Negative plate as well as preparation method and application thereof

Abstract

The invention discloses a negative plate as well as a preparation method and application thereof. The negative plate comprises a negative current collector and a composite active layer, the composite active layer is located on at least one side of the negative current collector and comprises a first area, a second area and a third area in the length direction of the negative current collector, the first area is located on one side of the second area, and the third area is located on the other side of the second area. The third region is positioned on one side, far away from the first region, of the second region; the second region comprises a first negative electrode active layer, a first 3D conductive network layer and a second negative electrode active layer which are sequentially stacked in the direction far away from the negative electrode current collector; the first negative electrode active layer comprises a first negative electrode active material, and the first negative electrode active material comprises a silicon carbon material; the first region is a second 3D conductive network layer; and the third area is a third 3D conductive network layer. The negative plate adopts the double active material layers, so that the energy density of the battery is improved, the transverse expansion of the silicon-carbon material can be inhibited, the increase of the internal resistance of the battery is avoided, and the cycling stability of the battery is improved.

Description

Technical Field

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

[0002] Lithium-ion batteries, with their advantages of high operating voltage, high energy density, long cycle life, and environmental friendliness, are widely used in electric vehicles. With the development of electric vehicles, the requirements for battery range, charging speed, and safety are becoming increasingly stringent. The development of high-energy, high-power, and safe lithium-ion batteries is urgently needed. Currently, there are two approaches to improving battery energy density: 1. Increasing the mass percentage of active materials or increasing the thickness of the electrode sheets to increase the mass percentage of active materials. However, thick electrode sheets increase the contact distance between the underlying active materials and the electrolyte, extending the lithium ion migration path. This prevents lithium ions from reaching the bottom of the electrode sheet smoothly and quickly during charge and discharge, resulting in significant concentration polarization. This can lead to a series of problems, including reduced battery capacity, decreased electrode peel strength, poor rate performance, and cycle capacity decay. 2. Increasing the specific capacity of the anode material, namely, replacing graphite with silicon-based anode materials. However, the significant volume changes of silicon-based materials during charge and discharge can cause the material to pulverize and peel from the current collector, resulting in rapid capacity decay and associated safety issues.

[0003] Therefore, there is an urgent need to develop a lithium-ion battery with high energy density, long cycle life and high safety. Summary of the Invention

[0004] The present application aims to solve one of the technical problems in the related art at least to a certain extent.

[0005] In a first aspect, the present application provides a negative electrode sheet. According to an embodiment of the present application, the negative electrode sheet includes: a negative electrode current collector and a composite active layer, wherein the composite active layer is located on at least one side of the negative electrode current collector. Along the length direction of the negative electrode current collector, the composite active layer includes a first region, a second region, and a third region, wherein the first region is located on one side of the second region, and the third region is located on a side of the second region away from the first region. In a direction away from the negative electrode current collector, the second region includes a first negative electrode active layer, a first 3D conductive network layer, and a second negative electrode active layer stacked in sequence. The first negative electrode active layer includes a first negative electrode active material, wherein the first negative electrode active material includes a silicon-carbon material. The first region is a second 3D conductive network layer. The third region is a third 3D conductive network layer.

[0006] The negative electrode sheet of this application utilizes a dual active material layer, which not only increases the battery's energy density but also inhibits the lateral expansion of the silicon-carbon material, preventing an increase in the battery's internal resistance and improving the battery's cycling stability. Furthermore, the negative electrode sheet has a strong electrolyte absorption capacity, ensuring good liquid-phase transport of active ions within the electrode sheet, preventing poor battery dynamics caused by insufficient lithium ion concentration at the electrode edge, and improving the battery's fast-charging performance. Furthermore, the negative electrode sheet has a strong hardness, which enhances the battery's safety performance.

[0007] According to an embodiment of the present application, the negative electrode sheet may further include at least one of the following additional technical features:

[0008] According to an embodiment of the present application, the first negative electrode active layer includes a first negative electrode active material, and the first negative electrode active material includes a silicon-carbon material.

[0009] According to an embodiment of the present application, the second negative electrode active layer includes a second negative electrode active material, and the second negative electrode active material includes graphite.

[0010] According to an embodiment of the present application, based on the total mass of the silicon-carbon material, the mass proportion of the silicon element is 5%-30%.

[0011] According to an embodiment of the present application, the width of the second zone is 10 mm-150 mm.

[0012] According to an embodiment of the present application, the width of the first area is 10 mm-50 mm.

[0013] According to an embodiment of the present application, the width of the third zone is 10 mm-50 mm.

[0014] According to an embodiment of the present application, the thickness of the second region is 10 μm-200 μm.

[0015] According to an embodiment of the present application, the thickness of the first region is 10 μm-200 μm.

[0016] According to an embodiment of the present application, the thickness of the third region is 10 μm-200 μm.

[0017] According to an embodiment of the present application, the thickness of the first negative electrode active layer is 20 μm-150 μm.

[0018] According to an embodiment of the present application, the thickness of the second negative electrode active layer is 10 μm-100 μm.

[0019] According to an embodiment of the present application, the thickness of the first 3D conductive network layer is 1 μm-10 μm.

[0020] According to an embodiment of the present application, the first negative electrode active layer further includes a first conductive agent, a first thickener, and a first binder.

[0021] According to an embodiment of the present application, the second negative electrode active layer further includes a second conductive agent, a second thickener, and a second binder.

[0022] According to an embodiment of the present application, the first 3D conductive network layer, the second 3D conductive network layer, and the third 3D conductive network layer independently include a third conductive agent and a third adhesive.

[0023] According to an embodiment of the present application, the mass ratio of the first negative electrode active material, the first conductive agent, the first thickener and the first binder is (90-98.5):(0.5-4):(0.5-3):(0.5-3).

[0024] According to an embodiment of the present application, the mass ratio of the second negative electrode active material, the second conductive agent, the second thickener and the second binder is (90-98.5):(0.5-4):(0.5-3):(0.5-3).

[0025] According to an embodiment of the present application, the mass ratio of the third conductive agent to the third binder is (90-99):(1-10).

[0026] According to an embodiment of the present application, the first conductive agent, the second conductive agent and the third conductive agent are independently selected from at least one of conductive carbon black, acetylene black, Ketjen black, Super P, graphene, carbon nanotubes (CNTs) and carbon nanofibers.

[0027] According to an embodiment of the present application, the first thickener, the second thickener, and the third thickener are independently selected from at least one of sodium carboxymethyl cellulose (CMC) and a polyether-modified silicone polymer.

[0028] According to an embodiment of the present application, the first binder, the second binder and the third binder are independently selected from at least one of styrene-butadiene rubber (SBR), nitrile rubber (NBR), polyvinylidene fluoride (PVDF) and sodium polyacrylate (PAA-Na).

[0029] In its second aspect, the present application provides a method for preparing the negative electrode sheet described in the first aspect. According to an embodiment of the present application, the method comprises: sequentially applying a first negative electrode active layer slurry, a 3D conductive network layer slurry, and a second negative electrode active layer slurry to the second region of the negative electrode current collector to form a stacked arrangement of the first negative electrode active layer, the first 3D conductive network layer, and the second negative electrode active layer; applying a 3D conductive network layer slurry to the first region of the negative electrode current collector to form a second 3D conductive network layer; and applying a 3D conductive network layer slurry to the third region of the negative electrode current collector to form a third 3D conductive network layer. Thus, using the method of the present application, the first negative electrode active layer containing silicon-carbon material can be coated on the surface of the current collector using the 3D conductive network layer, inhibiting its lateral or longitudinal expansion, reducing material pulverization, and extending the battery's service life. Furthermore, the 3D conductive network layer can enhance the electrode sheet's ability to absorb and store electrolyte, ensuring efficient transport of active ions and preventing a decrease in battery kinetic performance. Furthermore, the negative electrode sheet prepared by this method has a dual active layer, improving the battery's energy density. Those skilled in the art will appreciate that the battery has all the features and advantages of the negative electrode sheet described above, which will not be elaborated herein.

[0030] In the third aspect of the present application, the present application proposes a battery. According to an embodiment of the present application, the battery includes the negative electrode sheet described in the first aspect or the negative electrode sheet prepared by the method described in the second aspect. As mentioned above, the negative electrode sheet of the present application has a strong electrolyte absorption ability, a double active material layer and a strong hardness, so the battery containing the negative electrode sheet has good fast charging performance, high energy density and safety performance. Those skilled in the art will understand that the battery has all the features and advantages of the negative electrode sheet described above, and will not be elaborated on here.

[0031] In a fourth aspect of the present application, an electrical device is provided. According to an embodiment of the present application, the electrical device includes the battery described in the second aspect. As previously mentioned, the negative electrode sheet of the present application has a strong electrolyte absorption capacity, a dual active material layer, and a strong hardness, so the electrical device has a high energy density and safety performance. Those skilled in the art will understand that the electrical device has all the features and advantages of the negative electrode sheet described above, and no further details will be given here.

[0032] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0034] Figure 1 The figure shows the distribution of the first region, the second region and the third region on the surface of the current collector according to one embodiment of the present application;

[0035] Figure 2 Shows the structure of the negative electrode sheet of an embodiment of the present application Figure 1 ;

[0036] Figure 3 Shows the structure of the negative electrode sheet of an embodiment of the present application Figure 2 ;

[0037] Figure 4 Shows an experimental flow chart for preparing a negative electrode sheet according to one embodiment of the present application;

[0038] Figure 5 The figure shows the positional relationship between the first negative electrode active layer, the first 3D conductive network layer, and the second negative electrode active layer in the second region of one embodiment of the present application;

[0039] Figure 6 A schematic diagram of a negative electrode coating method for a comparative example of the present application is shown;

[0040] Reference numerals: 01 first region; 02 second region; 03 third region; 04 current collector; 001 first negative electrode active layer; 002 first 3D conductive network layer; 003 second negative electrode active layer. DETAILED DESCRIPTION

[0041] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0042] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of such features. Furthermore, in the description of this application, unless otherwise specified, "plurality" means two or more.

[0043] The endpoints of the ranges and any values disclosed in this application 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 and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in this application.

[0044] In this application, the term "comprise" or "include" is an open expression, that is, it includes the content specified in this application, but does not exclude other aspects of the content.

[0045] Since the commercialization of lithium-ion batteries in 1992, their applications have gradually expanded, from portable electronics to military equipment to renewable energy applications. With the advancement of technology and the worsening energy crisis, people are increasingly favoring high-capacity, high-energy-density lithium batteries. As a key component of lithium batteries, anode materials have become a research focus worldwide. Traditional lithium battery anodes are carbon-based materials with a theoretical specific capacity of 372 mAh / g, low lithium storage capacity, and a lithium insertion potential close to the deposition potential of metallic lithium, posing safety risks during high-rate charging.

[0046] Silicon, as a metal alloyed with lithium, has attracted widespread attention due to its potential in battery technology. The theoretical specific capacity of silicon is as high as 4200mAh / g (Li 22 Si5), which is more than 11 times that of carbon materials, which gives it a significant advantage in improving battery energy density. In addition, the lithium insertion potential of silicon is lower than the lithium precipitation potential, which helps to improve the safety of the battery under high-rate charging conditions. However, silicon undergoes structural changes during the process of lithium insertion and extraction, resulting in volume expansion and contraction (up to 300% or more). This drastic volume change will cause the active material to pulverize, thereby deteriorating its electrical contact with the current collector. This not only increases the irreversible capacity during the first charge and discharge process, but also seriously affects the cycle stability of the battery.

[0047] Based on this, the applicant has developed a new type of negative electrode sheet, which aims to solve the problems encountered when silicon-carbon materials are used in lithium-ion batteries. The negative electrode sheet includes a negative electrode current collector and a composite active layer. The composite active layer is composed of two layers of negative electrode active layers and multiple 3D conductive network layers. The 3D conductive network layer is not only distributed on both sides of the two negative electrode active layers, effectively preventing the degradation of battery kinetic performance caused by insufficient lithium ion concentration at the edge of the electrode sheet, but also reduces the contact resistance between them and improves the peel strength by separating the two layers of negative electrode active layers. This design cleverly coats the negative electrode active layer containing silicon-carbon material on the current collector, inhibits the lateral and longitudinal expansion of the silicon-carbon material, reduces material pulverization, and thus extends the service life of the battery. The negative electrode sheet, its preparation method and application will be introduced in detail below.

[0048] negative electrode

[0049] The present application proposes a negative electrode sheet. According to an embodiment of the present application, the negative electrode sheet comprises: a negative electrode current collector and a composite active layer, wherein the composite active layer is located on at least one side of the negative electrode current collector. Figure 1Along the length direction of the negative electrode current collector 04, the composite active layer includes a first region 01, a second region 02 and a third region 03, the first region 01 is located on one side of the second region 02, and the third region 03 is located on a side of the second region 02 away from the first region 01.

[0050] Among them, reference Figure 2 , along the direction away from the negative electrode current collector, the second region includes a first negative electrode active layer 001, a first 3D conductive network layer 002 and a second negative electrode active layer 003 stacked in sequence; the first negative electrode active layer 001 includes a first negative electrode active material, and the first negative electrode active material includes a silicon-carbon material; the first region 01 is a second 3D conductive network layer; and the third region 03 is a third 3D conductive network layer.

[0051] Therefore, the negative electrode sheet of the present application has achieved multiple performance optimizations by dividing the composite active layer into specific areas. Among them, setting the first area and the third area as a 3D conductive network layer can, on the one hand, improve the ability of the negative electrode sheet to absorb electrolyte, and serve as a storage layer for electrolyte in the negative electrode sheet, ensuring the effective transmission of active ions, and preventing the battery dynamics from deteriorating due to insufficient lithium ion concentration at the edge of the electrode sheet; on the other hand, it also effectively inhibits the lateral expansion of the silicon-carbon material in the first negative electrode active layer in the second area, reduces the shedding and pulverization of the material, and extends the service life of the battery. Setting the second area as a double active layer can improve the energy density of the battery. In addition, by setting the 3D conductive network layer between the first negative electrode active layer and the second negative electrode active layer, on the one hand, it can reduce the contact resistance between the first active material layer and the second active material layer, improve the peeling strength, promote the rapid transmission of electrons inside the battery, and improve the charge and discharge efficiency of the battery; on the other hand, it can inhibit the longitudinal expansion of the silicon-carbon material in the first negative electrode active layer, reduce the shedding and pulverization of the material, and further extend the service life of the battery. In addition, referring to Figure 3 (For ease of observation, the 3D conductive network layer in the composite active layer is patterned in this figure.) The 3D conductive network layer in the negative electrode sheet has an "I"-shaped structure, which can enhance the hardness of the electrode sheet and improve battery safety. Therefore, the negative electrode sheet of this application not only improves the energy density of the battery, but also enhances the battery's fast charging performance, safety, and cycle stability, providing a new direction for the development of high-energy, high-power, and safe lithium-ion batteries.

[0052] District 2

[0053] In some embodiments of the present application, in the first negative electrode active layer, the first negative electrode active layer includes a first negative electrode active material, and the first negative electrode active material includes a silicon-carbon material. According to an embodiment of the present application, based on the total mass of the silicon-carbon material, the mass proportion of the silicon element is 5%-30%. For example, it can be 5%, 7%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, etc., or it can be a range composed of any of the above numerical values. Thus, by making the mass proportion of the silicon element within the above range, it is possible to increase the energy density of the battery while reducing volume expansion, thereby improving the cycle life and reliability of the battery.

[0054] In some embodiments of the present application, the second negative electrode active layer includes a second negative electrode active material, and the second negative electrode active material includes graphite, thereby effectively preventing the expansion of silicon carbon.

[0055] In some embodiments of the present application, the width of the second zone is 10 mm to 150 mm, for example, 10 mm, 20 mm, 50 mm, 70 mm, 100 mm, 120 mm, 150 mm, etc., or any range thereof.

[0056] In some embodiments of the present application, the thickness of the second region is 10 μm-200 μm, for example, 10 μm, 30 μm, 50 μm, 70 μm, 100 μm, 130 μm, 150 μm, 170 μm, 200 μm, etc., or any range thereof.

[0057] In some embodiments of the present application, in the second region, the thickness of the first negative electrode active layer is 20 μm-150 μm, for example, 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 150 μm, etc., or any range thereof.

[0058] In some embodiments of the present application, in the second region, the thickness of the second negative electrode active layer is 10 μm-100 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc., or any range thereof.

[0059] In some embodiments of the present application, in the second region, the thickness of the first 3D conductive network layer is 1 μm-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc., or any range thereof.

[0060] In some embodiments of the present application, the first negative electrode active layer further includes a first conductive agent, a first thickener and a first binder. According to an embodiment of the present application, the mass ratio of the first negative electrode active material, the first conductive agent, the first thickener and the first binder is (90-98.5): (0.5-4): (0.5-3): (0.5-3). For example, it can be 90:4:3:3, 91:2:3:3, 92:4:2:2, 93:3:2:2, 95:3:1:1, 96:2:1:1, 97:1:1:1, 98:1:0.5:0.5, 98.5:0.5:0.5:0.5, etc., or it can be a range composed of any of the above values.

[0061] In some embodiments of the present application, the second negative electrode active layer further includes a second conductive agent, a second thickener, and a second binder. According to an embodiment of the present application, the mass ratio of the second negative electrode active material, the second conductive agent, the second thickener, and the second binder is (90-98.5):(0.5-4):(0.5-3):(0.5-3). For example, it can be 90:4:3:3, 91:2:3:3, 92:4:2:2, 93:3:2:2, 95:3:1:1, 96:2:1:1, 97:1:1:1, 98:1:0.5:0.5, 98.5:0.5:0.5:0.5, etc., or it can be a range composed of any of the above values.

[0062] In some embodiments of the present application, the first 3D conductive network layer includes a third conductive agent and a third binder. According to embodiments of the present application, the mass ratio of the third conductive agent to the third binder is (90-99):(1-10). For example, it can be 90:10, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2, 99:1, etc., or can be a range consisting of any of the above values.

[0063] Districts 1 and 3

[0064] In some embodiments of the present application, the width of the first region is 10 mm to 50 mm, for example, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, etc., or any range thereof.

[0065] In some embodiments of the present application, the width of the third region is 10 mm to 50 mm, for example, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, etc., or any range thereof.

[0066] In some embodiments of the present application, the thickness of the first region is 10 μm-200 μm, for example, 10 μm, 30 μm, 50 μm, 70 μm, 100 μm, 130 μm, 150 μm, 170 μm, 200 μm, etc., or any range thereof.

[0067] In some embodiments of the present application, the thickness of the third region is 10 μm-200 μm, for example, 10 μm, 30 μm, 50 μm, 70 μm, 100 μm, 130 μm, 150 μm, 170 μm, 200 μm, etc., or any range thereof.

[0068] In some embodiments of the present application, the second 3D conductive network layer and the third 3D conductive network layer independently include a third conductive agent and a third binder. According to an embodiment of the present application, the mass ratio of the third conductive agent to the third binder is (90-99):(1-10). For example, it can be 90:10, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2, 99:1, etc., or can be a range consisting of any of the above values.

[0069] In some embodiments of the present application, the first conductive agent, the second conductive agent, and the third conductive agent are independently selected from, but not limited to, at least one of conductive carbon black, acetylene black, Ketjen black, Super P, graphene, carbon nanotubes (CNTs), and carbon nanofibers. Thus, the above-mentioned conductive agents can improve electronic conductivity, ensuring rapid electron transfer from the composite active layer to the negative electrode current collector, thereby improving the charge and discharge efficiency of the battery.

[0070] In some embodiments of the present application, the first thickener, the second thickener, and the third thickener are each independently selected from, but not limited to, at least one of sodium carboxymethylcellulose (CMC) and a polyether-modified silicone polymer. Thus, these thickeners can increase the viscosity of the negative electrode slurry, making it more suitable for the coating process and improving coating uniformity and adhesion.

[0071] In some embodiments of the present application, the first binder, the second binder, and the third binder are independently selected from at least one of, but not limited to, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), polyvinylidene fluoride (PVDF), and sodium polyacrylate (PAA-Na). Thus, these types of binders can reduce the shedding of active materials during charge and discharge, thereby extending the cycle life of the battery.

[0072] Method for preparing negative electrode sheet

[0073] This application proposes a method for preparing the above-mentioned negative electrode sheet. According to the embodiment of this application, reference Figure 4 , the method comprising:

[0074] S100: sequentially coating the second region of the negative electrode current collector with a first negative electrode active layer slurry, a 3D conductive network layer slurry, and a second negative electrode active layer slurry

[0075] In this step, by sequentially coating the first negative electrode active layer slurry, the 3D conductive network layer slurry, and the second negative electrode active layer slurry on the second region of the negative electrode current collector, a stacked first negative electrode active layer, a first 3D conductive network layer, and a second negative electrode active layer can be formed. Figure 5 The negative electrode sheet has a dual active layer, which can increase the battery's energy density. The first 3D conductive network layer 002 is located between the first negative electrode active layer 001 and the second negative electrode active layer 003. As a highly efficient electron transport medium, it can effectively reduce the contact resistance between the first negative electrode active layer 001 and the second negative electrode active layer 003, improving the efficiency of electron transmission within the electrode. At the same time, it inhibits the longitudinal expansion of the first negative electrode active layer and reduces material pulverization. In addition, the first 3D conductive network layer 002 strengthens the adhesion between the two active material layers and improves the peel strength of the overall structure, thereby improving the battery's charge and discharge efficiency and cycle stability.

[0076] S200: Coating a 3D conductive network layer slurry on the first region of the negative electrode current collector

[0077] In this step, a second 3D conductive network layer can be formed by coating a 3D conductive network layer slurry on the first region of the negative electrode current collector.

[0078] S300: Coating a 3D conductive network layer slurry on the third region of the negative electrode current collector

[0079] In this step, a third 3D conductive network layer can be formed by coating a 3D conductive network layer slurry on the third region of the negative electrode current collector.

[0080] Therefore, the provision of the second and third 3D conductive network layers can effectively inhibit the lateral expansion of the silicon-carbon material, reduce material pulverization, and extend the battery's service life. Furthermore, the first, second, and third 3D conductive network layers can serve as electrolyte storage layers within the electrode, enhancing the electrode's ability to absorb and store electrolyte, ensuring the effective transfer of active ions and preventing a decrease in battery kinetic performance.

[0081] In some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite negative electrode current collector. For example, copper foil may be used as the metal foil. The composite negative electrode current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite negative electrode current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0082] application

[0083] The present application proposes a battery comprising the aforementioned negative electrode sheet. As previously mentioned, the negative electrode sheet of the present application has a strong electrolyte absorption capacity, a dual active material layer, and a strong hardness. Therefore, the battery containing the negative electrode sheet has good fast charging performance, high energy density, and safety performance. It will be understood by those skilled in the art that the battery has all the features and advantages of the negative electrode sheet described above, and no further details will be given here.

[0084] It can be understood that, in addition to the aforementioned negative electrode sheet, the battery has the necessary structures and components of a conventional battery. Taking lithium-ion batteries as an example, in addition to the above-mentioned negative electrode sheet, it generally also includes a positive electrode sheet, a separator, an electrolyte and an outer packaging. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. Among them, the positive electrode sheet, the separator and the negative electrode sheet are made into an electrode assembly by winding or lamination process, and the electrode assembly and the electrolyte (including electrolyte, semi-solid electrolyte, solid electrolyte, etc.) are contained in the outer packaging.

[0085] In some embodiments of the present application, the electrolyte includes an electrolyte salt and a solvent. In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate. In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, ethylene carbonate (EC), vinylene carbonate, fluoroethylene carbonate, fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, polystyrene (PS), sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0086] It can be understood that there is no special restriction on the specific type of the battery, which can be a primary battery, a secondary battery (including but not limited to lithium-ion batteries, sodium-ion batteries, etc.); the shape of the battery can be a cylindrical battery, a square battery, and according to the outer packaging classification, the battery can be a hard-shell battery, a soft-pack battery, etc.

[0087] This application proposes an electrical device. According to an embodiment of this application, the electrical device includes the aforementioned battery. As previously described, the negative electrode sheet of this application has a strong electrolyte absorption capacity, a dual active material layer, and a strong hardness, so the electrical device has a high energy density and safety performance. Those skilled in the art will understand that this electrical device has all the features and advantages of the negative electrode sheet described above, and no further details will be given here.

[0088] According to an embodiment of the present application, the battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0089] Below in conjunction with embodiment, the scheme of the application will be explained. Those skilled in the art will appreciate that the following examples are merely for illustration of the application and should not be considered as limiting the scope of the application. Where specific techniques or conditions are not indicated in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product specifications. Reagents used or instruments not indicated by the manufacturer are conventional products that can be obtained commercially.

[0090] Example 1

[0091] 1. Preparation of the positive electrode sheet: Lithium cobalt oxide is used as the positive electrode active material. It is then added to a mixing tank with conductive carbon black and polyvinylidene fluoride in a mass ratio of 97.2:1.5:1.3. NMP (N-methylpyrrolidone) solvent is added and thoroughly stirred according to a known batching process. The mixture is passed through a 200-mesh sieve to form a positive electrode slurry with a solids content of 70% to 75%. The slurry is then coated onto aluminum foil using a coating machine and dried at 120°C to obtain the positive electrode sheet.

[0092] 2. Preparation of the first negative electrode slurry: Silicon-carbon material (silicon material accounts for 20 wt%), conductive carbon black, SBR and CMC are prepared into a second negative electrode slurry in a mass ratio of 97:0.5:1.5:1, with a solid content of 45%.

[0093] 3. Preparation of 3D conductive network slurry: CNTs and PVDF were mixed and dissolved in NMP at a mass ratio of 97:3 to obtain a buffer slurry with a solid content of 45%.

[0094] 4. Preparation of the second negative electrode slurry: artificial graphite, conductive agent SP (Super P), SBR and CMC were prepared into the second negative electrode slurry according to the mass ratio of 97:0.5:1.5:1, with a solid content of 48%.

[0095] 5. Zoned coating of the negative electrode sheet: Apply the first negative electrode slurry to the second zone of the current collector to form a first coating layer, apply the 3D conductive network slurry on the first coating layer to form a second coating layer, and apply the second negative electrode slurry on the second coating layer to form a third coating layer. Then, apply the 3D conductive network slurry to the first and third zones of the current collector. In the second zone, the first coating layer has a thickness of 50 μm and a maximum width of 78 mm, the second coating layer has a thickness of 5 μm and a maximum width of 78 mm, and the third coating layer has a thickness of 30 μm and a maximum width of 78 mm. The width of the first and third zones is 30 mm and the thickness is 85 μm. Drying is performed to obtain the negative electrode sheet.

[0096] 6. Preparation of lithium-ion batteries: The prepared positive electrode sheet, negative electrode sheet, and separator (substrate + single-sided ceramic + double-sided adhesive-coated composite separator) are wound using a winder to produce a wound core with the positive electrode wrapped around it. The core is then encapsulated with aluminum-plastic film and baked under vacuum for 48 hours to remove moisture. The electrolyte is then injected and the battery is subjected to conventional formation and sorting to obtain a prismatic soft-pack lithium-ion battery. The electrolyte is prepared using a conventional electrolyte formula: LiPF6 + solvent (EC + FEC + DEC + DMC + PS).

[0097] Example 2

[0098] A lithium-ion battery was prepared according to the method of Example 1, except that the carbon nanotubes in the 3D conductive network layer were replaced by graphene.

[0099] Example 3

[0100] A lithium-ion battery was prepared according to the method of Example 1, except that the coating thickness on the surface of the negative electrode current collector was different, as shown in Table 1.

[0101] Example 4

[0102] A lithium-ion battery was prepared according to the method of Example 1, except that the coating width on the surface of the negative electrode current collector was different, as shown in Table 1.

[0103] Example 5

[0104] A lithium-ion battery was prepared according to the method of Example 1, except that in the 3D conductive network slurry, the mass ratio of carbon nanotubes and PVDF was 90:10, and they were mixed and dissolved in NMP to obtain a 3D conductive network slurry with a solid content of 45%.

[0105] Comparative Example 1

[0106] A lithium-ion battery was prepared according to the method of Example 1, except that the second coating layer was not applied to the second region of the current collector.

[0107] Comparative Example 2

[0108] A lithium-ion battery was prepared according to the method of Example 1, except that the negative electrode sheet was coated in a different manner: Figure 6 As shown:

[0109] In this comparative example, the first zone, the second zone and the third zone are not distinguished, and the first negative electrode slurry is first coated on the current collector to form a first coating layer, the 3D conductive network slurry is coated on the first coating layer to form a second coating layer, and the second negative electrode slurry is coated on the second coating layer to form a third coating layer.

[0110] Comparative Example 3

[0111] A lithium-ion battery was prepared according to the method of Example 1, except that, in the second area of the current collector, the first and third coating layers were not applied in separate areas, but were all coated with the second negative electrode slurry.

[0112] Table 1

[0113]

[0114]

[0115] Performance Testing

[0116] The lithium-ion batteries prepared according to the above examples and comparative examples were subjected to relevant tests, and the specific tests are as follows:

[0117] Test the bonding strength of the electrode: fix the electrode to a 25mm board with tape, then peel it off at a certain speed to test the bonding strength;

[0118] Internal resistance test: Apply a short high current pulse to the battery, measure the voltage change, and calculate the internal resistance;

[0119] Capacity retention rate: Charge the battery at constant current and constant voltage, then discharge it at constant current, record the discharge capacity, repeat the charge and discharge cycle for 500 times, and record the discharge capacity.

[0120]

[0121] Battery cycle expansion rate: Measure the initial battery thickness, charge and discharge the battery in reverse cycles, and measure the battery thickness after a certain number of cycles.

[0122]

[0123] Lithium deposition: disassemble the battery and observe whether there is lithium metal deposition on the negative electrode surface

[0124] It can be seen from Examples 1-5 and Comparative Examples 1-3 that the negative electrode provided by the present invention has high bonding strength, low internal resistance, high energy density, good cycle performance and safety performance. The 3D conductive network layer is sandwiched between two adjacent mixed negative electrode material layers, which increases the interaction between the first negative electrode active material layer and the second negative electrode active material layer, reduces the contact internal resistance, avoids the problem of peeling between the two negative electrode active material layers, and also improves the ability to absorb electrolyte. It can be used as a storage layer for electrolyte in the electrode, ensuring good liquid phase transmission of active ions in the electrode, and improving the Li-ion battery at the edge of the electrode. + The problem of large concentration polarization is solved and the edge dynamic performance is improved. In addition, the negative electrode active material layer is sandwiched between the 3D conductive network layer to buffer the expansion between the first active material and the second active material.

[0125] Table 2

[0126]

[0127]

[0128] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A negative electrode sheet, characterized in that: include: A negative electrode current collector and a composite active layer, wherein the composite active layer is located on at least one side of the negative electrode current collector. Along the length direction of the negative electrode current collector, the composite active layer includes a first region, a second region, and a third region. The first region is located on one side of the second region, and the third region is located on a side of the second region away from the first region. Along a direction away from the negative electrode current collector, the second region includes a first negative electrode active layer, a first 3D conductive network layer, and a second negative electrode active layer stacked in sequence; the first negative electrode active layer includes a first negative electrode active material, and the first negative electrode active material includes a silicon-carbon material; The first region is a second 3D conductive network layer; The third region is a third 3D conductive network layer.

2. The negative electrode sheet according to claim 1, characterized in that: The second negative electrode active layer includes a second negative electrode active material, and the second negative electrode active material includes graphite; And / or, based on the total mass of the silicon-carbon material, the mass proportion of the silicon element is 5%-30%.

3. The negative electrode sheet according to any one of claims 1 to 2, characterized in that: The width of the second zone is 10mm-150mm; And / or, the width of the first zone is 10 mm to 50 mm; And / or, the width of the third zone is 10 mm to 50 mm; and / or, the thickness of the second region is 10 μm-200 μm; and / or, the thickness of the first region is 10 μm-200 μm; And / or, the thickness of the third region is 10 μm-200 μm.

4. The negative electrode sheet according to claim 3, characterized in that: The thickness of the first negative electrode active layer is 20 μm-150 μm; and / or, the thickness of the second negative electrode active layer is 10 μm-100 μm; And / or, the thickness of the first 3D conductive network layer is 1 μm-10 μm.

5. The negative electrode sheet according to claim 4, characterized in that: The first negative electrode active layer further includes a first conductive agent, a first thickener and a first binder; And / or, the second negative active layer further comprises a second conductive agent, a second thickener and a second binder; And / or, the first 3D conductive network layer, the second 3D conductive network layer and the third 3D conductive network layer independently include a third conductive agent and a third binder.

6. The negative electrode sheet according to claim 5, characterized in that: The mass ratio of the first negative electrode active material, the first conductive agent, the first thickener and the first binder is (90-98.5):(0.5-4):(0.5-3):(0.5-3); And / or, the mass ratio of the second negative electrode active material, the second conductive agent, the second thickener and the second binder is (90-98.5):(0.5-4):(0.5-3):(0.5-3); And / or, the mass ratio of the third conductive agent to the third binder is (90-99):(1-10).

7. The negative electrode sheet according to claim 6, characterized in that: The first conductive agent, the second conductive agent and the third conductive agent are independently selected from at least one of conductive carbon black, acetylene black, Ketjen black, Super P, graphene, carbon nanotubes and carbon nanofibers; and / or, the first thickener, the second thickener and the third thickener are independently selected from at least one of sodium carboxymethyl cellulose and polyether-modified silicone polymer; And / or, the first binder, the second binder and the third binder are independently selected from at least one of styrene-butadiene rubber, nitrile rubber, polyvinylidene fluoride and sodium polyacrylate.

8. A method for preparing the negative electrode sheet according to any one of claims 1 to 7, characterized in that: include: sequentially coating a first negative electrode active layer slurry, a 3D conductive network layer slurry, and a second negative electrode active layer slurry on the second region of the negative electrode current collector to form a stacked arrangement of the first negative electrode active layer, the first 3D conductive network layer, and the second negative electrode active layer; coating a 3D conductive network layer slurry on the first region of the negative electrode current collector to form a second 3D conductive network layer; A 3D conductive network layer slurry is coated on the third region of the negative current collector to form a third 3D conductive network layer.

9. A battery, characterized in that: The invention comprises the negative electrode sheet according to any one of claims 1 to 7 or the negative electrode sheet prepared by the method according to claim 8.

10. An electrical device, characterized in that: A battery comprising the battery of claim 9.

Images