Negative plate, battery and electronic equipment

Abstract

The invention relates to a negative plate, a battery and electronic equipment. A negative electrode active material layer in the negative electrode plate comprises a negative electrode active material and an adhesive, the negative electrode active material comprises a carbon material and a silicon material, and the adhesive comprises a polypropylene compound and butadiene styrene rubber; the polypropylene compound coats the surface of the silicon material to form a first coating layer, and the butadiene styrene rubber is attached to the surface of the first coating layer to form a first adhesive layer; at least part of the surface of the carbon material is coated with at least one of a polypropylene compound and butadiene styrene rubber, and the butadiene styrene rubber is attached to the outermost layer of the carbon material; wherein the polypropylene compound forms a second coating layer on the surface of the carbon material, and the butadiene styrene rubber forms a second adhesion layer on the surface of the carbon material; the negative plate meets the following relational expression: H1 is greater than 1.2 H2; the thickness of the first coating layer is H1; and the thickness of the second coating layer is H2. According to the scheme provided by the invention, the cycle performance and the storage performance of the battery can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a negative electrode sheet, a battery and an electronic device. Background Art

[0002] Lithium-ion batteries are widely used in fields such as consumer electronics, new energy vehicles and energy storage. With the rapid development of the new energy vehicle industry, consumers have put forward higher requirements for the cruising range and application scenarios, that is, the battery has a higher energy density.

[0003] Currently, the commercially available negative electrode materials are mainly graphite negative electrodes, and their theoretical specific capacity is only 370 mAh / g, which can no longer meet the energy density requirements. Silicon negative electrodes have received extensive attention and research due to their advantages such as high theoretical capacity, low lithium insertion potential, rich raw materials, non-toxic and environmental protection, and are expected to replace graphite negative electrodes as the next-generation high-energy density negative electrode materials in the future. However, silicon materials will expand and contract to a large extent during charge and discharge, which easily causes electrode particle pulverization and active material shedding, reduces the conductivity of the negative electrode active material layer, and ultimately leads to obvious deterioration of the battery's cycle performance and storage performance. Moreover, the expansion degree of silicon materials is greater under high-temperature conditions, resulting in worse high-temperature cycle performance and high-temperature storage performance of the battery.

[0004] Therefore, there is an urgent need to develop a battery that takes into account high energy density, high cycle performance and storage performance. Summary of the Invention

[0005] To solve or partially solve the problems existing in the related art, the present application provides a negative electrode sheet, a battery and an electronic device, which can take into account high energy density, high cycle performance and storage performance.

[0006] The first aspect of the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material and a binder, the negative electrode active material includes a carbon material and a silicon material, and the binder includes a polypropylene compound and styrene-butadiene rubber; The polypropylene compound coats the surface of the silicon material to form a first coating layer, and the styrene-butadiene rubber adheres to the surface of the first coating layer to form a first adhesion layer; At least part of the surface of the carbon material is coated with at least one of the polypropylene compound and the styrene-butadiene rubber, and the styrene-butadiene rubber adheres to the outermost layer of the carbon material; wherein, the polypropylene compound forms a second coating layer on the surface of the carbon material, and the styrene-butadiene rubber forms a second adhesion layer on the surface of the carbon material; The negative electrode sheet satisfies the following relational expression: H 1 >1.2H 2 ; In the above relationship, the thickness of the first coating layer is H 1 ; the thickness of the second coating layer is H 2 .

[0007] The negative electrode sheet as described above, wherein, H 1 > 2.0H 2 .

[0008] The negative electrode sheet as described above, wherein the negative electrode active material layer further includes a conductive agent, the conductive agent is coated on at least part of the surface of the silicon material to form a first conductive layer, and the polypropylene compound is coated on at least part of the surface of the silicon material and / or the first conductive layer to form a first coating layer; at least part of the surface of the carbon material is coated with at least one of a conductive agent and the polypropylene compound, wherein the conductive agent forms a second conductive layer on the surface of the carbon material, and the polypropylene compound forms a second coating layer on the surface of the carbon material and / or the second conductive layer; preferably, the negative electrode sheet satisfies the following relationship: N 1 > 1.2N 2 ; In the above relationship, the number of conductive agents in a set square micron area in the first conductive layer is N 1 ; the number of conductive agents in a set square micron area in the second conductive layer is N 2 ; further preferably, N 1 > 2.0N 2 .

[0009] The negative electrode sheet as described above, wherein the conductive agent includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes; and / or, The mass percentage of the conductive agent in the negative electrode active material layer is 0.02% - 1.5%.

[0010] The negative electrode sheet as described above, wherein the negative electrode sheet satisfies the following relationship: 0.8S 2 < S 1 < 1.2S 2 ; In the above relationship, the percentage of the attachment area of the first attachment layer to the surface area of the silicon material is S 1 ; the percentage of the attachment area of the second attachment layer to the surface area of the carbon material is S 2 .

[0011] The negative electrode sheet as described above, wherein the carbon material includes one or more of artificial graphite, natural graphite, hard carbon, and soft carbon; and / or, The mass percentage content of the carbon material in the negative electrode active material layer is 85% to 98%; and / or, The silicon material includes one or more of silicon oxide, prelithiated silicon oxide, premagnesiated silicon oxide material, and silicon-carbon composite material; and / or, The mass percentage content of the silicon material in the negative electrode active material layer is 1% to 10%; and / or, The polypropylene compound includes one or more of polyacrylic acid, polyacrylonitrile, and polyacrylamide; and / or, The mass percentage content of the polypropylene compound in the negative electrode active material layer is 0.5% to 2%; and / or, The mass percentage content of the styrene-butadiene rubber in the negative electrode active material layer is 0.5% to 2%; and / or, The negative electrode active material layer further includes a dispersant, the dispersant includes one or more of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose, and the mass percentage content of the dispersant in the negative electrode active material layer is not higher than 1%.

[0012] The second aspect of the present application provides a method for preparing a negative electrode sheet, including the following steps: S1. Mix the silicon material and the polypropylene compound in an aqueous solvent to obtain a first mixture, and make the polypropylene compound in the first mixture coat the surface of the silicon material to form a first coating layer; S2. Mix the carbon material and the first mixture in an aqueous solvent to obtain a second mixture, and make the first coating layer in the first mixture partially peel off and transfer to at least part of the surface of the carbon material to form a second coating layer; S3. Mix the styrene-butadiene rubber and the second mixture to obtain a negative electrode slurry, and make the styrene-butadiene rubber in the negative electrode slurry attach to the surface of the first coating layer to form a first attachment layer, and make the styrene-butadiene rubber in the negative electrode slurry attach to at least part of the surface of the carbon material and / or the second coating layer to form a second attachment layer; S4. Coating the negative electrode slurry on at least one side surface of the negative electrode current collector, and after drying and rolling, a negative electrode sheet is obtained.

[0013] For the method for preparing a negative electrode sheet as described above, before the step S1, there is further a step S0: S0. Dry-mix the silicon material and the conductive agent to obtain a premix, and make the conductive agent in the premix coat the surface of the silicon material to form a first conductive layer; and, S1. Mix the premix and the polypropylene compound in an aqueous solvent to obtain a first mixture, and make the polypropylene compound in the first mixture coat the surface of the first conductive layer to form a first coating layer; S2. Mix the carbon material and the first mixture in an aqueous solvent to obtain a second mixture, causing a part of the polypropylene compound contained in the first coating layer in the first mixture to peel off, transfer to the surface of the carbon material, and form a second coating layer; a part of the conductive agent contained in the first conductive layer and a part of the polypropylene compound contained in the first coating layer in the first mixture peel off and transfer to the surface of the carbon material. Among them, the conductive agent forms a second conductive layer on the surface of the carbon material, and the polypropylene compound forms a second coating layer on the surface of the carbon material.

[0014] The method for preparing the negative electrode sheet as described above, wherein the stirring speed of the dry mixing treatment is 10 r / min to 30 r / min, and the stirring time is 10 min to 60 min; preferably, the stirring speed of the dry mixing treatment is 20 r / min to 30 r / min, and the stirring time is 30 min to 45 min.

[0015] The method for preparing the negative electrode sheet as described above, wherein in step S1, mixing is carried out by stirring, the revolution speed of the stirring is 10 r / min to 30 r / min, the rotation speed is 0 to 500 r / min, and the stirring time is 10 min to 120 min; preferably, the revolution speed of the stirring is 20 r / min to 30 r / min, the rotation speed is 100 r / min to 300 r / min, and the stirring time is 30 min to 100 min; and / or, In step S2, mixing is carried out by stirring, the revolution speed of the stirring is 10 r / min to 30 r / min, the rotation speed is 1000 r / min to 3000 r / min, and the stirring time is 60 min to 240 min; preferably, the revolution speed of the stirring is 20 r / min to 30 r / min, the rotation speed is 1500 r / min to 2000 r / min, and the stirring time is 120 min to 180 min; and / or, In step S3, mixing is carried out by stirring, the revolution speed of the stirring is 10 r / min to 30 r / min, the rotation speed is 200 r / min to 1000 r / min, and the stirring time is 30 min to 120 min; preferably, the revolution speed of the stirring is 10 r / min to 25 r / min, the rotation speed is 200 r / min to 500 r / min, and the stirring time is 30 min to 60 min.

[0016] The third aspect of the present application provides a battery, including the negative electrode sheet as described above or the negative electrode sheet prepared according to the method for preparing the negative electrode sheet as described above.

[0017] The technical solution provided by the present application may include the following beneficial effects: H 1 > 1.2H2 When, on the one hand, more polypropylene compounds coat the silicon material, enhancing the adhesion between the silicon material and the negative electrode current collector, it can inhibit the expansion of the silicon material, avoid pulverization and shedding of the negative electrode active material layer, thereby reducing the expansion rate of the negative electrode active material layer, and avoiding a decrease in the conductivity of the negative electrode active material layer caused by an increase in the gap between the silicon material and the carbon material. At the same time, the coating layer formed by the polypropylene compounds on the surface of the silicon material can reduce the side reaction between the silicon material and the electrolyte, inhibit the decomposition and gas generation of the electrolyte, thereby effectively improving the cycle performance and storage performance of the battery; on the other hand, fewer polypropylene compounds coat the carbon material, making the conductivity of the negative electrode active material layer higher, which is beneficial to reducing the internal resistance of the battery, thereby improving the cycle performance of the battery.

[0018] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit this application. Detailed implementation manners

[0019] The terms used in this application are only for the purpose of describing specific embodiments, and are not intended to limit this application. The singular forms "a", "the", and "said" used in this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0020] It should be understood that although the terms "first", "second", "third", etc. may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of this application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, "a plurality of" means two or more, unless otherwise clearly and specifically defined.

[0021] In the related art, the silicon material will undergo a large degree of expansion and contraction during charge and discharge, which easily causes electrode particle pulverization and active material shedding, ultimately leading to a significant deterioration in the cycle performance and storage performance of the battery. Moreover, the expansion degree of the silicon material is greater under high-temperature conditions, resulting in worse high-temperature cycle performance and high-temperature storage performance of the battery.

[0022] In view of the above problems, an embodiment of this application provides a negative electrode sheet, in which the distribution of the binder can inhibit the expansion of the silicon material, avoid pulverization and shedding of the negative electrode active material layer, thereby improving the cycle performance and storage performance of the battery.

[0023] The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material and a binder, the negative electrode active material includes a carbon material and a silicon material, and the binder includes a polypropylene compound and styrene-butadiene rubber; the polypropylene compound coats the surface of the silicon material to form a first coating layer, and the styrene-butadiene rubber adheres to the surface of the first coating layer to form a first adhesion layer; at least part of the surface of the carbon material is coated with at least one of a polypropylene compound and styrene-butadiene rubber, and the styrene-butadiene rubber adheres to the outermost layer of the carbon material; wherein, the polypropylene compound forms a second coating layer on the surface of the carbon material, and the styrene-butadiene rubber forms a second adhesion layer on the surface of the carbon material; The negative electrode sheet satisfies the following relationship: H 1 >1.2H 2 ; In the relationship, the thickness of the first coating layer is H 1 ; the thickness of the second coating layer is H 2 .

[0024] The present application does not limit the selection of the negative electrode current collector, which can be selected according to actual needs, such as copper foil, etc. The negative electrode active material layer of the present application includes a negative electrode active material and a binder. The negative electrode active material of the present application includes a carbon material and a silicon material. The present application does not limit the selection of the carbon material, which can be selected according to actual needs, such as graphite, carbon black, hard carbon, soft carbon, etc.; the present application does not limit the selection of the silicon material, which can be selected according to actual needs, such as silicon oxide, prelithiated silicon oxide, premagnesiated silicon oxide material, silicon-carbon composite material, elemental silicon, etc. The binder of the present application includes a polypropylene compound and styrene-butadiene rubber. The polypropylene compound refers to polypropylene derivatives, such as polyacrylic acid, polyacrylonitrile, polyacrylamide, methyl polyacrylate, etc.

[0025] The polypropylene compound and styrene-butadiene rubber of the present application can be mixed with the silicon material successively, so that the first added liquid polypropylene compound can first adhere to the surface of the silicon material to form a first coating layer, and the later added granular styrene-butadiene rubber can be loaded on the surface of the first coating layer formed by the polypropylene compound in a dot-like distribution form and form a first adhesion layer.

[0026] At least part of the surface of the carbon material of the present application is coated with at least one of a polypropylene compound and styrene-butadiene rubber, and the styrene-butadiene rubber adheres to the outermost layer of the carbon material; that is, the structure on the surface of the carbon material can be divided into several situations: The first type is that polypropylene compounds and styrene-butadiene rubber are coated on the surface of carbon materials in a mixed manner: there are multiple layers of coating on the surface of carbon materials. It can be that the polypropylene compounds are first coated to form a second coating layer, and then the styrene-butadiene rubber adheres to the surface of the polypropylene compounds to form a second adhesion layer; or it can be that a part of the surface of the carbon material is coated with polypropylene compounds to form a second coating layer, and another part of the surface of the carbon material is coated with styrene-butadiene rubber to form a second adhesion layer.

[0027] The second type is that only polypropylene compounds are coated on the surface of carbon materials to form a second coating layer.

[0028] The third type is that only styrene-butadiene rubber adheres to the surface of carbon materials to form a second adhesion layer.

[0029] In the active material layer of the negative electrode sheet of this application, the silicon material and the carbon material are in a mixed state, rather than the silicon material coating the carbon material or the carbon material coating the silicon material.

[0030] According to the above solution provided by this application, after applying this negative electrode sheet to a battery, the battery has excellent cycle performance and storage performance. The applicant analyzed this principle and believes that the reason is that the thickness of the first coating layer in this negative electrode sheet is greater than the thickness of the second coating layer. Since the first coating layer and the second coating layer are equivalent to dense coatings, the thickness of the first coating layer and the second coating layer can characterize the content of the first coating layer and the second coating layer. Under the condition of the same amount of silicon material, carbon material and polypropylene compounds, on the one hand, more polypropylene compounds coat the silicon material, and hydrogen bonds are formed between the polypropylene compounds, the silicon material and the negative electrode current collector, which improves the adhesion between the silicon material and the negative electrode current collector, can inhibit the expansion of the silicon material during the charge and discharge process of the battery, avoid the pulverization and shedding of the negative electrode active material layer, thereby reducing the expansion rate of the negative electrode active material layer, and avoiding the decrease in the conductivity of the negative electrode active material layer caused by the increase in the gap between the silicon material and the carbon material, and improving the insertion / extraction rate and transmission rate of lithium ions in the negative electrode active material layer. At the same time, the coating layer formed by the polypropylene compounds on the surface of the silicon material can reduce the side reaction between the silicon material and the electrolyte and inhibit the decomposition of the electrolyte to generate gas, thereby effectively improving the cycle performance and storage performance of the battery; on the other hand, less polypropylene compounds coat the carbon material, making the conductivity of the negative electrode active material layer higher, which is beneficial to reducing the internal resistance of the battery, thereby improving the cycle performance of the battery.

[0031] Specifically, the thickness of the first coating layer and the thickness of the second coating layer can be measured by transmission electron microscopy (TEM), including the following steps: performing TEM testing on the negative electrode sheet, maintaining a magnification of 20,000 times, selecting 10 different test points on the surface of the silicon material or carbon material for testing, and calculating the average value of the measured thicknesses of the 10 coating layers, which is the thickness of the polypropylene-based compound coating layer. Among them, the selected test points may or may not contain polypropylene-based compounds.

[0032] In a preferred embodiment, H 1 > 2.0H 2 . When the thickness of the first coating layer is greater than 2.0 times the thickness of the second coating layer, it can further inhibit the swelling of the silicon material during the charge and discharge process of the battery, and at the same time can reduce the side reaction between the silicon material and the electrolyte to a greater extent, inhibit the decomposition and gas generation of the electrolyte, and can further reduce the internal resistance of the battery, thereby making the cycle performance and storage performance of the battery better.

[0033] In a specific embodiment, the negative electrode active material layer further includes a conductive agent. The conductive agent is coated on at least part of the surface of the silicon material to form a first conductive layer, and the polypropylene-based compound is coated on at least part of the surface of the silicon material and / or the first conductive layer to form a first coating layer; at least part of the surface of the carbon material is coated with at least one of the conductive agent and the polypropylene-based compound. Among them, the conductive agent forms a second conductive layer on the surface of the carbon material, and the polypropylene-based compound forms a second coating layer on the surface of the carbon material.

[0034] A conductive agent is also added to the negative electrode active material layer of the present application. Adding a conductive agent to the negative electrode active material layer can improve the conductivity of the negative electrode active material, facilitate the rapid migration of lithium ions in the negative electrode active material layer, and help improve the cycle performance of the battery. Among them, the silicon material can be first mixed with the conductive agent and then mixed with the polypropylene-based compound, so that the surface of the silicon material is first coated with the conductive agent to form a first conductive layer, and then the polypropylene-based compound is coated on the surface of the first conductive layer to form a first coating layer, or part of the surface of the silicon material is coated with the conductive agent to form a first conductive layer, the surface of the first conductive layer is coated with the polypropylene-based compound to form a first coating layer, and the other part of the surface of the silicon material is also coated with the polypropylene-based compound to form a first coating layer.

[0035] At least part of the surface of the carbon material of the present application is coated with at least one of the conductive agent and the polypropylene-based compound. That is, the structure of the surface of the carbon material can be divided into several cases: The first type is that polypropylene compounds and conductive agents are coated on the surface of carbon materials in a mixed manner: there are multiple layers of coating on the surface of carbon materials. It can be that the surface of carbon materials is first coated with a conductive agent to form a second conductive layer, and then a polypropylene compound is coated on the surface of the second conductive layer to form a second coating layer; or the polypropylene compound first adheres to the surface of the carbon material to form a second coating layer, and then the conductive agent adheres to the surface of the second coating layer to form a second conductive layer; or both the inner and outer layers contain polypropylene compounds and conductive agents. A part of the surface of the carbon material is coated with a conductive agent to form a second conductive layer, and a polypropylene compound is coated on the surface of the second conductive layer to form a second coating layer. Another part of the surface of the carbon material is coated with a polypropylene compound to form a second coating layer, and a conductive agent is coated on the surface of the second coating layer to form a second conductive layer. This application does not limit this, as long as the adhesion of polypropylene compounds and conductive agents can be achieved.

[0036] The second type is that only a conductive agent is coated on the surface of the carbon material to form a second conductive layer.

[0037] The third type is that only a polypropylene compound is coated on the surface of the carbon material to form a second coating layer.

[0038] Therefore, in the negative electrode active material layer of this application, the structure on the surface of the silicon material is divided into two cases: the first case is that the surface of the silicon material is coated with a conductive agent to form a first conductive layer, a polypropylene compound is coated on the surface of the first conductive layer to form a first coating layer, and styrene-butadiene rubber adheres to the surface of the first coating layer to form a first adhesion layer; the second case is that a part of the surface of the silicon material is coated with a conductive agent to form a first conductive layer, a polypropylene compound is coated on the surface of the first conductive layer to form a first coating layer, and at the same time, another part of the surface of the silicon material is coated with a polypropylene compound to form a first coating layer, and styrene-butadiene rubber adheres to the surface of the first coating layer to form a first adhesion layer.

[0039] The structure on the surface of the carbon material is divided into several cases: the first is that a conductive agent is coated on the surface of the carbon material to form a second conductive layer, a polypropylene compound is coated on the surface of the second conductive layer to form a second coating layer, and styrene-butadiene rubber is attached to the surface of the second coating layer to form a second attachment layer; the second is that a polypropylene compound is coated on the surface of the carbon material to form a second coating layer, a conductive agent is coated on the surface of the second coating layer to form a second conductive layer, and styrene-butadiene rubber is attached to the surface of the second conductive layer to form a second attachment layer; the third is that a polypropylene compound is coated on a partial surface of the carbon material to form a second coating layer, a conductive agent is coated on another partial surface of the carbon material to form a second conductive layer, and then styrene-butadiene rubber is attached to the surface of the second coating layer or the second conductive layer to form a second attachment layer; the fourth is that a conductive agent is coated on the surface of the carbon material to form a second conductive layer, and styrene-butadiene rubber is attached to the surface of the second conductive layer to form a second attachment layer; the fifth is that a polypropylene compound is coated on the surface of the carbon material to form a second coating layer, and styrene-butadiene rubber is attached to the surface of the second coating layer to form a second attachment layer; the sixth is that only a polypropylene compound is coated on the surface of the carbon material to form a second coating layer; the seventh is that only a conductive agent is coated on the surface of the carbon material to form a second conductive layer; the eighth is that only styrene-butadiene rubber is coated on the surface of the carbon material to form a second attachment layer; the ninth is that a polypropylene compound is coated on the surface of the carbon material to form a second coating layer, and a conductive agent is coated on the surface of the second coating layer to form a second conductive layer. At least two of these cases exist, and the structures of at least two cases include a second coating layer and a second attachment layer, and the structure obtained in the first case is the preferred structure. In a preferred embodiment, the negative electrode sheet satisfies the following relational expression: N 1 >1.2N 2 ; In the relational expression, the number of conductive agents within a set square micrometer area in the first conductive layer is N 1 ; the number of conductive agents within a set square micrometer area in the second conductive layer is N 2 .

[0040] The present application does not limit the specific selection of the conductive agent. For example, it can be carbon nanotubes, conductive carbon black, graphene, etc., and can be selected according to actual needs. The number of conductive agents within a set square micrometer area in the first conductive layer of the present application refers to the number of conductive agents within a certain square micrometer area selected on the surface of the silicon material; if the conductive agent is carbon nanotubes, the number of conductive agents within a set square micrometer area in the first conductive layer refers to the number of carbon nanotube strips within a certain square micrometer area on the surface of the silicon material; if the conductive agent is conductive carbon black, the number of conductive agents within a set square micrometer area in the first conductive layer refers to the number of conductive carbon black particles within a certain square micrometer area on the surface of the silicon material. The number of conductive agents within a set square micrometer area in the second conductive layer of the present application refers to the number of conductive agents within a certain square micrometer area selected on the surface of the carbon material.

[0041] In this application, the amount of the conductive agent in the first conductive layer is controlled to be higher than that in the second conductive layer, so that the conductive agent can better form a continuous conductive network with the silicon material and the carbon material, which is beneficial to improving the transmission rate of lithium ions, thereby effectively enhancing the conductivity of the negative electrode sheet, reducing the internal resistance of the battery, and being beneficial to suppressing the swelling problem of the silicon material and avoiding side reactions between the electrolyte and the silicon material, thereby improving the cycle performance of the battery.

[0042] Specifically, the amount of the conductive agent within a set square micron area in the first conductive layer or the second conductive layer of this application can be tested by a scanning electron microscope (SEM), including the following steps: performing SEM testing on the negative electrode sheet, maintaining a magnification of 20,000 times, observing the conductive agent on the surface of the silicon or the carbon material, and selecting a set square micron S 设 (such as 9 square microns, 3μm×3μm, or other empirical values, and this application does not limit this) area, observing the number n of conductive agents within the observation area; repeating the above steps 10 times, calculating the average value of the number of the 10 conductive agents obtained from the testing, which is the amount of the conductive agent within the set square micron area on the surface of the silicon material or the carbon material.

[0043] In a preferred embodiment, N 1 >2.0N 2 When the amount of the conductive agent in the first conductive layer is higher than 2.0 times the amount of the conductive agent in the second conductive layer, the transmission rate of lithium ions is higher, making the conductivity of the negative electrode sheet better, and having a better inhibitory effect on the swelling of the silicon material, thereby further improving the cycle performance of the battery.

[0044] In a specific embodiment, the negative electrode sheet satisfies the following relationship: 0.8S 2 <S 1 <1.2S 2 ; In the relationship, the percentage of the attachment area of the first attachment layer in the surface area of the silicon material is S 1 ; the percentage of the attachment area of the second attachment layer in the surface area of the carbon material is S 2 .

[0045] The percentage of the adhesion area of the first adhesion layer of the present application to the surface area of the silicon material refers to the ratio of the area of the first adhesion layer formed by styrene-butadiene rubber on the surface of the silicon material to the surface area of the silicon material; the percentage of the adhesion area of the second adhesion layer of the present application to the surface area of the carbon material refers to the ratio of the area of the second adhesion layer formed by styrene-butadiene rubber on the surface of the carbon material to the surface area of the carbon material. When the relationship between the percentage of the adhesion area of the first adhesion layer to the surface area of the silicon material and the percentage of the adhesion area of the second adhesion layer to the surface area of the carbon material is within the range of the above relational expression, styrene-butadiene rubber adheres to the surfaces of the silicon material and the carbon material, which can improve the flexibility of the negative electrode active material layer, avoid problems such as fracture or damage of the negative electrode active material layer, and at the same time can avoid the increase in the thickness expansion caused by the increase in the gap between particles after cycling, and avoid the deterioration of the kinetic performance caused by the deterioration of local electron and ion conduction, thereby improving the cycle performance and storage performance of the battery.

[0046] Specifically, the percentage of the adhesion area of the first adhesion layer to the surface area of the silicon material or the percentage of the adhesion area of the second adhesion layer to the surface area of the carbon material can be tested by a scanning electron microscope (SEM), including the following steps: performing SEM testing on the negative electrode sheet, maintaining a magnification of 20,000 times, observing the styrene-butadiene rubber particles on the surface of the silicon material or the carbon material, and selecting a set square micron S 设 (such as 9 square microns, 3μm×3μm, or other empirical values, the present application does not limit this) of the area on the surface of the silicon material or the carbon material, observing the number n of styrene-butadiene rubber particles in the observation area, and at the same time measuring the diameter D of the styrene-butadiene rubber particles (the styrene-butadiene rubber particles are spherical particles), and calculating the area S’ of a single styrene-butadiene rubber particle = 1 / 4×π×D 2 , therefore, the adhesion area ratio of styrene-butadiene rubber = nS’× / S 设 ; repeat the above steps 10 times, and calculate the average value of the 10 adhesion area ratios of styrene-butadiene rubber obtained by testing, which is the percentage of the adhesion area of the first adhesion layer to the area of the silicon material or the percentage of the adhesion area of the second adhesion layer to the area of the carbon material.

[0047] In a specific embodiment, the conductive agent includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0048] In a specific embodiment, the mass percentage content of the conductive agent in the negative electrode active material layer is 0.02% to 1.5%, for example, the mass percentage content of the conductive agent in the negative electrode active material layer is 0.02%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3% or 1.5%, etc. When the conductive agent is selected as carbon nanotubes and the mass percentage content of the conductive agent is within the above range, sufficient carbon nanotubes can form a complete conductive layer on the surfaces of the silicon material and the carbon material, which is beneficial to improving the conductivity of the negative electrode active material layer, thereby improving the cycle performance of the battery.

[0049] In a specific embodiment, the carbon material includes one or more of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0050] In a specific embodiment, the mass percentage of the carbon material in the negative electrode active material layer is 85% - 98%, such as 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or 98%, etc. When the mass percentage of the carbon material is within the above range, a sufficient amount of the carbon material can improve the conductivity of the negative electrode active material layer, reduce the resistance of the battery, and thus improve the cycling performance of the battery.

[0051] In a specific embodiment, the silicon material includes one or more of silicon oxides, prelithiated silicon oxides, premagnesiated silicon oxide materials, and silicon-carbon composite materials.

[0052] In a specific embodiment, the mass percentage of the silicon material in the negative electrode active material layer is 1% - 10%, for example, the mass percentage of the silicon material in the negative electrode active material layer is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc. When the mass percentage of the silicon material is within the above range, the silicon material can fully exert its electrochemical performance, ensure the energy density of the battery, and at the same time, the expansion of the silicon material can be inhibited by the binder, avoiding the pulverization or shedding of the negative electrode active material layer caused by the excessive expansion of the silicon material, thereby improving the cycling performance and storage performance of the battery.

[0053] In a specific embodiment, the polypropylene-based compound includes one or more of polyacrylic acid (PAA), polyacrylonitrile (PAN), and polyacrylamide (PAM).

[0054] In a specific embodiment, the mass percentage of the polypropylene-based compound in the negative electrode active material layer is 0.5% - 2%, for example, the mass percentage of the polypropylene-based compound in the negative electrode active material layer is 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75%, or 2%, etc.

[0055] In this application, polyacrylic acid, polyacrylonitrile or polyacrylamide is selected as the polypropylene-based compound. Polyacrylic acid, polyacrylonitrile or polyacrylamide has groups such as carboxyl, cyano or amide groups, which can form stable hydrogen bonds between the silicon material and the current collector, improve the adhesion between the silicon material and the negative electrode current collector, inhibit the expansion of the silicon material. At the same time, polyacrylic acid, polyacrylonitrile or polyacrylamide is a water-soluble polymer, which is beneficial to the dispersion and mixing of the polypropylene-based compound during the preparation of the negative electrode sheet. And the polypropylene-based compound has low swelling in the electrolyte, avoiding deformation or shedding of the negative electrode active material layer, thereby improving the cycle performance and storage performance of the battery. When the mass percentage content of the polypropylene-based compound is within the above range, the polypropylene-based compound can fully coat the silicon material, inhibit the expansion of the silicon material, and to a greater extent improve the conductivity of the negative electrode active material layer and reduce the expansion rate of the negative electrode active material layer, so that the cycle performance and storage performance of the battery are better.

[0056] In a specific embodiment, the mass percentage content of styrene-butadiene rubber in the negative electrode active material layer is 0.5% - 2%. For example, the mass percentage content of styrene-butadiene rubber in the negative electrode active material layer is 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75% or 2%, etc. When the mass percentage content of styrene-butadiene rubber is within the above range, styrene-butadiene rubber can act synergistically with the polypropylene-based compound to inhibit the expansion of the silicon material, and at the same time can improve the flexibility of the negative electrode active material layer, avoiding problems such as fracture caused by excessive brittleness of the negative electrode active material layer, thereby improving the cycle performance and storage performance of the battery.

[0057] In a specific embodiment, the negative electrode active material layer further includes a dispersant. The dispersant includes one or more of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose. The mass percentage content of the dispersant in the negative electrode active material layer is not higher than 1%. For example, the mass percentage content of the dispersant in the negative electrode active material layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc. When the mass percentage content of the dispersant is within the above range, the dispersant can be dispersed on the surfaces of the silicon material and the carbon material, avoiding the agglomeration of the silicon material and the carbon material, ensuring the uniform distribution of the silicon material and the carbon material, and at the same time can enhance the stability of the negative electrode active material layer, reduce the sedimentation and agglomeration of the active substances during the cyclic charge and discharge process, and improve the cycle performance of the battery.

[0058] The second aspect of this application provides a method for preparing a negative electrode sheet, including the following steps: S1. Mix the silicon material and the polypropylene-based compound in an aqueous solvent to obtain a first mixture, and make the polypropylene-based compound in the first mixture coat the surface of the silicon material to form a first coating layer; S2. Mix the carbon material and the first mixture in an aqueous solvent to obtain a second mixture, causing a part of the first coating layer in the first mixture to peel off, transfer to at least a part of the surface of the carbon material, and form a second coating layer; S3. Mix styrene-butadiene rubber and the second mixture to obtain a negative electrode slurry, causing the styrene-butadiene rubber in the negative electrode slurry to adhere to the surface of the first coating layer to form a first adhesion layer, and causing the styrene-butadiene rubber in the negative electrode slurry to adhere to at least a part of the surface of the carbon material and / or the second coating layer to form a second adhesion layer; S4. Coat the negative electrode slurry on at least one surface of the negative electrode current collector, and after drying and rolling, obtain a negative electrode sheet.

[0059] Specifically, in step S1, add a silicon material and a polypropylene compound in an aqueous solvent, perform a mixing process to obtain a first mixture; in this first mixture, the polypropylene compound coats the surface of the silicon material to form a first coating layer.

[0060] This application does not limit the addition amounts of the silicon material and the polypropylene compound in step S1, and can be selected according to actual needs.

[0061] This application does not limit the specific method of the mixing process in step S1, and can be selected according to actual needs.

[0062] The first mixture prepared in step S1 of this application is a paste-like mixture.

[0063] In step S2, add the carbon material and the first mixture in an aqueous solvent, perform a mixing process to obtain a second mixture; during the mixing process, since the polypropylene compound is a water-soluble compound, a part of the polypropylene compound on the surface of the silicon material in the first mixture will dissolve in the aqueous solvent and peel off from the surface of the silicon material. The peeled-off polypropylene compound will gradually migrate to the surface of the carbon material during the mixing process with the carbon material and adhere to at least a part of the surface of the carbon material to form a second coating layer. In this application, basically the surfaces of all silicon materials are coated with polypropylene compounds because the polypropylene compound is first mixed with the silicon material and the amount of the polypropylene compound is sufficient to coat all silicon materials; and, it can be that the surfaces of all carbon materials are coated with polypropylene compounds, or it can be that the surfaces of some carbon materials are coated with polypropylene compounds, because whether the surface of the carbon material is coated with polypropylene compounds is limited by the amount of the polypropylene compound peeled off from the surface of the silicon material and is also limited by the preparation process. The silicon material and the carbon material of this application are mixed and present in the second mixture.

[0064] This application does not limit the addition amounts of the carbon material and the first mixture in step S2, and can be selected according to actual needs.

[0065] This application does not limit the specific method of the mixing process in step S2, and can be selected according to actual needs.

[0066] In step S3, styrene-butadiene rubber is added to the second mixture and mixed to obtain a negative electrode slurry. The styrene-butadiene rubber is large-particle spherical substances. During the mixing process, the styrene-butadiene rubber adheres to the surface of the first coating layer to form a first adhesion layer, the styrene-butadiene rubber adheres to the surface of the second coating layer to form a second adhesion layer, or the styrene-butadiene rubber adheres to the surface of the carbon material to form a second adhesion layer. In this application, substantially all the surfaces of the silicon materials are coated with styrene-butadiene rubber. This is because the content of the silicon materials is less than that of the carbon materials, and substantially all the surfaces of the silicon materials are coated with polypropylene compounds. The adhesion force between the polypropylene compounds and the styrene-butadiene rubber is greater than the adhesion force between the styrene-butadiene rubber and the carbon materials. Therefore, it is possible that all the surfaces of the carbon materials are coated with styrene-butadiene rubber.

[0067] This application does not limit the addition amounts of the styrene-butadiene rubber and the second mixture in step S3, which can be selected according to actual needs.

[0068] This application does not limit the specific method of the mixing process in step S3, which can be selected according to actual needs.

[0069] In step S4, the negative electrode slurry is coated on at least one side surface of the negative electrode current collector, and then the negative electrode current collector is dried and rolled so that the negative electrode slurry is transformed into a negative electrode active material layer to obtain a negative electrode sheet.

[0070] This application mixes the silicon materials and the carbon materials step by step, adds polypropylene compounds only when mixing with the silicon materials, and adds styrene-butadiene rubber finally, so that more polypropylene compounds are coated on the surfaces of the silicon materials, and the thickness and area of the polypropylene compounds and the styrene-butadiene rubber coated on the surfaces of the carbon materials can meet the foregoing relational expressions, thereby being able to ensure the inhibition effect of the polypropylene compounds on the expansion of the silicon materials and the improvement of the conductivity of the negative electrode active material layer by the conductive agent, and further making the cycle performance and storage performance of the battery higher. In addition, the preparation method has simple process, low equipment requirements and wide raw material sources, which is conducive to the industrial application of the preparation method.

[0071] In a specific embodiment, before step S1, there is also step S0: S0: Dry-mix the silicon materials and the conductive agent to obtain a premix, so that the conductive agent in the premix is coated on the surfaces of the silicon materials to form a first conductive layer; and, S1: Mix the premix and the polypropylene compounds in an aqueous solvent to obtain a first mixture, so that the polypropylene compounds in the first mixture are coated on the surface of the first conductive layer to form a first coating layer; S2. Mix the carbon material and the first mixture in an aqueous solvent to obtain a second mixture, causing a part of the polypropylene compound contained in the first coating layer in the first mixture to exfoliate, transfer to the surface of the carbon material, and form a second coating layer; a part of the conductive agent contained in the first conductive layer and a part of the polypropylene compound contained in the first coating layer in the first mixture exfoliate and transfer to the surface of the carbon material. Among them, the conductive agent forms a second conductive layer on the surface of the carbon material, and the polypropylene compound forms a second coating layer on the surface of the carbon material.

[0072] Before step S1 of this application, step S0 is carried out: dry-mix the silicon material and the conductive agent. During the dry-mixing process, the conductive agent adheres to at least part of the surface of the silicon material to form a first conductive layer, and a premix is obtained.

[0073] In step S1, the silicon material coated with the first conductive layer is mixed with the polypropylene compound to obtain a first mixture. In this first mixture, the polypropylene compound coats the surface of the first conductive layer to form a first coating layer, or the polypropylene compound coats the surface of the silicon material to form a first coating layer.

[0074] In step S2, the silicon material coated with the first conductive layer and the first coating layer is mixed with the carbon material to obtain a second mixture. During the mixing process, part of the first conductive layer and the first coating layer exfoliate from the silicon surface and gradually transfer to the surface of the carbon material, causing a second conductive layer and a second coating layer to be formed on the surface of the carbon material; the exfoliation of the first coating layer may be faster than that of the first conductive layer. Therefore, the first coating layer and the first conductive layer may exfoliate from the surface of the silicon material as a whole or separately, so that at least part of the surface of the carbon material is coated with at least one of the conductive agent and the polypropylene compound.

[0075] In step S3, styrene-butadiene rubber is added to the second mixture and mixed to obtain a negative electrode slurry. During the mixing process, the styrene-butadiene rubber adheres to the surface of the first coating layer to form a first adhesion layer, or the styrene-butadiene rubber adheres to the surface of the second coating layer to form a second adhesion layer, or the styrene-butadiene rubber adheres to the surface of the carbon material to form a second adhesion layer. Thus, the structure on the surface of the silicon material in the negative electrode active material layer is divided into two cases: The first case is that the surface of the silicon material is coated with a conductive agent to form a first conductive layer, the surface of the first conductive layer is coated with a polypropylene compound to form a first coating layer, and the styrene-butadiene rubber adheres to the surface of the first coating layer to form a first adhesion layer; The second case is that a part of the surface of the silicon material is coated with a conductive agent to form a first conductive layer, the surface of the first conductive layer is coated with a polypropylene compound to form a first coating layer, and the other part of the surface of the silicon material is also coated with a polypropylene compound to form a first coating layer, and the styrene-butadiene rubber adheres to the surface of the first coating layer to form a second adhesion layer. The structure on the surface of the carbon material is divided into several cases: The first case is that the surface of the carbon material is coated with a conductive agent to form a second conductive layer, the surface of the second conductive layer is coated with a polypropylene compound to form a second coating layer, and the styrene-butadiene rubber adheres to the surface of the second coating layer to form a second adhesion layer; The second case is that the surface of the carbon material is coated with a polypropylene compound to form a second coating layer, the surface of the second coating layer is coated with a conductive agent to form a second conductive layer, and the styrene-butadiene rubber adheres to the surface of the second conductive layer to form a second adhesion layer; The third case is that the polypropylene compound is coated on a part of the surface of the carbon material to form a second coating layer, the conductive agent is coated on the other part of the surface of the carbon material to form a second conductive layer, and then the styrene-butadiene rubber adheres to the surface of the second coating layer or the second conductive layer to form a second adhesion layer; The fourth case is that the surface of the carbon material is coated with a conductive agent to form a second conductive layer, and the styrene-butadiene rubber adheres to the surface of the second conductive layer to form a second adhesion layer; The fifth case is that the surface of the carbon material is coated with a polypropylene compound to form a second coating layer, and the styrene-butadiene rubber adheres to the surface of the second coating layer to form a second adhesion layer; The sixth case is that only the polypropylene compound is coated on the surface of the carbon material to form a second coating layer; The seventh case is that only the conductive agent is coated on the surface of the carbon material to form a second conductive layer; The eighth case is that only the styrene-butadiene rubber is coated on the surface of the carbon material to form a second adhesion layer; The ninth case is that the surface of the carbon material is coated with a polypropylene compound to form a second coating layer, and the surface of the second coating layer is coated with a conductive agent to form a second conductive layer.

[0076] In this application, the silicon material and the carbon material are mixed step by step, and the polypropylene compound and the conductive agent are added only when mixing with the silicon material, and the styrene-butadiene rubber is added finally, so that more conductive agent and polypropylene compound are coated on the surface of the silicon material, and the thickness, quantity and area of the polypropylene compound, conductive agent and styrene-butadiene rubber coated on the surfaces of the silicon material and the carbon material can meet the aforementioned relational expressions, thereby ensuring the inhibition effect of the polypropylene compound on the expansion of the silicon material and the improvement of the conductivity of the negative electrode active material layer by the conductive agent, and further making the cycle performance and storage performance of the battery higher.

[0077] In a specific embodiment, in step S1, a silicon material, a polypropylene compound, and a dispersant are mixed in an aqueous solvent to obtain a first mixture; in step S2, a carbon material, the first mixture, and a dispersant are mixed in an aqueous solvent to obtain a second mixture.

[0078] The dispersant of the present application includes one or more of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose.

[0079] In the present application, the dispersant is added in two steps, which can regulate the viscosity of the mixture, avoid the viscosity of the mixture being too high or too low, and avoid the difficulty of the finally prepared negative electrode paste being loaded on the surface of the negative electrode current collector, which is beneficial to reducing the preparation difficulty of the negative electrode sheet.

[0080] To ensure that the conductive agent is fully attached to the surface of the silicon material, the stirring speed for dry mixing is 10 r / min to 30 r / min, such as the stirring speed being 10 r / min, 15 r / min, 20 r / min, 25 r / min or 30 r / min, etc., and the stirring time is 10 min to 60 min, such as the stirring time being 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, etc. Preferably, the stirring speed for dry mixing is 20 r / min to 30 r / min, and the stirring time is 30 min to 45 min.

[0081] In the present application, by regulating the parameters of the stirring treatment in steps S1, S2, and S3, the polypropylene compound, the conductive agent, and styrene-butadiene rubber can be better attached to the surface of the silicon material, and at the same time, an appropriate amount of the polypropylene compound and the conductive agent can be ensured to fall off from the surface of the silicon material and transfer to the surface of the carbon material, so that a negative electrode paste with a specific dispersion state can be prepared, and finally a negative electrode sheet with the contents of the polypropylene compound, the conductive agent, and styrene-butadiene rubber coated on the surfaces of the silicon material and the carbon material satisfying the foregoing relational expression can be obtained, thereby improving the cycle performance and storage performance of the battery.

[0082] In a specific embodiment, mixing is carried out by stirring in step S1. The revolution speed of the stirring is 10 r / min to 30 r / min, for example, the revolution speed is 10 r / min, 15 r / min, 20 r / min, 25 r / min or 30 r / min, etc., the rotation speed is 0 to 500 r / min, for example, the rotation speed is 50 r / min, 100 r / min, 200 r / min, 300 r / min, 400 r / min or 500 r / min, etc., and the stirring time is 10 min to 120 min, for example, the stirring time is 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, etc. The present application does not limit the equipment used for stirring and mixing. For example, a planetary ball mill can be used for stirring and mixing in step S1. Preferably, the revolution speed of the stirring is 20 r / min to 30 r / min, the rotation speed is 100 r / min to 300 r / min, and the stirring time is 30 min to 100 min. When the stirring speed and stirring time in step S1 are within the above ranges, the polypropylene-based compound can fully coat the surface of the first conductive layer to form a first coating layer, which is beneficial to the preparation of the negative electrode paste in a specific dispersion state, helps to inhibit the volume expansion of the silicon material during the cycling process, and thus improves the electrochemical performance of the battery.

[0083] In a specific embodiment, mixing is performed by stirring in step S2. The revolution speed of the stirring is 10 r / min to 30 r / min. For example, the revolution speed is 10 r / min, 15 r / min, 20 r / min, 25 r / min, or 30 r / min, etc. The rotation speed is 1000 r / min to 3000 r / min. For example, the rotation speed is 1000 r / min, 1500 r / min, 2000 r / min, 2500 r / min, or 3000 r / min, etc. The stirring time is 60 min to 240 min. For example, the stirring time is 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, 180 min, 200 min, 220 min, or 240 min, etc. Preferably, the revolution speed of the stirring is 20 r / min to 30 r / min, the rotation speed is 1500 r / min to 2000 r / min, and the stirring time is 120 min to 180 min. When the stirring speed and stirring time in step S2 are within the above ranges, during the mixing process, a reasonable amount of the first conductive layer and the first coating layer peel off from the silicon surface and can gradually transfer to the surface of the carbon material, forming a second conductive layer and a second coating layer on the surface of the carbon material, so that the thickness and quantity of the polypropylene-based compound and the conductive agent coated on the surfaces of the silicon material and the carbon material satisfy the foregoing relationship, thereby ensuring the inhibitory effect of the polypropylene-based compound on the expansion of the silicon material and the improvement of the conductivity of the negative electrode active material layer by the conductive agent, and further improving the cycle performance and storage performance of the battery.

[0084] In a specific embodiment, mixing is performed by stirring in step S3. The revolution speed of the stirring is 10 r / min to 30 r / min, for example, the revolution speed is 10 r / min, 15 r / min, 20 r / min, 25 r / min or 30 r / min, etc., and the rotation speed is 200 r / min to 1000 r / min, for example, the rotation speed is 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min or 1000 r / min, etc. The stirring time is 30 min to 120 min, for example, the stirring time is 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, etc. Preferably, the revolution speed of the stirring is 10 r / min to 25 r / min, the rotation speed is 200 r / min to 500 r / min, and the stirring time is 30 min to 60 min. When the stirring speed and stirring time in step S3 are within the above ranges, styrene-butadiene rubber can be fully attached to the surfaces of the first coating layer, the second coating layer, and the second conductive layer, thereby improving the flexibility of the negative electrode active material layer and avoiding problems such as fracture and breakage of the negative electrode active material layer, and further enhancing the electrochemical performance of the battery.

[0085] In a specific embodiment, the mass percentage content of the silicon material in the negative electrode active material layer is 1% to 10%, for example, the mass percentage content of the silicon material in the negative electrode active material layer is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0086] In a specific embodiment, the mass percentage content of the carbon material in the negative electrode active material layer is 85% to 98%, for example, it is 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97% or 98%, etc.

[0087] In a specific embodiment, the mass percentage content of the polypropylene compound in the negative electrode active material layer is 0.5% to 2%, for example, the mass percentage content of the polypropylene compound in the negative electrode active material layer is 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75% or 2%, etc.

[0088] In a specific embodiment, the mass percentage content of the conductive agent in the negative electrode active material layer is 0.02% to 1.5%, for example, the mass percentage content of the conductive agent in the negative electrode active material layer is 0.02%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3% or 1.5%, etc.

[0089] In a specific embodiment, the mass percentage content of styrene-butadiene rubber in the negative electrode active material layer is 0.5% - 2%. For example, the mass percentage content of styrene-butadiene rubber in the negative electrode active material layer is 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75% or 2%, etc.

[0090] In a specific embodiment, the mass percentage content of the dispersant in the negative electrode active material layer is not higher than 1%. For example, the mass percentage content of the dispersant in the negative electrode active material layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc.

[0091] The third aspect of the present application provides a battery, including the above-mentioned negative electrode sheet or the negative electrode sheet prepared according to the preparation method of the above-mentioned negative electrode sheet.

[0092] In a specific embodiment, the battery of the present application further includes a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium manganate, nickel cobalt manganese ternary material, nickel manganese acid lithium, and lithium-rich manganese-based material. When the positive electrode active material selects the above compounds, the positive electrode active material can fully exert its performance and improve the electrochemical performance of the lithium-ion battery.

[0093] In the embodiments of the present application, there is no particular limitation on the type of the positive electrode current collector, and it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, etc. and carbon materials such as carbon cloth and carbon paper. Preferably, the positive electrode current collector is a metal material.

[0094] In a specific embodiment, the positive electrode active material layer further includes a conductive agent and a binder. The conductive agent includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene, etc. The binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0095] In a specific embodiment, the battery of the present application further includes an electrolyte. The electrolyte is a well-known electrolyte in the art that can be used in a battery and makes the battery have excellent electrochemical performance, including a lithium salt and an organic solvent, and can be specifically set according to needs.

[0096] In a specific embodiment, the battery further includes a separator. The embodiments of the present application do not particularly limit the material and shape of the separator, as long as the effects of the present application are not significantly impaired. It may include substances in the form of porous sheets or non-woven fabrics with excellent liquid retention properties, etc. The materials of the resin or glass fiber separator include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc., and can be specifically set according to needs.

[0097] In a specific embodiment, the battery may include an outer package, which can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0098] In a specific embodiment, the outer package of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0099] The present application does not particularly limit the shape of the secondary battery, which can be cylindrical, square, or any other arbitrary shape.

[0100] The present application does not particularly limit the application fields of the secondary battery, and it can be used in fields such as consumer electronics, new energy vehicles, and energy storage.

[0101] Hereinafter, the present application will be further described in detail through specific examples.

[0102] Example 1 1. Preparation of the negative electrode sheet Mix silicon carbide particles, graphite, carbon nanotubes, polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC-Na) according to a solid mass ratio of 5:90.4:0.1:2:2:0.5 and follow the following batching process for batching: Step 1: Dry-mix the silicon carbide particles and carbon nanotubes at a stirring speed of 25 r / min for 30 min to obtain a premix; Step 2: Add PAA and 50% of the total amount of CMC-Na glue solution to the premix for the first stirring treatment, with a revolution speed of 25 r / min, a rotation speed of 200 r / min, and a stirring time of 60 min to obtain a first mixture; Step 3: Add graphite, 50% of the total amount of CMC-Na glue solution, and deionized water accounting for 10% of the total solid weight to the first mixture for the second stirring treatment, with a revolution speed of 30 r / min, a rotation speed of 2000 r / min, and a stirring time of 120 min to obtain a second mixture; Step 4: Add SBR latex to the second mixture and perform a third stirring process with a revolution speed of 25 r / min, a rotation speed of 500 r / min, and a stirring time of 45 min. Then, perform vacuum degassing to obtain the negative electrode slurry. Step 5: Uniformly coat the negative electrode slurry on one surface of a negative electrode current collector copper foil with a thickness of 10 μm, and dry it at 110 °C to obtain a negative electrode sheet with a negative electrode material layer coated on one side and a coating thickness of 150 μm. Repeat the above steps on the other surface of the negative electrode sheet to obtain a negative electrode sheet with negative electrode active material layers coated on both sides. Then, cut the negative electrode sheet into a specification of 74 mm × 867 mm for standby.

[0103] 2. Preparation of the positive electrode sheet Mix the positive electrode active material lithium cobaltate, conductive carbon black, and polyvinylidene fluoride (PVDF) binder evenly in a mass ratio of 95:2.5:2.5, and fully stir and mix them in N-methylpyrrolidone solvent to prepare a slurry with a solid content of 75%. Stir it evenly to obtain the positive electrode slurry. Uniformly coat the positive electrode slurry on one surface of an aluminum foil with a thickness of 12 μm, and dry it at 90 °C. After cold pressing, obtain a positive electrode sheet with a positive electrode active material layer thickness of 110 μm. Then, repeat the above steps on the other surface of the positive electrode sheet to obtain a positive electrode sheet with positive electrode active material layers coated on both sides. Cut the positive electrode sheet into a specification of 76 mm × 851 mm, weld the electrode tabs, and then set it aside for use.

[0104] 3. Preparation of the electrolyte Under an environment with a water content of less than 10 ppm, mix propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a mass ratio of 1:3:6, and add 8% of butyl butyrate based on the total mass of the electrolyte; then add lithium hexafluorophosphate (LiPF 6 ) to the solvent to dissolve and mix it evenly, and then add fluoroethylene carbonate (FEC) to obtain the electrolyte. Among them, the molar concentration of LiPF 6 in the electrolyte is 1.15 mol / L, and the mass concentration of FEC in the electrolyte is 10.1%.

[0105] 4. Fabrication of the lithium-ion battery Use a polyethylene porous polymer film as the separator. Stack the positive electrode sheet, the separator, and the negative electrode sheet in sequence, with the separator in the middle of the positive and negative electrodes to play a separating role. Then, wind the stacked electrode sheets and the separator to obtain an electrode assembly. Place the electrode assembly in a formed aluminum-plastic film shell, remove the moisture at 80 °C, inject the prepared electrolyte, and obtain the lithium-ion battery through processes such as vacuum packaging, standing, forming, and shaping.

[0106] The main differences between Examples 2 to 12 and Example 1 are the different parameters of the stirring treatment in the preparation process of the negative electrode sheet. Refer to Table 1.

[0107] Comparative Example 1 The difference between this comparative example and Example 1 lies in the preparation of the negative electrode sheet: Mix silicon carbide particles, graphite, carbon nanotubes, polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC-Na) according to a solid mass ratio of 5:90.4:0.1:2:2:0.5 and follow the following batching process for batching: Step 1: Perform dry mixing on silicon particles, graphite, and carbon nanotubes at a stirring speed of 25 r / min for 30 min to obtain a premix. Step 2: Add PAA and 50% of the total weight of the CMC-Na solution to the premix for the first stirring treatment, with a revolution speed of 30 r / min, a rotation speed of 2000 r / min, and a stirring time of 60 min to obtain a first mixture. Step 3: Add 50% of the total weight of CMC-Na and 10% of the total solid weight of deionized water to the first mixture for the second stirring treatment, with a revolution speed of 30 r / min, a rotation speed of 2000 r / min, and a stirring time of 120 min to obtain a second mixture. Step 4: Add the SBR solution to the second mixture for the third stirring treatment, with a revolution speed of 25 r / min, a dispersion speed of 500 r / min, a rotation speed of 45 min, and vacuum degassing to obtain the negative electrode slurry. Step 5: Uniformly coat the negative electrode slurry on one surface of a negative electrode current collector copper foil with a thickness of 10 μm and dry it at 110 °C to obtain a negative electrode sheet with a negative electrode material layer coated on one side with a coating thickness of 150 μm. Repeat the above steps on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a negative electrode active material layer coated on both sides. Then, cut the negative electrode sheet into a specification of 74 mm × 867 mm for use.

[0108] Comparative Example 2 The difference between this comparative example and Example 1 lies in the preparation of the negative electrode sheet: Mix silicon carbide particles, graphite, carbon nanotubes, polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC-Na) according to a solid mass ratio of 5:90.4:0.1:2:2:0.5 and follow the following batching process for batching: Step 1: Stir silicon particles, graphite, carbon nanotubes, PAA, CMC-Na, SBR, and deionized water at a revolution speed of 30 r / min, a rotation speed of 2000 r / min, and a stirring time of 150 min to obtain the negative electrode slurry. Step 2: Uniformly coat the negative electrode paste on one surface of a negative electrode current collector copper foil with a thickness of 10 μm, and dry it at 110 °C to obtain a negative electrode sheet with a negative electrode material layer coated on one side and a coating thickness of 150 μm. Repeat the above steps on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a negative electrode active material layer coated on both sides. Then, cut the negative electrode sheet into a specification of 74 mm × 867 mm for use.

[0109] The main differences between Comparative Examples 3 to 11 and Example 1 are the parameters of the stirring treatment and the component ratios in the negative electrode active material layer during the preparation process of the negative electrode sheet. Refer to Table 1.

[0110] Comparative Example 12: The basic content is the same as that of Example 1, except that polyvinylpyrrolidone (PVP) is used to replace PAA.

[0111] Comparative Example 13: The basic content is the same as that of Example 1, except that PAA is not added.

[0112] Comparative Example 14: The basic content is the same as that of Example 1, except that SBR is not added.

[0113] Table 1

[0114] Test Example 1 Measurement of the thickness H of the first coating layer 1 and the thickness H of the second coating layer 2 Test: Perform TEM test on the negative electrode sheet, maintain a magnification of 20,000 times, measure the polypropylene-based compound coating layer on the surface of the silicon material or carbon material, obtain the coating layer thickness, select 10 different test points for testing, and calculate the average value of the 10 measured coating layer thicknesses, which is the thickness of the polypropylene-based compound coating layer. See Table 2.

[0115] Number of carbon nanotubes N within an area of 9 square micrometers in the first conductive layer or the second conductive layer 1 or N 2 ) Test: Perform SEM test on the negative electrode sheet, maintain a magnification of 20,000 times, observe the carbon nanotubes on the surface of the silicon or carbon material, select an area of 9 square micrometers (3 μm × 3 μm) on the surface of the silicon material or carbon material, and observe the number n of carbon nanotubes within the observation area; repeat the above steps 10 times, and calculate the average value of the 10 measured numbers of carbon nanotubes, which is the number of carbon nanotubes within an area of 9 square micrometers on the surface of the silicon material or carbon material. See Table 2.

[0116] Percentage S of the adhesion area of the first adhesion layer to the area of the silicon material 1Or the percentage S of the adhesion area of the second adhesion layer to the area of the carbon material 2 Test: Perform SEM test on the negative electrode sheet, keep the magnification at 20,000 times, observe the styrene-butadiene rubber particles on the surface of the silicon material or carbon material, select an area of 9 square micrometers (3μm×3μm) on the surface of the silicon material or carbon material, observe the number n of styrene-butadiene rubber particles in the observation area, and at the same time measure the diameter D of the styrene-butadiene rubber particles (the styrene-butadiene rubber particles are spherical particles), and calculate the area of a single styrene-butadiene rubber particle S’=1 / 4×π×D 2 Therefore, the adhesion area ratio of styrene-butadiene rubber = S’×n / 9; repeat the above steps 10 times, calculate the average value of the adhesion area ratios of the 10 styrene-butadiene rubbers obtained from the test, which is the adhesion area ratio of styrene-butadiene rubber on the surface of the silicon material or carbon material, as shown in Table 2.

[0117] Experimental Example 2 Test the following performances of the batteries prepared in the examples and comparative examples: 1. Internal resistance test Use an internal resistance tester to test the internal resistance.

[0118] 2. Capacity test In a constant temperature oven at (25±2)°C, charge the lithium-ion battery at a constant current of 0.7C and a constant voltage of 4.53V until the cut-off current is 0.05C, let it stand for 5 minutes, and then discharge it at 0.2C to 3V. The capacity of the battery cell is obtained through the above steps.

[0119] 3. Cycle performance test In a constant temperature oven at (45±2)°C and (25±2)°C respectively, charge the lithium-ion battery at a constant current of 0.7C and a constant voltage of 4.53V until the constant voltage charging reaches 0.05C, let it stand for 5 minutes, and then discharge it at 0.5C to 3V. The capacity obtained through this step is used as the initial capacity, and cycle tests are carried out with 0.7C charging / 0.5C discharging. The ratio of the capacity at the 600th cycle to the initial capacity is used to obtain the capacity retention rate.

[0120] For each group of 5 batteries, the average values of the room temperature cycle capacity retention rate and the high temperature cycle capacity retention rate calculated are recorded in Table 3.

[0121] 4. Swelling rate test Use a micrometer to test the thickness of the lithium-ion battery when it is half-charged, that is, at 50% state of charge (SOC), as the initial thickness. After 600 cycles of charging, when it is fully charged, that is, at 100% SOC state, use a micrometer to test the thickness of the lithium-ion battery at this time, and compare it with the thickness of the lithium-ion battery when it was initially half-charged, and the swelling rate of the fully charged lithium-ion battery at this time can be obtained.

[0122] For each group of 5 batteries, the average values of the room temperature cycle swelling rate and the high temperature cycle swelling rate calculated are recorded in Table 3.

[0123] Table 2

[0124] Table 3

[0125] The following conclusions can be drawn from the results of the examples and comparative examples: In Examples 1 to 5, under the conditions of the preferred batching parameters, H 1 / H 2 and N 1 / N 2 are both within the better range, and the performance of the battery cells is relatively good; In Examples 6 to 8, the batching parameters deviate from the optimal range, and H 1 / H 2 or N 1 / N 2 will also deviate from the better range, and the capacity retention and cycle expansion of the battery cells will deteriorate slightly; In Example 10, with the increase in the silicon content, the corresponding cycle retention rate decreases and the cycle expansion increases; In Examples 11 to 12, when comparing two different binders, PAN and PAM, the performance of the battery cells is equivalent to that of the PAA group; In Comparative Examples 1 and 2, the batching process was changed, and H 1 / H 2 and N 1 / N 2 The ratios are both lower than 1.2, resulting in a significant deterioration of the cycle capacity retention rate and cycle expansion; In Comparative Example 3, too much silicon content leads to a significant increase in the volume expansion of the battery cell; In Comparative Example 4, the content of the conductive agent is too low, and the electronic conductivity of the electrode is insufficient, resulting in a decrease in the cycle retention rate; In Comparative Examples 5 to 6, the addition amounts of polyacrylic acid and styrene-butadiene rubber are too much, which is beneficial to reducing the electrode expansion, but will also deteriorate the kinetic performance, resulting in a decrease in the cycle capacity retention rate; In Comparative Example 7, the addition ratio of the dispersant CMC-Na is too much, which is beneficial to improving the dispersion and slurry stability, but will deteriorate the kinetic performance, resulting in an increase in the brittleness of the electrode sheet, and the cycle capacity retention and thickness expansion will deteriorate; In Comparative Examples 8 to 11, the parameters of the dry mixing treatment, the first stirring treatment, the second stirring treatment, and the third stirring treatment are too high or too low, resulting in H 1 / H 2 or N 1 / N 2 The ratios are both lower than 1.2, resulting in an obvious deterioration of the battery performance; Comparative Example 12: Polyvinylpyrrolidone (PVP) was used to replace PAA. Since the elastic modulus of polyvinylpyrrolidone is small, it cannot effectively restrain the volume expansion of silicon, and the thickness expansion of the battery cell increases; In Comparative Example 13, PAA was not added, and the expansion of silicon materials could not be effectively inhibited, resulting in a significant deterioration of the thickness expansion of the battery cell; In Comparative Example 14, SBR was not added, resulting in excessive brittleness of the electrode sheet and a reduced inhibitory effect on the expansion of silicon materials, leading to a significant deterioration of the thickness expansion of the battery cell.

[0126] The embodiments of the present application have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode sheet, characterized in that: It comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector; the negative electrode active material layer comprises a negative electrode active material and a binder, the negative electrode active material comprises a carbon material and a silicon material, and the binder comprises a polypropylene compound and styrene-butadiene rubber; The polypropylene compound is coated on the surface of the silicon material to form a first coating layer, and the styrene-butadiene rubber is attached to the surface of the first coating layer to form a first adhesion layer; At least a portion of the surface of the carbon material is coated with at least one of the polypropylene compound and the styrene-butadiene rubber, and the styrene-butadiene rubber is attached to the outermost layer of the carbon material; wherein the polypropylene compound forms a second coating layer on the surface of the carbon material, and the styrene-butadiene rubber forms a second attachment layer on the surface of the carbon material; The negative electrode sheet satisfies the following relationship: H1>1.2H2; In the relationship, the thickness of the first coating layer is H1; the thickness of the second coating layer is H2.

2. The negative electrode sheet according to claim 1, characterized in that: H1>2.0H2.

3. The negative electrode sheet according to claim 1, characterized in that: The negative electrode active material layer further includes a conductive agent, the conductive agent is coated on at least part of the surface of the silicon material to form a first conductive layer, and the polypropylene compound is coated on at least part of the surface of the silicon material and / or the first conductive layer to form a first coating layer; at least part of the surface of the carbon material is coated with at least one of the conductive agent and the polypropylene compound, wherein the conductive agent forms a second conductive layer on the surface of the carbon material, and the polypropylene compound forms a second coating layer on the surface of the carbon material and / or the second conductive layer; preferably, the negative electrode sheet satisfies the following relationship: N1>1.2N2; In the relationship, the number of conductive agents in the first conductive layer within an area of ​​square micrometers is set to N1; the number of conductive agents in the second conductive layer within an area of ​​square micrometers is set to N2; further preferably, N1>2.0N2.

4. The negative electrode sheet according to claim 3, characterized in that: The conductive agent includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes; and / or, The mass percentage of the conductive agent in the negative electrode active material layer is 0.02% to 1.5%.

5. The negative electrode sheet according to claim 1, characterized in that: The negative electrode sheet satisfies the following relationship: 0.8S2<S1<1.2S2; In the relationship, the percentage of the attachment area of ​​the first attachment layer to the surface area of ​​the silicon material is S1; the percentage of the attachment area of ​​the second attachment layer to the surface area of ​​the carbon material is S2.

6. The negative electrode sheet according to claim 1, characterized in that: The carbon material includes one or more of artificial graphite, natural graphite, hard carbon, and soft carbon; and / or, The mass percentage of the carbon material in the negative electrode active material layer is 85% to 98%; and / or, The silicon material includes one or more of silicon oxide, pre-lithiation silicon oxide, pre-magnesiation silicon oxide material, and silicon-carbon composite material; and / or, The mass percentage of the silicon material in the negative electrode active material layer is 1% to 10%; and / or, The polypropylene compound includes one or more of polyacrylic acid, polyacrylonitrile and polyacrylamide; and / or, The mass percentage of the polypropylene compound in the negative electrode active material layer is 0.5% to 2%; and / or, The mass percentage of the styrene-butadiene rubber in the negative electrode active material layer is 0.5% to 2%; and / or, The negative electrode active material layer further includes a dispersant, which includes one or more of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose. The mass percentage of the dispersant in the negative electrode active material layer is not higher than 1%.

7. A method for preparing a negative electrode sheet, characterized in that: The following steps are involved: S1, mixing a silicon material and a polypropylene compound in a water solvent to obtain a first mixture, and coating the surface of the silicon material with the polypropylene compound in the first mixture to form a first coating layer; S2, mixing the carbon material and the first mixture in an aqueous solvent to obtain a second mixture, so that the polypropylene compound contained in the first coating layer in the first mixture partially falls off and transfers to at least a portion of the surface of the carbon material to form a second coating layer; S3, mixing the styrene-butadiene rubber and the second mixture to obtain a negative electrode slurry, so that the styrene-butadiene rubber in the negative electrode slurry adheres to the surface of the first coating layer to form a first adhesion layer, and so that the styrene-butadiene rubber in the negative electrode slurry adheres to at least a portion of the surface of the carbon material and / or the second coating layer to form a second adhesion layer; S4, coating the negative electrode slurry onto at least one side of the surface of the negative electrode current collector, and obtaining a negative electrode sheet after drying and rolling.

8. The method for preparing a negative electrode sheet according to claim 7, characterized in that: The step S1 also includes a step S0: S0, dry-mixing the silicon material and the conductive agent to obtain a premix, so that the conductive agent in the premix is ​​coated on the surface of the silicon material to form a first conductive layer; as well as, S1, mixing the premix and the polypropylene compound in a water solvent to obtain a first mixture, and coating the polypropylene compound in the first mixture on the surface of the first conductive layer to form a first coating layer; S2. Mixing the carbon material and the first mixture in an aqueous solvent to obtain a second mixture, so that part of the polypropylene compound contained in the first coating layer in the first mixture falls off and is transferred to the surface of the carbon material to form a second coating layer; part of the conductive agent contained in the first conductive layer in the first mixture and part of the polypropylene compound contained in the first coating layer fall off and are transferred to the surface of the carbon material, wherein the conductive agent forms a second conductive layer on the surface of the carbon material, and the polypropylene compound forms a second coating layer on the surface of the carbon material.

9. The preparation method according to claim 7, characterized in that: The stirring speed of the dry mixing is 10 r / min~30 r / min, and the stirring time is 10 min~60 min; preferably, the stirring speed of the dry mixing is 20 r / min~30 r / min, and the stirring time is 30 min~45 min.

10. The preparation method according to claim 7, characterized in that: In step S1, mixing is performed by stirring, the revolution speed of stirring is 10 r / min-30 r / min, the rotation speed is 0-500 r / min, and the stirring time is 10 min-120 min; preferably, the revolution speed of stirring is 20 r / min-30 r / min, the rotation speed is 100 r / min-300 r / min, and the stirring time is 30 min-100 min; and / or, In step S2, mixing is performed by stirring, the revolution speed of stirring is 10 r / min-30 r / min, the rotation speed is 1000 r / min-3000 r / min, and the stirring time is 60 min-240 min; preferably, the revolution speed of stirring treatment is 20 r / min-30 r / min, the rotation speed is 1500 r / min-2000 r / min, and the stirring time is 120 min-180 min; and / or, In step S3, stirring is used for mixing, the revolution speed of stirring is 10r / min~30r / min, the rotation speed is 200r / min~1000r / min, and the stirring time is 30min~120min; preferably, the revolution speed of stirring treatment is 10r / min~25r / min, the rotation speed is 200r / min~500r / min, and the stirring time is 30min~60min.

11. A battery, characterized in that: The battery comprises the negative electrode sheet according to any one of claims 1 to 6 or a negative electrode sheet prepared by the method for preparing a negative electrode sheet according to any one of claims 7 to 10.

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