Negative plate, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, in particular to a negative plate, a preparation method thereof and a battery. The negative electrode plate comprises a current collector, a first negative electrode coating, a second negative electrode coating and a third negative electrode coating, and the content of a first silicon-based material in the first negative electrode coating is larger than that of a second silicon-based material in the second negative electrode coating; the first functional additive and the second functional additive have empty shell structures; the first functional additive comprises a conductive polymer; the second functional additive includes a viscous polymer. In the three coatings of the negative electrode plate, through reasonable matching of all substances, the overall porosity, structural strength and conductivity of the electrode plate are effectively improved, so that the electrode plate has relatively excellent fast charging performance and relatively long service life.

Description

Technical Field

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

[0002] In recent years, with the continuous development of science and technology and economy, people's demand for lithium-ion batteries that take into account both fast charging performance and energy density is also increasing. At present, the use of multi-layer coating to match silicon-based materials with higher capacity with graphite materials with stronger fast charging capabilities has become an effective means to improve the overall performance of batteries. However, during the rolling process, the difference in the force and deformation degree of different layers of the multi-layer coating will cause the local porosity to be too low, affecting the electrolyte infiltration effect, and further leading to a significant deterioration in the fast charging capacity and cycle performance. For example, Chinese patent technology CN113745463A discloses that a thin porous diffusion layer with high porosity is set between the upper and lower layers of the negative electrode sheet to improve the electrolyte infiltration effect near the current collector layer. However, when the lower layer itself is relatively thick or the pores are insufficient, the improvement effect of the porous diffusion layer is limited.

[0003] Therefore, it is necessary to take effective measures to improve the overall wetting effect of the electrode, so that the capacity and fast charging capabilities of each layer can be fully utilized, thereby improving the performance and service life of the electrode. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially address one of the technical problems in the related art. To this end, the present invention provides a negative electrode sheet, a method for preparing the same, and a battery, which can improve the overall wettability of the electrode sheet, increase the capacity of each layer, and enhance the fast charging performance and service life of the negative electrode sheet.

[0005] In order to solve the above technical problems, this application is implemented as follows:

[0006] According to one aspect of the present application, an embodiment of the present application provides a negative electrode sheet, the negative electrode sheet comprising:

[0007] current collector;

[0008] a first negative electrode coating, disposed on at least one side of the current collector in a thickness direction, the first negative electrode coating comprising a first carbon-based material, a first silicon-based material, and a first functional additive;

[0009] a second negative electrode coating, disposed on a surface of the first negative electrode coating away from the current collector, the second negative electrode coating comprising a second carbon-based material, a second silicon-based material, and a second functional additive; and

[0010] a third negative electrode coating, disposed on a surface of the second negative electrode coating away from the first negative electrode coating, the third negative electrode coating comprising a third carbon-based material;

[0011] wherein the content of the first silicon-based material in the first negative electrode coating is greater than the content of the second silicon-based material in the second negative electrode coating;

[0012] The first functional additive and the second functional additive both have a hollow shell structure;

[0013] The first functional additive includes a conductive polymer; the second functional additive includes a sticky polymer.

[0014] In some embodiments, the conductive polymer includes at least one of polyaniline, polypyrrole, or poly(ethylenedioxythiophene).

[0015] In some embodiments, the thickness of the first functional additive shell is 50-100 nm.

[0016] In some embodiments, the inner diameter of the hollow shell of the first functional additive is 300-600 nm.

[0017] In some embodiments, the first functional additive shell has a porous structure.

[0018] In some embodiments, the porosity of the first functional additive shell is 30-50%.

[0019] In some embodiments, the adhesive polymer includes at least one of polymethyl methacrylate, polyacrylic acid, or polyvinylidene fluoride.

[0020] In some embodiments, the thickness of the second functional additive shell is 50-100 nm.

[0021] In some embodiments, the inner diameter of the hollow shell of the second functional additive is 400-800 nm.

[0022] In some embodiments, the second functional additive shell has a porous structure.

[0023] In some embodiments, the porosity of the hollow shell of the second functional additive is 30-50%.

[0024] In some embodiments, the mass ratio of the first carbon-based material to the first silicon-based material is (50-60):(30-40).

[0025] In some embodiments, the first carbon-based material includes graphite.

[0026] In some embodiments, the graphite includes at least one of natural graphite or artificial graphite.

[0027] In some embodiments, the first silicon-based material includes at least one of a silicon-oxygen composite material, a silicon-carbon composite material, or pure silicon.

[0028] In some embodiments, the first negative electrode coating further includes a first conductive agent and a first binder.

[0029] In some embodiments, the mass ratio of the first carbon-based material, the first silicon-based material, the first functional additive, the first conductive agent and the first binder is (50-60): (30-40): (0.2-1.5): (1-5): (3-6).

[0030] In some embodiments, the surface density of the first negative electrode coating is 20 to 50 g / m 2 .

[0031] In some embodiments, the thickness of the first negative electrode coating is 10 to 30 μm.

[0032] In some embodiments, the porosity of the first negative electrode coating layer is 26-30%.

[0033] In some embodiments, the mass ratio of the second carbon-based material to the second silicon-based material is (70-80):(10-30).

[0034] In some embodiments, the second carbon-based material includes graphite.

[0035] In some embodiments, the graphite includes at least one of natural graphite or artificial graphite.

[0036] In some embodiments, the second silicon-based material includes at least one of a silicon-oxygen composite material, a silicon-carbon composite material, or pure silicon.

[0037] In some embodiments, the second negative electrode coating further includes a second conductive agent and a second binder.

[0038] In some embodiments, the mass ratio of the second carbon-based material, the second silicon-based material, the second functional additive, the second conductive agent and the second binder is (70-80): (10-30): (0.3-1.8): (1-5): (3-6).

[0039] In some embodiments, the surface density of the second negative electrode coating is 20 to 50 g / m 2 .

[0040] In some embodiments, the second negative electrode coating has a thickness of 10 to 30 μm.

[0041] In some embodiments, the porosity of the second negative electrode coating layer is 28-32%.

[0042] In some embodiments, the third carbon-based material includes graphite.

[0043] In some embodiments, the graphite includes at least one of natural graphite or artificial graphite.

[0044] In some embodiments, the third negative electrode coating further includes a third conductive agent and a third binder.

[0045] In some embodiments, the mass ratio of the third carbon-based material, the third conductive agent and the third binder is (90-95): (1-5): (3-6).

[0046] In some embodiments, the surface density of the third negative electrode coating is 30 to 80 g / m 2 .

[0047] In some embodiments, the thickness of the third negative electrode coating layer is 20 to 50 μm.

[0048] In some embodiments, the third negative electrode coating layer has a porous structure.

[0049] In some embodiments, the porosity of the third negative electrode coating layer is 30-34%.

[0050] In some embodiments, the pore structure of the third negative electrode coating has a pore size of 800 to 1000 nm.

[0051] According to another aspect of the present application, an embodiment of the present application provides a method for preparing a negative electrode sheet, comprising the following steps:

[0052] Coating a first negative electrode slurry on at least one side of the current collector to obtain a first negative electrode coating;

[0053] coating a second negative electrode slurry on the surface of the first negative electrode coating to obtain a second negative electrode coating;

[0054] coating a third negative electrode slurry on the surface of the second negative electrode coating to obtain a third negative electrode coating;

[0055] Roll-pressing, unwinding and baking the current collector coated with the first negative electrode coating, the second negative electrode coating and the third negative electrode coating;

[0056] Wherein, the first negative electrode slurry includes a first carbon-based material, a first silicon-based material and a first functional additive source;

[0057] The second negative electrode slurry includes a second carbon-based material, a second silicon-based material, and a second functional additive source;

[0058] The third negative electrode slurry includes a third carbon-based material.

[0059] In some embodiments, the third negative electrode slurry further includes a pore former.

[0060] In some embodiments, the pore former includes at least one of ammonium carbonate, urea, or oxalic acid.

[0061] In some embodiments, the mass ratio of the third carbon-based material, the third conductive agent, the third binder and the pore-forming agent is (90-95): (1-5): (3-6): (4-8).

[0062] In some embodiments, the preparation of the first negative electrode slurry includes: uniformly mixing a first carbon-based material, a first silicon-based material, a first functional additive source, a first conductive agent, and a first binder in a solvent to obtain the first negative electrode slurry.

[0063] In some embodiments, the mass ratio of the first carbon-based material, the first silicon-based material, the first functional additive source, the first conductive agent and the first binder is (50-60): (30-40): (2-5): (1-5): (3-6).

[0064] In some embodiments, the preparation of the second negative electrode slurry includes: uniformly mixing a second carbon-based material, a second silicon-based material, a second functional additive source, a second conductive agent, and a second binder in a solvent to obtain a second negative electrode slurry.

[0065] In some embodiments, the mass ratio of the second carbon-based material, the second silicon-based material, the second functional additive source, the second conductive agent and the second binder is (70-80): (10-30): (3-6): (1-5): (3-6).

[0066] In some embodiments, the preparation of the third negative electrode slurry includes: uniformly mixing a third carbon-based material, a third conductive agent, a third binder, and a pore-forming agent in a solvent to obtain the third negative electrode slurry.

[0067] In some embodiments, the compaction density of the roller is 1.3 to 1.6 g / cm 3 .

[0068] In some embodiments, the uncoiling and baking temperature is 130-170° C., and the tape travel speed is 5-20 m / min.

[0069] In some embodiments, the first negative electrode slurry is coated on the surface of the current collector, and after drying, a first negative electrode coating is formed on the surface of the current collector; the second negative electrode slurry is coated on the first negative electrode coating, and after drying, a second negative electrode coating is formed on the surface of the first negative electrode coating; the third negative electrode slurry is coated on the second negative electrode coating and dried; the current collector coated with the first negative electrode coating, the second negative electrode coating, and the third negative electrode coating is roll-pressed, uncoiled, and baked to obtain a negative electrode sheet.

[0070] In some embodiments, the first functional additive source has a core-shell structure.

[0071] In some embodiments, the inner core of the first functional additive source includes at least one of ammonium carbonate, urea, or oxalic acid.

[0072] In some embodiments, the shell material of the first functional additive source includes at least one of polyaniline, polypyrrole, or poly(ethylenedioxythiophene).

[0073] In some embodiments, the second functional additive source has a core-shell structure.

[0074] In some embodiments, the inner core of the second functional additive source includes at least one of ammonium carbonate, urea, or oxalic acid.

[0075] In some embodiments, the shell material of the second functional additive source includes at least one of polymethyl methacrylate, polyacrylic acid, or polyvinylidene fluoride.

[0076] In some embodiments, the method for preparing the first functional additive source includes: mixing a suspension containing a first core material and a solution containing a first shell material to obtain the first functional additive source.

[0077] In some embodiments, the first core material includes at least one of ammonium carbonate, urea, or oxalic acid.

[0078] In some embodiments, the first shell material includes at least one of polyaniline, polypyrrole, or poly(ethylenedioxythiophene).

[0079] In some embodiments, the mixing includes stirring, and the stirring time is 40 to 80 minutes and the temperature is 25 to 45°C.

[0080] In some embodiments, the preparation method of the second functional additive source includes: mixing a shell material monomer, an emulsifier, a second core material, and an initiator, and reacting the mixture to obtain the second functional additive source.

[0081] In some embodiments, the shell material monomer includes at least one of acrylic acid, methyl methacrylate, or vinylidene fluoride.

[0082] In some embodiments, the second core material includes at least one of ammonium carbonate, urea, or oxalic acid.

[0083] In some embodiments, the reaction temperature is 45-60° C. and the reaction time is 1-4 h.

[0084] According to another aspect of the present application, an embodiment of the present application provides a battery, including a negative electrode sheet, wherein the negative electrode sheet is the aforementioned negative electrode sheet, or a negative electrode sheet prepared according to the aforementioned preparation method.

[0085] The implementation of the technical solution of the present invention has at least the following beneficial effects:

[0086] In the negative electrode sheet of the present application, the first functional additive has a hollow shell structure. While increasing the porosity of the first negative electrode coating, the conductive polymer remaining in the pores acts as a conductive agent to make up for the defect of insufficient electron conduction capacity of this layer due to the large silicon content in the first negative electrode coating. The second functional additive has a hollow shell structure. While increasing the porosity of the second negative electrode coating, the sticky polymer remaining in the pores can enhance the bonding force between particles around the pores, improve the mechanical strength of the second negative electrode coating, thereby enhancing the overall structural stability of the electrode sheet and inhibiting electrode cracks caused by the rebound difference between particles in different layers. Only carbon-based materials are used as active materials in the third negative electrode coating, which has good conductivity and small rebound. In the three-layer coating of the negative electrode sheet of the present application, the overall porosity, structural strength and conductivity of the electrode sheet are effectively improved through the reasonable combination of various substances, so that the electrode sheet has relatively excellent fast charging performance and a long service life.

[0087] Additional aspects and advantages of the present application will be given in part in the following description and in part will become obvious from the following description or will be learned through practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 Shown is an electron microscope image of the first functional additive provided in Example 1 of the present invention;

[0089] Figure 2 Shown is an electron microscope image of the first functional additive provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0090] The present application will be further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0091] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0092] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0093] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0094] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0095] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0096] [Negative electrode]

[0097] In the related art, a thin porous diffusion layer with high porosity is set between the upper and lower layers of the negative electrode to improve the electrolyte infiltration effect near the current collector layer. However, when the lower layer itself is thick or has insufficient pores, the improvement effect of the porous diffusion layer is limited.

[0098] In view of this, an embodiment of the present application provides a negative electrode sheet, the negative electrode sheet comprising:

[0099] current collector;

[0100] A first negative electrode coating is provided on at least one side of the current collector in the thickness direction, the first negative electrode coating comprising a first carbon-based material, a first silicon-based material and a first functional additive;

[0101] a second negative electrode coating, disposed on a surface of the first negative electrode coating away from the current collector, the second negative electrode coating comprising a second carbon-based material, a second silicon-based material, and a second functional additive; and

[0102] a third negative electrode coating, disposed on a surface of the second negative electrode coating away from the first negative electrode coating, the third negative electrode coating comprising a third carbon-based material;

[0103] wherein the content of the first silicon-based material in the first negative electrode coating is greater than the content of the second silicon-based material in the second negative electrode coating;

[0104] The first functional additive and the second functional additive both have a hollow shell structure;

[0105] The first functional additive includes a conductive polymer; the second functional additive includes a sticky polymer.

[0106] The phrase "the first negative electrode coating is disposed on at least one surface of the current collector along the thickness direction" means that the first negative electrode coating can be disposed on one surface of the current collector along the thickness direction, or on both surfaces of the current collector along the thickness direction. The "surface" here can be the entire area of ​​the current collector or a portion of the current collector. For example, in this embodiment, the surface can be the entire area of ​​the current collector. This is not particularly limited in this application, as long as the objectives of this application can be achieved.

[0107] As an example, the current collector has two surfaces that are opposite to each other in its thickness direction, and the first negative electrode coating is disposed on the two opposing surfaces of the current collector. Furthermore, a second negative electrode coating is formed on the surfaces of the first negative electrode coating on both sides. Still further, a third negative electrode coating is formed on the surfaces of the second negative electrode coating on both sides. It is understood that in other embodiments, the first negative electrode coating can also be laminated on either of the two surfaces of the current collector.

[0108] In the present application, the material of the current collector in the negative electrode sheet is not particularly limited.

[0109] In the present application, in the negative electrode sheet, the content of the first silicon-based material in the first negative electrode coating is greater than the content of the second silicon-based material in the second negative electrode coating, which can improve the overall capacity of the electrode sheet.

[0110] In the negative electrode sheet of the present application, the first functional additive has a hollow shell structure. While increasing the porosity of the first negative electrode coating, the conductive polymer remaining in the pores acts as a conductive agent to make up for the defect of insufficient electron conduction capacity of this layer due to the large silicon content in the first negative electrode coating. The second functional additive has a hollow shell structure. While increasing the porosity of the second negative electrode coating, the sticky polymer remaining in the pores can enhance the bonding force between particles around the pores, improve the mechanical strength of the second negative electrode coating, thereby enhancing the overall structural stability of the electrode sheet and inhibiting electrode cracks caused by the rebound difference between particles in different layers. Only carbon-based materials are used as active materials in the third negative electrode coating, which has good conductivity and small rebound. In the three-layer coating of the negative electrode sheet of the present application, the overall porosity, structural strength and conductivity of the electrode sheet are effectively improved through the reasonable combination of various substances, so that the electrode sheet has relatively excellent fast charging performance and a long service life.

[0111] In some embodiments, the conductive polymer includes, but is not limited to, at least one of polyaniline, polypyrrole, or poly(ethylenedioxythiophene). As an example, the conductive polymer may be polyaniline or polypyrrole.

[0112] In some embodiments, the thickness of the first functional additive shell is 50-100 nm. For example, the thickness of the first functional additive shell can be 50 nm, 70 nm, 90 nm, 100 nm, etc., or any value within the aforementioned range, without specific limitation. Limiting the thickness of the first functional additive shell to this range improves the conductivity of the first negative electrode coating while allowing the core to be completely expelled at high temperatures, ensuring that the first functional additive has a hollow shell structure.

[0113] In some embodiments, the inner diameter of the first functional additive shell is 300-600 nm. As an example, the inner diameter of the first functional additive shell can be 300 nm, 400 nm, 500 nm, 600 nm, etc., or any point within the above range, and is not specifically limited here.

[0114] In some embodiments, the first functional additive shell has a porous structure.

[0115] In some embodiments, the porosity of the first functional additive shell is 30% to 50%. As an example, the porosity of the first functional additive shell can be 30%, 40%, 50%, etc., or any point within the above range, which is not specifically limited here.

[0116] In some embodiments, the adhesive polymer includes, but is not limited to, at least one of polymethyl methacrylate, polyacrylic acid, or polyvinylidene fluoride. As an example, the adhesive polymer may be polymethyl methacrylate or polyacrylic acid.

[0117] In some embodiments, the thickness of the second functional additive shell is 50-100 nm. For example, the thickness of the second functional additive shell can be 50 nm, 70 nm, 90 nm, 100 nm, etc., or any value within the aforementioned range, without specific limitation. Limiting the thickness of the second functional additive shell to this range improves the adhesion of the second negative electrode coating while allowing the core to be completely expelled at high temperatures, ensuring that the first functional additive has an empty shell structure.

[0118] In some embodiments, the inner diameter of the second functional additive shell is 400-800 nm. As an example, the inner diameter of the second functional additive shell can be 400 nm, 500 nm, 600 nm, 800 nm, etc., or any value within the above range, and is not specifically limited here.

[0119] In some embodiments, the second functional additive shell has a porous structure.

[0120] In some embodiments, the porosity of the second functional additive shell is 30% to 50%. As an example, the porosity of the second functional additive shell can be 30%, 40%, 50%, etc., or any point within the above range, which is not specifically limited here.

[0121] It should be noted that by limiting the internal diameter and porosity of the first functional additive and the second functional additive to the above ranges, the electrode piece as a whole can have a certain porosity, thereby ensuring that the electrode piece has a better wetting effect.

[0122] In some embodiments, the mass ratio of the first carbon-based material to the first silicon-based material is (50-60): (30-40). As an example, the mass ratio of the first carbon-based material to the first silicon-based material can be 50:30, 55:35, 60:40, etc., and of course it can also be a ratio within the above range, which is not specifically limited here. In the first negative electrode coating, the proportion of silicon-based material is relatively high, which can maximize the capacity of the electrode.

[0123] In some embodiments, the first carbon-based material includes graphite.

[0124] In some embodiments, the graphite includes, but is not limited to, at least one of natural graphite and artificial graphite. As an example, the graphite can be natural graphite, artificial graphite, or a mixture of the two.

[0125] In some embodiments, the first silicon-based material includes, but is not limited to, at least one of a silicon-oxygen composite material, a silicon-carbon composite material, or pure silicon. As an example, the first silicon-based material may be a silicon-oxygen composite material or a silicon-carbon composite material.

[0126] In some embodiments, the first negative electrode coating further includes a first conductive agent and a first binder.

[0127] In some embodiments, the mass ratio of the first carbon-based material, the first silicon-based material, the first functional additive, the first conductive agent, and the first binder is (50-60): (30-40): (0.2-1.5): (1-5): (3-6). As an example, the mass ratio of the first carbon-based material, the first silicon-based material, the first functional additive, the first conductive agent, and the first binder can be 50:30:0.2:1:3, 55:35:1:3:5, 60:40:1.5:5:6, etc. Of course, it can also be any ratio within the above range, and is not specifically limited here.

[0128] In some embodiments, the surface density of the first negative electrode coating is 20 to 50 g / m 2 As an example, the surface density of the first negative electrode coating can be 20 g / m 2 , 30g / m 2 , 40g / m 2 , 50g / m 2 Of course, it can also be a certain point value within the above range, which is not specifically limited here.

[0129] In some embodiments, the thickness of the first negative electrode coating is 10-30 μm. As an example, the thickness of the first negative electrode coating can be 10 μm, 20 μm, 30 μm, etc., or any value within the above range, which is not specifically limited here.

[0130] In some embodiments, the porosity of the first negative electrode coating is 26% to 30%. As an example, the porosity of the first negative electrode coating can be 26%, 28%, 30%, etc., or any point within the above range, which is not specifically limited here.

[0131] In some embodiments, the pore structure of the first negative electrode coating has a pore size of 600 to 800 nm. As an example, the pore size of the first negative electrode coating can be 600 nm, 700 nm, 800 nm, etc., or any point within the above range, which is not specifically limited here.

[0132] In some embodiments, the mass ratio of the second carbon-based material and the second silicon-based material is (70-80): (10-30). As an example, the mass ratio of the second carbon-based material and the second silicon-based material can be 70:10, 75:20, 80:30, etc., and of course it can also be a ratio within the above range, which is not specifically limited here. In the second negative electrode coating, the proportion of silicon-based materials is relatively low (compared with the first negative electrode coating), which can improve the capacity while ensuring fast charging capability. At the same time, the appropriate amount of silicon doping can ensure good bonding between the binder and the upper and lower layers, thereby improving the stability of the pole piece structure.

[0133] In some embodiments, the second carbon-based material includes graphite.

[0134] In some embodiments, the graphite includes, but is not limited to, at least one of natural graphite and artificial graphite. As an example, the graphite can be natural graphite or artificial graphite.

[0135] In some embodiments, the second silicon-based material includes, but is not limited to, at least one of a silicon-oxygen composite material, a silicon-carbon composite material, or pure silicon. For example, the second silicon-based material can be a silicon-oxygen composite material, a silicon-carbon composite material, or a mixture of a silicon-oxygen composite material and a silicon-carbon composite material.

[0136] In some embodiments, the second negative electrode coating further includes a second conductive agent and a second binder.

[0137] In some embodiments, the mass ratio of the second carbon-based material, the second silicon-based material, the second functional additive, the second conductive agent, and the second binder is (70-80):(10-30):(0.3-1.8):(1-5):(3-6). As an example, the mass ratio of the second carbon-based material, the second silicon-based material, the second functional additive, the second conductive agent, and the second binder can be 70:10:0.3:1:3, 75:20:1:3:5, 80:30:1.8:5:6, etc. Of course, it can also be any ratio within the above range, and is not specifically limited here.

[0138] In some embodiments, the surface density of the second negative electrode coating is 20-50 g / m 2 As an example, the surface density of the second negative electrode coating can be 20 g / m 2 , 30g / m 2 , 40g / m 2 , 50g / m 2 Of course, it can also be a certain point value within the above range, which is not specifically limited here.

[0139] In some embodiments, the thickness of the second negative electrode coating is 10-30 μm. As an example, the thickness of the second negative electrode coating can be 10 μm, 20 μm, 30 μm, etc., or any value within the above range, which is not specifically limited here.

[0140] In some embodiments, the porosity of the second negative electrode coating is 28% to 32%. As an example, the porosity of the second negative electrode coating can be 28%, 30%, 32%, etc., or any point within the above range, which is not specifically limited here.

[0141] In some embodiments, the pore structure of the second negative electrode coating has a pore size of 700 to 900 nm. As an example, the pore size of the second negative electrode coating can be 700 nm, 800 nm, 900 nm, etc., or any point within the above range, which is not specifically limited here.

[0142] In some embodiments, the third carbon-based material includes graphite.

[0143] In some embodiments, the graphite includes, but is not limited to, at least one of natural graphite and artificial graphite. The graphite includes, but is not limited to, at least one of natural graphite and artificial graphite. As an example, the graphite can be natural graphite or artificial graphite.

[0144] In some embodiments, the third negative electrode coating further includes a third conductive agent and a third binder.

[0145] In some embodiments, the mass ratio of the third carbon-based material, the third conductive agent, and the third binder is (90-95):(1-5):(3-6). As an example, the mass ratio of the third carbon-based material, the third conductive agent, and the third binder can be 90:1:3, 93:3:5, 95:5:6, etc. Of course, it can also be any ratio within the above range, and is not specifically limited here.

[0146] In some embodiments, the surface density of the third negative electrode coating is 30-80 g / m 2 As an example, the area density of the third negative electrode coating layer may be 30 g / m 2 , 50g / m 2 , 70g / m 2 , 80g / m 2 Of course, it can also be a certain point value within the above range, which is not specifically limited here.

[0147] In some embodiments, the thickness of the third negative electrode coating is 20-50 μm. As an example, the thickness of the third negative electrode coating can be 20 μm, 40 μm, 50 μm, etc., or any value within the above range, which is not specifically limited here.

[0148] In some embodiments, the third negative electrode coating layer has a porous structure.

[0149] In some embodiments, the porosity of the third negative electrode coating is 30-34%. As an example, the porosity of the third negative electrode coating can be 30%, 32%, 34%, etc., or any point within the above range, and is not specifically limited here. If the porosity is lower than 30%, the electrolyte infiltration effect will be affected, and ion transport will be deteriorated. If the porosity is higher than 34%, the ion transport effect will not be greatly improved, and internal space will be wasted, affecting the energy density of the battery cell.

[0150] In some embodiments, the pore structure of the third negative electrode coating has a pore size of 800 to 1000 nm. As an example, the pore size of the third negative electrode coating can be 800 nm, 900 nm, 1000 nm, etc., or a value within the above range, without specific limitation. If the pore size of the third negative electrode coating is less than 800 nm, it will affect the electrolyte infiltration effect and deteriorate ion transport. If the pore size of the third negative electrode coating is greater than 1000 nm, it will increase the electron transport path and deteriorate electron transport.

[0151] Limiting the porosity of the third negative electrode coating and the pore size of the pore structure within the above range can ensure the overall wetting effect of the negative electrode sheet, thereby improving the lithium ion transmission efficiency, improving the rate performance, and reducing the structural damage and volume expansion of the active material during charging and discharging.

[0152] It should be noted that the first conductive agent, the second conductive agent, and the third conductive agent each independently include, but are not limited to, at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, or graphene. The conductive carbon black includes acetylene black, Ketjen black, and the like. The conductive carbon fiber includes vapor-grown carbon fiber.

[0153] It should also be noted that the first binder, the second binder, and the third binder each independently include, but are not limited to, at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, or polyacrylic acid.

[0154] It is understandable that the mass ratio of the first carbon-based active material, the first conductive agent, the first binder and the first thickener, the mass ratio of the second carbon-based active material, the second conductive agent, the second binder and the second thickener, and the mass ratio of the third carbon-based active material, the third conductive agent, the third binder and the third thickener are related to the electrochemical performance of the corresponding battery, and further affect the structural stability of the negative electrode sheet. By controlling the ratio of each substance in the first negative electrode coating, the second negative electrode coating and the third negative electrode coating within the above range, the interaction between the materials is fully utilized, and the cycle performance, fast charging performance and structural stability of the negative electrode sheet are effectively improved.

[0155] It can also be understood that the surface thickness of the coating will affect the electrical properties of the battery (such as energy density, cycle performance and rate performance), preparation cost and safety performance. If the thickness of the first negative electrode coating, the second negative electrode coating and the third negative electrode coating is too large, the electron transmission distance increases, the electronic resistance increases, and the rate performance decreases, which has an adverse effect on the electrical performance of the battery and further increases the difficulty of thermal management of the battery. However, if the thickness of the first negative electrode coating, the second negative electrode coating and the third negative electrode coating is too low, the structural stability of the positive electrode sheet will not be significantly improved, which will have an adverse effect on the safety and long-term cycle stability of the battery.

[0156] In some embodiments, the current collector includes, but is not limited to, at least one of copper foil, nickel foam, nickel mesh, or composite copper foil. As an example, the current collector can be copper foil or nickel foam.

[0157] Thus, based on the above scheme, in the negative electrode sheet of the present application, the first functional additive has a hollow shell structure. While increasing the porosity of the first negative electrode coating, the conductive polymer remaining in the pores acts as a conductive agent to make up for the defect of insufficient electronic conductivity of this layer due to the large silicon content in the first negative electrode coating. The second functional additive has a hollow shell structure. While increasing the porosity of the second negative electrode coating, the sticky polymer remaining in the pores can enhance the bonding force between particles around the pores, improve the mechanical strength of the second negative electrode coating, thereby enhancing the overall structural stability of the electrode sheet and inhibiting electrode cracks caused by the rebound difference between particles in different layers. Only carbon-based materials are used as active materials in the third negative electrode coating, which has good conductivity and small rebound, and the third negative electrode coating also has a porous structure. It can also be understood that the three layers of coating of the negative electrode sheet of the present application all have a porous structure, so that the negative electrode sheet can have a good wetting effect, thereby improving the lithium ion transmission efficiency, improving the rate performance, and reducing the structural damage and volume expansion of the active material during charging and discharging.

[0158] Furthermore, in the three-layer coating of the negative electrode plate of the present application, the overall porosity, structural strength and conductivity of the electrode plate are effectively improved through the reasonable combination of various substances, so that the electrode plate has relatively excellent fast charging performance and a longer service life.

[0159] [Method for preparing negative electrode sheet]

[0160] According to another aspect of the present application, an embodiment of the present application provides a method for preparing a negative electrode sheet, comprising the following steps:

[0161] Coating a first negative electrode slurry on at least one side of the current collector to obtain a first negative electrode coating;

[0162] coating a second negative electrode slurry on the surface of the first negative electrode coating to obtain a second negative electrode coating;

[0163] coating a third negative electrode slurry on the surface of the second negative electrode coating to obtain a third negative electrode coating;

[0164] Roll-pressing, unwinding and baking the current collector coated with the first negative electrode coating, the second negative electrode coating and the third negative electrode coating;

[0165] Wherein, the first negative electrode slurry includes a first carbon-based material, a first silicon-based material and a first functional additive source;

[0166] The second negative electrode slurry includes a second carbon-based material, a second silicon-based material, and a second functional additive source;

[0167] The third negative electrode slurry includes a third carbon-based material.

[0168] It should be understood that all the features and advantages described above for the “negative electrode sheet” are also applicable to the “method for preparing the negative electrode sheet” and will not be described in detail here.

[0169] In some embodiments, the third negative electrode slurry further includes a pore former, that is, the third negative electrode slurry includes a third carbon-based material, a third conductive agent, a third binder, and a pore former.

[0170] In some embodiments, the pore-forming agent includes, but is not limited to, at least one of ammonium carbonate, urea, or oxalic acid. As an example, the pore-forming agent may be ammonium carbonate or urea.

[0171] In some specific embodiments, the method for preparing the negative electrode sheet specifically includes steps S1 to S6:

[0172] S1: preparing a first negative electrode slurry.

[0173] In step S1 , preparing the first negative electrode slurry includes: uniformly mixing a first carbon-based material, a first silicon-based material, a first functional additive source, a first conductive agent, and a first binder in a solvent to obtain the first negative electrode slurry.

[0174] In some embodiments, the mass ratio of the first carbon-based material, the first silicon-based material, the first functional additive source, the first conductive agent, and the first binder is (50-60):(30-40):(2-5):(1-5):(3-6). As an example, the mass ratio of the first carbon-based material, the first silicon-based material, the first functional additive source, the first conductive agent, and the first binder can be 50:30:2:1:3, 55:35:4:3:5, 60:40:5:5:6, etc. Of course, it can also be any ratio within the above range, and is not specifically limited here.

[0175] S2 prepares a second negative electrode slurry.

[0176] In step S2 , preparing the second negative electrode slurry includes: uniformly mixing a second carbon-based material, a second silicon-based material, a second functional additive source, a second conductive agent, and a second binder in a solvent to obtain a second negative electrode slurry.

[0177] In some embodiments, the mass ratio of the second carbon-based material, the second silicon-based material, the second functional additive source, the second conductive agent, and the second binder is (70-80):(10-30):(3-6):(1-5):(3-6). As an example, the mass ratio of the second carbon-based material, the second silicon-based material, the second functional additive source, the second conductive agent, and the second binder can be 70:10:3:1:3, 75:20:5:3:4, 80:30:6:5:6, etc. Of course, it can also be any ratio within the above range, and is not specifically limited here.

[0178] S3 prepares a third negative electrode slurry.

[0179] In step S3 , preparing the third negative electrode slurry includes: uniformly mixing the third carbon-based material, the third conductive agent, the third binder, and the pore-forming agent in a solvent to obtain the third negative electrode slurry.

[0180] In some embodiments, the mass ratio of the third carbon-based material, the third conductive agent, the third binder, and the pore-forming agent is (90-95):(1-5):(3-6):(4-8). As an example, the mass ratio of the third carbon-based material, the third conductive agent, the third binder, and the pore-forming agent can be 90:1:3:4, 93:3:4:6, 95:5:6:8, etc. Of course, it can also be any ratio within the above range, and is not specifically limited here.

[0181] The solvent involved in steps S1 to S3 of the present application includes at least one of water, ethanol or N-methylpyrrolidone, preferably water.

[0182] S4 coating.

[0183] In step S4, the first negative electrode slurry is applied to the surface of the current collector and dried to complete the first negative electrode coating; the second negative electrode slurry is applied to the surface of the first negative electrode coating and dried to complete the second negative electrode coating; the third negative electrode slurry is applied to the surface of the second negative electrode coating and dried to complete the third negative electrode coating.

[0184] In step S4, a three-layer coating die is preferably used to coat the first negative electrode slurry, the second negative electrode slurry, and the third negative electrode slurry onto the current collector in order from bottom to top, and then dry them.

[0185] In some embodiments, the drying temperature is 60-80° C. As an example, the drying temperature can be 60° C., 70° C., 80° C., etc., or any value within the above range, which is not specifically limited here.

[0186] S5 roller pressing.

[0187] In step S5, the coated electrode is rolled.

[0188] In some embodiments, the compaction density of the roller is 1.3 to 1.6 g / cm 3 As an example, the roller compaction density can be 1.3 g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 Of course, it can also be other values ​​within the above range, which is not limited here.

[0189] S6 unrolling and baking.

[0190] In step S6, the rolled electrode is unwound and baked.

[0191] In some embodiments, the uncoiling baking temperature is 130-170°C, and the tape running speed is 5-20 m / min. As an example, the uncoiling baking temperature can be 130°C, 150°C, 170°C, etc., and of course other values ​​within the above range are also possible, and are not limited here. As an example, the tape running speed can be 5 m / min, 10 m / min, 15 m / min, 20 m / min, etc., and of course other values ​​within the above range are also possible, and are not limited here.

[0192] In the present application, through the unwinding and baking steps, the gas-generating components in the first negative electrode slurry, the second negative electrode slurry, and the third negative electrode slurry will produce gas discharge, leaving a large number of pores in the negative electrode sheet.

[0193] [First functional additive source and its preparation]

[0194] In some embodiments, the first functional additive source has a core-shell structure.

[0195] In some embodiments, the core of the first functional additive source includes at least one of ammonium carbonate, urea, or oxalic acid. As an example, the core of the first functional additive source can be ammonium carbonate or oxalic acid.

[0196] In some embodiments, the core diameter of the first functional additive source is 300-600 nm. As an example, the core diameter of the first functional additive source can be 300 nm, 500 nm, 600 nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0197] In some embodiments, the shell material of the first functional additive source includes at least one of polyaniline, polypyrrole, or poly(ethylenedioxythiophene). As an example, the shell material of the first functional additive source can be polyaniline or polypyrrole.

[0198] In some embodiments, the preparation method of the first functional additive source includes: mixing a suspension containing the first core material and a solution containing the first shell material to obtain the first functional additive source.

[0199] In some embodiments, the volume ratio of the suspension containing the first core material to the solution containing the first shell material is (1.5-2):1. As an example, the volume ratio of the suspension containing the first core material to the solution containing the first shell material can be 1.5:1, 1.8:1, 2:1, etc., and can also be any ratio within the above range, which is not specifically limited here.

[0200] In some embodiments, the molar concentration of the first core material in the suspension containing the first core material is 1 to 2 mol / L. As an example, the molar concentration of the first core material in the suspension containing the first core material can be 1 mol / L, 1.5 mol / L, 2 mol / L, etc., and of course, other values ​​within the above range are also possible and are not limited here.

[0201] In some embodiments, the molar concentration of the first shell material in the solution containing the first shell material is 1 to 2 mol / L. For example, the molar concentration of the first shell material in the suspension containing the first shell material can be 1 mol / L, 1.5 mol / L, 2 mol / L, etc., and other values ​​within the above range are also possible and are not limited herein.

[0202] In some embodiments, the solvent in the suspension containing the first core material and the solution containing the first shell material is selected from at least one of N-methylpyrrolidone, m-cresol, 1,4-cyclohexanediamine, ethanol, and water.

[0203] In some embodiments, mixing includes stirring, and the stirring time is 40 to 80 minutes, the temperature is 25 to 45°C, and the stirring speed is 25 to 60 rpm. As an example, the stirring time can be 40 minutes, 60 minutes, 80 minutes, etc., and of course it can also be other values ​​within the above range, which is not limited here. As an example, the temperature during stirring can be 25°C, 35°C, 45°C, etc., and of course it can also be other values ​​within the above range, which is not limited here. As an example, the stirring speed can be 25rpm, 35rpm, 55rpm, 60rpm, etc., and of course it can be other values ​​within the above range, which is not limited here. After this stirring step, the coating of the first core material by the first shell material is completed.

[0204] In some embodiments, the preparation further includes separation, washing, and drying steps. For example, separation can be performed by filtration or centrifugation. For example, washing can be performed using an ethanol solution. For example, the drying temperature can be 45-60°C, and the drying time can be 10-24 hours.

[0205] [Second functional additive source and its preparation]

[0206] In some embodiments, the second functional additive source has a core-shell structure.

[0207] In some embodiments, the core of the second functional additive source includes at least one of ammonium carbonate, urea, or oxalic acid. As an example, the core of the second functional additive source can be ammonium carbonate or oxalic acid.

[0208] In some embodiments, the core diameter of the first functional additive source is 400-800 nm. As an example, the core diameter of the first functional additive source can be 400 nm, 600 nm, 800 nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0209] In some embodiments, the shell material of the second functional additive source includes at least one of polymethyl methacrylate, polyacrylic acid, or polyvinylidene fluoride. As an example, the shell material of the second functional additive source can be polymethyl methacrylate or polyacrylic acid.

[0210] In some embodiments, the preparation method of the second functional additive source includes: mixing a shell material monomer, an emulsifier, a second core material, and an initiator, and reacting the mixture to obtain the second functional additive source.

[0211] In some embodiments, the preparation method of the second functional additive source includes: first mixing the shell material monomer, an emulsifier, and the second core material in water to form an emulsion system, then adding an initiator and reacting to obtain the second functional additive source. In this reaction system, under the action of the emulsifier, the material monomer forms latex particles in the aqueous phase, and the polymerization reaction proceeds within the latex particles, encapsulating the core particles.

[0212] In some embodiments, the shell material monomer includes at least one of acrylic acid, methyl methacrylate, or vinylidene fluoride. As an example, the shell material monomer can be acrylic acid or methyl methacrylate.

[0213] In some embodiments, the mass concentration of the shell monomer is 50 to 200 g / L, based on the mass of water. For example, based on the mass of water, the mass concentration of the shell monomer can be 50 g / L, 100 g / L, 150 g / L, 200 g / L, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0214] In some embodiments, the second core material is 1 to 2 times the mass of the outer shell. As an example, the second core material can be 1, 1.5, or 2 times the mass of the outer shell.

[0215] In some embodiments, the emulsifier is 5-10% of the mass of the shell monomer. As an example, the emulsifier can be 5%, 8%, 10%, etc., of course, other values ​​within the above range are also possible and are not limited here.

[0216] In some embodiments, the emulsifier includes, but is not limited to, at least one of sodium stearate, sodium lauryl sulfate, or polyvinyl alcohol. As an example, the emulsifier can be sodium stearate or sodium lauryl sulfate.

[0217] In some embodiments, the initiator is 0.5-2% by weight of the shell monomer. As an example, the initiator can be 0.5%, 1%, 2%, etc., of the shell monomer. Of course, other values ​​within the above range are also possible and are not limited here.

[0218] In some embodiments, the initiator includes, but is not limited to, at least one of azobisisobutyronitrile, azobisisoheptanenitrile, or dibenzoyl peroxide. As an example, the initiator may be azobisisobutyronitrile.

[0219] In some embodiments, the reaction temperature is 45-60°C and the reaction time is 1-4 hours. As an example, the reaction temperature can be 45°C, 55°C, 60°C, etc., and of course it can be other values ​​within the above range, which is not limited here. As an example, the reaction time can be 1 hour, 2 hours, 3 hours, 4 hours, etc., and of course it can be other values ​​within the above range, which is not limited here.

[0220] In some embodiments, the preparation further includes washing and drying steps. For example, washing can be performed with an ethanol solution. For example, the drying temperature can be 45-60° C., and the drying time can be 10-24 hours.

[0221] Thus, based on the above scheme, when preparing the negative electrode sheet, the gas-generating components in the first negative electrode slurry (first functional additive source), the second negative electrode slurry (second functional additive source), and the third negative electrode slurry (pore former) will produce gas discharge after the unwinding and baking steps, leaving a large number of pores in the negative electrode sheet. After the core structure of the first functional additive source produces gas and is discharged, while increasing the porosity of the first negative electrode coating, the conductive polymer remaining in the pores acts as a conductive agent to make up for the defect of insufficient electron conduction capacity of this layer due to the large silicon content in the first negative electrode coating. After the core structure of the second functional additive source produces gas and is discharged, while increasing the porosity of the second negative electrode coating, the sticky polymer remaining in the pores can enhance the bonding force between the particles around the pores, improve the mechanical strength of the second negative electrode coating, thereby enhancing the overall structural stability of the electrode sheet and suppressing the electrode sheet cracks caused by the rebound difference of particles between different layers. After the pore former in the third negative electrode slurry produces gas and is discharged, the third negative electrode coating also has a porous structure. In this way, the negative electrode sheet can have a good infiltration effect, thereby improving the lithium ion transmission efficiency, improving the rate performance, and reducing the structural damage and volume expansion of the active material during the charge and discharge process.

[0222] Furthermore, in the three-layer coating of the negative electrode plate of the present application, the overall porosity, structural strength and conductivity of the electrode plate are effectively improved through the reasonable combination of various substances, so that the electrode plate has relatively excellent fast charging performance and a longer service life.

[0223] Based on the same inventive concept, an embodiment of the present application provides a battery, including a negative electrode sheet, wherein the negative electrode sheet includes the aforementioned negative electrode sheet, or includes a negative electrode sheet prepared according to the aforementioned preparation method.

[0224] Since the battery includes the negative electrode sheet provided in the embodiment of the present application, it has relatively excellent fast charging performance and a long service life.

[0225] In some embodiments, the battery may be a lithium-ion battery. The battery stack type may be, for example, a wound or laminated battery, and the battery structure may be, for example, a prismatic (aluminum, steel, etc.) battery, a soft-pack battery, or a cylindrical battery, without limitation.

[0226] In some embodiments, the battery further comprises a positive electrode sheet, an electrolyte, and a separator. That is, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator.

[0227] In this embodiment, there is no limitation on the materials and structures of the positive electrode sheet, the positive current collector, the conductive agent, the binder in the positive active material layer, and the like. Positive electrode sheet structures and components known in the art that can be used for secondary batteries can be selected.

[0228] In this embodiment, there is no limitation on the specific material or type of the separator, and any separator known in the art that can be used in secondary batteries can be selected.

[0229] It should also be noted that the battery of the present application is not limited to the specific material or type of the electrolyte, and any components and types that are known in the art and can be used for secondary batteries can be selected as long as the purpose of the present application can be achieved.

[0230] Since the battery provided by the embodiment of the present invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0231] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents, materials, or instruments used that do not specify the manufacturer are all conventional products that can be purchased commercially.

[0232] Example 1

[0233] Preparation of negative electrode sheet

[0234] S1: adding the first negative electrode slurry material into solvent water in proportion and stirring to obtain a slurry;

[0235] In the first negative electrode slurry, the mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the first functional additive source is 33.5:55:3.6:1.6:2.8:3.5;

[0236] The solid content of the first negative electrode slurry is 50%;

[0237] The preparation of the first functional additive source includes: dispersing oxalic acid in water to form a uniform suspension (1 mol / L); dispersing the synthesized polyaniline in N-methylpyrrolidone to form a solution (1 mol / L); then slowly adding the suspension to the solution at a volume ratio of 1.5:1 between the suspension and the solution; stirring at 40°C and 40 rpm for 60 minutes; after the coating is completed, separating the product by filtration, washing with ethanol three times, and finally drying at 50°C for 12 hours;

[0238] The obtained first functional additive source has a shell thickness of 75 nm and a core diameter of 450 nm.

[0239] S2: adding the second negative electrode slurry material into solvent water according to a proportion and stirring to obtain a slurry;

[0240] In the second negative electrode slurry, the mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the second functional additive source is 18:73.2:1:1.1:2.2:4.5;

[0241] The solid content of the second negative electrode slurry is 50%;

[0242] The preparation of the second functional additive source includes: adding acrylic acid, sodium stearate, and oxalic acid in a mass ratio of 100:5:150 to water to form an emulsion system, wherein the mass concentration of acrylic acid is 100 g / L, adding azobisisobutyronitrile (1% by mass of acrylic acid) to initiate polymerization at 55° C. for 2 hours, then washing with ethanol five times, and finally drying at 50° C. for 12 hours;

[0243] The obtained second functional additive source has a shell thickness of 75 nm and a core diameter of 600 nm.

[0244] S3: adding the third negative electrode slurry material into solvent water in proportion and stirring to obtain a slurry;

[0245] In the third negative electrode slurry, the mass ratio of artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and oxalic acid is 90:1:1.4:1.6:6;

[0246] The diameter of oxalic acid is 900nm;

[0247] The solid content of the third negative electrode slurry is 50%;

[0248] S4: Using a three-layer coating die head, the first negative electrode slurry, the second negative electrode slurry, and the third negative electrode slurry are coated on a copper foil (thickness 8 μm) in order from bottom to top, and then dried;

[0249] Among them, the drying temperature is 70℃;

[0250] The first negative electrode coating area density is 35g / m 2 , thickness 23 μm;

[0251] The second negative electrode coating area density is 35 g / m 2 , thickness 23 μm;

[0252] The third negative electrode coating surface density is 55g / m 2 , thickness 37μm.

[0253] S5: Roll the coated electrode to a compaction density of 1.45 g / cm 3 .

[0254] S6: After rolling, the negative electrode sheet is subjected to an unwinding and baking process, with a temperature of 170°C and a conveying speed of 10m / min.

[0255] The morphology and structure of the first functional additive in the first negative electrode coating of the negative electrode sheet are shown in FIG. Figure 1 and Figure 2 .

[0256] Example 2

[0257] The only difference between Example 2 and Example 1 is that the mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the first functional additive source in the first negative electrode slurry of Example 2 is 35:55:3.6:1.6:2.8:2;

[0258] The mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the second functional additive source in the second negative electrode slurry is 19.5:73.2:1:1.1:2.2:3;

[0259] The mass ratio of artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and oxalic acid in the third negative electrode slurry is 91:1:1.4:1.6:5.

[0260] Example 3

[0261] The only difference between Example 3 and Example 1 is that the mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the first functional additive source in the first negative electrode slurry of Example 3 is 32:55:3.6:1.6:2.8:5;

[0262] The mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the second functional additive source in the second negative electrode slurry is 16.5:73.2:1:1.1:2.2:6;

[0263] The mass ratio of artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and oxalic acid in the third negative electrode slurry is 92:1:2:1.8:4.2.

[0264] Example 4

[0265] The only difference between Example 4 and Example 1 is that in Example 4, the core diameter of the first functional additive source is 300 nm and the shell thickness is 50 nm; the core diameter of the second functional additive source is 400 nm and the shell thickness is 50 nm; and the diameter of oxalic acid in the third negative electrode slurry is 800 nm.

[0266] Example 5

[0267] The only difference between Example 5 and Example 1 is that in Example 5, the core diameter of the first functional additive source is 600 nm and the shell thickness is 100 nm; the core diameter of the second functional additive source is 800 nm and the shell thickness is 100 nm; and the diameter of oxalic acid in the third negative electrode slurry is 1000 nm.

[0268] Example 6

[0269] The only difference between Example 6 and Example 1 is that in Example 6, oxalic acid, the core material of the first functional additive source, oxalic acid, the core material of the second functional additive source, and oxalic acid in the third negative electrode slurry are all replaced by ammonium carbonate.

[0270] Example 7

[0271] The only difference between Example 7 and Example 1 is that the mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the first functional additive source in the first negative electrode slurry in Example 7 is 30:57:3.6:1.6:2.8:5;

[0272] The mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the second functional additive source in the second negative electrode slurry is 10:80:1:1.2:1.8:6.

[0273] Example 8

[0274] The only difference between Example 8 and Example 1 is that the mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the first functional additive source in the first negative electrode slurry in Example 8 is 40:50:3.6:1.6:2.8:2;

[0275] The mass ratio of the silicon-oxygen composite material, artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and the second functional additive source in the second negative electrode slurry is 22:70:1:1.1:2.2:3.7.

[0276] Example 9

[0277] The only difference between Example 9 and Example 1 is that the silicon-based materials in the first negative electrode slurry and the second negative electrode slurry in Example 9 are both pure silicon.

[0278] Example 10

[0279] The only difference between Example 10 and Example 1 is that the carbon-based materials in the first negative electrode slurry and the second negative electrode slurry, and the carbon-based material in the third negative electrode coating layer in Example 10 are all natural graphite.

[0280] Comparative Example 1

[0281] The only difference between Comparative Example 1 and Example 1 is that oxalic acid is used in the first negative electrode slurry of Comparative Example 1 to replace the first functional additive source.

[0282] Comparative Example 2

[0283] The only difference between Comparative Example 2 and Example 1 is that oxalic acid is used in the second negative electrode slurry of Comparative Example 2 to replace the second functional additive source.

[0284] Comparative Example 3

[0285] The only difference between Comparative Example 3 and Example 1 is that the third negative electrode slurry in Comparative Example 3 does not contain oxalic acid.

[0286] Performance Testing

[0287] 1. Battery preparation

[0288] Preparation of positive electrode sheet: LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (SP), carbon nanotubes, and binder polyvinylidene fluoride (PVDF5130) are mixed in a mass ratio of 97:1.5:0.5:1, and then N-methylpyrrolidone (NMP) is added, stirred and mixed uniformly to form a stable positive electrode slurry with a solid content of 75%. The positive electrode slurry is evenly coated on a 10μm aluminum foil of the positive electrode current collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0289] Separator: A polyethylene (PE) membrane with a thickness of 12 μm was selected as the separator.

[0290] Electrolyte: In a glove box filled with inert gas, ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then lithium salt LiPF6 was dissolved in the organic solvent. The concentration of the lithium salt was 1.2 mol / L to obtain an electrolyte.

[0291] Battery assembly: The positive electrode sheet, separator, and negative electrode sheet are arranged in sequence by winding. The electrolyte is injected into the dry battery cell, and after formation and aging, the lithium battery is obtained.

[0292] 2. Porosity test

[0293] The porosity of the negative electrode sheets prepared in the examples and comparative examples was tested using the national standard GBT33052-2016 test method.

[0294] 3. Test the electrochemical performance of the battery

[0295] (1) Constant current ratio test: The batteries prepared in each embodiment and comparative example were discharged and charged to 4.25 V at 0.05C and 5C respectively, and the 5C capacity / 0.05C capacity was recorded as the charging constant current ratio (Note: The larger the charging constant current ratio, the higher the fast charging capability of the electrode).

[0296] (2) Capacity retention test after 500 cycles: Take the batteries prepared in each embodiment and comparative example, let them rest at 25°C for 30 minutes, charge them at a constant current of 2C to 4.25V, and then charge them at a constant voltage of 0.05C. Let them rest for 30 minutes. Then discharge them at a constant current of 2C to 2.5V (the capacity at this step is recorded as the discharge capacity). Let them rest for 30 minutes. Repeat these steps 500 times, and record the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle as the capacity retention rate (Note: A higher capacity retention rate indicates a longer electrode life).

[0297] The specific test results are shown in Table 1.

[0298] Table 1

[0299] Porosity Constant current ratio 500-cycle capacity retention rate Example 1 29.40％ 94.80％ 95.70％ Example 2 27.50％ 94.20％ 95.20％ Example 3 30.20％ 94.60％ 95.90％ Example 4 28.20％ 94.60％ 95.30％ Example 5 30.40％ 95.10％ 96.10％ Example 6 29.35％ 94.67％ 95.60％ Example 7 29.50％ 95.10％ 95.90％ Example 8 29.10％ 94.60％ 95.30％ Example 9 29.05％ 94.20％ 95.10％ Example 10 29.40％ 94.70％ 95.20％ Comparative Example 1 26.70％ 82.20％ 89.65％ Comparative Example 2 26.80％ 89.20％ 83.20％ Comparative Example 3 22.40％ 87.10％ 85.20％

[0300] From the test results, it can be seen that all parameters of the embodiment are within the specifications, the porosity is high, and the constant current ratio and capacity retention rate are excellent. The negative electrode sheet of Comparative Example 1 does not contain the first functional additive, and the overall porosity decreases slightly. Due to the lack of the promoting effect of the conductive polymer on electron transfer, the constant current ratio deteriorates significantly. The low electron transfer efficiency will also lead to local lithium precipitation in the lower layer and excessive temperature rise, triggering a series of side reactions, causing the capacity retention rate to decay seriously. Comparative Example 2 does not contain the second functional additive, and the overall porosity and constant current ratio decrease slightly. The middle layer lacks the reinforcement effect of the binder shell on the positive electrode structure of the electrode sheet. During the cycle, the repeated expansion of the three-layer active material cannot be effectively suppressed, resulting in peeling and cracking between the layers and the particles of the second active layer, and the cycle capacity retention rate is greatly attenuated. Comparative Example 3 cancels the addition of the pore-forming agent (oxalic acid), and the third active layer cannot obtain sufficient pores. Even if the porosity of the first and second active layers is high, it is difficult for the electrolyte to infiltrate, and the constant current ratio and capacity retention rate are significantly deteriorated.

[0301] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0302] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in the present invention are merely illustrative and non-limiting, and should not be construed as necessarily possessed by each embodiment of the present invention. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, and are not intended to be limiting. These details do not necessarily limit the present invention to being implemented using these specific details.

[0303] It should be noted that the terms "and / or" or " / " used herein are merely a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone. The singular forms "a," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0304] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0305] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The negative electrode sheet comprises: current collector; a first negative electrode coating, disposed on at least one side of the current collector in a thickness direction, the first negative electrode coating comprising a first carbon-based material, a first silicon-based material, and a first functional additive; a second negative electrode coating, disposed on a surface of the first negative electrode coating away from the current collector, the second negative electrode coating comprising a second carbon-based material, a second silicon-based material, and a second functional additive; and a third negative electrode coating, disposed on a surface of the second negative electrode coating away from the first negative electrode coating, the third negative electrode coating comprising a third carbon-based material; wherein the content of the first silicon-based material in the first negative electrode coating is greater than the content of the second silicon-based material in the second negative electrode coating; The first functional additive and the second functional additive both have a hollow shell structure; The first functional additive includes a conductive polymer; the second functional additive includes a sticky polymer.

2. The negative electrode sheet according to claim 1, characterized in that: The first functional additive and the second functional additive meet at least one of the following characteristics (1) to (8): (1) The conductive polymer comprises at least one of polyaniline, polypyrrole or poly(ethylenedioxythiophene); (2) The thickness of the first functional additive shell is 50 to 100 nm; (3) The inner diameter of the first functional additive shell is 300 to 600 nm; (4) The first functional additive shell has a porous structure; Preferably, the porosity of the hollow shell of the first functional additive is 30-50%; (5) the adhesive polymer comprises at least one of polymethyl methacrylate, polyacrylic acid or polyvinylidene fluoride; (6) The thickness of the second functional additive shell is 50 to 100 nm; (7) The inner diameter of the second functional additive shell is 400 to 800 nm; (8) The second functional additive shell has a porous structure; Preferably, the porosity of the hollow shell of the second functional additive is 30-50%.

3. The negative electrode sheet according to claim 1, characterized in that: The first negative electrode coating satisfies at least one of the following characteristics (1) to (7): (1) The mass ratio of the first carbon-based material to the first silicon-based material is (50-60):(30-40); (2) The first carbon-based material includes graphite; Preferably, the graphite includes at least one of natural graphite or artificial graphite; (3) The first silicon-based material includes at least one of a silicon-oxygen composite material, a silicon-carbon composite material, or pure silicon; (4) The first negative electrode coating further includes a first conductive agent and a first binder; Preferably, the mass ratio of the first carbon-based material, the first silicon-based material, the first functional additive, the first conductive agent and the first binder is (50-60): (30-40): (0.2-1.5): (1-5): (3-6); (5) The surface density of the first negative electrode coating is 20 to 50 g / m 2 ; (6) The thickness of the first negative electrode coating is 10 to 30 μm; (7) The porosity of the first negative electrode coating layer is 26-30%.

4. The negative electrode sheet according to claim 1, characterized in that: The second negative electrode coating satisfies at least one of the following characteristics (1) to (7): (1) The mass ratio of the second carbon-based material to the second silicon-based material is (70-80):(10-30); (2) The second carbon-based material includes graphite; Preferably, the graphite includes at least one of natural graphite or artificial graphite; (3) The second silicon-based material includes at least one of a silicon-oxygen composite material, a silicon-carbon composite material, or pure silicon; (4) The second negative electrode coating further includes a second conductive agent and a second binder; Preferably, the mass ratio of the second carbon-based material, the second silicon-based material, the second functional additive, the second conductive agent and the second binder is (70-80): (10-30): (0.3-1.8): (1-5): (3-6); (5) The surface density of the second negative electrode coating is 20 to 50 g / m 2 ; (6) The thickness of the second negative electrode coating is 10 to 30 μm; (7) The porosity of the second negative electrode coating layer is 28-32%.

5. The negative electrode sheet according to claim 1, characterized in that: The third negative electrode coating satisfies at least one of the following characteristics (1) to (5): (1) The third carbon-based material includes graphite; Preferably, the graphite includes at least one of natural graphite or artificial graphite; (2) The third negative electrode coating further includes a third conductive agent and a third binder; Preferably, the mass ratio of the third carbon-based material, the third conductive agent and the third binder is (90-95): (1-5): (3-6); (3) The surface density of the third negative electrode coating is 30 to 80 g / m 2 ; (4) The thickness of the third negative electrode coating is 20 to 50 μm; (5) The third negative electrode coating has a porous structure; Preferably, the porosity of the third negative electrode coating is 30-34%; Preferably, the pore size of the pore structure of the third negative electrode coating is 800-1000 nm.

6. A method for preparing a negative electrode sheet, characterized in that: The following steps are involved: Coating a first negative electrode slurry on at least one side of the current collector to obtain a first negative electrode coating; coating a second negative electrode slurry on the surface of the first negative electrode coating to obtain a second negative electrode coating; coating a third negative electrode slurry on the surface of the second negative electrode coating to obtain a third negative electrode coating; Roll-pressing, unwinding and baking the current collector coated with the first negative electrode coating, the second negative electrode coating and the third negative electrode coating; Wherein, the first negative electrode slurry includes a first carbon-based material, a first silicon-based material and a first functional additive source; The second negative electrode slurry includes a second carbon-based material, a second silicon-based material, and a second functional additive source; The third negative electrode slurry includes a third carbon-based material.

7. The method for preparing a negative electrode sheet according to claim 6, wherein: The third negative electrode slurry further includes a pore former; Preferably, the pore-forming agent comprises at least one of ammonium carbonate, urea or oxalic acid; Preferably, the mass ratio of the third carbon-based material, the third conductive agent, the third binder and the pore-forming agent is (90-95): (1-5): (3-6): (4-8).

8. The method for preparing a negative electrode sheet according to claim 6, wherein: The preparation of the first negative electrode slurry includes: uniformly mixing a first carbon-based material, a first silicon-based material, a first functional additive source, a first conductive agent, and a first binder in a solvent to obtain a first negative electrode slurry; Preferably, the mass ratio of the first carbon-based material, the first silicon-based material, the first functional additive source, the first conductive agent and the first binder is (50-60): (30-40): (2-5): (1-5): (3-6); The preparation of the second negative electrode slurry includes: uniformly mixing a second carbon-based material, a second silicon-based material, a second functional additive source, a second conductive agent, and a second binder in a solvent to obtain a second negative electrode slurry; Preferably, the mass ratio of the second carbon-based material, the second silicon-based material, the second functional additive source, the second conductive agent and the second binder is (70-80): (10-30): (3-6): (1-5): (3-6); The preparation of the third negative electrode slurry comprises: uniformly mixing a third carbon-based material, a third conductive agent, a third binder and a pore-forming agent in a solvent to obtain a third negative electrode slurry; Preferably, the compaction density of the roller is 1.3 to 1.6 g / cm 3 ; Preferably, the uncoiling and baking temperature is 130-170°C, and the tape speed is 5-20 m / min; Preferably, the first negative electrode slurry is coated on the surface of the current collector, and after drying, a first negative electrode coating is formed on the surface of the current collector; the second negative electrode slurry is coated on the first negative electrode coating, and after drying, a second negative electrode coating is formed on the surface of the first negative electrode coating; the third negative electrode slurry is coated on the second negative electrode coating and dried; the current collector coated with the first negative electrode coating, the second negative electrode coating, and the third negative electrode coating is roll-pressed, uncoiled, and baked to obtain a negative electrode sheet.

9. The method for preparing a negative electrode sheet according to claim 6, wherein: The first functional additive source has a core-shell structure; Preferably, the core of the first functional additive source includes at least one of ammonium carbonate, urea or oxalic acid; Preferably, the shell material of the first functional additive source includes at least one of polyaniline, polypyrrole or poly(ethylenedioxythiophene); and / or, the second functional additive source has a core-shell structure; Preferably, the core of the second functional additive source includes at least one of ammonium carbonate, urea or oxalic acid; Preferably, the shell material of the second functional additive source includes at least one of polymethyl methacrylate, polyacrylic acid or polyvinylidene fluoride; And / or, the method for preparing the first functional additive source comprises: mixing a suspension containing the first core material and a solution containing the first shell material to obtain the first functional additive source; Preferably, the first core material comprises at least one of ammonium carbonate, urea or oxalic acid; Preferably, the first shell material includes at least one of polyaniline, polypyrrole or poly(ethylenedioxythiophene); Preferably, the mixing includes stirring, and the stirring time is 40 to 80 minutes and the temperature is 25 to 45°C; And / or, the preparation method of the second functional additive source comprises: mixing a shell material monomer, an emulsifier, a second core material and an initiator, and reacting the mixture to obtain the second functional additive source; Preferably, the shell material monomer includes at least one of acrylic acid, methyl methacrylate or vinylidene fluoride; Preferably, the second core material comprises at least one of ammonium carbonate, urea or oxalic acid; Preferably, the reaction temperature is 45-60° C. and the reaction time is 1-4 h.

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

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