Negative plate, preparation method thereof and battery

Abstract

The invention relates to a negative plate, a preparation method thereof and a battery. The negative plate comprises a current collector, and a first active material layer, a second active material layer and a safety coating which are sequentially laminated on at least one side surface of the current collector, wherein the first active material layer comprises a first negative electrode active material, and the first negative electrode active material comprises a first silicon-based material and a first carbon material; the second active material layer comprises a second negative electrode active material, and the second negative electrode active material comprises a second silicon-based material and a second carbon material; and the material of the safety coating comprises cordierite. By using the negative plate with the multi-layer coating structure, the problems of volume expansion and low ionic conductivity caused by lithium intercalation of a silicon negative electrode can be effectively inhibited. In addition, the excellent lithium storage capacity of cordierite is utilized, and the cordierite is pre-lithiated in advance, so that the reversible capacity of the battery is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and particularly to a negative electrode sheet, a preparation method thereof, and a battery. Background Art

[0002] In recent years, with the continuous expansion of the industrialization of lithium-ion batteries and the continuous development of technology, the requirements for lithium-ion batteries have gradually increased. Lithium-ion batteries with high energy density, long cycle life, and high safety have become the focus of research and development.

[0003] Currently, the main ways to improve the energy density of batteries are as follows: 1. Increasing the compaction density of the positive and negative electrode materials. However, high compaction will lead to a low porosity of the electrode sheet, and the liquid retention capacity will decrease accordingly, resulting in insufficient cycle life of the battery. 2. Increasing the specific capacity of the negative electrode material, that is, using a silicon-based negative electrode material to replace graphite. However, the large volume change of the silicon-based material during charge and discharge will cause the material to powder and peel off from the current collector, resulting in a sharp attenuation of the capacity, and at the same time, safety problems will occur. Currently, in order to maximize the advantages of each negative electrode material, double (multi)-layer coating has become a new coating method. However, the problem of the increased thickness of the negative electrode sheet brought about by multi-layer coating has increased the volume energy density of the whole battery, posing a new problem for multi-layer coating.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] In view of this, an embodiment of the present application provides a negative electrode sheet, a preparation method thereof, and a battery to solve at least one problem in the background art.

[0006] In the first aspect of the present invention, a negative electrode sheet is provided. The negative electrode sheet includes a current collector, and a first active material layer, a second active material layer, and a safety coating sequentially stacked on at least one surface of the current collector. Among them,

[0007] The first active material layer includes a first negative electrode active material, and the first negative electrode active material includes a first silicon-based material and a first carbon material;

[0008] The second active material layer includes a second negative electrode active material, and the second negative electrode active material includes a second silicon-based material and a second carbon material;

[0009] The material of the safety coating includes cordierite.

[0010] Preferably, the material of the safety coating further includes a first binder and a first conductive agent. The safety coating satisfies at least one of the following characteristics (1) to (5):

[0011] (1) The D90 particle size range of the cordierite is 50 nm to 200 nm; the specific surface area of the cordierite is 1 m 2 / g to 5 m 2 / g;

[0012] (2) The cordierite is loaded with a lithium salt, and the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)amide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(oxalato)borate, lithium dioxalate borate, lithium tetrafluoroborate, lithium phosphate, and lithium difluorophosphate;

[0013] (3) The first binder includes one or more of polyvinylidene fluoride, silicone resin adhesive, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinyl alcohol; preferably, the first binder is polyvinylidene fluoride and silicone resin adhesive, and the mass ratio of polyvinylidene fluoride to silicone resin adhesive is (10 to 20):(0.3 to 1);

[0014] (4) The first conductive agent includes one or more of conductive carbon black, carbon fiber, graphene, and carbon nanotubes;

[0015] (5) The mass ratio of the cordierite, the first binder, and the first conductive agent is (75 to 85):(10.3 to 21):(1 to 5);

[0016] (6) The thickness of the safety coating is 2 μm to 4 μm.

[0017] Preferably, the first carbon material includes first graphite; the material of the first active material layer further includes a second conductive agent, a second binder, and a first thickening agent; the first active material layer satisfies at least one of the following characteristics (1) to (7):

[0018] (1) The first silicon-based material is selected from one or more of prelithiated silicon monoxide, porous nanosilicon, and silicon-carbon materials; the D50 particle size of the first silicon-based material is 1 μm to 10 μm;

[0019] (2) The D50 particle size of the first graphite is 1 μm to 15 μm;

[0020] (3) The mass ratio of the first graphite to the first silicon-based material is (70 to 80):(20 to 30);

[0021] (4) The second conductive agent includes one or more of conductive carbon black, carbon fiber, graphene, and carbon nanotubes;

[0022] (5) The second binder includes one or more of styrene-butadiene rubber, polyvinylidene fluoride, and polyvinyl alcohol;

[0023] (6) The first thickening agent includes one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, and xanthan gum;

[0024] (7) The mass ratio of the first negative electrode active material, the second conductive agent, the second binder, and the first thickening agent is (95-99):(0.1-2):(0.5-3):(0.1-2);

[0025] (8) The thickness of the first active material layer is 45 μm to 55 μm.

[0026] Preferably, the second carbon material includes second graphite; the material of the second active material layer further includes a third conductive agent, a third binder, and a second thickening agent; the second active material layer satisfies at least one of the following characteristics (1)-(7):

[0027] (1) The second silicon-based material includes one or more of prelithiated silicon monoxide, porous nanosilicon, and silicon-carbon material; the particle size D50 of the second silicon-based material is 5 μm to 15 μm;

[0028] (2) The particle size D50 of the second graphite is 10 μm to 25 μm;

[0029] (3) The mass ratio of the second graphite and the second silicon-based material is (20-30):(70-80);

[0030] (4) The third conductive agent includes one or more of conductive carbon black, carbon fiber, graphene, and carbon nanotubes;

[0031] (5) The third binder includes one or more of styrene-butadiene rubber, polyvinylidene fluoride, and polyvinyl alcohol;

[0032] (6) The second thickening agent includes one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, and xanthan gum;

[0033] (7) The mass ratio of the second negative electrode active material, the third conductive agent, the third binder, and the second thickening agent is (95-99):(0.1-2):(0.5-3):(0.1-2);

[0034] (8) The thickness of the second active material layer is 25 μm to 35 μm.

[0035] Preferably, the compaction density of the negative electrode sheet is 1.5 g / cm 3 ~1.8 g / cm 3 .

[0036] In the second aspect of the present invention, a method for preparing the negative electrode sheet provided in the first aspect of the present invention is provided, and the method includes:

[0037] S1: Prepare the cordierite.

[0038] S2: Mix the cordierite obtained in step S1 with a first conductive agent, add solvent A to obtain a cordierite slurry; disperse the first binder in solvent B to obtain a glue solution; add the cordierite slurry to the glue solution and mix to obtain a safety coating slurry;

[0039] Mix the first negative electrode active material, a second conductive agent, a second binder, and a first thickening agent in solvent C to obtain a first active material layer slurry;

[0040] Mix the second negative electrode active material, a third conductive agent, a third binder, and a second thickening agent in solvent D to obtain a second active material layer slurry;

[0041] S3: Coating the first active material layer slurry, the second active material layer slurry, and the safety coating slurry obtained in step S2 on the current collector in sequence to obtain the negative electrode sheet.

[0042] Preferably, in step S1, the steps for preparing the cordierite include: adding an aluminum source and a magnesium source to anhydrous ethanol for dissolution, adding an organosilicon source and an ethanol solution to obtain a sol; adding a lithium salt and performing lithium mixing and pre-calcination; adding a pH regulator to obtain a cordierite ceramic gel, and calcining and grinding to obtain the cordierite.

[0043] Preferably, the steps for preparing the cordierite satisfy one or more of the following characteristics (1) to (11):

[0044] (1) The aluminum source includes one or more of aluminum nitrate, aluminum sulfate, and aluminum hydroxide;

[0045] (2) The magnesium source includes one or more of magnesium nitrate, magnesium sulfate, and magnesium hydroxide;

[0046] (3) The organosilicon source includes one or more of tetraethyl orthosilicate and sodium silicate;

[0047] (4) The molar ratio of the aluminum source, the magnesium source, and the organosilicon source is 4:2:5;

[0048] (5) The volume ratio of the organosilicon source to ethanol is 1:(3 - 5);

[0049] (6) The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)amide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(oxalato)borate, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium phosphate, and lithium difluorophosphate;

[0050] (7) The mass of the lithium salt accounts for 30% - 40% of the mass of the sol;

[0051] (8) The temperature of the mixed lithium pre-calcination is 300°C to 500°C;

[0052] (9) The pH regulator includes a mixed solution of nitric acid and ethanol or ammonia water;

[0053] (10) The pH of the cordierite ceramic gel is 5 to 7;

[0054] (11) The temperature of the calcination is 500°C to 700°C, and the time of the calcination is 1 h to 3 h.

[0055] Preferably, in step S2, the solvent A is selected from deionized water; the solvent B is selected from deionized water; the solvent C is selected from deionized water; the solvent D is selected from deionized water.

[0056] The third aspect of the present invention provides a battery, which includes the negative electrode sheet provided by the first aspect of the present invention or the negative electrode sheet prepared by the preparation method provided by the second aspect of the present invention.

[0057] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0058] The present invention provides a negative electrode sheet, a preparation method thereof and a battery. The negative electrode sheet includes a current collector, and a first active material layer, a second active material layer and a safety coating which are sequentially laminated on at least one surface of the current collector. By using the negative electrode sheet with such a multi-layer coating structure, the defects of the silicon negative electrode in the prior art are improved. The safety coating therein can not only inhibit the volume expansion caused by lithium insertion of the silicon negative electrode, but also improve the problem of low ionic conductivity of the silicon negative electrode. In addition, by utilizing the excellent lithium storage capacity of cordierite and pre-lithiating it in advance, the problem of low first efficiency caused by the safety coating is effectively improved, and the pre-lithiated cordierite can replace the inorganic layer part of the SEI film, thereby significantly improving the reversible capacity of the battery. Description of the Drawings

[0059] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0060] Figure 1 A cross-sectional schematic view of the negative electrode sheet in some embodiments of the present application.

[0061] Description of the Reference Numerals

[0062] 100. Current collector;

[0063] 200. First active material layer;

[0064] 300. Second active material layer;

[0065] 400. Safety coating. Detailed implementation manners

[0066] To make the technical solutions and beneficial effects of the present invention more obvious and understandable, the following will be described in detail by listing specific embodiments. Among them, the drawings are not necessarily drawn to scale, and local features can be enlarged or reduced to more clearly show the details of local features. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are usually in accordance with conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0067] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features well known in the art are not described; that is, not all features of the actual embodiments are described here, and the well-known functions and steps are not described in detail.

[0068] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present application. When used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, determine the presence of the described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. When used herein, the term "and / or" includes any and all combinations of the related listed items.

[0069] To thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solutions of the present application. The preferred embodiments of the present application are described in detail as follows. However, in addition to these detailed descriptions, the present application may also have other implementation manners.

[0070] Unless otherwise defined, the technical and scientific terms used in the present application have the same meanings as those in the technical and scientific fields to which the present application belongs.

[0071] For those not specifically noted for technical or conditions in the following embodiments, they are usually in accordance with the conventional techniques or conditions described in the literature in the art, or in accordance with the conditions recommended in the product manuals and by the manufacturers. The numerical ranges in the following embodiments all include the end point values.

[0072] Currently, the commonly used safety coating is an alumina ceramic coating, but it often faces the phenomena of powder shedding and film peeling.

[0073] The chemical formula of cordierite ceramics is 2MgO·2Al2O3·5SiO2, which has the characteristics of strong acid resistance, good chemical stability, high insulation, corrosion resistance, high ionic conductivity, and excellent lithium storage capacity. Due to the large voids in the crystal structure of cordierite, its symmetry is low and the structure is not compact, so it has the characteristic of being porous. When the temperature rises, the molecules in the crystal structure of cordierite have enough space to vibrate due to heat, so its thermal expansion coefficient is very small. Combining the above characteristics, cordierite is commonly used in the crucibles for sintering the positive electrode materials of lithium batteries, and is particularly suitable for the sintering of lithium iron phosphate and lithium cobaltate materials. In addition, it is also widely used in the powder material industry such as ceramic powder on battery separator membranes.

[0074] In view of this, the present invention provides the following technical solutions:

[0075] [Negative electrode sheet]

[0076] The first aspect of the present invention provides a negative electrode sheet, which includes a current collector 100, and a first active material layer 200, a second active material layer 300, and a safety coating 400 that are sequentially stacked on at least one surface of the current collector 100;

[0077] Among them, the first active material layer 200 includes a first negative electrode active material, and the first negative electrode active material includes a first silicon-based material and a first carbon material; the second active material layer 300 includes a second negative electrode active material, and the second negative electrode active material includes a second silicon-based material and a second carbon material; the material of the safety coating 400 includes cordierite.

[0078] In the present invention, by using the negative electrode sheet with a multi-layer coating structure, the defects of the silicon negative electrode in the prior art are improved. The safety coating therein can not only inhibit the volume expansion caused by lithium intercalation of the silicon negative electrode, but also improve the problem of low ionic conductivity of the silicon negative electrode. In addition, by utilizing the excellent lithium storage capacity of cordierite and pre-lithiating it in advance, the problem of low initial efficiency caused by the safety coating is effectively improved, and the pre-lithiated cordierite can replace the inorganic layer part of the SEI film, thereby significantly improving the reversible capacity of the battery.

[0079] In some embodiments, the material of the safety coating 400 further includes a first binder and a first conductive agent.

[0080] In some embodiments, the D90 particle size range of the cordierite is 50nm to 200nm.

[0081] In some embodiments, the D90 particle size of the cordierite ranges from 50 nm to 100 nm, such as 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0082] In some embodiments, the specific surface area of the cordierite is 1 m 2 / g to 5 m 2 / g.

[0083] In some embodiments, the specific surface area of the cordierite is 2 m 2 / g to 3 m 2 / g, such as 2 m 2 / g, 2.5 m 2 / g, or 3 m 2 / g, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0084] In some embodiments, the cordierite is loaded with a lithium salt.

[0085] In some embodiments, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)amide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(oxalato)borate, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium phosphate, and lithium difluorophosphate.

[0086] In some embodiments, the first binder includes one or more of polyvinylidene fluoride, silicone resin adhesive, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinyl alcohol.

[0087] In some embodiments, the first binder is polyvinylidene fluoride and silicone resin adhesive.

[0088] In some embodiments, the mass ratio of polyvinylidene fluoride to silicone resin adhesive is (10 to 20):(0.3 to 1), such as 10:0.3, 13:0.5, 15:0.6, 18:0.9, or 20:1, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0089] In the present invention, adding a silicone resin adhesive to the safety coating can be used to fix the cordierite powder, thereby inhibiting powder shedding of the safety coating. In addition, when the addition ratio of the silicone resin adhesive is within the above range, it can effectively avoid the situation of poor ionic conductivity and excessive sealing caused by adding too much silicone resin adhesive, resulting in a sharp increase in impedance or even insulation, and can avoid the difficulties in stirring and coating during the homogenization process.

[0090] The silicone resin adhesive can be prepared by first generating a polymer mixture through the reaction of the base gum, and then reacting with a silane coupling agent and a catalyst.

[0091] In some embodiments, the base gum includes one or more of dimethylsiloxane capped with vinyl diisopropoxysilyl, bis(p-glycidylphenyl) propane, and styrene.

[0092] In some embodiments, the base gum is dimethylsiloxane capped with vinyl diisopropoxysilyl, bis(p-glycidylphenyl) propane, and styrene.

[0093] In some embodiments, in the base gum, the molar ratio of dimethylsiloxane capped with vinyl diisopropoxysilyl, bis(p-glycidylphenyl) propane, and styrene is (7-9):(1-3):(6-8), such as 7:1:6, 8:2:7, or 9:3:8, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0094] In some embodiments, the molar ratio of the polymer mixture to dimethylsiloxane capped with vinyl diisopropoxysilyl is 1:1.

[0095] In some embodiments, the molar ratio of the polymer mixture, the silane coupling agent, and the catalyst is (7-9):(0.1-0.3):(0.001-0.003), such as 7:0.1:0.001, 8:0.2:0.002, or 9:0.3:0.003, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0096] In some embodiments, the substance added simultaneously with the silane coupling agent further includes butyl acrylate, and the molar ratio of the butyl acrylate to the silane coupling agent is (5-7):(7-9), such as 5:7, 6:8, or 7:9, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0097] In some embodiments, the preparation method of the silicone resin adhesive is as follows: First, 80 parts of dimethylsiloxane capped with vinyl diisopropoxysilyl, 20 parts of bis(p-glycidylphenyl) propane, and 70 parts of styrene are copolymerized at 160°C for 6 hours to obtain a product. Then, 80 parts of the prepared polymer mixture, 2 parts of a silane coupling agent (γ-aminopropyltriethoxysilane), 60 parts of butyl acrylate, and 0.02 parts of a catalyst (dimethoxydibutyltin) are combined to form B, and after mixing, a heat-cured silicone resin adhesive is obtained.

[0098] In some embodiments, the first conductive agent includes one or more of conductive carbon black, carbon fiber, graphene, and carbon nanotubes.

[0099] In some embodiments, the mass ratio of the cordierite, the first binder, and the first conductive agent is (75 to 85):(10.3 to 21):(1 to 5), such as 75:20:5, 80:15:5, or 84:11:5, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0100] In some embodiments, the thickness of the safety coating 400 is 2 μm to 4 μm, such as 2 μm, 3 μm, or 4 μm, but is not limited to the listed values, and other unlisted values within the value range are equally applicable.

[0101] In some embodiments, the first carbon material includes first graphite.

[0102] In some embodiments, the material of the first active material layer 200 further includes a second conductive agent, a second binder, and a first thickening agent.

[0103] In some embodiments, the first silicon-based material is selected from one or more of pre-lithiated silicon monoxide, porous nanosilicon, and silicon-carbon materials.

[0104] In some embodiments, the particle size D50 of the first silicon-based material is 1 μm to 10 μm.

[0105] In some embodiments, the particle size D50 of the first silicon-based material is 1 μm to 5 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm, but is not limited to the listed values, and other unlisted values within the value range are equally applicable.

[0106] In some embodiments, the particle size D50 of the first graphite is 1 μm to 15 μm.

[0107] In some embodiments, the particle size D50 of the first graphite is 1 μm to 10 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, but is not limited to the listed values, and other unlisted values within the value range are equally applicable.

[0108] In some embodiments, the mass ratio of the first graphite and the first silicon-based material is (70 to 80):(20 to 30), such as 70:20, 70:25, 70:30, 75:20, 75:25, 75:30, 80:20, 80:25, or 80:30, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0109] In some embodiments, the second conductive agent includes one or more of conductive carbon black, carbon fiber, graphene, and carbon nanotubes.

[0110] In some embodiments, the second binder includes one or more of styrene-butadiene rubber, polyvinylidene fluoride, and polyvinyl alcohol.

[0111] In some embodiments, the first thickening agent includes one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, and xanthan gum.

[0112] In some embodiments, the mass ratio of the first negative electrode active material, the second conductive agent, the second binder, and the first thickening agent is (95-99):(0.1-2):(0.5-3):(0.1-2), such as 95:0.1:0.5:0.1, 96:1:1:0.5, 97:0.5:1.5:1, or 98:2:3:2, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0113] In some embodiments, the thickness of the first active material layer 200 is 45μm - 55μm, such as 45μm, 46μm, 47μm, 48μm, 49μm, 50μm, 51μm, 52μm, 53μm, 54μm, or 55μm, but is not limited to the listed values, and other unlisted values within the value range are equally applicable.

[0114] In some embodiments, the second carbon material includes second graphite.

[0115] In some embodiments, the material of the second active material layer 300 further includes a third conductive agent, a third binder, and a second thickening agent.

[0116] In some embodiments, the second silicon-based material includes one or more of pre-lithiated silicon monoxide, porous nano-silicon, and silicon-carbon materials.

[0117] In some embodiments, the particle size D50 of the second silicon-based material is 5μm - 15μm.

[0118] In some embodiments, the particle size D50 of the second silicon-based material is 7μm - 10μm, such as 7μm, 8μm, 9μm, or 10μm, but is not limited to the listed values, and other unlisted values within the value range are equally applicable.

[0119] In some embodiments, the particle size D50 of the second graphite is 10μm - 25μm.

[0120] In some embodiments, the particle size D50 of the second graphite is 15 μm to 20 μm, such as 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0121] In some embodiments, the mass ratio of the second silicon-based material to the second graphite is (70 to 80):(20 to 30), such as 70:20, 70:25, 70:30, 75:20, 75:25, 75:30, 80:20, 80:25 or 80:30, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0122] In some embodiments, the third conductive agent includes one or more of conductive carbon black, carbon fiber, graphene, and carbon nanotubes.

[0123] In some embodiments, the third binder includes one or more of styrene-butadiene rubber, polyvinylidene fluoride, and polyvinyl alcohol.

[0124] In some embodiments, the second thickener includes one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, and xanthan gum.

[0125] In some embodiments, the mass ratio of the second negative electrode active material, the third conductive agent, the third binder, and the second thickener is (95 to 99):(0.1 to 2):(0.5 to 3):(0.1 to 2), such as 95:0.1:0.5:0.1, 96:1:1:0.5, 97:0.5:1.5:1 or 98:2:3:2, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0126] In some embodiments, the thickness of the second active material layer 300 is 25 μm to 35 μm, such as 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm or 35 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0127] Preferably, the compaction density of the negative electrode sheet is 1.5 g / cm 3 ~1.8 g / cm 3 For example, 1.5 g / cm 3 、1.55 g / cm 3 、1.6 g / cm 3 、1.65 g / cm 3 、1.7 g / cm 3 、1.75 g / cm 3or 1.8 g / cm 3 , but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0128] [Preparation method of negative electrode sheet]

[0129] The second aspect of the present invention provides a preparation method of the negative electrode sheet provided in the first aspect of the present invention, and the method includes:

[0130] S1: Prepare the cordierite;

[0131] S2: Mix the cordierite obtained in step S1 with a first conductive agent, add solvent A to obtain a cordierite slurry; Disperse the first binder in solvent B to obtain a glue solution; Add the cordierite slurry to the glue solution and mix to obtain a safety coating slurry;

[0132] Mix the first negative electrode active material, a second conductive agent, a second binder, and a first thickening agent in solvent C to obtain a first active material layer slurry;

[0133] Mix the second negative electrode active material, a third conductive agent, a third binder, and a second thickening agent in solvent D to obtain a second active material layer slurry;

[0134] S3: Coat the first active material layer slurry, the second active material layer slurry, and the safety coating slurry obtained in step S2 on the current collector 100 in sequence to obtain the negative electrode sheet.

[0135] In some embodiments, in step S1, the step of preparing the cordierite includes: adding an aluminum source and a magnesium source to anhydrous ethanol to dissolve, adding an organosilicon source and an ethanol solution to obtain a sol; adding a lithium salt and performing lithium mixing and pre-calcination; adding a pH regulator to obtain a cordierite ceramic gel, and calcining and grinding to obtain the cordierite.

[0136] In some embodiments, in the step of preparing the cordierite, the aluminum source includes one or more of aluminum nitrate, aluminum sulfate, and aluminum hydroxide.

[0137] In some embodiments, in the step of preparing the cordierite, the magnesium source includes one or more of magnesium nitrate, magnesium sulfate, and magnesium hydroxide.

[0138] In some embodiments, in the step of preparing the cordierite, the organosilicon source includes one or more of tetraethyl orthosilicate and sodium silicate.

[0139] In some embodiments, in the step of preparing the cordierite, the molar ratio of the aluminum source, the magnesium source, and the organosilicon source is 4:2:5.

[0140] In some embodiments, in the step of preparing the cordierite, the volume ratio of the organosilicon source to ethanol is 1:(3-5), such as 1:3, 1:4 or 1:5, but not limited to the listed ratios, and other unlisted ratios within the ratio range are equally applicable.

[0141] In some embodiments, in the step of preparing the cordierite, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)amide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(oxalato)borate, lithium dioxalate borate, lithium tetrafluoroborate, lithium phosphate, and lithium difluorophosphate.

[0142] In some embodiments, in the step of preparing the cordierite, the mass of the lithium salt accounts for 30%-40% of the mass of the sol, such as 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39% or 40%, but not limited to the listed values, and other unlisted values within the value range are equally applicable.

[0143] In some embodiments, in the step of preparing the cordierite, the temperature of the mixed lithium pre-calcination is 300°C - 500°C, such as 300°C, 350°C, 400°C, 450°C or 500°C, but not limited to the listed values, and other unlisted values within the value range are equally applicable.

[0144] In some embodiments, in the step of preparing the cordierite, the pH regulator includes a mixed solution of nitric acid and ethanol or ammonia water.

[0145] In some embodiments, in the step of preparing the cordierite, the pH of the cordierite ceramic gel is 5 - 7.

[0146] In the present invention, controlling the pH within the range of 5 - 7 is to reduce the residual lithium content of the cordierite and improve the stability of the subsequent slurry. In addition, in a slightly acidic environment, it is not easy to generate overly small particles and densified cordierite powder, avoiding the problem of internal heat expansion space of small molecules, thereby increasing the thermal expansion coefficient of the cordierite and reducing the thermal stability of the cordierite.

[0147] In some embodiments, in the step of preparing the cordierite, the temperature of the calcination is 500°C - 700°C, such as 500°C, 600°C or 700°C, but not limited to the listed values, and other unlisted values within the value range are equally applicable.

[0148] In some embodiments, in the step of preparing the cordierite, the time of the calcination is 1h - 3h, such as 1h, 2h or 3h, but not limited to the listed values, and other unlisted values within the value range are equally applicable.

[0149] In some embodiments, in the step of preparing the cordierite, before the calcination, the steps of standing, drying, and heating are further included.

[0150] In some embodiments, the standing is carried out at room temperature for 8 h.

[0151] In some embodiments, the drying temperature is 70°C to 90°C, such as 70°C, 80°C, or 90°C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0152] In some embodiments, the heating is to remove organic substances and water, and the heating temperature is 150°C to 250°C, such as 150°C, 200°C, or 250°C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0153] In some embodiments, in the step of preparing the cordierite, after the calcination, the step of ball milling is further included.

[0154] In some embodiments, in step S2, the solvent A is selected from deionized water.

[0155] In some embodiments, in step S2, the solvent B is selected from deionized water.

[0156] In some embodiments, in step S2, the solvent C is selected from deionized water.

[0157] In some embodiments, in step S2, the solvent D is selected from deionized water.

[0158] [Battery]

[0159] The third aspect of the present invention provides a battery, which includes the negative electrode sheet provided by the first aspect of the present invention or the negative electrode sheet prepared by the preparation method provided by the second aspect of the present invention.

[0160] In some embodiments, the battery can be a secondary battery or a primary battery, preferably a secondary battery. For example, the above battery can be a lithium-ion battery, etc., but is not limited thereto. The battery structure of the present application includes but is not limited to soft-pack lithium-ion batteries, square hard-shell batteries, or cylindrical hard-shell batteries, etc.

[0161] In some embodiments, the battery further includes a positive electrode sheet, an electrolyte, and a separator. Generally, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, and the separator is disposed between the positive electrode sheet and the negative electrode sheet. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0162] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector. The positive electrode current collector can be aluminum foil, copper foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The positive electrode active material layer includes positive electrode active materials. The positive electrode active materials applicable to the present invention can be various known positive electrode active materials that can be used in lithium-ion batteries and can reversibly intercalate and deintercalate lithium ions. The positive electrode active materials can be selected from composite oxides containing lithium and at least one selected from cobalt, manganese, nickel, and iron, preferably lithium-containing composite oxides. The lithium-containing composite oxide is preferably LiM x O y 、LiM x PO4 or LiNi x Co y Mn 1-x-y O2, or one or more of them, where M is a combination of one or more transition metals, 0 < x ≤ 3, 0 < y ≤ 4. Examples of the positive electrode active materials include lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium nickel cobalt manganese aluminate, lithium iron phosphate (LiFePO4), etc.

[0163] The positive electrode active material layer may further include one or two selected from a conductive agent and a binder. The conductive agent is used to improve the electrode conductivity. Examples of the conductive agent for the positive electrode include one or more of conductive carbon black, carbon fiber (CF), acetylene black, Ketjen black, graphene, and carbon nanotubes. The binder for the positive electrode improves the bonding performance between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the binder for the positive electrode include at least one of fluororesin, polypropylene resin, fiber-type binder, rubber-type binder, and polyimide-type binder. In some embodiments, the conductive agent in the positive electrode active material layer is conductive carbon black and single-walled carbon nanotubes, and the binder is polyvinylidene fluoride. The mass ratio of each component in the positive electrode active material layer can be conventional.

[0164] The positive electrode active material layer is obtained by coating a positive electrode slurry containing each component of the positive electrode active material layer and a solvent onto the positive electrode current collector, and then through rolling and slitting. The solvent of the positive electrode slurry can be N-methylpyrrolidone (NMP).

[0165] The separator can be a polymer porous separator, an inorganic porous separator, or a polymer-inorganic composite porous separator. The polymer porous separator includes a single-layer polymer porous separator and a multi-layer polymer porous separator.

[0166] The electrolyte includes an organic solvent and an electrolyte salt.

[0167] The organic solvents applicable to the electrolyte of the present invention may include carbonate solvents, carboxylate solvents, ether solvents or other aprotic solvents. In some embodiments, the electrolyte contains carbonate solvents. In the electrolyte of the present invention, the mass of the carbonate solvents may be 80% - 100% of the total mass of the organic solvents, such as 85%, 90%, 95%. Examples of the carbonate solvents include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, etc. In some embodiments, the organic solvents are selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate. In some embodiments, the organic solvents contain at least one cyclic carbonate and at least one chain carbonate. Examples of the cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, etc. Examples of the chain carbonates include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.

[0168] The electrolyte salt may include or be selected from lithium salts. The lithium salt may be selected from one or more of organic lithium salts and inorganic lithium salts. In some embodiments, the electrolyte salt is selected from at least one of LiPF6, LiBF4, LiFSI, LiTFSI, LiBOB, LiODFB and LiPO2F2. In some embodiments, the concentration of the electrolyte salt in the electrolyte is 0.5 - 2 mol / L, such as 1 mol / L, 1.5 mol / L.

[0169] The battery of the present application further includes a packaging case for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the art in a lithium-ion battery. The present application does not limit the above other components. The present application has no particular limitation on the packaging case, and it may be a packaging case well-known in the art as long as it can achieve the purpose of the present application.

[0170] The present invention has no special limitation on the preparation method of the battery, and the technical solution of preparing a negative electrode material into a battery such as a secondary battery well-known to those skilled in the art can be adopted.

[0171] It should be understood that since the battery provided by the present application includes the negative electrode sheet provided by the first aspect of the present invention or the negative electrode sheet prepared by the preparation method provided by the second aspect of the present invention, the beneficial effects of the negative electrode sheet or its preparation method described in any of the above embodiments are applicable to the battery.

[0172] [Power-consuming device]

[0173] In a fourth aspect of the present invention, an electrical device is provided, which includes the battery described in the third aspect of the present invention.

[0174] The use of the battery of the present application is not particularly limited, and it can be used in any electrical device known in the prior art. In some embodiments, the battery of the present application can be used in, but not limited to, laptop computers, pen input computers, mobile computers, e-book players, mobile phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal TVs, portable cleaners, portable CD players, minidiscs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, drones, and lithium-ion capacitors, etc.

[0175] It should be understood that since the electrical device provided by the present application includes the battery described in the third aspect of the present invention, the beneficial effects of the negative electrode sheet or its preparation method described in any of the above embodiments are applicable to this electrical device.

[0176] The method of the present invention will be described below through specific examples. It should be understood that these examples are used to illustrate the basic principles, main features, and advantages of the present invention, and the present invention is not limited by the scope of the following examples; the implementation conditions adopted in the examples can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0177] Example 1:

[0178] (1) Preparation of the first active material layer slurry:

[0179] Prepare a first active material layer slurry from silicon-carbon material (silicon: graphite = 2:8), conductive carbon black, SBR, and CMC according to a mass ratio of 97:0.5:1.5:1. The particle sizes of the silicon and graphite are in the ranges of 1 - 5 μm and 5 - 10 μm respectively, and the solid content is 45%.

[0180] (2) Preparation of the second active material layer slurry:

[0181] Prepare a second active material layer slurry from silicon-carbon material (silicon: graphite = 8:2), conductive carbon black, SBR, and CMC according to a mass ratio of 97:0.5:1.5:1. The D50 of the silicon and graphite are in the ranges of 7 - 10 μm and 15 - 20 μm respectively, and the solid content is 45%.

[0182] (3) Preparation of the safety coating slurry:

[0183] Al(NO3)3 and Mg(NO3)2 were added to absolute ethanol at a molar ratio of 4:2 and left to stand for a period of time. Then, it was heated under reflux to dissolve all the powder. After the mixture was cooled to room temperature, tetraethyl orthosilicate (TEOS) and an ethanol solution (the volume ratio of TEOS to ethanol was 1:4; the molar ratio of TEOS to aluminum nitrate was 5:4) were added and stirred evenly to obtain a sol. A 37 wt% Li salt (lithium hexafluorophosphate) was added during the sol stage and stirred thoroughly. Thereafter, a mixed solution of ammonia water or nitric acid and ethanol was added while stirring to adjust the pH of the solution to 6, forming a three-dimensional networked cordierite ceramic gel. The secondary gel was left to stand at room temperature for 8 h, dried at 80 °C, and then the organic matter and moisture were removed at 200 °C. Finally, it was calcined at 600 °C for 2 h, and the obtained powder was put into a ball mill and ground thoroughly to obtain cordierite ceramic powder;

[0184] The cordierite ceramic powder and a conductive agent (carbon black) were mixed at a mass ratio of 1:0.05 and dry-stirred in a stirring kettle for 30 min. Then, deionized water was added (until the solid content was 10 wt%) and stirred for another 30 min. During this period, a binder (PVDF) and a silicone resin adhesive were dispersed in deionized water at a ratio of 19:1 to make a glue solution with a solid content of 15 wt%. After the cordierite slurry was stirred, the glue solution was added (the ratio of cordierite, conductive agent, binder, and silicone resin adhesive in the glue solution was 75:5:19:1), and then stirring was continued for 2 h before discharging. The particle size of the cordierite ceramic was in the range of 50 nm < D90 < 100 nm, and the specific surface area was in the range of 2 - 3 m 2 / g, obtaining a safety slurry with a solid content of 40%.

[0185] (4) Preparation of the negative electrode sheet:

[0186] A double-layer die head was used to uniformly coat a first active material layer and a second active material layer on a 6-μm-thick copper foil, followed by drying treatment. After drying, the safety slurry was continuously coated at a coating speed of 5 m / min. After coating, it was dried in a five-stage oven, and the temperature of each oven section was 90 °C, 95 °C, 100 °C, 95 °C, and 90 °C respectively; the thickness of the first negative electrode active material layer was 50 μm, the thickness of the second negative electrode active material layer was 30 μm, and the thickness of the safety coating was 3 μm; the coating was repeated to complete the coating of both surfaces of the copper foil, and then a roll press was used for pressure treatment to obtain a negative electrode sheet with a compaction density of 1.65 g / cm 3 of the negative electrode sheet.

[0187] (5) Preparation of the positive electrode sheet:

[0188] The positive electrode active material LiNi x Co y Mn 1-x-yO2, binder PVDF, and conductive agent Super P were dissolved in N-methylpyrrolidone (NMP) in a mass ratio of 97:1.1:1.9 and stirred evenly to form a slurry, which was evenly coated on both surfaces of the positive current collector aluminum foil. It was baked at 100 - 150 °C for 30 min, and then made into the positive electrode sheet of the lithium-ion battery after cold pressing and slitting. The compaction density was 3.5 g / cm 3 。

[0189] (6) Preparation of lithium-ion battery:

[0190] The negative electrode sheet and positive electrode sheet prepared by the above method, as well as a separator (selected from a composite separator of PP / PE substrate + single-sided ceramic + double-sided coating (9 + 3 + 3 + 3)) were provided, and then a core with a wound structure with the positive electrode on the outside was wound using a winding machine. It was encapsulated with an aluminum-plastic film, baked for 48 h under vacuum to remove moisture, and then an electrolyte was injected (in the electrolyte, the solvent, solute, and additive accounted for 89%, 10%, and 1% respectively. The solvent was selected as ethylene carbonate and dimethyl carbonate, with a ratio of 1:2. The solutes LiPF6 and LiBF4 had a ratio of 1:1, and the additive was vinylene carbonate (VC)). Then, the battery was subjected to conventional formation and sorting to obtain a square soft-pack lithium-ion battery.

[0191] Example 2:

[0192] The difference between Example 2 and Example 1 is only that: in step (3), cordierite ceramic powder with D90 ≤ 50 nm was selected to prepare the safety coating.

[0193] Example 3:

[0194] The difference between Example 3 and Example 1 is only that: in step (3), cordierite ceramic powder with 200 nm ≤ D90 ≤ 400 nm was selected to prepare the safety coating.

[0195] Example 4:

[0196] The difference between Example 4 and Example 1 is only that: in step (3), cordierite ceramic, PVDF, and carbon black were selected in a mass ratio of 80:18:2 to prepare the safety coating.

[0197] Example 5:

[0198] The difference between Example 5 and Example 1 is only that: in step (3), cordierite ceramic, PVDF, and carbon black were selected in a mass ratio of 95:4:1 to prepare the safety coating.

[0199] Comparative Example 1:

[0200] The difference between Comparative Example 1 and Example 1 is only as follows: in step (1), the D50 of silicon and graphite in the first active material layer is 15 - 20 μm and 20 - 25 μm respectively; in step (2), the D50 of silicon and graphite in the second active material layer is 20 - 25 μm and 25 - 30 μm respectively.

[0201] Comparative Example 2:

[0202] The difference between Comparative Example 2 and Example 1 is only as follows: in step (1), the D50 of silicon and graphite in the first active material layer is 0.05 - 1 μm and 0.01 - 1 μm respectively; in step (2), the D50 of silicon and graphite in the second active material layer is 1 - 5 μm and 5 - 10 μm respectively.

[0203] Comparative Example 3:

[0204] The difference between Comparative Example 3 and Example 1 is only as follows: in step (3), mullite ceramic (3Al2O3·2SiO2) is selected to replace cordierite ceramic.

[0205] Comparative Example 4:

[0206] The difference between Comparative Example 4 and Example 1 is only as follows: in step (3), spinel ceramic (MgO·Al2O3) is selected to replace cordierite ceramic.

[0207] Comparative Example 5:

[0208] The difference between Comparative Example 5 and Example 1 is only as follows: in step (3), no silicone resin adhesive is added, and only PVDF is used as the binder to make the safety coating.

[0209] Performance Test

[0210] 1. Peel strength test: The negative electrode sheets obtained in the examples and comparative examples (the width of the test negative electrode sheet is 3 cm and the length is 20 cm) are respectively fixed on the clamping jaws of the tensile machine. One end of the tape is adhered to the electrode sheet, and the other end is folded 180° and then fixed on the lower clamping jaw of the tensile machine. It is pulled at a test rate of 50 mm / min, and the peel strength (N / m) is measured by the force required to continuously peel the tape from the electrode sheet.

[0211] 2. First efficiency test: During formation, it is charged with a current of 0.1C until 85% SOC, and the charging capacity at this time is recorded as C1; after standing for 5 minutes, during grading, it is continued to be charged with a small current of 0.05C until 4.25V, and the charging capacity at this time is recorded as C2; after standing for 5 minutes, it is discharged at a constant current of 1C until 2.8V, and then after standing for 5 minutes, it is discharged at a constant current of 0.2C until 2.8V, and the total discharge capacity of the two steps is recorded as C3. The charge and discharge capacities obtained from the battery are respectively collected, and the first efficiency = ((C1 + C2) / C3) * 100%.

[0212] 3. Capacity retention after 500 cycles at 1C: Charge the battery at 1C constant current to 4.25V, then switch to 4.25V constant voltage charging until the current drops to 0.05C, then cut off the cycle. After 10 minutes, discharge the battery at 1C constant current to 2.2V. This constitutes one cycle, and the discharge capacity at this point is recorded as C0. Repeat the charge-rest-discharge cycle. Record the discharge capacity Cn at the 500th cycle. Capacity retention = (Cn / C0) * 100%.

[0213] Volume Growth Test after 30 Days of Storage at 70°C: Before testing, the battery's initial volume was measured. The battery was then charged at a constant current rate of 1C to 4.25V, followed by constant voltage charging with a cutoff current of 0.05C. The battery was then stored in a 70°C incubator for 30 days, and the capacity and volume of the battery were measured. The 30-day volume growth rate = (volume out of the incubator / initial volume) * 100%, where volume was measured using the water displacement method.

[0214] 5.130°C Hot Box Test: The battery was charged to 4.25V using a constant current of 1C. The battery cells were then clamped with clamps and placed in a heated explosion-proof box. The temperature in the box was heated to 130°C and maintained for 60 minutes. Each example was tested 10 times in parallel. Whether the hot box test passed was determined by whether a fire occurred. The result was recorded as x / 10 Pass (x out of 10 parallel tests passed).

[0215] 6. Needle Penetration Test: A needle penetration test was conducted using a needle penetration tester, charging at a constant current and constant voltage of 0.2C to a charge cutoff voltage of 4.25V. Using the Dongguan Bell Battery Penetration Tester, a 3mm diameter, rust-free steel needle was used to penetrate the center of the largest surface of the battery at a speed of 2m / min for at least 1 hour. Each example was tested 10 times in parallel. Pass or fail was determined based on whether or not a fire occurred. The final result was recorded as x / 10 passes (x out of 10 parallel tests).

[0216] The results of the above performance tests are shown in Table 1.

[0217] Table 1

[0218]

[0219] As shown in the table above, the negative electrode sheets and batteries obtained in Examples 1-5 exhibited superior performance compared to Comparative Examples 1-5 in terms of peel strength, initial efficiency, capacity retention, volume growth rate, thermal stability, and needle penetration tests. Example 1 exhibited the best overall performance. The results showed that gas production increased during high-temperature storage due to the smaller cordierite particles, resulting in fewer gas storage channels in the system. However, this did not affect safety performance.

[0220] In Example 2, the gas generation during high-temperature storage increased somewhat. This was because the cordierite particles were smaller, resulting in fewer gas storage channels in the system, but it did not affect the safety performance.

[0221] In Example 3, the volume growth rate and peel strength showed a pattern exactly opposite to that of Example 2, but the passing rate of the needle-punching test decreased. This might be because the particles were too large, resulting in poor adhesion, and cordierite particles scattered after needle punching.

[0222] Example 4 showed that when the binder content decreased, the peel strength decreased significantly. At this time, the safety coating was prone to peeling off after repeated volume expansion, resulting in a decline in cycle and safety performance.

[0223] Example 5 showed that when the binder content increased, the overall peel strength did not increase much, indicating that further increasing the binder would not have a significant impact on the peel force of the safety coating.

[0224] Comparative Example 1 showed that the active material with larger particles reduced the capacity retention rate after cycling. This was because the kinetic performance of the large particles was poor, and it might be difficult for active lithium to be released. In addition, the peel strength also decreased. Its failure mainly occurred between the first layer and the second layer of active materials, and the safety coating did not peel off on a large scale, indicating that larger particles could make the safety coating penetrate better, but overly large particles would lead to poor adhesion between the active materials.

[0225] Comparative Example 2 showed that after the particle size of the active material decreased, the peel strength still did not increase. At this time, the failure mainly occurred between the safety coating and the second layer of active materials, indicating that when the particle sizes of the active material and the cordierite particles were not much different, the permeability decreased significantly, making the safety coating prone to peeling off, thus affecting the long-term and safety performance.

[0226] Comparative Example 3 showed that compared with cordierite, mullite had poorer high-temperature gas generation and hot-box performance. This was because mullite had a high coefficient of thermal expansion and a large volume expansion rate at high temperatures, and could not effectively inhibit the expansion of the silicon anode, deteriorating the high-temperature performance.

[0227] Comparative Example 4 showed that compared with cordierite, spinel had poorer peel strength and safety performance. This was because spinel had a high hardness, which resulted in a more brittle safety coating formed by spinel under the same formulation. After the needle-punching test, the safety coating could not effectively extend, causing the positive and negative electrodes to short-circuit, resulting in differences in safety performance.

[0228] Comparative Example 5 shows that after the silicone resin adhesive is not added, all its properties deteriorate significantly. This is because the unbonded cordierite is extremely easy to fall off, and the bonding between the electrode sheets is not tight, resulting in difficult lithium ion transmission and deteriorated kinetics. In addition, the peel strength of the safety coating without the silicone resin adhesive drops significantly, which also has a certain impact on the safety performance.

[0229] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners included in the claims. Without departing from the scope of the present disclosure, various deformations and changes can also be made on the basis of the above embodiments. Similarly, the various technical features of the above embodiments can also be arbitrarily combined to form additional embodiments of the present invention that may not be clearly described. Therefore, the above embodiments only represent several implementation manners of the present invention and do not limit the protection scope of the present invention patent.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector, and a first active material layer, a second active material layer, and a safety coating that are sequentially stacked on at least one surface of the current collector; wherein, The first active material layer includes a first negative electrode active material, and the first negative electrode active material includes a first silicon-based material and a first carbon material; The second active material layer includes a second negative electrode active material, and the second negative electrode active material includes a second silicon-based material and a second carbon material; The material of the safety coating includes cordierite.

2. The negative electrode sheet according to claim 1, wherein, The material of the safety coating further includes a first binder and a first conductive agent; the safety coating satisfies at least one of the following characteristics (1) to (5): (1) The D90 particle size range of the cordierite is 50 nm to 200 nm; the specific surface area of the cordierite is 1 m 2 / g to 5 m 2 / g; (2) A lithium salt is loaded in the cordierite, and the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)amide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(oxalato)borate, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium phosphate, and lithium difluorophosphate; (3) The first binder includes one or more of polyvinylidene fluoride, silicone resin adhesive, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinyl alcohol; preferably, the first binder is polyvinylidene fluoride and silicone resin adhesive, and the mass ratio of polyvinylidene fluoride to silicone resin adhesive is (10-20):(0.3-1); (4) The first conductive agent includes one or more of conductive carbon black, carbon fiber, graphene, and carbon nanotubes; (5) The mass ratio of the cordierite, the first binder, and the first conductive agent is (75-85):(10.3-21):(1-5); (6) The thickness of the safety coating is 2 μm to 4 μm.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The first carbon material includes first graphite; the material of the first active material layer further includes a second conductive agent, a second binder, and a first thickening agent; the first active material layer satisfies at least one of the following characteristics (1) to (7): (1) The first silicon-based material is selected from one or more of prelithiated silicon monoxide, porous nanosilicon, and silicon-carbon materials; the particle size D50 of the first silicon-based material is 1 μm to 10 μm; (2) The particle size D50 of the first graphite is 1 μm to 15 μm; (3) The mass ratio of the first graphite to the first silicon-based material is (70-80):(20-30); (4) The second conductive agent includes one or more of conductive carbon black, carbon fiber, graphene, and carbon nanotubes; (5) The second binder includes one or more of styrene-butadiene rubber, polyvinylidene fluoride, and polyvinyl alcohol; (6) The first thickening agent includes one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, and xanthan gum; (7) The mass ratio of the first negative electrode active material, the second conductive agent, the second binder, and the first thickening agent is (95-99):(0.1-2):(0.5-3):(0.1-2); (8) The thickness of the first active material layer is 45 μm to 55 μm.

4. The negative electrode sheet according to claim 1 or 2, characterized in that, The second carbon material includes second graphite; the material of the second active material layer further includes a third conductive agent, a third binder, and a second thickening agent; the second active material layer satisfies at least one of the following characteristics (1) to (7): (1) The second silicon-based material includes one or more of pre-lithiated silicon monoxide, porous nano-silicon, and silicon-carbon material; the particle size D50 of the second silicon-based material is 5 μm to 15 μm; (2) The particle size D50 of the second graphite is 10 μm to 25 μm; (3) The mass ratio of the second graphite to the second silicon-based material is (20 to 30):(70 to 80); (4) The third conductive agent includes one or more of conductive carbon black, carbon fiber, graphene, and carbon nanotubes; (5) The third binder includes one or more of styrene-butadiene rubber, polyvinylidene fluoride, and polyvinyl alcohol; (6) The second thickening agent includes one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, and xanthan gum; (7) The mass ratio of the second negative electrode active material, the third conductive agent, the third binder, and the second thickening agent is (95 to 99):(0.1 to 2):(0.5 to 3):(0.1 to 2); (8) The thickness of the second active material layer is 25 μm to 35 μm.

5. The negative electrode sheet according to claim 1, wherein, The compaction density of the negative electrode sheet is 1.5 g / cm 3 ~1.8 g / cm 3 .

6. A method for preparing a negative electrode sheet according to any one of claims 1-5, characterized in that, The method includes: S1: Prepare the cordierite; S2: Mix the cordierite obtained in step S1 with a first conductive agent, add solvent A to obtain a cordierite slurry; disperse the first binder in solvent B to obtain a glue solution; add the cordierite slurry to the glue solution and mix to obtain a safety coating slurry; Mix the first negative electrode active material, a second conductive agent, a second binder, and a first thickening agent in solvent C to obtain a first active material layer slurry; Mix the second negative electrode active material, a third conductive agent, a third binder, and a second thickening agent in solvent D to obtain a second active material layer slurry; S3: Coating the first active material layer slurry, the second active material layer slurry, and the safety coating slurry obtained in step S2 on the current collector in sequence to obtain the negative electrode sheet.

7. The preparation method according to claim 6, characterized in that, In step S1, the steps of preparing the cordierite include: adding an aluminum source and a magnesium source to anhydrous ethanol for dissolution, adding an organosilicon source and an ethanol solution to obtain a sol; adding a lithium salt and performing pre-burning with lithium; adding a pH regulator to obtain a cordierite ceramic gel, and calcining and grinding to obtain the cordierite.

8. The preparation method according to claim 7, characterized in that, The steps of preparing the cordierite satisfy one or more of the following characteristics (1) to (11): (1) The aluminum source includes one or more of aluminum nitrate, aluminum sulfate, and aluminum hydroxide; (2) The magnesium source includes one or more of magnesium nitrate, magnesium sulfate, and magnesium hydroxide; (3) The organosilicon source includes one or more of tetraethyl orthosilicate and sodium silicate; (4) The molar ratio of the aluminum source, the magnesium source, and the organosilicon source is 4:2:5; (5) The volume ratio of the organosilicon source to ethanol is 1:(3 to 5); (6) The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)amide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(oxalato)borate, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium phosphate, and lithium difluorophosphate; (7) The mass of the lithium salt accounts for 30% - 40% of the mass of the sol; (8) The temperature of the mixed lithium pre - calcination is 300°C - 500°C; (9) The pH regulator includes a mixed solution of nitric acid and ethanol or ammonia water; (10) The pH of the cordierite ceramic gel is 5 - 7; (11) The temperature of the calcination is 500°C - 700°C, and the time of the calcination is 1h - 3h.

9. The preparation method according to claim 6, characterized in that, In step S2, the solvent A is selected from deionized water; the solvent B is selected from deionized water; the solvent C is selected from deionized water; the solvent D is selected from deionized water.

10. A battery, characterized in that, It includes the negative electrode sheet according to any one of claims 1 - 5 or the negative electrode sheet prepared by the preparation method according to any one of claims 6 - 9.

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