Silicon-based negative plate and preparation method and application thereof

Abstract

The invention discloses a silicon-based negative electrode piece and a preparation method and application thereof, and relates to the technical field of batteries, the silicon-based negative electrode piece comprises a negative electrode current collector and a negative electrode coating located on the surface of the negative electrode current collector, the negative electrode coating contains a negative electrode active material, and a plurality of micro-nano holes are formed in the surface of the negative electrode coating; the negative electrode coating comprises a first coating close to the negative electrode current collector and a second coating positioned above the first coating; the first negative electrode active substance in the first coating comprises first graphite, and the second negative electrode active substance in the second coating comprises second graphite and a silicon-based negative electrode material. Graphite serves as the first layer, a solid foundation is provided for the silicon-based negative plate, and the basic performance of the battery is guaranteed; and the second layer is formed by compounding a conductive agent modified silicon-based material and graphite, precise coating is carried out by virtue of a micro-concave coating technology, an electron conduction path of the silicon-based material is improved, and the overall electrochemical performance is optimized by virtue of precise control on the thickness and the uniformity of the coating by virtue of micro-concave coating.

Description

Technical Field

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

[0002] In the development process of lithium-ion batteries, the pursuit of higher energy density and better fast charging performance has always been the core goal. As an important component of lithium-ion batteries, the structure and performance of silicon-based negative electrodes directly affect the overall performance of the battery.

[0003] Although the traditional graphite anode has mature technology and low cost, the energy density has limited room for improvement, and the lithium ion transmission efficiency is gradually insufficient under high-rate charge and discharge. Silicon-based materials have become the most promising next-generation anode materials with their ultra-high theoretical specific capacity (up to 4200mAh / g, a huge advantage over graphite's 340-370mAh / g).

[0004] The current lithium-ion batteries made of silicon-based negative electrode sheets have a huge volume expansion (up to 300%) during the charge and discharge process, which can easily lead to pulverization of the electrode structure, shedding of active materials, and a sharp decrease in cycle life. At the same time, their intrinsic conductivity is poor, which hinders the rapid conduction of lithium ions and electrons, resulting in the performance of silicon-based negative electrode lithium-ion batteries unable to meet the needs of power and other fields. Summary of the invention

[0005] Based on the problem of poor conductivity of current silicon-based negative electrode materials, the purpose of the present invention is to provide a silicon-based negative electrode sheet and its preparation method and application, and to improve the rate performance and cycle performance of silicon-based lithium-ion batteries through the dual strategies of double-layer coating and constructing a conductive network system.

[0006] The present invention is achieved through the following technical solutions:

[0007] In a first aspect, the present application provides a silicon-based negative electrode sheet, comprising a negative electrode current collector and a negative electrode coating located on the surface of the negative electrode current collector, wherein the negative electrode coating contains a negative electrode active material, and a plurality of micro-nano pores are opened on the surface of the negative electrode coating;

[0008] The negative electrode coating comprises a first coating close to the negative electrode current collector and a second coating located above the first coating;

[0009] The first negative electrode active material in the first coating layer includes a first graphite, and the second negative electrode active material in the second coating layer includes a second graphite and a silicon-based negative electrode material.

[0010] By using graphite as the first layer, with its stable structure, good cycle performance and excellent conductivity, it provides a solid foundation for the silicon-based negative electrode sheet and ensures the basic performance of the battery; the second layer uses a conductive agent to modify the silicon-based material and graphite composite, which is precisely applied with the help of micro-concave coating technology. It aims to introduce high-capacity silicon-based components to improve energy density while using conductive agents to improve the electronic conduction path of silicon-based materials. In addition, micro-concave coating can be used to accurately control the thickness and uniformity of the coating, thereby alleviating the negative impact of the volume expansion of silicon-based materials and optimizing the overall electrochemical performance.

[0011] Furthermore, the second coating layer is coated by a micro-dimpled coating method.

[0012] The second coating is applied using a micro-concave coating method, which can achieve a more uniform and precise coating effect, reduce defects caused by unevenness during the coating process, and reduce the weakening of electrochemical performance caused by uneven distribution of silicon-based materials.

[0013] Furthermore, the particle sizes D90, D50 and D10 of the first graphite satisfy 1.05≤(D90-D10) / D50≤1.60.

[0014] The graphite used in the first coating has a particle size distribution that satisfies 1.05≤(D90-D10) / D50≤1.60. The particle size distribution optimizes the stacking structure and conductive path between the particles, while improving the volume density and flatness of the material, thereby providing the silicon-based negative electrode sheet with better mechanical stability and conductive properties, while increasing the compaction density of the system.

[0015] Furthermore, the first coating layer also includes a first conductive agent, a first dispersant and a first binder;

[0016] The first conductive agent accounts for 0-5% of the total mass of the first coating layer, the first dispersant accounts for 0.1%-1.5% of the total mass of the first coating layer, and the first binder accounts for 0.5%-3% of the total mass of the first coating layer.

[0017] Furthermore, the first conductive agent includes any one or more combinations of conductive carbon black, acetylene black, Ketjen black, and conductive carbon fiber.

[0018] Furthermore, the first dispersant includes sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

[0019] Furthermore, the first binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, and polymethyl methacrylate.

[0020] Furthermore, the particle sizes D90, D50 and D10 of the second graphite satisfy 1.05≤(D90-D10) / D50≤1.40.

[0021] Furthermore, the silicon-based negative electrode material includes silicon oxygen and / or silicon carbon; the particle size of the silicon-based negative electrode material satisfies 4μm≤D50≤10μm; and the content of the silicon-based negative electrode material is 5% to 60% of the total mass of the total active material of the silicon-based negative electrode sheet.

[0022] Furthermore, the mass ratio of the second graphite in the second coating layer to the silicon-based negative electrode material is (5% to 95%): (95% to 5%).

[0023] Furthermore, the second coating layer also includes a second conductive agent, a second dispersant and a second binder;

[0024] The second conductive agent accounts for 0-5% of the total mass of the second coating, the second dispersant accounts for 0.1%-2% of the total mass of the second coating, and the second binder accounts for 0.5%-8% of the total mass of the second coating.

[0025] Furthermore, the thickness of the first coating layer and / or the second coating layer is 5 μm-130 μm.

[0026] Furthermore, the compaction density of the negative electrode coating is 1.4 g / cm 3 -1.85g / cm 3 .

[0027] Furthermore, the silicon-based negative electrode material of the second coating layer is a silicon-oxygen or silicon-carbon material coated with a 2D nanomaterial.

[0028] Furthermore, the coating method is as follows: the silicon-based negative electrode material, the 2D nanomaterial and the surfactant are loaded into a ball milling jar in proportion and subjected to high-energy ball milling;

[0029] The silicon-based negative electrode material accounts for 90% to 99.95% of the total mass; the 2D nanomaterial accounts for 0.05% to 10% of the total mass; and the surfactant accounts for 0 to 1% of the total mass.

[0030] The ball milling time is 2 to 10 hours, and the ball milling speed is 300 to 800 rpm; the temperature during the ball milling process is controlled between room temperature and 60° C.; the drying temperature after ball milling is controlled between 80° C. and 120° C., and the drying time is 2 to 6 hours.

[0031] The second coating modifies the silicon-based material with 2D nanomaterials prepared by high-energy ball milling technology, optimizes the distribution of the conductive agent in the silicon-based negative electrode material, alleviates the cycle stability problem of the silicon-based negative electrode material caused by volume expansion, and at the same time, the addition of 2D nanosheets can effectively improve the conductivity of the silicon-based negative electrode material and enhance the overall electrochemical performance of the material.

[0032] Furthermore, the 2D nano-conductive agent includes any one or more of graphene, michelene, titanium disulfide, black phosphorene, and molybdenum disulfide.

[0033] Furthermore, the surfactant includes any one or more of oleic acid, sodium dodecylbenzene sulfonate, and stearic acid.

[0034] Furthermore, the micro-nanopores are circular or elliptical micro-nanopores arranged in a periodic positive row, with a pore diameter of 50nm to 10μm, a depth of 5μm to 130μm, a pore spacing of 0.01mm to 0.2mm, and a porosity controlled at 10% to 20%.

[0035] Among them, the silicon-based negative electrode sheet is laser-pored after coating, drying and rolling processes; the type of laser is one of femtosecond, picosecond or nanosecond laser.

[0036] Laser is used to form a regular micro-nanopore array with a pore size of 50nm to 10μm on the surface of the silicon-based negative electrode sheet area. The pore depth is 5-130μm, and the micro-nanopore spacing is 0.01 to 0.05mm. The three-dimensional conductive network formed by the holes effectively reduces the interface resistance and the tortuosity of the lithium ion transmission path, thereby improving the battery's rate performance and cycle performance.

[0037] In a second aspect, the present application provides a method for preparing a silicon-based negative electrode sheet, comprising the following steps:

[0038] Preparing a first negative electrode active material slurry: mixing a first graphite, a first conductive agent, a first binder and a first dispersant in proportion, and then adding water and stirring to prepare a first negative electrode slurry;

[0039] Preparing a second negative electrode active material slurry: mixing a second graphite, a silicon-based negative electrode material, a second conductive agent, a second binder, and a second dispersant in proportion, and then adding water and stirring to prepare a second negative electrode slurry;

[0040] The first negative electrode slurry is coated on both sides of the negative electrode current collector and dried to obtain a first coating layer, and then the second negative electrode slurry is coated on the first coating layer by a micro-concave coating method, and then dried to obtain a second coating layer, and the dried electrode roll is rolled and cut to obtain a negative electrode sheet;

[0041] The prepared negative electrode plate is subjected to laser pore making to obtain a silicon-based negative electrode plate having a plurality of micro-nanopores.

[0042] In a third aspect, the present application provides a battery, comprising the above-mentioned silicon-based negative electrode plate or the silicon-based negative electrode plate prepared by the above-mentioned preparation method.

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0044] The graphite used in the first coating of the present invention makes its particle size distribution satisfy 1.05≤(D90-D10) / D50≤1.60, and its particle size distribution optimizes the stacking structure and conductive path between particles, while improving the volume density and flatness of the material, thereby providing good mechanical stability and conductive performance for the silicon-based negative electrode sheet, and at the same time being able to increase the compaction density of the system; the second coating uses 2D nanomaterials prepared by high-energy ball milling technology to modify the silicon-based material, optimize the distribution of the conductive agent in the silicon-based material, alleviate the cyclic stability problem caused by the volume expansion of the silicon-based material, and at the same time the addition of 2D nanosheets can effectively improve the conductivity of the silicon-based material rate, enhancing the overall electrochemical properties of the material; the micro-dimpled coating technology is used to coat the second layer of silicon-based materials, which can achieve a more uniform and precise coating effect, reduce the defects caused by uneven coating process, and reduce the weakening of electrochemical performance caused by uneven distribution of silicon-based materials; laser is used to form a regular micro-nanopore array with a pore size of 50nm-10μm on the surface of the silicon-based negative electrode sheet area, the pore depth is 5-130μm, and the micro-nanopore spacing is 0.01-0.05mm, and the three-dimensional conductive network formed by the pores effectively reduces the interface resistance and reduces the tortuosity of the lithium ion transmission path, thereby improving the rate performance and cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0046] Figure 1 It is a schematic structural diagram of a silicon-based negative electrode sheet of the present invention.

[0047] Reference numerals:

[0048] 10-negative electrode current collector, 20-first coating layer, 30-second coating layer. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0050] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is apparent to one of ordinary skill in the art that these specific details need not be employed to practice the present invention. In other embodiments, in order to avoid confusing the present invention, well-known materials or methods are not specifically described.

[0051] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment," "an embodiment," "an example," or "an example" that appear in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any appropriate combination and / or sub-combination. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. In addition, those skilled in the art will be able to combine and combine different embodiments or examples described in this specification and features of different embodiments or examples, without contradicting each other.

[0052] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0054] Example 1

[0055] This embodiment provides a method for preparing a silicon-based negative electrode sheet, which is carried out according to the following steps:

[0056] S1, 2D nano-conductive agent coated silicon-based material (denoted as silicon carbon A)

[0057] Silicon carbon, graphene and sodium dodecyl sulfate were added into a planetary high-energy ball mill at a mass ratio of 99.4:0.5:0.1. The ball milling speed was 500 rpm and the ball milling was performed for 5 hours. The ball milling temperature was controlled between room temperature and 60°C. After completion, the ball milling was dried in a vacuum oven at 105°C for 5 hours to prepare silicon carbon A.

[0058] S2. Preparation of silicon-based negative electrode sheet

[0059] S2-1. Preparation of the first negative electrode active material slurry (referred to as negative electrode slurry A)

[0060] The first graphite (artificial graphite, (D90-D10) / D50 is 1.42), the first conductive agent (conductive carbon black), the first binder (CMC) and the first dispersant (CMC-Na) are mixed in a mass ratio of 96.5:0.5:1:2, and then water is added and stirred to prepare negative electrode slurry A.

[0061] S2-2. Preparation of the second negative electrode active material slurry (referred to as negative electrode slurry B)

[0062] The second graphite (artificial graphite, (D90-D10) / D50 is 1.33), the first silicon material (silicon carbon A, D50 is 7.5μm), the second conductive agent (conductive carbon black), the second binder (styrene-butadiene rubber and polyacrylic acid in a mass ratio of 1:3) and the second dispersant (CMC-Na) are mixed in a mass ratio of 45:50:0.5:1:3:0.5, and then water is added and stirred to form negative electrode slurry B.

[0063] S3. Double-sided coating and drying of negative electrode slurry A on the negative electrode current collector are performed by coating equipment to obtain a first coating layer, and then negative electrode slurry B is coated on the first coating layer by micro-concave coating technology, and a second coating layer is obtained after drying. The dried electrode roll is rolled and cut to prepare a negative electrode sheet. The thickness of the first coating layer (single side) and the second coating layer (single side) in the negative electrode sheet are 25 μm and 25 μm respectively; the proportion of silicon material blending in the entire negative electrode active material is 25wt%.

[0064] S4. The prepared electrode piece is subjected to laser pore making, using a 355nm laser wavelength, a pulse energy of 35μJ, a pulse width of 75ns, a repetition frequency of 80kHZ, and a focused spot size of 1μm to make holes in the electrode roll, and a silicon-based negative electrode piece with a pore diameter of 50nm, a depth of 30μm, and a micro-nanopore spacing of 0.015mm is prepared.

[0065] S5, die-cutting the product prepared in step S4 to prepare a silicon-based negative electrode sheet. The structure of the prepared silicon-based negative electrode sheet is as follows: Figure 1 As shown, the negative electrode current collector 10 is included, and a first coating layer 20 and a second coating layer 30 are sequentially formed on the negative electrode current collector 10 .

[0066] The above silicon-based negative electrode sheet is used to prepare a battery, and the specific method is as follows:

[0067] S6. Preparation of positive electrode sheet

[0068] The positive electrode active material (ternary material Ni9055), the first conductive agent (conductive carbon black), the second conductive agent (multi-walled carbon nanotubes), and the binder (PVDF) are mixed in a mass ratio of 95.5:0.5:1:1.5:1.5, and then N-methylpyrrolidone is added and stirred and dispersed to form a positive electrode slurry; then the positive electrode slurry is coated on the positive electrode collector (double-sided coating), dried, rolled, slit, and die-cut to prepare a positive electrode sheet.

[0069] S7. Preparation of batteries

[0070] The prepared positive and negative electrode sheets and separators are trial-produced into dry battery cells through processes such as lamination, welding, and heat sealing, and then undergo processes such as liquid injection, aging, formation, capacity division, secondary packaging, and sorting. Finally, the prepared batteries are tested for electrical performance such as capacity, rate, and cycle.

[0071] Example 2

[0072] This embodiment provides a method for preparing a silicon-based negative electrode sheet. Different from Example 1, this embodiment uses a 1064nm laser wavelength, a pulse energy of 40μJ, a pulse width of 65ns, a repetition frequency of 70kHZ, and a focused spot size of 1μm to make holes in the electrode roll, and prepares a silicon-based negative electrode sheet with a pore diameter of 500nm, a depth of 45μm, and a micro-nanopore spacing of 0.02mm.

[0073] Example 3

[0074] This embodiment provides a method for preparing a silicon-based negative electrode sheet. Different from Example 1, this embodiment uses a 1064nm laser wavelength, a pulse energy of 120μJ, a pulse width of 75ns, a repetition frequency of 70kHZ, and a focused spot size of 2μm to make holes in the electrode roll, and prepares a silicon-based negative electrode sheet with a pore diameter of 600nm, a depth of 65μm, and a micro-nanopore spacing of 0.02mm.

[0075] Among them, Example 2 and Example 3 are used to illustrate the preparation of silicon-based negative electrode sheets with different specifications of apertures by laser.

[0076] Example 4

[0077] This embodiment provides a method for preparing a silicon-based negative electrode sheet. The difference from Embodiment 1 is that the thickness of the first coating layer and the second coating layer are changed in this embodiment, but the formula of the first coating layer and the second coating layer remains unchanged. The thickness of the first coating layer (single side) and the second coating layer (single side) in the negative electrode sheet are 15 μm and 35 μm respectively; the proportion of silicon material blending in the entire negative electrode active material is 35wt%.

[0078] Example 5

[0079] This embodiment provides a method for preparing a silicon-based negative electrode sheet. Different from Embodiment 1, this embodiment changes the thickness of the first coating layer and the second coating layer, but the formula of the first coating layer and the second coating layer remains unchanged. The thickness of the first coating layer (single side) and the second coating layer (single side) in the negative electrode sheet are 35 μm and 15 μm respectively; the proportion of silicon material blending in the entire negative electrode active material is 15wt%.

[0080] Example 6

[0081] This embodiment provides a method for preparing a silicon-based negative electrode sheet. Different from Embodiment 1, this embodiment changes the thickness of the first coating layer and the second coating layer, but the formula of the first coating layer and the second coating layer remains unchanged. The thickness of the first coating layer (single side) and the second coating layer (single side) in the negative electrode sheet are 45 μm and 5 μm respectively; the proportion of silicon material blending in the entire negative electrode active material is 5wt%.

[0082] Example 7

[0083] This embodiment provides a method for preparing a silicon-based negative electrode sheet. The difference from Embodiment 1 is that the thickness of the first coating layer and the second coating layer are changed in this embodiment, but the formula of the first coating layer and the second coating layer remains unchanged. The thickness of the first coating layer (single side) and the second coating layer (single side) in the negative electrode sheet are 5 μm and 45 μm respectively; the proportion of silicon material blending in the entire negative electrode active material is 45wt%.

[0084] Among them, Examples 4 to 7 are used to illustrate the preparation of silicon-based negative electrode sheets when the thickness of the first coating layer and the second coating layer are different.

[0085] Example 8

[0086] This embodiment provides a method for preparing a silicon-based negative electrode sheet. Different from Embodiment 1, this embodiment uses michelene, silicon carbon and sodium dodecyl sulfate for ball milling to obtain a 2D nano-conductive agent-coated silicon-based material (denoted as silicon carbon B).

[0087] Example 9

[0088] This embodiment provides a method for preparing a silicon-based negative electrode sheet. Different from Embodiment 1, this embodiment uses black phosphorene, silicon carbon and sodium dodecyl sulfate for ball milling to obtain a 2D nano-conductive agent-coated silicon-based material (denoted as silicon carbon C).

[0089] Among them, Example 8 and Example 9 are used to illustrate the preparation of silicon-based negative electrode sheets when different 2D nanomaterials are coated with silicon carbon.

[0090] Example 10

[0091] This embodiment provides a method for preparing a silicon-based negative electrode sheet. Different from Example 1, this embodiment uses pre-lithium silicon oxide, graphene and sodium dodecyl sulfate for ball milling to obtain a 2D nano-conductive agent-coated silicon-based material (denoted as silicon oxide A).

[0092] Embodiment 11

[0093] This embodiment provides a method for preparing a silicon-based negative electrode sheet. Different from Example 1, this embodiment uses pre-magnesium silicon oxide, graphene, and sodium dodecyl sulfate for ball milling to obtain a 2D nano-conductive agent-coated silicon-based material (denoted as silicon oxide B).

[0094] Among them, Example 10 and Example 11 are used to illustrate the preparation of silicon-based negative electrode sheets using different silicon-based materials.

[0095] Comparative Example 1

[0096] This comparative example provides a method for preparing a silicon-based negative electrode sheet. Different from Example 1, this comparative example directly uses a double-layer coating device to coat the first layer and the second layer to prepare a silicon-based negative electrode sheet, and then assembles a battery.

[0097] This comparative example is used to illustrate the preparation of a silicon-based negative electrode sheet using normal double-layer coating without using the micro-concave coating technology for the second layer.

[0098] Comparative Example 2

[0099] This comparative example provides a method for preparing a silicon-based negative electrode sheet. Unlike Example 1, the negative electrode of this comparative example adopts a mixed slurry of the two formulations of Example 1, and is coated by direct single-layer coating to prepare a silicon-based negative electrode sheet (the specific formulation is as follows), and then the battery is assembled.

[0100] Specific formula: Graphite (artificial graphite, (D90-D10) / D50 is 1.42), silicon-based material (silicon carbon A, D50 is 7.5μm), conductive agent (conductive carbon black), binder (styrene-butadiene rubber and polyacrylic acid in a mass ratio of 1:3) and dispersant (CMC-Na) are mixed in a mass ratio of 70.75:25:0.5:1:1.5:1.25, and then water is added and stirred to form negative electrode slurry A.

[0101] The slurry A is directly coated by a coating machine to prepare a single-layer silicon-based negative electrode sheet.

[0102] This comparative example is used to illustrate the preparation of a silicon-based negative electrode sheet when graphite and a coated silicon-based material are directly mixed and homogenized for single-layer coating.

[0103] Comparative Example 3

[0104] This comparative example provides a method for preparing a silicon-based negative electrode sheet. Different from Example 1, the first silicon-based material used in the preparation of the second negative electrode active material slurry (referred to as negative electrode slurry B) of this comparative example is silicon carbon without a conductive agent, which is prepared into a silicon-based negative electrode sheet and then assembled into a battery.

[0105] This comparative example is used to illustrate a silicon-based negative electrode sheet prepared by directly mixing an uncoated material and a second graphite into a slurry as the second layer.

[0106] Comparative Example 4

[0107] This comparative example provides a method for preparing a silicon-based negative electrode sheet. Unlike Example 1, the first graphite (artificial graphite, (D90-D10) / D50=1.7) and the second graphite (artificial graphite, (D90-D10) / D50=1.5) in this comparative example are homogenized to prepare a silicon-based negative electrode sheet, and then the battery is assembled.

[0108] This comparative example is used to illustrate the preparation of a silicon-based negative electrode sheet using the first graphite and the second graphite when the (D90-D10) / D50 parameters are outside the protection range.

[0109] Comparative Example 5

[0110] This comparative example provides a method for preparing a silicon-based negative electrode sheet. Different from Example 1, this comparative example does not use laser pore making to process the electrode sheet to prepare the silicon-based negative electrode sheet, and then assemble the battery.

[0111] This comparative example is used to illustrate the preparation of a negative electrode sheet without laser pore formation.

[0112] The electrical properties of the batteries assembled with the silicon-based negative electrode sheets prepared in Examples 1 to 11 and Comparative Examples 1 to 5 were tested, and the test results are shown in Table 1.

[0113] Table 1

[0114]

[0115]

[0116] By comparing the results of Examples 1 to 11 with those of Comparative Example 1, it can be seen that the micro-concave coating technology used in the second layer coating of the present invention is compared with the conventional double-layer coating. The micro-concave coating accurately controls the coating thickness and uniformity, avoids stress concentration caused by uneven coating of silicon-based materials, and can reduce the tortuosity of the lithium ion transmission path, thereby significantly improving the rate charge and discharge performance and cycle performance of the battery. By comparing the results of Examples 1 to 11 with those of Comparative Example 3, it can be seen that the modification of 2D nanomaterials and silicon-based materials used in the present invention can effectively improve the rate performance of the battery. By comparing the results of Examples 1 to 11 with those of Comparative Example 4, it can be seen that by limiting the range of the particle size (D90-D10) / D50 of the first graphite and the second graphite, the compaction density of the pole piece can be significantly improved, the ion transmission path can be optimized, and the proportion of active substances can be increased, thereby improving the overall energy density of the battery cell. By comparing the results of Examples 1 to 11 with those of Comparative Example 5, it can be seen that the holes formed by laser pore making construct a three-dimensional conductive network for the pole piece to effectively reduce the interface resistance, thereby improving the overall dynamic performance of the battery cell and improving the rate and cycle performance of the battery cell.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that it is still possible to modify the technical solutions described in the aforementioned embodiments, or to replace some or all of the technical features therein by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A silicon-based negative electrode sheet, characterized in that: It comprises a negative electrode current collector and a negative electrode coating located on the surface of the negative electrode current collector, wherein the negative electrode coating contains a negative electrode active material and a plurality of micro-nano pores are opened on the surface of the negative electrode coating; The negative electrode coating comprises a first coating close to the negative electrode current collector and a second coating located above the first coating; The first negative electrode active material in the first coating layer includes a first graphite, and the second negative electrode active material in the second coating layer includes a second graphite and a silicon-based negative electrode material.

2. A silicon-based negative electrode sheet according to claim 1, characterized in that: The second coating layer is coated by a micro-dimpled coating method.

3. The silicon-based negative electrode sheet according to claim 1, characterized in that: The particle sizes D90, D50 and D10 of the first graphite satisfy 1.05≤(D90-D10) / D50≤1.

60.

4. The silicon-based negative electrode sheet according to claim 1, characterized in that: The first coating layer also includes a first conductive agent, a first dispersant and a first binder; The first conductive agent accounts for 0-5% of the total mass of the first coating layer, the first dispersant accounts for 0.1%-1.5% of the total mass of the first coating layer, and the first binder accounts for 0.5%-3% of the total mass of the first coating layer.

5. The silicon-based negative electrode sheet according to claim 4, characterized in that: The first conductive agent includes any one or more combinations of conductive carbon black, acetylene black, Ketjen black, and conductive carbon fiber.

6. The silicon-based negative electrode sheet according to claim 4, characterized in that: The first dispersant includes sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

7. The silicon-based negative electrode sheet according to claim 4, characterized in that: The first binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, and polymethyl methacrylate.

8. The silicon-based negative electrode sheet according to claim 1, characterized in that: The particle sizes D90, D50 and D10 of the second graphite satisfy 1.05≤(D90-D10) / D50≤1.

40.

9. The silicon-based negative electrode sheet according to claim 1, characterized in that: The silicon-based negative electrode material includes silicon oxygen and / or silicon carbon; the particle size of the silicon-based negative electrode material satisfies 4μm≤D50≤10μm; the content of the silicon-based negative electrode material is 5% to 60% of the total mass of the total active material of the silicon-based negative electrode sheet.

10. The silicon-based negative electrode sheet according to claim 1, characterized in that: The mass ratio of the second graphite in the second coating layer to the silicon-based negative electrode material is (5% to 95%): (95% to 5%).

11. The silicon-based negative electrode sheet according to claim 1, characterized in that: The second coating layer also includes a second conductive agent, a second dispersant and a second binder; The second conductive agent accounts for 0-5% of the total mass of the second coating, the second dispersant accounts for 0.1%-2% of the total mass of the second coating, and the second binder accounts for 0.5%-8% of the total mass of the second coating.

12. The silicon-based negative electrode sheet according to claim 1, characterized in that: The thickness of the first coating layer and / or the second coating layer is 5 μm-130 μm.

13. The silicon-based negative electrode sheet according to claim 1, characterized in that: The compaction density of the negative electrode coating is 1.4 g / cm 3 -1.85g / cm 3 .

14. The silicon-based negative electrode sheet according to claim 1, characterized in that: The silicon-based negative electrode material of the second coating is a silicon-oxygen or silicon-carbon material coated with a 2D nanomaterial.

15. The silicon-based negative electrode sheet according to claim 14, characterized in that: The coating method is as follows: silicon-based negative electrode material, 2D nanomaterial and surfactant are placed in a ball mill according to proportion and subjected to high-energy ball milling; The silicon-based negative electrode material accounts for 90% to 99.95% of the total mass; the 2D nanomaterial accounts for 0.05% to 10% of the total mass; and the surfactant accounts for 0 to 1% of the total mass.

16. The silicon-based negative electrode sheet according to claim 14, characterized in that: The 2D nano conductive agent includes any one or more of graphene, michelene, titanium disulfide, black phosphorene, and molybdenum disulfide.

17. The silicon-based negative electrode sheet according to claim 15, characterized in that: The surfactant includes any one or more of oleic acid, sodium dodecylbenzene sulfonate, and stearic acid.

18. The silicon-based negative electrode sheet according to claim 1, characterized in that: The micro-nano pores are circular or elliptical micro-nano pores arranged in a periodic regular row, with a pore diameter of 50nm-10μm, a depth of 5μm-130μm, a pore spacing of 0.01mm-0.2mm, and a porosity controlled at 10%-20%.

19. A method for preparing a silicon-based negative electrode sheet, characterized in that: The following steps are involved: Preparing a first negative electrode active material slurry: mixing a first graphite, a first conductive agent, a first binder and a first dispersant in proportion, and then adding water and stirring to prepare a first negative electrode slurry; Preparing a second negative electrode active material slurry: mixing a second graphite, a silicon-based negative electrode material, a second conductive agent, a second binder, and a second dispersant in proportion, and then adding water and stirring to prepare a second negative electrode slurry; The first negative electrode slurry is coated on both sides of the negative electrode current collector and dried to obtain a first coating layer, and then the second negative electrode slurry is coated on the first coating layer by a micro-concave coating method, and then dried to obtain a second coating layer, and the dried electrode roll is rolled and cut to obtain a negative electrode sheet; The prepared negative electrode plate is subjected to laser pore making to obtain a silicon-based negative electrode plate having a plurality of micro-nanopores.

20. A battery, characterized in that: It comprises the silicon-based negative electrode sheet as described in any one of claims 1 to 18 or the silicon-based negative electrode sheet prepared by the preparation method as described in claim 19.

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