Silicon-based negative active material composition, negative pole piece and secondary battery

Abstract

The invention relates to the technical field of secondary batteries, in particular to a silicon-based negative electrode active material composition, a negative electrode pole piece and a secondary battery. The fluororesin dispersion liquid containing one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer and perfluoroethylene propylene copolymer is adopted as a binder to bond a silicon-containing material, a conductive agent and graphite together, and hydrophobic coating of the silicon-carbon surface is achieved in the drying process; the problem that the bonding force between the silicon-containing materials and between the silicon-containing materials and the current collector is reduced due to volume expansion in the silicon circulation process is effectively solved, meanwhile, the water absorption of the silicon-containing materials is also improved, and the capacity and the circulation stability of the battery are further improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a silicon-based negative electrode active material composition, a negative electrode sheet, and a secondary battery. Background Technology

[0002] Lithium-ion batteries have been widely used in automobiles, smart home appliances, and other fields due to their advantages such as high energy density, small size, and environmental friendliness. Improving the overall performance of lithium-ion batteries, including energy density and cycle life, is crucial in the industry. Existing silicon anode materials, including silicon-carbon, silicon-oxygen, and novel silicon-carbon anode materials, still have some inherent problems and defects. For example, irreversible expansion of the material volume during cycling leads to poor adhesion between silicon anode materials and between the silicon anode material and the current collector, making them prone to detachment and affecting the cycle stability of the battery. Summary of the Invention

[0003] This application provides a silicon-based anode active material composition, anode sheet, and secondary battery to solve the problem of irreversible expansion of silicon anode materials during cycling in the prior art, which affects the poor cycle stability of the battery.

[0004] In a first aspect, this application provides a method for preparing a silicon-based negative electrode active material composition, comprising the following steps: mixing a conductive agent, graphite, a silicon-containing material and a fluororesin dispersion, and drying the mixture to obtain a silicon-based negative electrode active material composition; wherein the fluororesin in the fluororesin dispersion comprises one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, and perfluoroethylene propylene copolymer.

[0005] In one optional embodiment, the solid content of the fluororesin dispersion is 5-60%; and / or, the particle size D50 of the graphite is 2-5 μm; and / or, the mass ratio of the conductive agent, graphite, silicon-containing material, and fluororesin dispersion is 1-5:60-93:5-30:1-5; and / or, the conductive agent comprises one or more of conductive carbon black and carbon nanotubes; and / or, the silicon-containing material comprises one or more of silicon suboxide and silicon carbide.

[0006] In one alternative embodiment, the solvent of the fluoropolymer dispersion includes water.

[0007] In one optional embodiment, the solid content of the mixed material is adjusted to 3%-20%, optionally to 5%-15%, using water before drying.

[0008] In one optional embodiment, mixing is carried out by stirring at a speed of 1000-5000 rpm for 3-10 hours; and / or, the drying is spray drying, with an inlet temperature of 100-200°C, an outlet temperature of 50-80°C, and a feeding rate of 0.5-2 L / min.

[0009] Secondly, this application also provides a silicon-based negative electrode active material composition prepared by any of the above-described preparation methods for the negative electrode sheet.

[0010] In one optional embodiment, the particle size D50 of the silicon-based anode active material composition is 3-40 μm; optionally, it is 8-20 μm.

[0011] In one optional embodiment, the mass ratio of the conductive agent, graphite, silicon-containing material, and fluororesin is 1-5:60-93:5-30:0.5-2.

[0012] Thirdly, this application also provides a negative electrode sheet comprising a current collector, wherein at least one active layer is disposed on the current collector, the active layer comprising a conductive layer, a first active material layer and a second active material layer stacked sequentially, wherein the active material of the conductive layer comprises a conductive agent; the active material of the first active material layer comprises a silicon-based negative electrode active material composition prepared by any of the above-described preparation methods; the active material of the second active material layer comprises graphite.

[0013] In one optional embodiment, the first active material layer or the second active material layer further includes one or more of a binder, an anti-settling agent, and a conductive agent, and the conductive layer further includes one or more of a binder and an anti-settling agent;

[0014] Optionally, the adhesive comprises one or more of waterborne polyurethane, polyacrylate, styrene-butadiene rubber, and polyacrylic acid;

[0015] Optionally, the anti-settling agent comprises one or more of lithium carboxymethyl cellulose.

[0016] Optionally, the graphite may comprise one or more of artificial graphite and natural graphite;

[0017] Optionally, the conductive agent comprises one or more of conductive carbon black, carbon nanotubes, and graphene;

[0018] Optionally, in the conductive layer, the mass ratio of the conductive agent, binder, and anti-settling agent is 94-98:1-3:1-3;

[0019] Optionally, in the first active material layer, the mass ratio of the silicon-based negative electrode active material composition, conductive agent, binder, and anti-settling agent is 91-97:1-3:1-3:1-3;

[0020] Optionally, in the second active material layer, the mass ratio of graphite, conductive agent, binder and anti-settling agent is 91-97:1-3:1-3:1-3.

[0021] In one optional embodiment, the areal density of the conductive layer on one side is 0.5-5 mg / cm³. 2 The surface density of the first active material layer is 3-15 mg / cm³. 2 The areal density of the second active material layer is 3-10 mg / cm³. 2 .

[0022] In one optional embodiment, the areal density of the conductive layer on one side is 1-2 mg / cm³. 2 The surface density of the first active substance layer is 5-10 mg / cm³. 2 The areal density of the second active material layer is 4-8 mg / cm³. 2 .

[0023] Fourthly, this application also provides a method for preparing a negative electrode sheet, comprising the following steps;

[0024] Step S1: Mix the components of the conductive layer, the first active material layer, and the second active material layer with a solvent to obtain the conductive layer slurry, the first active material layer slurry, and the second active material layer slurry.

[0025] Step S2: The conductive layer slurry, the first active material layer slurry, and the second active material layer slurry are sequentially coated onto the current collector and dried to obtain the negative electrode sheet.

[0026] Fifthly, this application provides a secondary battery, including the negative electrode sheet described above.

[0027] Sixthly, this application provides an electrical device including the aforementioned secondary battery.

[0028] The technical solution of this application has the following advantages:

[0029] 1. The preparation method of the silicon-based negative electrode active material composition provided in this application includes the following steps: mixing a conductive agent, graphite, silicon-containing material, and a fluororesin dispersion, and drying to obtain the silicon-based negative electrode active material composition; the fluororesin dispersion contains one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, and perfluoroethylene propylene copolymer. This application uses a fluororesin dispersion containing one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, and perfluoroethylene propylene copolymer as a binder to bond the silicon-containing material, conductive agent, and graphite together. During the drying process, hydrophobic coating of the silicon-carbon surface is achieved, effectively solving the problem of decreased adhesion between silicon-containing materials and between the silicon-containing material and the current collector due to volume expansion during silicon negative electrode material cycling. It also reduces the water absorption of the silicon-containing material, thereby improving the cycle stability of the battery.

[0030] 2. The silicon-based anode active material composition provided in this application has a particle size D50 of 3-40 μm; in particular, the range of 8-20 μm not only allows the silicon-carbon material to be well coated by the hydrophobic adhesive, but also gives the material good homogenization and coating performance. In addition, a more suitable particle size can improve the compaction of the material and increase the energy density of the battery.

[0031] 3. The negative electrode sheet provided in this application, by controlling the solid content of the mixed material to be adjusted to 3%-20%, especially 5%-15%, by using water before drying, can further improve the uniformity of the silicon-based negative electrode active material composition obtained after drying and improve the cycle stability of the battery.

[0032] 4. The negative electrode sheet provided in this application includes a current collector, on which at least one active layer is disposed. The active layer includes a conductive layer, a first active material layer, and a second active material layer stacked sequentially. The active material of the conductive layer includes a conductive agent. The active material of the first active material layer includes a silicon-based negative electrode active material composition prepared by any of the above-described preparation methods. The active material of the second active material layer includes graphite. By forming a conductive layer including a conductive agent on the surface of the current collector, not only is the adhesion between the current collector and the silicon-based negative electrode active material composition in the first active material layer enhanced, but the expansion of silicon during cycling is also avoided, indirectly improving the problem of decreased adhesion of the electrode sheet due to expansion. By forming a second active material layer including graphite on the side of the first active material layer opposite to the current collector, the side reactions between silicon and the electrolyte can be effectively reduced, enhancing the cycle performance of the battery. The adhesion between the silicon-based anode active material composition and the conductive layer is greater than the adhesion between the silicon-based anode active material composition and the current collector. By placing the first active material layer containing the silicon-based anode active material composition between the conductive layer containing the conductive agent and the second active material layer containing graphite, expansion can be buffered, structural stability can be improved, thereby improving the safety and cycle performance of the battery.

[0033] 5. The negative electrode sheet provided in this application controls the single-sided areal density of the conductive layer to be 0.5-5 mg / cm³. 2 The surface density of the first active material layer is 3-15 mg / cm³. 2 The areal density of the second active material layer is 3-10 mg / cm³. 2 In particular, the areal density of the conductive layer on one side is controlled to be 1-2 mg / cm³. 2 The surface density of the first active substance layer is 5-10 mg / cm³. 2 The areal density of the second active material layer is 4-8 mg / cm³. 2 This can further improve the cycle stability of the battery. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of a single-sided structure of the negative electrode sheet provided in Embodiment B1 of this application;

[0036] Among them, 1 is the current collector, 2 is the conductive layer, 3 is the first active material layer, and 4 is the second active material layer. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0039] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0040] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0041] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0043] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0044] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0045] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0046] Existing silicon anode materials, including silicon-carbon, silicon-oxygen, and novel silicon-carbon anode materials, still have some inherent problems and defects. For example, the material volume undergoes irreversible expansion during cycling, resulting in poor adhesion between silicon anode materials and between silicon anode materials and current collectors, making them prone to detachment and thus affecting the cycle stability of the battery.

[0047] To address the problems existing in the aforementioned related technologies, according to a first aspect of this application, a method for preparing a silicon-based negative electrode active material composition is provided, comprising the following steps: mixing a conductive agent, graphite, a silicon-containing material, and a fluororesin dispersion, and drying to obtain a silicon-based negative electrode active material composition; wherein the fluororesin dispersion contains one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, and perfluoroethylene propylene copolymer.

[0048] This application uses a fluororesin dispersion containing one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, and perfluoroethylene propylene copolymer as a binder to bond silicon-containing materials, conductive agents, and graphite together. During the drying process, hydrophobic coating of the silicon-carbon surface is achieved, effectively solving the problem of decreased adhesion between silicon-containing materials and between silicon-containing materials and current collectors due to volume expansion during silicon cycling. It also reduces the water absorption of silicon-containing materials, thereby improving the cycle stability of the battery.

[0049] Fluorinated ethylene propylene copolymer, abbreviated as FEP, is commonly known as F46. FEP is a copolymer of tetrafluoroethylene and hexafluoropropylene, with hexafluoropropylene content of about 15%. It is a modified material of polytetrafluoroethylene.

[0050] Tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, also known as perfluoroalkylate, soluble polytetrafluoroethylene, is abbreviated as PFA. PFA is a copolymer of a small amount of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene.

[0051] Polytetrafluoroethylene (PTFE) is a high molecular weight polymer obtained by polymerizing tetrafluoroethylene as a monomer.

[0052] In one optional embodiment, the solid content of the fluoropolymer dispersion is 5-60%. For example, the solid content of the fluoropolymer dispersion is 20%, 30%, 40%, or 50%.

[0053] In one alternative embodiment, the graphite has a particle size D50 of 2-5 μm. For example, the graphite has a particle size D50 of 2 μm, 3 μm, 4 μm, or 5 μm.

[0054] In one optional embodiment, the mass ratio of the conductive agent, graphite, silicon material, and fluoropolymer dispersion is 1-5:60-93:5-30:1-5. For example, the mass ratio of the conductive agent, graphite, silicon material, and polytetrafluoroethylene aqueous dispersion is 1:93:5:1, 5:60:30:5, or 3:75:20:2.

[0055] In one alternative embodiment, the conductive agent comprises one or more of conductive carbon black (SP) and carbon nanotubes (CNTs).

[0056] In one optional embodiment, the silicon-containing material comprises one or more of silicon suboxide and silicon-carbon materials. The silicon-carbon material can be processed using existing methods, such as hydrothermal methods, mechanical ball milling, spray drying, and chemical vapor deposition. It can be a mixture of silicon and carbon materials, or a coating material (with silicon as the core and carbon material coating the silicon surface, or vice versa).

[0057] In an optional embodiment, the solid content of the mixed material is further adjusted to 3%-20% using water before drying, for example, 3%, 5%, 10%, 15%, and 20%.

[0058] In one alternative embodiment, mixing is performed by stirring at a speed of 1000-5000 rpm for 3-10 hours. For example, the stirring speed may be 1000 rpm, 3000 rpm, or 5000 rpm, and the stirring time may be 3 hours, 5 hours, or 10 hours.

[0059] In one optional embodiment, the drying is spray drying, with an inlet temperature of 100-200°C and an outlet temperature of 50-80°C. For example, the inlet temperature of the spray dryer may be 100°C, 150°C, or 200°C, and the outlet temperature may be 50°C, 70°C, or 80°C.

[0060] Secondly, this application also provides a silicon-based negative electrode active material composition prepared by any of the above-described preparation methods for the negative electrode sheet.

[0061] In one optional embodiment, the particle size D50 of the silicon-based anode active material composition is 3-40 μm; optionally, it is 8-20 μm. For example, the particle size D50 of the silicon-based anode active material composition is 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, or 40 μm. By controlling the particle size of the silicon-based anode active material composition within the range of 3-40 μm, especially the range of 8-20 μm, not only can the silicon-carbon material be well encapsulated by the hydrophobic adhesive, but the material also exhibits good homogenization and coating properties. Furthermore, a more suitable particle size can improve material compaction and increase the energy density of the battery.

[0062] In one optional embodiment, the mass ratio of the conductive agent, graphite, silicon-containing material, and fluororesin is 1-5:60-93:5-30:0.5-2. For example, the mass ratio of the conductive agent, graphite, silicon material, and polytetrafluoroethylene is 1:93:5:0.5, 5:60:30:2, or 3:75:20:1.

[0063] Thirdly, this application also provides a negative electrode sheet comprising a current collector, wherein at least one active layer is disposed on the current collector, the active layer comprising a conductive layer, a first active material layer and a second active material layer stacked sequentially, wherein the active material of the conductive layer comprises a conductive agent; the active material of the first active material layer comprises a silicon-based negative electrode active material composition prepared by any of the above-described preparation methods; the active material of the second active material layer comprises graphite.

[0064] By forming a conductive layer including a conductive agent on the surface of the current collector, not only is the adhesion between the current collector and the silicon-based negative electrode active material composition in the first active material layer enhanced, but the expansion of silicon during cycling is also avoided, indirectly improving the problem of decreased adhesion of the electrode due to expansion. By forming a second active material layer including graphite on the side of the first active material layer away from the current collector, the side reactions between silicon and the electrolyte can be effectively reduced, enhancing the cycle performance of the battery. The adhesion between the silicon-based negative electrode active material composition and the conductive layer is greater than the adhesion between the silicon-based negative electrode active material composition and the current collector. Placing the first active material layer containing the silicon-based negative electrode active material composition between the conductive layer containing the conductive agent and the second active material layer containing graphite can buffer expansion, improve structural stability, and thus improve the safety and cycle performance of the battery.

[0065] At least one active layer means that the active layer on the current collector can be one layer or multiple layers, such as two, three, or five layers. When multiple active layers are provided, the conductive layer of each active layer is located close to the current collector, the second active layers are located away from the current collector, and the first active layer is located between the conductive layer and the second active layer.

[0066] In one optional embodiment, the first active material layer or the second active material layer further includes one or more of a binder, an anti-settling agent, and a conductive agent, and the conductive layer further includes one or more of a binder and an anti-settling agent.

[0067] In one alternative embodiment, the adhesive comprises one or more of waterborne polyurethane, polyacrylate, styrene-butadiene rubber, and acrylate.

[0068] In one alternative embodiment, the conductive agent comprises one or more of conductive carbon black, carbon nanotubes, and graphene.

[0069] In one alternative embodiment, the anti-settling agent comprises one or more of lithium carboxymethyl cellulose.

[0070] In one alternative embodiment, the graphite comprises one or more of artificial graphite and natural graphite.

[0071] In one optional embodiment, the mass ratio of the conductive agent, binder, and anti-settling agent in the conductive layer is 94-98:1-3:1-3. For example, the mass ratio of the conductive agent, binder, and anti-settling agent in the conductive layer is 98:1:1, 94:3:3, or 96:2:2.

[0072] In one optional embodiment, the mass ratio of the silicon-based anode active material composition, conductive agent, binder, and anti-settling agent in the first active material layer is 91-97:1-3:1-3:1-3. For example, the mass ratio of the silicon-based anode active material composition, binder, and anti-settling agent in the first active material layer is 97:1:1:1, 91:3:3:3, or 94:2:2:2.

[0073] In one optional embodiment, the mass ratio of graphite, conductive agent, binder, and anti-settling agent in the second active material layer is 91-97:1-3:1-3:1-3. For example, the mass ratio of graphite, conductive agent, binder, and anti-settling agent is 97:1:1:1, 91:3:3:3, or 94:2:2:2.

[0074] In one optional embodiment, the areal density of the conductive layer on one side is 0.5-5 mg / cm³. 2The surface density of the first active material layer is 3-15 mg / cm³. 2 The areal density of the second active material layer is 3-10 mg / cm³. 2 For example, the areal density of the conductive layer on one side is 0.5 mg / cm³. 2 1mg / cm 2 3mg / cm 2 Or 5mg / cm 2 The surface density of the first active material layer is 3 mg / cm³. 2 5mg / cm 2 10mg / cm 2 Or 15mg / cm 2 The surface density of the second active material layer is 3 mg / cm³. 2 5mg / cm 2 Or 10mg / cm 2 The test method for single-sided surface density is as follows: A sample of 1540.25 mm² is taken. 2 The small copper foil discs (S) are weighed and recorded as M0. Then, a conductive layer is coated, and the weight is M1. The areal density of the conductive layer on one side is calculated using the following formula: (M1 - M0) / S. Each sample group is measured three times, and the average value is taken. Next, the first active material layer is coated, and the weight is M2. The areal density of the conductive layer on one side is calculated using the following formula: (M2 - M1) / S. Each sample group is measured three times, and the average value is taken. Then, the second active material layer is coated, and the weight is M3. The areal density of the conductive layer on one side is calculated using the following formula: (M3 - M2) / S. Each sample group is measured three times, and the average value is taken.

[0075] The surface density of each layer is controlled by adjusting the distance between the doctor blade of the coating machine and the collector.

[0076] Fourthly, this application also provides a method for preparing a negative electrode sheet, comprising the following steps;

[0077] Step S1: Mix the components of the conductive layer, the first active material layer, and the second active material layer with a solvent to obtain the conductive layer slurry, the first active material layer slurry, and the second active material layer slurry.

[0078] Step S2: The conductive layer slurry, the first active material layer slurry, and the second active material layer slurry are sequentially coated onto the current collector and dried to obtain the negative electrode sheet.

[0079] In some embodiments, the negative electrode current collector can be made of conventional metal foil, carbon-coated metal foil, or porous metal plate. For example, the negative electrode current collector can be made of copper foil or aluminum foil.

[0080] Fifth aspect, the present application provides a secondary battery, including the negative electrode sheet described above.

[0081] In some embodiments, the secondary battery further includes a positive electrode sheet, an electrolyte, and a separator.

[0082] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0083] The secondary battery may be a lithium-ion battery. In the lithium-ion battery, the specific type of the positive electrode active material is not limited, and active materials known in the art that can be used for the positive electrode of a lithium-ion battery can be adopted. The positive electrode active material may include, but is not limited to, lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (Li2FeP2O7), lithium cobalt oxide (LiCoO2), spinel-type lithium manganese oxide (LiMn2O4), spinel-type lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), layered lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2), lithium niobate (LiNbO2), lithium ferrite (LiFeO2), lithium manganate (LiMgO2), lithium calcium oxide (LiCaO2), lithium copper oxide (LiCuO2), lithium zinc oxide (LiZnO2), lithium molybdate (LiMoO2), lithium tantalate (LiTaO2), lithium tungstate (LiWO2), lithium nickel cobalt aluminum oxide (LiNi x Co y Al 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 0.8 Co 0.15 Al 0.05 O2), lithium nickel cobalt manganese oxide (LiNi x Co y Mn 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1At least one of the following: O2, lithium-rich materials (e.g., lithium-rich nickel-cobalt-manganese oxide), manganese oxide (MnO2), vanadium oxide, sulfur oxide, silicate oxide, and their respective modified compounds. These materials may be used alone or in combination of two or more.

[0084] The modified compounds for the above-mentioned positive electrode active materials can be modified by doping, surface coating, or both doping and coating.

[0085] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0086] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0088] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0089] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0090] As for the aforementioned separator, this application does not have any particular limitations. Any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, it can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0091] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte may include lithium salts and solvents.

[0092] As an example, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethanesulfonyl)imide.

[0093] As an example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), and methyl butyrate. One or more of the following: (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), diethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, 1,3-dioxopentane, 1,3-dioxane, 1,4-dioxane, tetrahydropyran, methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0094] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0095] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0096] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0097] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0098] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0099] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0100] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0101] Sixthly, this application provides an electrical device including the aforementioned secondary battery.

[0102] In some embodiments, the aforementioned electrical device may also include a battery module or battery pack assembled from the aforementioned secondary batteries. The secondary batteries, battery modules, or battery packs can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0103] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements. An example electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0104] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0105] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0106] Example A1

[0107] This embodiment provides a method for preparing a silicon-based negative electrode active material composition, comprising the following steps:

[0108] Step S1: Weigh conductive carbon black (SP), artificial graphite (D50 of 5μm), silica, and PTFE aqueous dispersion (solid content of 40%, Aladdin reagent) in a mass ratio of 2:80:16:2, add them to water, mix under stirring at a stirring speed of 2000 rpm for 4 hours to form a precursor slurry with a solid content of 10%.

[0109] Step S2: The precursor slurry is spray-dried to obtain a black powder, which is the silicon-based anode active material composition. The spray drying process involves an inlet temperature of 150°C, an outlet temperature of 80°C, a feed rate of 1 L / min, and a particle size D50 of 12 μm for the silicon-based anode active material composition.

[0110] Example A2

[0111] This embodiment provides a method for preparing a silicon-based negative electrode active material composition, comprising the following steps:

[0112] Step S1: Weigh carbon nanotubes, artificial graphite (D50 of 15μm), silicon carbide material (purchased from Liyang Tianmu Pioneer, brand name: SC2A), and PTFE aqueous dispersion (solid content of 30%) in a mass ratio of 5:60:30:5, add them to water, mix under stirring at a stirring speed of 4000rpm for 6h to form a precursor slurry with a solid content of 15%.

[0113] Step S2: The precursor slurry is spray-dried to obtain a black powder, which is the silicon-based anode active material composition. The spray drying process involves an inlet temperature of 140°C, an outlet temperature of 75°C, and a feed rate of 0.8 L / min. The particle size D50 of the silicon-based anode active material composition is 20 μm.

[0114] Example A3

[0115] This embodiment provides a method for preparing a silicon-based anode active material composition, which is basically the same as that in Example A1, except that the inlet temperature of the spray dryer is adjusted to 130°C, the outlet temperature is adjusted to 85°C, and the feeding rate is adjusted to 2L / min, so that the particle size D50 of the final silicon-based anode active material composition is 4μm.

[0116] Example A4

[0117] This embodiment provides a method for preparing a silicon-based anode active material composition, which is basically the same as that in Example A1, except that the inlet temperature of the spray dryer is adjusted to 150°C, the outlet temperature is adjusted to 90°C, and the feeding rate is adjusted to 0.5 L / min. The particle size D50 of the silicon-based anode active material composition is 40 μm.

[0118] Example A5

[0119] This embodiment provides a method for preparing a silicon-based anode active material composition, which is basically the same as that in Example A1, except that water is added before spray drying to adjust the solid content of the precursor slurry to 3%.

[0120] Example A6

[0121] This embodiment provides a method for preparing a silicon-based anode active material composition, which is basically the same as that in Example A1, except that water is added before spray drying to adjust the solid content of the precursor slurry to 20%.

[0122] Example B1

[0123] This embodiment provides a negative electrode sheet, see... Figure 1 As shown, the device includes a current collector 1, on which a conductive layer 2, a first active material layer 3, and a second active material layer 4 are sequentially stacked. The conductive layer comprises a conductive agent (conductive carbon black SP), a binder (polyacrylate PAA), and an anti-settling agent (lithium carboxymethyl cellulose) in a mass ratio of 96:2:2. The active material of the first active material layer comprises a silicon-based negative electrode active material composition prepared in Example 1 in a mass ratio of 94:2:2:2, a conductive agent (conductive carbon black SP), a binder (aqueous polyurethane PUD), and an anti-settling agent (lithium carboxymethyl cellulose) in a mass ratio of 94:2:2:2. The active material of the second active material layer comprises graphite (natural graphite), a conductive agent (conductive carbon black SP), a binder (aqueous polyurethane PUD), and an anti-settling agent (lithium carboxymethyl cellulose) in a mass ratio of 94:2:2:2.

[0124] Its preparation method is as follows:

[0125] (1) The conductive agent, binder, and anti-settling agent in the conductive layer are mixed with a solvent (water) to prepare a conductive layer slurry (solid content of 55%); the silicon-based negative electrode active material composition, conductive agent, binder, and anti-settling agent in the first active material layer are mixed with a solvent (water) to prepare a first active material layer slurry (solid content of 50%); the graphite, conductive agent, binder, and anti-settling agent in the second active material layer are mixed with a solvent (water) to prepare a second active material layer slurry (solid content of 55%).

[0126] (2) Conductive layer slurry, first active material layer slurry, and second active material layer slurry are sequentially coated on both sides of the current collector (copper foil, 8 μm thick). After drying, conductive layer, first active material layer, and second active material layer are sequentially formed on both sides of the current collector. The areal density of the conductive layer on one side is 1.2 mg / cm³. 2 The surface density of the first active material layer is 6 mg / cm³. 2 The surface density of the second active material layer is 5 mg / cm³. 2 Roll pressing yields a compacted density of 1.5 g / cm³. 3 The negative electrode sheet.

[0127] This embodiment provides a secondary battery and its preparation method. The negative electrode obtained above, an electrolyte composed of ethylene carbonate EC (20% by mass), ethyl methyl carbonate EMC (37.5% by mass), dimethyl carbonate DMC (28% by mass), fluoroethylene carbonate FEC (2% by mass), and lithium hexafluorophosphate (12.5% ​​by mass), a PE separator (the PE separator itself is 14μm thick) coated with a 2μm thick alumina ceramic layer on each side, a lithium sheet, and an outer packaging structure are assembled into a coin cell using conventional methods to obtain a coin cell lithium battery.

[0128] Example B2

[0129] This embodiment provides a negative electrode sheet comprising a current collector, on which a conductive layer, a first active material layer, and a second active material layer are sequentially stacked. The conductive layer comprises a conductive agent (conductive carbon black SP), a binder (polyacrylate PAA), and an anti-settling agent (lithium carboxymethyl cellulose) in a mass ratio of 98:1:1. The active material of the first active material layer comprises a silicon-based negative electrode active material composition prepared in Example 1 in a mass ratio of 91:3:3:3, a conductive agent (conductive carbon black SP), a binder (aqueous polyurethane PUD), and an anti-settling agent (lithium carboxymethyl cellulose). The active material of the second active material layer comprises graphite (artificial graphite), a conductive agent (conductive carbon black SP), a binder (aqueous polyurethane PUD), and an anti-settling agent (lithium carboxymethyl cellulose) in a mass ratio of 97:1:1:1.

[0130] Its preparation method is as follows:

[0131] (1) The conductive agent, binder, and anti-settling agent in the conductive layer are mixed with a solvent (water) to prepare a conductive layer slurry (solid content of 50%); the silicon-based negative electrode active material composition, conductive agent, binder, and anti-settling agent in the first active material layer are mixed with a solvent (water) to prepare a first active material layer slurry (solid content of 53%); the graphite, conductive agent, binder, and anti-settling agent in the second active material layer are mixed with a solvent (water) to prepare a second active material layer slurry (solid content of 50%).

[0132] (2) Conductive layer paste, first active material layer paste, and second active material layer paste are sequentially coated on both sides of the current collector (copper foil, 8 μm thick), forming a conductive layer, a first active material layer, and a second active material layer on both sides of the current collector. The areal density of the conductive layer on one side is 1.5 mg / cm³. 2 The surface density of the first active material layer is 5.2 mg / cm³. 2 The surface density of the second active material layer is 6 mg / cm³. 2 Roll pressing yields a compacted density of 1.5 g / cm³. 3 The negative electrode sheet.

[0133] This embodiment provides a secondary battery and its preparation method, which is basically the same as that in embodiment B1, except that the negative electrode sheet prepared in this embodiment is used instead of the negative electrode sheet prepared in embodiment B1.

[0134] Example B3

[0135] This embodiment provides a negative electrode sheet and its preparation method, which is basically the same as that in Embodiment B1, except that the areal density of each layer is different, and the areal density of the conductive layer is 1.2 mg / cm³. 2 The surface density of the first active substance layer is 8 mg / cm³. 2 The surface density of the second active material layer is 3 mg / cm³. 2 .

[0136] This embodiment provides a secondary battery and its preparation method, which is basically the same as that in embodiment B1, except that the negative electrode sheet prepared in this embodiment is used instead of the negative electrode sheet prepared in embodiment B1.

[0137] Example B4

[0138] This embodiment provides a negative electrode sheet and its preparation method, which is basically the same as that in Embodiment B1, except that the areal density of each layer is different, and the areal density of the conductive layer is 1.2 mg / cm³. 2 The surface density of the first active material layer is 3 mg / cm³. 2 The surface density of the second active material layer is 8 mg / cm³. 2 .

[0139] This embodiment provides a secondary battery and its preparation method, which is basically the same as that in embodiment B1, except that the negative electrode sheet prepared in this embodiment is used instead of the negative electrode sheet prepared in embodiment B1.

[0140] Example B5

[0141] This embodiment provides a negative electrode sheet and its preparation method, which is basically the same as that in Embodiment B1, except that the areal density of each layer is different, and the areal density of the conductive layer is 3 mg / cm². 2 The surface density of the first active substance layer is 3.6 mg / cm³. 2 The surface density of the second active material layer is 5 mg / cm³. 2 .

[0142] This embodiment provides a secondary battery and its preparation method, which is basically the same as that in embodiment B1, except that the negative electrode sheet prepared in this embodiment is used instead of the negative electrode sheet prepared in embodiment B1.

[0143] Example B6

[0144] This embodiment provides a negative electrode sheet and its preparation method, which is basically the same as that in embodiment B1, except that the silicon-based negative electrode active material composition prepared in embodiment A2 is used instead of the silicon-based negative electrode active material composition prepared in embodiment A1.

[0145] This embodiment provides a secondary battery and its preparation method, which is basically the same as that in embodiment B1, except that the negative electrode sheet prepared in this embodiment is used instead of the negative electrode sheet prepared in embodiment B1.

[0146] Example B7

[0147] This embodiment provides a negative electrode sheet and its preparation method, which is basically the same as that in embodiment B1, except that the silicon-based negative electrode active material composition prepared in embodiment A3 is used instead of the silicon-based negative electrode active material composition prepared in embodiment A1.

[0148] This embodiment provides a secondary battery and its preparation method, which is basically the same as that in embodiment B1, except that the negative electrode sheet prepared in this embodiment is used instead of the negative electrode sheet prepared in embodiment B1.

[0149] Example B8

[0150] This embodiment provides a negative electrode sheet and its preparation method, which is basically the same as that in embodiment B1, except that the silicon-based negative electrode active material composition prepared in embodiment A4 is used instead of the silicon-based negative electrode active material composition prepared in embodiment A1.

[0151] This embodiment provides a secondary battery and its preparation method, which is basically the same as that in embodiment B1, except that the negative electrode sheet prepared in this embodiment is used instead of the negative electrode sheet prepared in embodiment B1.

[0152] Example B9

[0153] This embodiment provides a negative electrode sheet and its preparation method, which is basically the same as that in embodiment B1, except that the silicon-based negative electrode active material composition prepared in embodiment A5 is used instead of the silicon-based negative electrode active material composition prepared in embodiment A1.

[0154] This embodiment provides a secondary battery and its preparation method, which is basically the same as that in embodiment B1, except that the negative electrode sheet prepared in this embodiment is used instead of the negative electrode sheet prepared in embodiment B1.

[0155] Example B10

[0156] This embodiment provides a negative electrode sheet and its preparation method, which is basically the same as that in embodiment B1, except that the silicon-based negative electrode active material composition prepared in embodiment A6 is used instead of the silicon-based negative electrode active material composition prepared in embodiment A1.

[0157] This embodiment provides a secondary battery and its preparation method, which is basically the same as that in embodiment B1, except that the negative electrode sheet prepared in this embodiment is used instead of the negative electrode sheet prepared in embodiment B1.

[0158] Comparative Example 1

[0159] This comparative example provides a method for preparing a silicon-based negative electrode active material composition, which is basically the same as that in Example A1, except that the binder used is different. This comparative example uses polyvinylidene fluoride (PVDF) aqueous dispersion with the same solid content and the same mass instead of PTFE aqueous dispersion.

[0160] This comparative example provides a negative electrode sheet and its preparation method, which is basically the same as that in Example B1, except that the silicon-based negative electrode active material composition prepared in this comparative example is used instead of the silicon-based negative electrode active material composition prepared in Example A1.

[0161] This comparative example provides a secondary battery and its preparation method, which is basically the same as that of Example B1, except that the negative electrode sheet prepared in this comparative example is used instead of the negative electrode sheet prepared in Example B1.

[0162] Comparative Example 2

[0163] This comparative example provides a method for preparing a silicon-based negative electrode active material composition, which is basically the same as that in Example A1, except that the binder used is different. This comparative example uses styrene-butadiene rubber latex with the same solid content and the same mass instead of PTFE aqueous dispersion.

[0164] This comparative example provides a negative electrode sheet and its preparation method, which is basically the same as that in Example B1, except that the silicon-based negative electrode active material composition prepared in this comparative example is used instead of the silicon-based negative electrode active material composition prepared in Example A1.

[0165] This comparative example provides a secondary battery and its preparation method, which is basically the same as that of Example B1, except that the negative electrode sheet prepared in this comparative example is used instead of the negative electrode sheet prepared in Example B1.

[0166] Comparative Example 3

[0167] This comparative example provides a method for preparing a silicon-based negative electrode active material composition, which includes weighing SP, artificial graphite, and silicon suboxide in a mass ratio of 2:80:16 and mixing them evenly to obtain the final product.

[0168] This comparative example provides a negative electrode sheet and its preparation method, which is basically the same as that in Example B1, except that the silicon-based negative electrode active material composition prepared in this comparative example is used instead of the silicon-based negative electrode active material composition prepared in Example A1.

[0169] This comparative example provides a secondary battery and its preparation method, which is basically the same as that of Example B1, except that the negative electrode sheet prepared in this comparative example is used instead of the negative electrode sheet prepared in Example B1.

[0170] Comparative Example 4

[0171] This comparative example provides a negative electrode sheet and its preparation method, which is basically the same as that in Example B1, except that the positions of the three layers are different. The current collector includes a first active material layer, a conductive layer and a second active material layer stacked in sequence.

[0172] This comparative example provides a secondary battery and its preparation method, which is basically the same as that of Example B1, except that the negative electrode sheet prepared in this comparative example is used instead of the negative electrode sheet prepared in Example B1.

[0173] Comparative Example 5

[0174] This comparative example provides a negative electrode sheet and its preparation method, which is basically the same as that in Example B1, except that the positions of the three layers are different. The current collector includes a first active material layer, a second active material layer and a conductive layer stacked in sequence.

[0175] This comparative example provides a secondary battery and its preparation method, which is basically the same as that of Example B1, except that the negative electrode sheet prepared in this comparative example is used instead of the negative electrode sheet prepared in Example B1.

[0176] Comparative Example 6

[0177] This comparative example provides a negative electrode sheet and its preparation method, which is basically the same as that in Example B1, except that the conductive layer is omitted. The current collector includes a first active material layer and a second active material layer stacked sequentially.

[0178] This comparative example provides a secondary battery and its preparation method, which is basically the same as that of Example B1, except that the negative electrode sheet prepared in this comparative example is used instead of the negative electrode sheet prepared in Example B1.

[0179] Test Example 1

[0180] The full-load electrode rebound rate and electrode adhesion of the electrodes prepared in each embodiment and comparative example were tested according to the following method.

[0181] Test method for electrode rebound rate at full charge: Before battery assembly, measure the thickness of the negative electrode, H1 (μm) = negative electrode thickness minus current collector thickness 8 μm. After obtaining coin-type lithium batteries using the negative electrode sheets provided in each embodiment and comparative example according to the method in Example B1, discharge them to 0.05V to reach full charge. Then disassemble the battery, measure the thickness, subtract the current collector thickness 8 μm, and record it as H2 μm. Calculate the electrode rebound rate using the following formula: Electrode rebound rate = (H2 - H1) / H1 * 100%.

[0182] Electrode adhesion test method: Cut the electrode strips using a paper cutter, with a strip width of 15-15.5mm. Apply double-sided tape to the mirror-finish stainless steel, then attach the cut strips to the tape. Use a 2kg standard pressure roller to press the strips ten times (one pass counts as one). Tear off one end of the strip, manually peeling it halfway. Place the torn end of the strip into the upper clamp of the tensile testing machine, and the other end into the lower clamp. Ensure vertical placement to avoid curling or wrinkling. Close the clamp switch; turn on the tensile testing machine to perform the adhesion test.

[0183] Table 1 Test Results

[0184]

[0185]

[0186] As shown in the table above, compared with Comparative Examples 1-6, the full electrode rebound rate of the electrode sheets obtained in each embodiment of the present invention is significantly reduced, and the electrode adhesion is significantly improved, indicating that the electrode sheet has good structural stability.

[0187] Test Example 2

[0188] Initial efficiency: Discharge to 0.05V at 0.1C, then charge to 1.5V at 0.1C. Calculate the initial efficiency as follows: Initial efficiency = Initial charge capacity / Initial discharge capacity * 100%.

[0189] Cycle life: Charge to 1.5V at 0.2C, discharge to 0.05V at 0.2C, cycle 100 times, and calculate the capacity retention rate after 100 cycles. Capacity retention rate = (100-cycle discharge capacity / initial discharge capacity) * 100%.

[0190] Table 2 Cyclic performance results

[0191]

[0192]

[0193] As shown in the table above, compared to Comparative Examples 1-6, the batteries obtained in each embodiment of the present invention exhibit significantly improved initial efficiency and cycle stability. Specifically, in Comparative Examples 1-3, the lack of a binder or the use of other types of binders during the preparation of the silicon-based negative electrode active material composition resulted in insufficient adhesion between the first active layer and adjacent layers. Furthermore, the materials were prone to water absorption, leading to severe volume expansion during cycling, which in turn resulted in poor initial efficiency and cycle stability. In Comparative Examples 4-6, the first active layer was directly bonded to the current collector, resulting in insufficient adhesion and severe volume expansion during cycling, which also led to poor initial efficiency and cycle stability.

[0194] Compared with Examples B3-B5, Examples B1-B2 can further improve the first efficiency and cycle stability of the battery by controlling the single-sided areal density of the conductive layer, the single-sided areal density of the first active material layer, and the single-sided areal density of the second active material layer within the preferred range.

[0195] Compared with Examples B7-B8, Examples B1-B2, by using silicon-based anode active materials with particle size controlled within a preferred range, can further improve the first-efficiency and cycle stability of the battery.

[0196] Compared with Examples B9-B10, Examples B1-B2 show that the silicon-based anode active material used in Examples B1 can further improve the first-cycle efficiency and cycle stability of the battery by adjusting the solid content of the precursor slurry by adding water before spray drying.

[0197] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for preparing a silicon-based negative electrode active material composition, characterized in that, The process includes the following steps: mixing a conductive agent, graphite, a silicon-containing material, and a fluororesin dispersion, and drying the mixture to obtain a silicon-based negative electrode active material composition; wherein the fluororesin in the fluororesin dispersion comprises one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, and perfluoroethylene propylene copolymer.

2. The method for preparing the silicon-based negative electrode active material composition according to claim 1, characterized in that, The solid content of the fluororesin dispersion is 5-60%; and / or, the particle size D50 of the graphite is 2-5 μm; and / or, the mass ratio of the conductive agent, graphite, silicon-containing material and fluororesin dispersion is 1-5:60-93:5-30:1-5; and / or, the conductive agent comprises one or more of conductive carbon black and carbon nanotubes; and / or, the silicon-containing material comprises one or more of silicon suboxide and silicon carbide.

3. The method for preparing the silicon-based negative electrode active material composition according to claim 1 or 2, characterized in that, Before drying, the solid content of the mixed material is adjusted to 3%-20% using water, optionally to 5%-15%.

4. The method for preparing the silicon-based negative electrode active material composition according to any one of claims 1-3, characterized in that, The mixing is carried out by stirring at a speed of 1000-5000 rpm for 3-10 hours; and / or the drying is spray drying, with an inlet temperature of 100-200℃, an outlet temperature of 60-100℃, and a feeding rate of 0.5-2 L / min.

5. A silicon-based anode active material composition prepared by any one of the preparation methods according to claims 1-4; Optionally, the particle size D50 of the silicon-based anode active material composition is 3-40 μm; Optionally, in the silicon-based negative electrode active material composition, the mass ratio of the conductive agent, graphite, silicon-containing material and fluororesin is 1-5:60-93:5-30:0.5-2.

6. A negative electrode sheet, characterized in that, The device includes a current collector, on which at least one active layer is disposed. The active layer comprises a conductive layer, a first active material layer, and a second active material layer stacked sequentially, wherein the conductive layer comprises a conductive agent; the active material of the first active material layer comprises a silicon-based negative electrode active material composition prepared by any one of the preparation methods of claims 1-5; and the active material of the second active material layer comprises graphite.

7. The negative electrode sheet according to claim 6, characterized in that, The first active material layer or the second active material layer further includes one or more of a binder, an anti-settling agent, and a conductive agent, and the conductive layer further includes one or more of a binder and an anti-settling agent; Optionally, the adhesive comprises one or more of waterborne polyurethane, polyacrylate, styrene-butadiene rubber, and polyacrylic acid; Optionally, the anti-settling agent comprises one or more of lithium carboxymethyl cellulose. Optionally, the graphite may comprise one or more of artificial graphite and natural graphite; Optionally, the conductive agent comprises one or more of conductive carbon black, carbon nanotubes, and graphene; Optionally, in the conductive layer, the mass ratio of the conductive agent, binder, and anti-settling agent is 94-98:1-3:1-3; Optionally, in the first active material layer, the mass ratio of the silicon-based negative electrode active material composition, conductive agent, binder, and anti-settling agent is 91-97:1-3:1-3:1-3; Optionally, in the second active material layer, the mass ratio of graphite, conductive agent, binder and anti-settling agent is 91-97:1-3:1-3:1-3.

8. The negative electrode sheet according to claim 6, characterized in that, The areal density of the conductive layer on one side is 0.5-5 mg / cm³. 2 The surface density of the first active material layer is 3-15 mg / cm³. 2 The areal density of the second active material layer is 3-10 mg / cm³. 2 Optionally, the areal density of the conductive layer on one side is 1-2 mg / cm³. 2 The surface density of the first active substance layer is 5-10 mg / cm³. 2 The areal density of the second active material layer is 4-8 mg / cm³. 2 .

9. The method for preparing the negative electrode sheet according to any one of claims 6-8, characterized in that, Includes the following steps; Step S1: Mix the components of the conductive layer, the first active material layer, and the second active material layer with a solvent to obtain the conductive layer slurry, the first active material layer slurry, and the second active material layer slurry. Step S2: The conductive layer slurry, the first active material layer slurry, and the second active material layer slurry are sequentially coated onto the current collector and dried to obtain the negative electrode sheet.

10. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 6-8 or the negative electrode sheet prepared by the preparation method described in claim 9.

11. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 10.

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