Silicon-based negative electrode sheet, and preparation method and application thereof

Abstract

The application discloses a silicon-based negative electrode sheet and a preparation method and application thereof, and relates to the technical field of batteries. The silicon-based negative electrode sheet comprises a negative electrode current collector and a negative electrode coating 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 arranged 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 on the first coating. The first negative electrode active material in the first coating comprises first graphite, and the second negative electrode active material in the second coating comprises second graphite and a silicon-based negative electrode material. The graphite is used as the first layer to provide a solid foundation for the silicon-based negative electrode sheet and guarantee the basic performance of the battery. The second layer is composed of the conductive agent modified silicon-based material and the graphite, the micro-concave coating technology is used for accurate application, the electronic conduction path of the silicon-based material is improved, and the thickness and uniformity of the coating are accurately controlled by the micro-concave coating, so that the overall electrochemical performance is optimized.

Description

TECHNICAL FIELD

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

[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 electrode sheets directly affect the overall performance of the battery.

[0003] Although the traditional graphite negative electrode has mature technology and low cost, the space for improving energy density is limited, and the lithium ion transmission efficiency is gradually insufficient under high-rate charging and discharging. Silicon-based materials have become a potential next-generation negative electrode material due to their ultra-high theoretical specific capacity (up to 4200 mAh / g, which is much higher than the advantage of 340-370 mAh / g of graphite).

[0004] The lithium ion battery prepared by the current silicon-based negative electrode sheet has a huge volume expansion (up to 300%) during charging and discharging, which easily leads to electrode structure pulverization, active material shedding, and rapid decrease in cycle life. At the same time, its intrinsic conductivity is poor, hindering the rapid conduction of lithium ions and electrons, thereby causing the performance of the silicon-based negative electrode lithium ion battery to fail to meet the needs of the power field. SUMMARY

[0005] Based on the problem of poor conductivity of the current silicon-based negative electrode material, the purpose of the present application is to provide a silicon-based negative electrode sheet and a preparation method and application thereof, which improves the rate performance and cycle performance of silicon-based lithium ion batteries through the double strategy of double-layer coating and constructing a conductive network system.

[0006] The present application is realized by the following technical solutions:

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

[0008] The negative electrode coating layer comprises a first coating layer close to the negative electrode current collector and a second coating layer on the first coating layer.

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

[0010] By taking graphite as the first layer, a solid foundation is provided for the silicon-based negative electrode sheet, guaranteeing the basic performance of the battery, with its stable structure, good cycle performance and excellent electrical conductivity; the second layer adopts a conductive agent modified silicon-based material and graphite composite, which is precisely applied by means of micro-recess coating technology, aiming to introduce high-capacity silicon-based components to improve the energy density, while improving the electron conduction path of the silicon-based material by means of the conductive agent, and precisely controlling the thickness and uniformity of the coating by means of micro-recess coating, to alleviate the negative effects of the volume expansion of the silicon-based material and optimize the overall electrochemical performance.

[0011] Further, the second coating layer is coated by means of micro-recess coating.

[0012] The second coating layer is coated by means of micro-recess coating, which can achieve more uniform and precise coating effect, reducing defects caused by unevenness during the coating process, and at the same time reducing the weakening of the electrochemical performance caused by uneven distribution of the silicon-based material.

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

[0014] The particle size distribution of the graphite used in the first coating layer satisfies 1.05≤(D90-D10) / D50≤1.60, which optimizes the packing structure and conduction path between particles, and at the same time improves the bulk density and flatness of the material, thereby providing better mechanical stability and electrical conductivity for the silicon-based negative electrode sheet, while increasing the compaction density of the system.

[0015] Further, the first coating layer further comprises a first conductive agent, a first dispersing agent and a first binder.

[0016] The first conductive agent accounts for 0-5% of the total mass of the first coating layer, the first dispersing agent 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] Further, the first conductive agent includes any one or more combinations of conductive carbon black, acetylene black, ketjen black, and conductive carbon fiber.

[0018] Further, the first dispersing agent includes sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

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

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

[0021] Further, the silicon-based negative electrode material includes silicon oxide and / or silicon carbon; the particle size of the silicon-based negative electrode material satisfies 4pm≤D50≤10pm; 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] Further, the mass ratio of the second graphite to the silicon-based negative electrode material in the second coating layer is (5% to 95%):(95% to 5%).

[0023] Further, the second coating layer further includes a second conductive agent, a second dispersing agent, and a second binder.

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

[0025] Further, the thickness of the first coating layer and / or the second coating layer is 5pm to 130pm.

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

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

[0028] Further, the coating method is: proportionally loading the silicon-based negative electrode material, the 2D nanomaterial, and the surfactant into a ball milling tank for 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, the ball milling rotation speed is 300 to 800 revolutions per minute, the temperature during the ball milling process is controlled between room temperature and 60°C, and the drying temperature after the ball milling is controlled between 80°C and 120°C, and the drying time is 2 to 6 hours.

[0031] The second coating layer is a 2D nanomaterial-modified silicon-based material prepared by high-energy ball milling technology, which optimizes the distribution of the conductive agent in the silicon-based negative electrode material, alleviates the cycle stability problem caused by the volume expansion of the silicon-based negative electrode material, and the addition of the 2D nanosheet can effectively improve the electrical conductivity of the silicon-based negative electrode material and enhance the overall electrochemical performance of the material.

[0032] Further, the 2D nanometer conductive agent includes any one or more of graphene, miche, titanium disulfide, black phosphorus, molybdenum disulfide.

[0033] Further, the surfactant includes any one or more of oleic acid, sodium dodecyl benzene sulfonate, and stearic acid.

[0034] Further, the micro-nano hole is a circular or elliptical micro-nano hole arranged in a periodic positive column, with a pore size of 50nm-10um, a depth of 5um-130um, a hole spacing of 0.01mm-0.2mm, and a porosity controlled at 10%-20%.

[0035] The silicon-based negative electrode sheet is subjected to laser pore forming after the coating, drying, and rolling processes.

[0036] The laser forms regular micro-nano hole arrays with a pore size of 50nm-10um on the surface of the silicon-based negative electrode sheet, a hole depth of 5-130um, and a micro-nano hole spacing of 0.01-0.05mm, and a three-dimensional conductive network formed by the holes 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.

[0037] In a second aspect, the application provides a preparation method of a silicon-based negative electrode sheet, including the following steps:

[0038] Preparation of a first negative electrode active material slurry: the first graphite, the first conductive agent, the first binder, and the first dispersant are mixed in proportion, and then water is added for stirring to prepare a first negative electrode slurry;

[0039] Preparation of a second negative electrode active material slurry: the second graphite, the silicon-based negative electrode material, the second conductive agent, the second binder, and the second dispersant are mixed in proportion, and then water is added for 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 after drying, a second coating layer is obtained, and the dried electrode roll is rolled and cut to prepare a negative electrode sheet.

[0041] The prepared negative electrode sheet is subjected to laser pore forming to obtain a silicon-based negative electrode sheet with a plurality of micro-nano holes.

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

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

[0044] The graphite used in the first coating layer makes the particle size distribution thereof satisfy 1.05 <= (D90-D10) / D50 <= 1.60, the particle size distribution optimizes the stacking structure and the conductive path between particles, and meanwhile improves the bulk density and flatness of the material, thereby providing the silicon-based negative electrode sheet with better mechanical stability and conductive performance, and meanwhile increasing the compaction density of the system; the second coating layer uses the 2D nanomaterial modified silicon-based material prepared through high-energy ball milling technology, optimizes the distribution of the conductive agent in the silicon-based material, and relieves the cycle stability problem of the silicon-based material caused by volume expansion, and meanwhile the addition of the 2D nanosheet can effectively improve the electrical conductivity of the silicon-based material and enhance the overall electrochemical performance of the material; the micro-concave coating technology is used to coat the second layer of silicon-based material, which can realize more uniform and precise coating effect, reduce the defects caused by unevenness in the coating process, and meanwhile reduce the weakening of the electrochemical performance caused by uneven distribution of the silicon-based material; the laser is used to form a regular micro-nano hole array with a pore size of 50nm-10um on the surface of the silicon-based negative electrode sheet material area, the hole depth is 5-130um, the micro-nano hole spacing is 0.01-0.05mm, and the three-dimensional conductive network formed by the holes 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 DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the example embodiments of the present application, the following will briefly introduce the drawings needed to be used in the examples, and it should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings. In the drawings:

[0046] Figure 1 The structure of the silicon-based negative electrode sheet of the present application is shown in the figure.

[0047] Reference signs:

[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 application more clear and explicit, the following will further describe the present application in combination with examples, and the example embodiments of the present application and their descriptions are only used to explain the present application, and should not be regarded as a limitation on the present application.

[0050] In the following description, numerous specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present application.

[0051] Reference throughout this specification to "one embodiment", "an embodiment", "one example", or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the application. Thus, appearances of the phrases "one embodiment", "an embodiment", "one example", or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics can be combined in any suitable

[0052] "ranges" disclosed herein are defined by both a lower and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and a range of 80-110 are listed, it is understood that a range of 60-110 and a range of 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 are listed, and if a maximum range value of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" means a range of any combination of the numbers between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] If not otherwise specified, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0054] Example 1

[0055] The present example provides a preparation method of a silicon-based negative electrode sheet, which is performed 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 sulfonate are added into a planetary high-energy ball mill pot at a mass ratio of 99.4:0.5:0.1, the ball milling speed is 500 revolutions per minute, the ball milling time is 5 hours, and the ball milling temperature is controlled between room temperature and 60°C. After completion, drying is performed in a vacuum oven at 105°C for 5 hours to prepare silicon-carbon A.

[0058] S2, preparation of a silicon-based negative electrode sheet

[0059] S2-1, preparation of a first negative electrode active material slurry (denoted 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 at a mass ratio of 96.5:0.5:1:2, and then water is added for stirring to prepare negative electrode slurry A.

[0061] S2-2, preparation of a second negative electrode active material slurry (denoted 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 (mass ratio of 1:3 of styrene-butadiene rubber and polyacrylic acid) and the second dispersant (CMC-Na) are mixed at a mass ratio of 45:50:0.5:1:3:0.5, and then water is added for stirring to prepare negative electrode slurry B.

[0063] S3, double-sided coating of the negative electrode slurry A on the negative electrode current collector by the coating equipment, drying, obtaining the first coating, then coating the negative electrode slurry B on the first coating by the micro-recess coating technology, drying to obtain the second coating, rolling, slitting the electrode roll after drying to prepare the negative electrode sheet. The thickness of the first coating (single side) and the second coating (single side) in the negative electrode sheet is 25 μm and 25 μm respectively; the mixing amount of the silicon material in the entire negative electrode active material is 25wt%.

[0064] S4, laser pore forming of the prepared electrode sheet, using 355 nm laser wavelength, pulse energy of 35 μJ, pulse width of 75 ns, repetition frequency of 80 kHZ, focusing spot size of 1 μm to form pores on the electrode roll, to prepare the silicon-based negative electrode sheet with a pore diameter of 50 nm, a depth of 30 μm, and a micro-nano pore spacing of 0.015 mm.

[0065] S5, die cutting of the product prepared in step S4 to prepare the silicon-based negative electrode sheet. The structure of the prepared silicon-based negative electrode sheet is as shown in Figure 1

[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 the 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 nanotube), and the binder (PVDF) are mixed in a mass ratio of 95.5:0.5:1:1.5:1.5, then N-methyl pyrrolidone is added and stirred and dispersed to prepare a positive electrode slurry; then the positive electrode slurry is coated on the positive electrode current collector (double-sided coating), dried, rolled, slitted, and die cut to prepare the positive electrode sheet.

[0069] S7, preparation of the battery

[0070] The prepared positive and negative electrode sheets and the separator are prepared into dry cells through processes such as lamination, welding, and heat sealing, then the processes such as liquid injection, aging, formation, capacity, rate, and cycle are carried out, and finally the prepared battery is tested for electrical properties such as capacity, rate, and cycle.

[0071] Example 2

[0072] ​The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, in the embodiment, a 1064 nm laser wavelength is used, a pulse energy is 40 muJ, a pulse width is 65 ns, a repetition frequency is 70 kHZ, a focused light spot size is 1 mu m, and a pole roll is perforated to prepare a silicon-based negative electrode sheet with a pore diameter of 500 nm, a depth of 45 mu m and a micro-nano pore spacing of 0.02 mm.

[0073] Embodiment 3

[0074] The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, in the embodiment, a 1064 nm laser wavelength is used, a pulse energy is 120 muJ, a pulse width is 75 ns, a repetition frequency is 70 kHZ, a focused light spot size is 2 mu m, and a pole roll is perforated to prepare a silicon-based negative electrode sheet with a pore diameter of 600 nm, a depth of 65 mu m and a micro-nano pore spacing of 0.02 mm.

[0075] Among them, the embodiment 2 and the embodiment 3 are used for explaining preparation of silicon-based negative electrode sheets with different specifications of pore diameters by laser.

[0076] Embodiment 4

[0077] The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, in the embodiment, thicknesses of a first coating layer and a second coating layer are changed, but formulas of the first coating layer and the second coating layer are not changed. The thicknesses of the first coating layer (single side) and the second coating layer (single side) in the negative electrode sheet are respectively 15 mu m and 35 mu m, and a silicon material blending amount accounts for 35 wt% in the whole negative electrode active material.

[0078] Embodiment 5

[0079] The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, in the embodiment, thicknesses of a first coating layer and a second coating layer are changed, but formulas of the first coating layer and the second coating layer are not changed. The thicknesses of the first coating layer (single side) and the second coating layer (single side) in the negative electrode sheet are respectively 35 mu m and 15 mu m, and a silicon material blending amount accounts for 15 wt% in the whole negative electrode active material.

[0080] Embodiment 6

[0081] The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, in the embodiment, thicknesses of a first coating layer and a second coating layer are changed, but formulas of the first coating layer and the second coating layer are not changed. The thicknesses of the first coating layer (single side) and the second coating layer (single side) in the negative electrode sheet are respectively 45 mu m and 5 mu m, and a silicon material blending amount accounts for 5 wt% in the whole negative electrode active material.

[0082] Embodiment 7

[0083] The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, the embodiment changes the thicknesses of the first coating and the second coating but the formulations of the first coating and the second coating are not changed. The thicknesses of the first coating (single side) and the second coating (single side) in the negative electrode sheet are 5 microns and 45 microns respectively; and the mixing amount of the silicon material in the whole negative electrode active material is 45 wt%.

[0084] Among them, the embodiments 4-7 are used to illustrate the preparation of the silicon-based negative electrode sheet when the thicknesses of the first coating and the second coating are different.

[0085] Embodiment 8

[0086] The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, the embodiment adopts the ball milling of the micene and the silicon carbon and sodium dodecyl sulfonate to obtain a 2D nanometer conductive agent coated silicon-based material (denoted as silicon carbon B).

[0087] Embodiment 9

[0088] The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, the embodiment adopts the ball milling of the black phosphorus and the silicon carbon and sodium dodecyl sulfonate to obtain a 2D nanometer conductive agent coated silicon-based material (denoted as silicon carbon C).

[0089] Among them, the embodiments 8 and 9 are used to illustrate the preparation of the silicon-based negative electrode sheet when different 2D nanometer materials are coated on the silicon carbon.

[0090] Embodiment 10

[0091] The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, the embodiment adopts the ball milling of the pre-lithium silicon oxide and the graphene and sodium dodecyl sulfonate to obtain a 2D nanometer conductive agent coated silicon-based material (denoted as silicon oxide A).

[0092] Embodiment 11

[0093] The embodiment provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, the embodiment adopts the ball milling of the pre-magnesium silicon oxide and the graphene and sodium dodecyl sulfonate to obtain a 2D nanometer conductive agent coated silicon-based material (denoted as silicon oxide B).

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

[0095] Comparative example 1

[0096] The comparative example provides a preparation method of a silicon-based negative electrode sheet, and different from the embodiment 1, the comparative example directly uses a double-layer coating device to coat the first layer and the second layer to prepare the 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 technique for the second layer.

[0098] Comparative Example 2

[0099] This comparative example provides a method for preparing a silicon-based negative electrode sheet, which is different from Example 1 in that the negative electrode of this comparative example uses a mixture of the two formulations of Example 1, and the coating is prepared into a silicon-based negative electrode sheet using direct single-layer coating (the specific formulation is described below), and then the battery is assembled.

[0100] Specific formulation: graphite (artificial graphite, (D90-D10) / D50 = 1.42), silicon-based material (silicon-carbon A, D50 = 7.5 μm), conductive agent (conductive carbon black), binder (mass ratio 1:3 of butadiene-styrene rubber and polyacrylic acid), 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 prepare negative electrode slurry A.

[0101] The slurry A is coated directly 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 using a mixture of graphite and coated silicon-based material 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, which is different from Example 1 in that the first silicon-based material used in the preparation of the second negative electrode active material slurry (denoted as negative electrode slurry B) of this comparative example is a silicon-carbon without coated conductive agent, which is prepared into a silicon-based negative electrode sheet, and then the battery is assembled.

[0105] This comparative example is used to illustrate the preparation of a silicon-based negative electrode sheet using a mixture of uncoated material and second graphite directly mixed and homogenized for the second layer.

[0106] Comparative Example 4

[0107] This comparative example provides a method for preparing a silicon-based negative electrode sheet, which is different from Example 1 in that the first graphite (artificial graphite, (D90-D10) / D50 = 1.7) and the second graphite (artificial graphite, (D90-D10) / D50 = 1.5) of 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 a first graphite and a second graphite with (D90-D10) / D50 parameters outside the protection range.

[0109] Comparative Example 5

[0110] The comparative example provides a preparation method of a silicon-based negative electrode sheet, and the difference between the comparative example and example 1 is that the silicon-based negative electrode sheet is not processed by laser pore forming to prepare the silicon-based negative electrode sheet, and then the battery is assembled.

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

[0112] The electrical performance of the batteries assembled by the silicon-based negative electrode sheets prepared in examples 1-11 and comparative examples 1-5 is detected, and the detection results are shown in Table 1.

[0113] Table 1

[0114]

[0115]

[0116] By comparing the results of examples 1-11 and comparative example 1, it can be known that the micro-recess coating technology used in the second layer coating of the application can precisely control the thickness and uniformity of the coating compared with the conventional double-layer coating, avoid stress concentration of the silicon-based material due to uneven coating, and reduce the tortuosity of the lithium ion transmission path, thereby significantly improving the rate charge-discharge performance and cycle performance of the battery. By comparing the results of examples 1-11 and comparative example 3, it can be known that the modification of the 2D nanomaterial and the silicon-based material used in the application can effectively improve the rate performance of the battery. By comparing the results of examples 1-11 and comparative example 4, it can be known that by limiting the particle size (D90-D10) / D50 range of the first graphite and the second graphite, the electrode sheet compaction density can be obviously improved, the ion transmission path can be optimized, the active material ratio can be increased, and the overall energy density of the battery can be improved. By comparing the results of examples 1-11 and comparative example 5, it can be known that the pores formed by laser pore forming construct a three-dimensional conductive network for the electrode sheet, effectively reducing the interface resistance, thereby improving the overall kinetic performance of the battery and improving the rate and cycle performance of the battery.

[0117] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the examples of the application, and they should be covered in the scope of the claims and the description of the application.

Claims

1. A silicon-based negative electrode sheet, characterized by, The negative electrode coating layer contains a negative active material, and a plurality of micro-nano holes are opened on the surface of the negative electrode coating layer; The negative electrode coating layer includes a first coating layer close to the negative electrode current collector and a second coating layer on the first coating layer; The first negative active material in the first coating layer includes first graphite, and the second negative active material in the second coating layer includes second graphite and a silicon-based negative electrode material; The second coating layer is coated by a micro-concave coating method; The silicon-based negative electrode material in the second coating layer is a 2D nano conductive agent coated modified silicon-oxygen or silicon-carbon material; The coating method is that the silicon-based negative electrode material, the 2D nano conductive agent and the surfactant are proportionally loaded into a ball mill jar for high-energy ball milling; The silicon-based negative electrode material accounts for 90% to 99.95% of the total mass, the 2D nano conductive agent accounts for 0.05% to 10% of the total mass, and the surfactant accounts for 0.1% to 1% of the total mass.

2. The silicon-based negative electrode sheet according to claim 1, wherein The particle size D90, D50 and D10 of the first graphite satisfy 1.05≤(D90-D10) / D50≤1.

60.

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

4. The silicon-based negative electrode sheet according to claim 3, wherein The first conductive agent includes any one or more combinations of conductive carbon black and conductive carbon fiber.

5. The silicon-based negative electrode sheet according to claim 3, wherein The first dispersant includes sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

6. The silicon-based negative electrode sheet according to claim 3, wherein The first binder includes any one or more of styrene butadiene rubber, polyacrylic acid, polyacrylonitrile and polymethyl methacrylate.

7. The silicon-based negative electrode sheet according to claim 1, wherein The particle size D90, D50 and D10 of the second graphite satisfy 1.05≤(D90-D10) / D50≤1.

40.

8. The silicon-based negative electrode sheet according to claim 1, wherein 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.

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

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

11. The silicon-based negative electrode sheet according to claim 1, wherein The thickness of the first coating layer and / or the second coating layer is 5μm-130μm.

12. The silicon-based negative electrode sheet according to claim 1, wherein The compacted density of the negative electrode coating is 1.4 g / cm 3 - 1.85 g / cm 3 .

13. The silicon-based negative electrode sheet according to claim 1, wherein The 2D nano conductive agent includes any one or more of graphene, miche, titanium disulfide, black phosphorus, and molybdenum disulfide.

14. The silicon-based negative electrode sheet according to claim 1, wherein The surfactant includes any one or more of oleic acid, sodium dodecyl benzene sulfonate and stearic acid.

15. The silicon-based negative electrode sheet according to claim 1, wherein The micro-nano holes are circular or elliptical micro-nano holes arranged in a periodic positive column, with a pore size of 50 nm to 10 μm, a depth of 5 μm to 130 μm, a hole spacing of 0.01 mm to 0.2 mm, and a porosity controlled at 10% to 20%.

16. The method of claim 1, wherein the silicon-based negative electrode sheet is prepared by the steps of: The method comprises the following steps: ​ Preparation of a first negative electrode active material slurry: mixing the first graphite, the first conductive agent, the first binder and the first dispersant in a proportion, and then adding water to stir to prepare the first negative electrode slurry; Preparation of a second negative electrode active material slurry: mixing the second graphite, the silicon-based negative electrode material, the second conductive agent, the second binder and the second dispersant in a proportion, and then adding water to stir to prepare the second negative electrode slurry; Double-sided coating and drying of the first negative electrode slurry on the negative electrode current collector to obtain a first coating, then coating the second negative electrode slurry on the first coating by a micro-concave coating method, drying to obtain a second coating, and then roll pressing and slitting the dried electrode roll to prepare the negative electrode sheet. The prepared negative electrode sheet is subjected to laser hole forming to obtain a silicon-based negative electrode sheet with a plurality of micro-nano holes.

17. A battery, characterized by The silicon-based negative electrode sheet prepared by the method of any one of claims 1-15 or the method of claim 16.

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