active material, the second binder, and the third conductive agent are related to the electrochemical performance of the corresponding battery, and further affect the structural stability of the negative electrode sheet. By controlling the proportions of the substances in the first negative electrode coating 20, the second negative electrode coating 30, and the third negative electrode coating 40 within the above ranges, the functions of each active material and each polymerization unit are fully exerted, and the cycle performance, fast charging performance, and structural stability of the silicon-doped negative electrode sheet are effectively improved.

[0111] It can also be understood that the thickness of the coating will affect the electrical performance of the battery (such as energy density, cycle performance, and rate performance), manufacturing cost, and safety performance. If the thicknesses of the first negative electrode coating 20, the second negative electrode coating 30, and the third negative electrode coating 40 are too large, the electron transfer distance will increase, the electron resistance will increase, the rate performance will decrease, which will have an adverse effect on the electrical performance of the battery, and will further increase the difficulty of battery thermal management. However, if the thicknesses of the first negative electrode coating 20, the second negative electrode coating 30, and the third negative electrode coating 40 are too low, the improvement of the structural stability of the silicon-based negative electrode sheet is not obvious, which will have an adverse effect on the safety and long-term cycle stability of the battery.

[0112] In some embodiments, the current collector 10 includes at least one of copper foil, copper foam, nickel foam, nickel mesh, or composite copper foil. As an example, the current collector 10 can be copper foil, can be copper foam, or can be composite copper foil.

[0113] Thus, based on the above, a silicon-based negative electrode sheet is provided. By setting the first negative electrode coating 20 as a carbon-based active material layer, the carbon-based active material has an expansion rate property and has a better adhesion to the current collector 10. At the same time, the carbon-based active material itself has good electrical conductivity, which can reduce the resistance in the electron transmission path and improve the overall electrical conductivity of the battery. Furthermore, the carbon-based active material layer is adjacent to the current collector 10, which can also make the current evenly distributed on a larger surface, avoiding problems caused by too high local current density, and thus improving the safety and stability of the battery. Further, by setting the second negative electrode coating 30 as a functional layer, the functional layer has a larger pore size and pore structure, and the functional layer also has a flexible polymer and a binder. On the one hand, the presence of pores will cause the slurry of the negative electrode coating in the third negative electrode coating 40 to flow into the second negative electrode coating 30, thereby achieving the effect of suppressing the expansion of the silicon-based material in the slurry of the third negative electrode coating 40, improving the interface contact effect, and reducing the risk of peeling off of the third negative electrode coating 40. On the other hand, the presence of the flexible polymer and the binder can further enhance the inhibitory effect of the pore structure of the functional layer on the expansion of the silicon-based material. Even further, by simultaneously providing a carbon-based active material and a silicon-based active material in the third negative electrode coating 40, the fast charging ability of the battery can be improved. In addition, by controlling the particle size of the main materials in the first negative electrode coating 20, the second negative electrode coating 30, and the third negative electrode coating 40, the porosity of the first negative electrode coating 20, the second negative electrode coating 30, and the third negative electrode coating 40 increases in turn, constructing a gradient pore 1 in the vertical direction, which is beneficial to the full infiltration of the electrolyte into the silicon-based negative electrode sheet.

[0114] Based on the same inventive concept, an embodiment of the present application also provides a preparation method of a silicon-based negative electrode sheet, including the following steps:

[0115] Coat a first negative electrode slurry on at least one surface of the current collector 10 to obtain a first negative electrode coating 20;

[0116] Coat a second negative electrode slurry on the surface of the first negative electrode coating 20 to obtain a second negative electrode coating 30;

[0117] Coat a third negative electrode slurry on the surface of the second negative electrode coating 30 to obtain a third negative electrode coating 40;

[0118] Wherein, the first negative electrode slurry includes a first carbon-based active material;

[0119] The second negative electrode slurry includes a flexible polymer and a binder;

[0120] The third negative electrode slurry includes a silicon-based active material and a second carbon-based active material.

[0121] It should be understood that all the features and advantages described above for the "silicon-based anode electrode sheet" also apply to the "method for preparing the silicon-based anode electrode sheet", and will not be elaborated herein one by one.

[0122] In some embodiments, the second anode slurry further includes a pore-forming agent. That is to say, the second anode slurry includes a flexible polymer, a binder, a second conductive agent, and a pore-forming agent.

[0123] In some embodiments, the pore-forming agent includes at least one of an ammonium salt or a carbonate. As an example, the pore-forming agent can be an ammonium salt or a carbonate. For example, the pore-forming agent is selected from at least one of ammonium bicarbonate, ammonium chloride, or ammonium nitrate.

[0124] In some specific embodiments, the method for preparing the silicon-based anode electrode sheet specifically includes the following steps S1 to S3:

[0125] S1 Prepare the first anode coating 20.

[0126] In step S1, preparing the first anode coating 20 includes: uniformly mixing the first carbon-based active material, the first conductive agent, and the first binder in a solvent to obtain the first anode slurry. Coating the slurry on the surface of the current collector 10 and drying to complete the coating of the first anode coating 20.

[0127] In some embodiments, the mass ratio of the carbon-based active material, the first binder, and the first conductive agent is 90-98:1.5-5:0.5-2. As an example, the mass ratio of the carbon-based active material, the first binder, and the first conductive agent can be 90:1.5:0.5, 91:2:1, 93:3:1.5, 96:4:1.6, 98:5:2, etc. Of course, it can also be a certain ratio within the above range, and no specific limitation is made here.

[0128] Preferably, graphite, carboxymethyl cellulose, styrene-butadiene rubber, and a conductive agent are uniformly mixed in a ratio of 90-98:0.5-2:1-3:0.5-2 to prepare the first anode slurry. As an example, the mass ratio of graphite, carboxymethyl cellulose, styrene-butadiene rubber, and the conductive agent can be 90:0.5:1:0.5, 95:1:2:1, 98:2:3:2, etc.

[0129] In some embodiments, the drying temperature in step S1 is 50-80°C. As an example, the drying temperature in step S1 can be 50°C, 60°C, 70°C, 80°C, etc.

[0130] S2 Prepare the second anode coating 30.

[0131] In step S2, the preparation of the second negative electrode coating 30 includes: uniformly mixing a flexible polymer, a binder, a second conductive agent, and a pore-forming agent in a solvent to obtain a second negative electrode slurry. Coating the slurry on the surface of the first negative electrode coating 20, and drying and performing high-temperature treatment to complete the coating of the second negative electrode coating 30.

[0132] In some embodiments, the mass ratio of the flexible polymer, the binder, the second conductive agent, and the pore-forming agent is 20-40:40-60:10-20:10-30. As an example, the mass ratio of the flexible polymer, the binder, the second conductive agent can be 20:40:10:10, 25:43:11:15, 30:50:17:20, 40:60:20:30, etc. Of course, it can also be a certain ratio within the above range, and no specific limitation is made here.

[0133] In some embodiments, the drying temperature in step S2 is 50-80°C. As an example, the drying temperature in step S1 can be 50°C, 60°C, 70°C, 80°C, etc.

[0134] In some embodiments, the high-temperature treatment temperature in step S2 is 100-200°C. As an example, the high-temperature treatment temperature can be 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, etc.

[0135] In some embodiments, the high-temperature treatment time in step S2 is 4-6h. As an example, the high-temperature treatment time can be 4h, 5h, 6h, etc.

[0136] S3 prepares a third negative electrode coating 40.

[0137] In step S3, the preparation of the third negative electrode coating 40 includes: uniformly mixing a silicon-based active material, a second carbon-based active material, a second binder, and a third conductive agent in a solvent to obtain a third negative electrode slurry. Coating the slurry on the surface of the second negative electrode coating 30, and drying to complete the coating of the third negative electrode coating 40.

[0138] In some embodiments, the mass ratio of the silicon-based active material, the second carbon-based active material, the second binder, and the third conductive agent is 20-60:40-80:3-15:1-5. As an example, the mass ratio of the silicon-based active material, the second carbon-based active material, the second binder, and the third conductive agent can be 20:40:3:1, 30:50:5:3, 50:60:10:2, 40:70:10:4, 60:80:15:5, etc.

[0139] Preferably, graphite, a silicon-based anode material, polyacrylic acid, styrene-butadiene rubber, and a conductive agent are uniformly mixed in a ratio of 20-60:40-80:2-10:1-5:1-5 to prepare a third anode slurry. As an example, the mass ratio of graphite, the silicon-based anode material, polyacrylic acid, styrene-butadiene rubber, and the conductive agent can be 20:40:2:1:1, 40:60:6:3:2, 60:80:10:5:5, etc.

[0140] In some embodiments, the viscosity of the third anode slurry is 800-1200 mPa·s. As an example, the viscosity of the third anode slurry can be 800, 900, 1100, 1200, etc.

[0141] In some embodiments, the drying temperature in step S3 is 50-80 °C. As an example, the drying temperature in step S3 can be 50 °C, 60 °C, 70 °C, 80 °C, etc.

[0142] S4 Roll pressing.

[0143] In step S4, the coated electrode sheet is roll pressed.

[0144] In some embodiments, the compaction density of the roll pressing is 1.3-1.6 g / cm 3 . As an example, the compaction density of the roll pressing can be 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 etc.

[0145] In some embodiments, the solvents used in the first anode slurry, the second anode slurry, and the third anode slurry each independently include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or ethylene carbonate. As an example, the solvents used in the first anode slurry, the second anode slurry, and the third anode slurry can be dimethyl carbonate, can be diethyl carbonate, can be ethyl methyl carbonate.

[0146] Thus, based on the above, in the present invention, by setting the first negative electrode coating 20 as a carbon-based active material layer, the carbon-based active material has an expansion rate property and has a better adhesion with the current collector 10. At the same time, the carbon-based active material itself has good electrical conductivity, which can reduce the resistance in the electron transmission path and improve the overall electrical conductivity of the battery. Moreover, the carbon-based active material layer is adjacent to the current collector 10, which can also make the current evenly distributed on a larger surface, avoiding problems caused by too high local current density, and thus improving the safety and stability of the battery. Further, a pore-forming agent is added to the second negative electrode slurry, which will decompose at 100-200 °C, leaving larger pore diameters and pore structures. And the functional layer also has a flexible polymer and a binder. On the one hand, the presence of pores will cause the slurry of the negative electrode coating in the third negative electrode coating 40 to flow into the second negative electrode coating 30, thereby achieving the effect of suppressing the expansion of the silicon-based material in the slurry of the third negative electrode coating 40, improving the interface contact effect, and reducing the risk of peeling off of the third negative electrode coating 40. On the other hand, the presence of the flexible polymer and the binder can further enhance the inhibitory effect of the pore structure of the functional layer on the expansion of the silicon-based material. Furthermore, by simultaneously providing a carbon-based active material and a silicon-based active material in the third negative electrode coating 40, the fast charging ability of the battery can be improved. In addition, by controlling the particle size of the main materials in the first negative electrode coating 20, the second negative electrode coating 30, and the third negative electrode coating 40, the porosity of the first negative electrode coating 20, the second negative electrode coating 30, and the third negative electrode coating 40 increases in turn, constructing a gradient pore 1 in the vertical direction, which is beneficial to the full infiltration of the electrolyte into the silicon-based negative electrode sheet.

[0147] Based on the same inventive concept, an embodiment of the present application provides a battery, including a negative electrode sheet, and the negative electrode sheet includes the aforementioned silicon-based negative electrode sheet or a silicon-based negative electrode sheet prepared by the aforementioned preparation method.

[0148] Since the battery includes the silicon-based negative electrode sheet provided by the embodiment of the present application, it has relatively excellent structural stability and electrical properties.

[0149] In some embodiments, the battery can be a lithium-ion battery. The stacking type of the battery is, for example, a wound type or a laminated type battery, and the structural type is, for example, a square shell (aluminum shell, steel shell, etc.) battery, a soft package battery or a cylindrical battery, etc., which is not specifically limited. The battery has low expansibility and relatively excellent electrical properties.

[0150] In some embodiments, the above battery further includes a positive electrode sheet, an electrolyte and a separator. That is, the battery includes a positive electrode sheet, a silicon-doped negative electrode sheet, an electrolyte and a separator.

[0151] In this embodiment, for the positive electrode sheet, materials and structures such as the positive current collector, conductive agent, binder, etc. in the positive active material layer are not limited, and the positive electrode sheet structure and composition that can be used in secondary batteries and are well-known to those skilled in the art can be selected.

[0152] In this embodiment, the specific material or type of the separator is not limited, and the separator that can be used in secondary batteries and is well-known to those skilled in the art can be selected.

[0153] It should also be noted that for the battery of this application, the specific material or type of the electrolyte is not limited, and the components and types that can be used in secondary batteries and are well-known to those skilled in the art can be selected, as long as the purpose of this application can be achieved.

[0154] Since the battery provided by the embodiment of the present invention adopts all the technical solutions of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment, which will not be elaborated here one by one.

[0155] Hereinafter, the implementation manners of this application will be described. The implementation manners described below are exemplary and are only used to explain this application, and should not be construed as a limitation to this application. For those without specific technical or conditions noted in the implementation manners, the techniques or conditions described in the literature in this field or according to the product specifications are followed. For reagents, materials or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0156] Example 1

[0157] S1: Graphite, carboxymethyl cellulose, styrene-butadiene rubber, and acetylene black are uniformly mixed in a ratio of 96:1:2:1 to prepare the first negative electrode slurry. The first active slurry is uniformly coated on the copper foil current collector and baked at 60 °C to obtain the first negative electrode coating; among them, the particle size of the graphite is 8 μm;

[0158] The thickness of the first negative electrode coating is 20 μm;

[0159] S2: Polystyrene, styrene-butadiene rubber, acetylene black, and ammonium bicarbonate are mixed in a mass ratio of 20:50:10:20 and stirred under vacuum for 2 h to obtain the second negative electrode slurry; the second negative electrode slurry is uniformly coated on the surface of the first negative electrode coating. After drying in an oven at 60 °C, the electrode sheet is transferred to an incubator at 150 °C and left standing for 5 h to obtain the second negative electrode coating;

[0160] The thickness of the second negative electrode coating is 6 μm;

[0161] The porosity of the second negative electrode coating is 40%;

[0162] S3: Uniformly mix graphite, silicon oxide composite material, polyacrylic acid, styrene-butadiene rubber, and conductive agent in a ratio of 27:60:6:4:3, adjust the slurry viscosity to 1000 mPa·s, and then coat it on the second negative electrode coating. After drying in an oven at 80°C, the third negative electrode coating is obtained; among them, the particle size of graphite is 14 μm, and the particle size of the silicon oxide composite material is 8 μm;

[0163] The thickness of the third negative electrode coating is 6 μm;

[0164] S4: Roll press the coated electrode sheet, and the compaction density is 1.5 g / cm 3 .

[0165] Example 2

[0166] The difference between Example 2 and Example 1 is only that the thickness of the second negative electrode coating in Example 2 is 8 μm, and the rest are the same as those in Example 1.

[0167] Example 3

[0168] The difference between Example 3 and Example 1 is only that the thickness of the second negative electrode coating in Example 3 is 10 μm, and the rest are the same as those in Example 1.

[0169] Example 4

[0170] The difference between Example 4 and Example 1 is only that the thickness of the second negative electrode coating in Example 4 is 15 μm, and the rest are the same as those in Example 1.

[0171] Example 5

[0172] The difference between Example 5 and Example 1 is only that in the second negative electrode slurry of Example 5, the mass ratio of polystyrene, styrene-butadiene rubber, acetylene black, and ammonium bicarbonate is 20:45:10:25, and the rest are the same as those in Example 1.

[0173] Among them, the porosity of the second negative electrode coating is 50%.

[0174] Example 6

[0175] The difference between Example 6 and Example 1 is only that in the second negative electrode slurry of Example 6, the mass ratio of polystyrene, styrene-butadiene rubber, acetylene black, and ammonium bicarbonate is 25:55:15:5, and the rest are the same as those in Example 1.

[0176] Among them, the porosity of the second negative electrode coating is 20%.

[0177] Example 7

[0178] Example 7 is only different from Example 1 in that the mass ratio of polystyrene, styrene-butadiene rubber, acetylene black, and ammonium bicarbonate in the second negative electrode paste of Example 7 is 30:40:10:20, and the rest are the same as those in Example 1.

[0179] Among them, the porosity of the second negative electrode coating is 40%.

[0180] Example 8

[0181] Example 8 is only different from Example 1 in that polystyrene in the second negative electrode paste of Example 8 is replaced by polyamide, and acetylene black is replaced by vapor-grown carbon fiber.

[0182] Example 9

[0183] Example 9 is only different from Example 1 in that the average particle size D50 of graphite in the first negative electrode paste of Example 9 is 10 μm, and the thickness of the first negative electrode coating is 30 μm, and the rest are the same as those in Example 1.

[0184] Example 10

[0185] Example 10 is only different from Example 1 in that the thickness of the third negative electrode coating of Example 10 is 50 μm, and the rest are the same as those in Example 1.

[0186] Example 11

[0187] Example 11 is different from Example 1 in that the particle size of the silicon-oxygen composite material in Example 11 is 10 μm, and the rest are the same as those in Example 1.

[0188] Example 12

[0189] Example 12 is only different from Example 1 in that the viscosity of the third negative electrode paste of Example 12 is 1200 mPa·s, and the rest are the same as those in Example 1.

[0190] Example 13

[0191] Example 13 is only different from Example 1 in that the viscosity of the third negative electrode paste of Example 13 is 2000 mPa·s, and the rest are the same as those in Example 1.

[0192] Comparative Example 1

[0193] Comparative Example 1 is only different from Example 1 in that Comparative Example 1 does not have a second negative electrode coating, and the rest are the same as those in Example 1.

[0194] Comparative Example 2

[0195] The difference between Comparative Example 2 and Example 1 is only that the first negative electrode coating in Comparative Example 2 further contains a silicon-oxygen composite material, and the mass ratio of graphite, carboxymethyl cellulose, styrene-butadiene rubber, acetylene black, and silicon-oxygen composite material in the first negative electrode coating is 96:1:2:1:5, and the rest are the same as in Example 1.

[0196] Comparative Example 3

[0197] The difference between Comparative Example 3 and Comparative Example 1 is only that the second negative electrode coating in Comparative Example 3 does not contain polystyrene, and the rest are the same as in Example 1.

[0198] Comparative Example 4

[0199] The difference between Comparative Example 4 and Example 1 is that the second negative electrode slurry in Comparative Example 4 does not contain ammonium bicarbonate, that is, the second negative electrode coating is a coating without a porous structure, and the rest are the same as in Example 1.

[0200] Performance Test

[0201] 1. Physical and Chemical Tests

[0202] (1) Specific Surface Area Test: Samples of the same mass are taken, and the specific surface area is measured by the N2 adsorption method, and the specific surface area contained in the multi-layer electrode sheet is characterized by the gas adsorption amount.

[0203] (2) Maximum Compaction Density Test: The electrode sheet is roll-pressed under different pressures, and the roll-pressed electrode sheet is taken to test whether there is any breakage in the functional layer by SEM observation.

[0204] (3) Conductivity Test: Samples of the same mass of silicon-based negative electrode materials are extruded into blocks of the same thickness, and then placed on a four-probe resistivity tester to test the electrical conductivity of the materials.

[0205] (4) Liquid Absorption Time Test: Negative electrode sheets of the same area are taken, the same mass of electrolyte is dropped onto their surfaces, and the time for the electrolyte to penetrate is observed until it completely disappears. This time is recorded as the liquid absorption time.

[0206] The test results of each example and comparative example are shown in Table 1.

[0207] Table 1

[0208]

[0209] From the comparison of the results of physical and chemical tests in Examples 1-4, it can be seen that as the thickness of the second negative electrode coating increases, due to the pore characteristics inside it, the specific surface area increases accordingly. However, due to the increase in pores, the pressure resistance of the electrode sheet decreases, resulting in a decrease in its energy density; in Example 6, the proportion of the pore-forming agent is too low, resulting in fewer pores in the functional layer and a decrease in the specific surface area of the electrode sheet. Although it can improve compaction, it causes difficulty in the diffusion of the upper slurry, ultimately resulting in a poor interface contact problem with the third negative electrode coating; in Examples 7 and 8, slightly changing the ratio or replacing the polymer component has little impact on the overall electrode sheet, so its physical and chemical data indicators are close to those of Example 1; from Examples 9 and 11, it can be seen that a slight increase in the particle size of the active particles has little impact on the overall structure of the negative electrode sheet; in Examples 12 and 13, the viscosity of the slurry of the third active coating is increased, making it difficult for the slurry to diffuse downward, so it will also cause an interface contact problem; it can be seen that when a certain component exceeds the range defined in this application, the final effect will also deteriorate.

[0210] In addition, in Comparative Example 1, the second negative electrode coating is cancelled. Although the compaction of the electrode sheet is improved to a certain extent, due to the large expansion of the silicon-based material, the contact effect between the first negative electrode coating and the third negative electrode coating is poor, and the electrochemical performance of the electrode sheet deteriorates; in Comparative Example 2, the first negative electrode slurry contains a silicon-based material. Due to the expansion of the silicon-based material, there will ultimately be a risk of demolding at the copper foil interface; in Comparative Example 4, there is no pore-forming agent. Although the compaction density increases, the specific surface area and pores decrease, making it impossible to accommodate the penetration of the upper slurry and resulting in an extended liquid absorption time, which is not conducive to the performance of power.

[0211] 2. Electrochemical performance test

[0212] Battery preparation

[0213] Preparation of the positive electrode sheet: The positive electrode active material is ternary lithium nickel cobalt manganate LiNi 0.8 Co 0.1 Mn 0.1 , the conductive agent is selected as SP and carbon nanotubes, the binder is selected as PVDF5130, the positive electrode current collector is selected as 13μm aluminum foil. After mixing the positive electrode active material, SP, carbon nanotubes, and binder in a ratio of 97:2:1, NMP is added and stirred into a uniformly mixed and stable positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector, and the coating surface density is 195g / m 2 , and after drying and cold pressing, the positive electrode sheet is obtained, and the selected compaction density is 3.4g / cm 3 .

[0214] Separator: A composite separator (polyethylene (PE) and ceramic) is selected, where the thickness of the polyethylene layer is 9μm and the thickness of the ceramic layer is 5μm.

[0215] Electrolyte: LiPF6 was selected and dissolved in a solvent with a volume ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate of 1:1:1 at a concentration of 1.2 mol / L to obtain the electrolyte.

[0216] Battery assembly: The positive electrode sheet, separator, negative electrode sheet, and separator were arranged in sequence, and the winding method was selected for assembly. The electrolyte was injected into the dry battery cell and infiltrated for 24 h, and then formation was carried out at 45 °C. The formation process: charge at 0.05C to 3.4V, and then charge at 0.2C to 3.75V; after aging at room temperature for 24 h, the battery production was completed.

[0217] Perform electrochemical performance tests on the battery

[0218] (1) Rate retention test: The battery was charged at a constant current and constant voltage of 0.5C to 4.25V, left standing for 30 min, and then discharged at currents of 1C / 2C / 3C / 5C to 2.5V, left standing for 30 min; repeat the above steps until the test is completed, and the capacities at different discharge rates can be obtained. The 5C rate retention = 5C discharge capacity / 1C standard discharge capacity.

[0219] (2) 1C cycle test for 500 cycles: The battery was charged at a constant current and constant voltage of 0.5C to 4.25V, left standing for 30 min, and then discharged at a current of 1C to 2.5V, left standing for 30 min. Perform charge and discharge tests according to the above cycle process until the discharge capacity of the battery is lower than 80% of the initial capacity or 500 cycles are reached to stop the test.

[0220] (3) 1C energy density test: 1C energy density = 1C discharge capacity * 1C average discharge voltage / total weight of the battery.

[0221] (4) Peel strength test: Use tape to bond the negative electrode sheet, press it 3 times with a steel rod, and then test the peel strength between the electrode coating and the copper foil on a tensile testing instrument.

[0222] (5) Cohesion test: Use double-sided tape to bond the negative electrode sheet. After the powder is peeled off, use double-sided tape to press it 3 times on the electrode sheet with a steel rod, and then test the peel strength of the powder between the electrode sheets on a tensile testing instrument.

[0223] The test results of each example and comparative example are shown in Table 2.

[0224] Table 2

[0225]

[0226] As can be seen from Examples 1-3, the batteries obtained from the negative electrode sheets prepared in the examples have good electrochemical performance. Also, as can be seen from Examples 2 and 3, as the second coating thickens, it becomes slightly more difficult for the upper slurry to penetrate, so the inhibitory effect is relatively reduced, the capacity retention rate and cycling performance are slightly reduced, and since the inhibitory effect of the second coating on the silicon-based coating is reduced, the cohesive force between the two layers decreases slightly; in Example 4, due to the extremely thick second coating, the inhibitory force on the third coating becomes poor, resulting in poor contact between the two layers, so the cycling stability and rate performance deteriorate; in Example 5, due to the increased porosity, the third coating slurry penetrates more easily, so the inhibitory effect becomes stronger and the cycling and rate performance are improved. In Example 5, the electrochemical performance is opposite due to too low porosity; in Examples 7 and 8, since only the polymer composition is changed and other conditions remain unchanged, the overall structure of the electrode sheet changes little and has little impact on the high electrochemical performance; in Examples 9 and 11, the particle size of the active material changes slightly and has little impact on the overall structure of the negative electrode, so the electrochemical performance is close to that of Example 1; in Examples 12 and 13, the viscosity increases relatively, resulting in poor penetration of the third coating slurry, so less slurry penetrates into the second coating, leading to a poor inhibitory effect, so both the cohesive force and cycling stability deteriorate; in Comparative Example 1, due to the cancellation of the second coating, there are no pores to accommodate the third coating slurry. Since the silicon-oxygen material expands greatly, interface peeling occurs and the electrochemical performance deteriorates. Similarly, the same result is obtained for Comparative Example 4; in Comparative Example 2, since the first coating contains silicon-based material, it expands greatly and the contact between the coating and the foil becomes poor, ultimately resulting in deterioration of the battery's electrochemical performance; compared with Example 1, in Comparative Example 3, the polymer is cancelled, and it is obvious that the cohesive force of the electrode sheet decreases, indicating that the elasticity of the polymer has a synergistic inhibitory effect on the expansion of the silicon-based material. Therefore, after cancelling the polymer, the interface performance deteriorates and the overall electrochemical performance deteriorates.

[0227] The parts not detailed in the present invention are well-known technologies to those skilled in the art.

[0228] The basic principles of the present invention have been described above in combination with specific examples. However, it should be noted that the advantages, advantages, effects, etc. mentioned in the present invention are only examples and not limitations. It cannot be considered that these advantages, advantages, effects, etc. are essential for each embodiment of the present invention. In addition, the above-disclosed specific details are only for the purposes of illustration and easy understanding, and are not limitations. These details do not limit the present invention to necessarily adopt the above specific details to implement.

[0229] It should be noted that the term "and / or" or " / " used in this text is merely a description of the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. The singular forms of "a", "the", and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0230] In the specific embodiments and the claims, a list of items connected by the terms "at least one of", "at least one in", "at least one kind in", or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then 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.

[0231] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-based negative electrode plate, characterized in that: The silicon-based negative electrode plate comprises: current collector; A first negative electrode coating is disposed on at least one side of the current collector along the thickness direction, and the first negative electrode coating includes a first carbon-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 flexible polymer and a binder; 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 silicon-based active material and a second carbon-based active material; Wherein, the second negative electrode coating is a porous coating with a porous structure.

2. The silicon-based negative electrode plate according to claim 1, characterized in that: The porosity of the second negative electrode coating is 40-60%, and the pore size is 1-3 μm.

3. The silicon-based negative electrode plate according to claim 1, characterized in that: The first negative electrode coating satisfies at least one of the following characteristics (1) to (4): (1) The first carbon-based active material includes at least one of natural graphite or artificial graphite; (2) the average particle size D50 of the first carbon-based active material is 6-12 μm; (3) The first negative electrode coating further includes a first binder and a first conductive agent; Preferably, the first binder includes at least one of carboxymethyl cellulose and styrene-butadiene rubber; preferably, the first binder is a mixture of carboxymethyl cellulose and styrene-butadiene rubber; Preferably, the first conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene; Preferably, the mass ratio of the carbon-based active material, the first binder, and the first conductive agent is 90-98:1.5-5:0.5-2; (4) The thickness of the first negative electrode coating layer is 12-100 μm.

4. The silicon-based negative electrode plate 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 flexible polymer comprises at least one of polystyrene, polyamide or polypropylene; (2) The binder comprises at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid or polyacrylonitrile; (3) The second negative electrode coating further includes a second conductive agent; Preferably, the second conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene; Preferably, the mass ratio of the flexible polymer, the binder, and the second conductive agent is 20-40:40-60:10-20; (4) The thickness of the second negative electrode coating is 5-10 μm.

5. The silicon-based negative electrode plate according to claim 1, characterized in that: The third negative electrode coating satisfies at least one of the following characteristics (1) to (6): (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 average particle size D50 of the silicon-based active material is 6-12 μm; (3) the second carbon-based active material comprises at least one of natural graphite or artificial graphite; (4) The average particle size D50 of the second carbon-based active material is 12-20 μm; (5) The third negative electrode coating further includes a second binder and a third conductive agent; Preferably, the second binder includes at least one of polyacrylic acid or styrene-butadiene rubber; preferably, the second binder is a mixture of polyacrylic acid and styrene-butadiene rubber; Preferably, the third conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene; Preferably, the mass ratio of the silicon-based active material, the second carbon-based active material, the second binder, and the third conductive agent is 20-60:40-80:3-15:1-5; (6) The thickness of the third negative electrode coating is 12-100 μm.

6. The silicon-based negative electrode plate 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-based 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; Wherein, the first negative electrode slurry includes a first carbon-based active material; The second negative electrode slurry includes a flexible polymer and a binder; The third negative electrode slurry includes a silicon-based active material and a second carbon-based active material.

8. The method for preparing a silicon-based negative electrode sheet according to claim 7, characterized in that: The second negative electrode slurry further includes a pore former; Preferably, the pore former comprises at least one of an ammonium salt or a carbonate; Preferably, the mass ratio of the flexible polymer, the binder, the second conductive agent and the pore-forming agent is 20-40:40-60:10-20:10-30.

9. The method for preparing a silicon-based negative electrode sheet according to claim 7 or 8, characterized in that: The preparation of the first negative electrode slurry includes: uniformly mixing a first carbon-based active material, a first conductive agent and a first binder in a solvent to obtain a first negative electrode slurry; The preparation of the second negative electrode slurry includes: uniformly mixing a flexible polymer, a binder, a second conductive agent, and a pore-forming agent in a solvent to obtain a second negative electrode slurry; The preparation of the third negative electrode slurry includes: uniformly mixing the silicon-based active material, the second carbon-based active material, the second binder and the third conductive agent in a solvent to obtain the third negative electrode slurry; 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 to obtain the silicon-based negative electrode sheet.

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

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