Negative plate, battery and electric device

Abstract

The invention provides a negative electrode plate, a battery and a power utilization device, the negative electrode plate comprises a negative electrode current collector and a negative electrode coating located on at least one side surface of the negative electrode current collector, the negative electrode coating comprises a carbon nanotube, and the carbon nanotube contains a nickel element. The invention can reduce the internal resistance of the resistor and improve the fast charging performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of electrochemical devices, specifically to a negative electrode, a battery, and an electrical device. Background Technology

[0002] Rechargeable batteries are widely used in electric vehicles (such as electric cars and electric motorcycles), aerospace, and many other fields. With technological advancements, increasingly higher demands are being placed on the fast-charging performance of batteries. However, in related technologies, high internal resistance in batteries is detrimental to their fast-charging performance. For example, to increase the energy density of a battery, the areal density of the electrode plates (such as the negative electrode) is typically increased, but this increases the battery impedance, thus deteriorating the battery's fast-charging performance. Summary of the Invention

[0003] This invention provides a negative electrode sheet, a battery, and an electrical device that can reduce internal resistance, improve the fast charging performance of the battery, and effectively overcome the defects of the prior art.

[0004] In one aspect, the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode coating located on at least one side surface of the negative electrode current collector, the negative electrode coating comprising carbon nanotubes containing nickel.

[0005] According to one embodiment of the present invention, the diameter of the carbon nanotube is 20-80 nm.

[0006] According to one embodiment of the present invention, the diameter of the carbon nanotube is 30-60 nm.

[0007] According to one embodiment of the present invention, the length of the carbon nanotube is 0.5 to 20 μm.

[0008] According to one embodiment of the present invention, the negative electrode coating includes a first dressing layer and a second dressing layer located on the side surface of the first dressing layer opposite to the negative electrode current collector, the second dressing layer including the carbon nanotubes.

[0009] According to one embodiment of the present invention, the second dressing layer includes a second negative electrode active material, wherein the mass ratio of the carbon nanotubes in the second dressing layer to the second negative electrode active material is 0.09% to 3%.

[0010] According to one embodiment of the present invention, the content of carbon nanotubes in the first dressing layer is 0.

[0011] According to one embodiment of the present invention, the second dressing layer includes a conductive agent, wherein the conductive agent in the second dressing layer includes a first conductive agent and a second conductive agent, wherein the first conductive agent is the carbon nanotube, and the second conductive agent is a conductive material other than the carbon nanotube.

[0012] According to one embodiment of the present invention, the mass ratio of the first conductive agent to the second conductive agent is 1:(1-20).

[0013] According to one embodiment of the present invention, the second conductive agent includes one or more of conductive carbon black, graphene, carbon fiber materials, and nickel-free carbon nanotubes.

[0014] According to one embodiment of the present invention, the first dressing layer includes a first negative electrode active material and a conductive agent, the second dressing layer includes a second negative electrode active material and a conductive agent, and the conductive agent in the second dressing layer includes the carbon nanotubes; the mass ratio of the conductive agent in the first dressing layer to the first negative electrode active material is greater than or equal to the mass ratio of the conductive agent in the second dressing layer to the second negative electrode active material.

[0015] According to one embodiment of the present invention, the areal density of the first dressing layer is less than or equal to the areal density of the second dressing layer.

[0016] According to one embodiment of the present invention, the first dressing layer includes a first negative electrode active material, which includes one or more of natural graphite, artificial graphite, hard carbon, and silicon carbide; and / or, the second dressing layer includes a second negative electrode active material, which includes one or more of natural graphite, artificial graphite, hard carbon, and silicon carbide.

[0017] In another aspect, the present invention provides a battery comprising the aforementioned negative electrode.

[0018] In another aspect, the present invention provides an electrical device including the battery described above.

[0019] The implementation of this invention has at least the following beneficial effects: by introducing carbon nanotubes containing nickel into the negative electrode coating and building a conductive network in the negative electrode coating, the impedance of the negative electrode sheet can be reduced, thereby reducing the internal resistance of the battery and improving the battery's fast charging performance. At the same time, the high energy density of the negative electrode sheet and the battery can be maintained, further ensuring the electrochemical performance of the battery. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the negative electrode structure according to an embodiment of the present invention;

[0021] Figure 2 This is an electron microscope image of the nickel-containing CNTs in the example.

[0022] Explanation of reference numerals in the attached figures: 1. Negative electrode current collector; 2. Negative electrode coating; 21. First dressing layer; 22. Second dressing layer. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a negative electrode sheet, such as... Figure 1 As shown, the negative electrode includes a negative current collector 1 and a negative electrode coating 2 located on at least one side surface of the negative current collector 1. The negative electrode coating 2 includes carbon nanotubes (CNTs) containing nickel (Ni).

[0025] According to the inventors' research, by introducing CNTs containing nickel into the negative electrode coating and building a conductive network in the negative electrode coating, the impedance of the negative electrode sheet can be reduced, thereby reducing the internal resistance of the battery and improving the battery's fast charging performance. At the same time, the high energy density of the negative electrode sheet and the battery can be maintained, further ensuring the electrochemical performance of the battery.

[0026] Normally, the Ni element in CNTs exists in the form of nickel compounds, which are dispersed inside the CNTs.

[0027] In this embodiment of the invention, CNTs can be commercially available or self-made using conventional methods in the art. For example, CNTs can be prepared using a moving bed or fixed bed growth process. Specifically, CNTs containing Ni can be CNTs synthesized by catalysis of a nickel-based catalyst, such as using a nickel-based catalyst and growing CNTs using a fixed bed process. The synthesized CNTs contain Ni, which exists in the form of a compound inside the CNT.

[0028] In some embodiments, the diameter of the nickel-containing CNT can be 20–80 nm. Exemplarily, the diameter of the CNT can be a range of 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, or any combination thereof.

[0029] According to the inventors' research, by introducing CNTs with a diameter of 20–80 nm into the negative electrode coating 2, the CNTs have a more suitable size. This allows for improved compaction performance and energy density of the negative electrode sheet, while also ensuring the CNTs' connection to the conductive pathways in the negative electrode coating 2, improving the active ion diffusion capability of the negative electrode coating 2, and reducing the impedance of the negative electrode sheet and the internal resistance of the battery. Therefore, by controlling the CNT diameter within the aforementioned range (20–80 nm), it is beneficial to further maintain a high compaction density of the negative electrode coating 2, thereby maintaining a high energy density of the negative electrode sheet and the battery, while further reducing the impedance of the negative electrode sheet, thereby reducing the internal resistance of the battery and improving the fast-charging performance of the battery.

[0030] Further research revealed that the diameter of the aforementioned nickel-containing CNTs can be 30–60 nm. According to the inventors' research, in the negative electrode structure system of this invention, by introducing CNTs with a diameter of 30–60 nm into the negative electrode coating 2, their curvature is reduced, which facilitates the construction of a good conductive network in the negative electrode coating 2 and promotes the diffusion of active ions within the negative electrode coating 2, thereby reducing the impedance of the negative electrode. Simultaneously, it does not significantly affect the compaction density of the negative electrode coating 2, maintaining a high energy density for the negative electrode. This reduces the internal resistance of the battery, improves its fast-charging performance, and also enhances other battery performance aspects such as capacity.

[0031] Furthermore, the length (tube length) of the aforementioned nickel-containing CNTs can be 0.5–20 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm or any combination thereof, which helps to reduce battery impedance and improve battery fast charging performance.

[0032] Generally, the negative electrode coating 2 includes a negative electrode active material, a conductive agent, and a binder, and may also include a thickener. The conductive agent includes the aforementioned nickel-containing CNTs. These nickel-containing CNTs act as a conductive agent in the negative electrode coating 2, building a good conductive network between the negative electrode active material particles. They also improve the electrolyte absorption and retention capacity of the negative electrode sheet, enhance its electrolyte wettability, promote the diffusion of active ions within the negative electrode sheet, reduce its impedance, and consequently reduce the battery's internal resistance, improving its fast-charging performance and other properties.

[0033] Specifically, the negative electrode active material may include carbon-based negative electrode active materials and / or silicon-based negative electrode active materials. Carbon-based negative electrode active materials include, for example, graphite and / or hard carbon. Graphite may include natural graphite and / or artificial graphite. Silicon-based negative electrode active materials include, for example, silicon-carbon materials.

[0034] In some embodiments, the negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, and silicon carbon.

[0035] The embodiments of the present invention may employ a conventional negative electrode current collector 1 in the art, for example, the negative electrode current collector 1 includes copper foil.

[0036] In this embodiment of the invention, the negative electrode coating 2 can be a single-layer structure (e.g., the second dressing layer 22 described below) or a double-layer or more-layer structure.

[0037] In some embodiments, such as Figure 1 As shown, the negative electrode coating 2 includes a first coating layer 21 (lower layer) and a second coating layer 22 (upper layer) located on the side of the first coating layer 21 facing away from the negative electrode current collector 1. The second coating layer 22 includes the aforementioned CNTs containing nickel. Through this double-layer structure design and the introduction of the aforementioned CNTs containing nickel in the upper layer, a good conductive network is built, which is conducive to the formation of a good void structure in the upper layer. This promotes the uniformity of the reaction of the negative electrode sheet during the charging and discharging process of the battery, which is conducive to further reducing the impedance of the negative electrode sheet, thereby reducing the internal resistance of the battery and improving the battery's fast charging performance.

[0038] Specifically, both the first dressing layer and the second dressing layer include a negative electrode active material (the negative electrode active material in the first dressing layer is called the first negative electrode active material, and the negative electrode active material in the second dressing layer is called the second negative electrode active material), and the first negative electrode active material and the second negative electrode active material may be the same or different.

[0039] In some embodiments, the first negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, and silicon carbon.

[0040] In some embodiments, the second negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, and silicon carbon.

[0041] In some embodiments, the mass ratio of carbon nanotubes in the second dressing layer 22 to the second negative electrode active material in the second dressing layer 22 is 0.09% to 3%, for example, a range of 0.09%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or any two of these, which is beneficial for reducing battery internal resistance and improving battery fast charging performance.

[0042] In addition, the content of nickel-containing CNTs in the first dressing layer 21 is 0, that is, the first dressing layer 21 does not contain the aforementioned nickel-containing CNTs. The first dressing layer 21 may include other conductive materials (hereinafter referred to as the third conductive agent) besides nickel-containing CNTs. The third conductive agent includes, for example, one or more of conductive carbon black (SP), graphene, carbon fiber materials, and nickel-free carbon nanotubes.

[0043] Specifically, the conductive agent in the second dressing layer 22 may include a first conductive agent and a second conductive agent. The first conductive agent is a carbon nanotube containing nickel, and the second conductive agent is a conductive material other than a carbon nanotube containing nickel. Specifically, the second conductive agent may include one or more of conductive carbon black (SP), graphene, carbon fiber materials, and carbon nanotubes that do not contain nickel.

[0044] Specifically, the aforementioned nickel-free carbon nanotubes can be thin tubes with a diameter of less than 15 nm.

[0045] In some embodiments, the mass ratio of the first conductive agent to the second conductive agent can be 1:(1 to 20), for example, a range consisting of 1:1, 1:3, 1:5, 1:8, 1:10, 1:13, 1:15, 1:18, 1:20 or any two of these.

[0046] Furthermore, the mass ratio w1 of the conductive agent to the first negative electrode active material in the first dressing layer 21 can be greater than or equal to the mass ratio w2 of the conductive agent to the second negative electrode active material in the second dressing layer 22 (i.e., w1 / w2≥1).

[0047] Furthermore, the areal density ρ1 of the first dressing layer 21 can be less than or equal to the areal density ρ2 of the second dressing layer 22 (i.e., ρ1 / ρ2≤1).

[0048] In this embodiment of the invention, the areal density of the negative electrode coating 2 and different regions of the negative electrode coating 2 (such as the first dressing layer 21 and the second dressing layer 22) can be tested using a scanning electron microscope (SEM). The characteristics of CNT, such as the tube diameter and tube length, can be measured using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The specific testing standards can be found in standard GB / T30544.13-2018.

[0049] In practice, the negative electrode sheet can be placed in an HCl solution of a certain concentration. The dissolution process is accelerated by stirring or ultrasonic treatment to remove the negative electrode current collector 1 (e.g., copper foil), the binder (e.g., SBR) and thickener (e.g., CMC) in the coating layer, and the SEI film in the negative electrode active material and conductive agent (e.g., carbon materials such as graphite and CNT). The resulting solution and insoluble components are then separated into solid and liquid phases through filtration or centrifugation to obtain the insoluble components (i.e., the solid phase, mainly the negative electrode active material and conductive agent). The insoluble components are dried and ground into fine particles of a certain size. These particles are then mixed with an appropriate amount of solvent or dispersant and placed in an ultrasonic bath or ultrasonically treated using an ultrasonic probe to form a uniform suspension. During ultrasonic treatment, due to the different characteristics of the negative electrode active material (e.g., graphite) and CNT, minute aggregation and dispersion phenomena occur. After ultrasonication, centrifugation is performed, and the centrifugation rate is adjusted to separate the CNTs and the negative electrode active material, and then perform physical property tests on them separately. For example, after separating the CNTs from the negative electrode sheet through this process, the diameter and length of the CNTs can be tested according to the standard GB / T 30544.13-2018.

[0050] Specifically, FIB-SEM can be used to directly characterize the surface and cross-section of the negative electrode coating, including features such as the conductivity of the coating (e.g., whether each region of the negative electrode coating contains carbon nanotubes, and the diameter and length of the carbon nanotubes).

[0051] In this embodiment of the invention, the presence of Ni in CNTs can be detected by TEM and inductively coupled plasma (ICP) testing. Specifically, a TEM image of the CNT can be obtained through TEM testing, and ICP-assisted testing can be used to perform qualitative analysis of the elements in the CNT to detect the presence of nickel inside the CNT.

[0052] Specifically, based on the total mass of the first dressing layer 21, the mass fraction of the first negative electrode active material (i.e., the ratio of the mass of the first negative electrode active material to the total mass of the first dressing layer 21) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass fraction of the conductive agent (i.e., the ratio of the total mass of the conductive agent in the first dressing layer 21 to the total mass of the first dressing layer 21) can be 0.3% to 15%, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%. The mass fraction of the binder can be 0.3% to 15%, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any two of these. The mass fraction of the thickener can be 0.3% to 15%, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any two of these.

[0053] Furthermore, based on the total mass of the second dressing layer 22, the mass fraction of the second negative electrode active material (i.e., the ratio of the mass of the second negative electrode active material to the total mass of the second dressing layer 22) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass fraction of the conductive agent (i.e., the ratio of the total mass of the conductive agent in the second dressing layer 22 to the total mass of the second dressing layer 22) can be 0.3% to 15%, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%. The mass fraction of the binder can be 0.3% to 15%, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any two of these. The mass fraction of the thickener can be 0.3% to 15%, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any two of these.

[0054] In this embodiment of the invention, the binder in the negative electrode coating 2 (first dressing layer 21, second dressing layer 22) can be a conventional adhesive material in the art. For example, the binder in the negative electrode coating 2 can include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. The thickener can be a conventional thickener in the art, such as a carboxymethyl cellulose (CMC) thickener, for example, a carboxymethyl cellulose salt, such as sodium carboxymethyl cellulose (CMC-Na).

[0055] In this embodiment of the invention, a negative electrode coating 2 (positive electrode active material layer) can be provided on one side surface of the negative electrode current collector 1, or a negative electrode coating 2 can be provided on both opposite sides of the negative electrode current collector 1 in the thickness direction (e.g., ...). Figure 1 As shown, when negative electrode coatings 2 are respectively provided on the surfaces of opposite sides of the negative electrode current collector 1, the negative electrode coating 2 on one side of the surface can be the aforementioned negative electrode coating 2 containing nickel CNTs, or the negative electrode coatings 2 on the opposite sides of the negative electrode current collector 1 can both be the aforementioned negative electrode coating 2 containing nickel CNTs.

[0056] In this embodiment of the invention, the negative electrode sheet can be prepared by a conventional coating method in the art. Specifically, the components used to form the negative electrode coating 2, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a first solvent, such as water (specifically, deionized water). Following this process, a first slurry for forming the first coating layer 21 and a second slurry for forming the second coating layer 22 are prepared respectively. Then, a double-layer coating process is used to coat the second slurry and the first slurry onto the surface of the negative electrode current collector 1. After drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method and are not particularly limited thereto.

[0057] This invention also provides a battery including the above-described negative electrode sheet, which has advantages corresponding to the above-described negative electrode sheet, and will not be described in detail here.

[0058] The battery in this embodiment of the invention can be a lithium-ion battery, but is not limited thereto.

[0059] Generally, a battery includes an electrolyte, a battery cell, and a casing that encapsulates the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked battery cell, meaning it is composed of a positive electrode, a separator, and a negative electrode stacked together.

[0060] Specifically, the positive electrode sheet includes a positive current collector and a positive electrode coating located on at least one side surface of the positive current collector. Specifically, the positive electrode coating may be provided on one side surface of the positive current collector, or the positive electrode coating may be provided on both sides (both positive and negative surfaces) of opposite sides in the thickness direction of the positive current collector.

[0061] Specifically, the positive electrode coating (positive electrode active material layer) may include a positive electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the positive electrode active material may include lithium-containing positive electrode active materials used in lithium-ion batteries, such as one or more of lithium iron phosphate (LiFePO4), lithium cobalt oxide, and ternary positive electrode materials. Ternary positive electrode materials may include, for example, nickel-cobalt-manganese ternary materials and / or nickel-cobalt-aluminum ternary materials. The conductive agent may include one or more of conductive carbon black (SP), carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber. The binder may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0062] Based on the total mass of the positive electrode coating, the mass fraction of the positive electrode active material (i.e., the ratio of the mass of the positive electrode active material to the total mass of the positive electrode coating) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof; and the mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0063] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0064] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder and other components used to form the positive electrode coating can be dispersed in a second solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry, which is then coated on the surface of the positive electrode current collector. After drying, rolling and other processes, the positive electrode sheet is obtained.

[0065] The electrolyte in this embodiment of the invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include an organic solvent and an electrolyte salt. The organic solvent may include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The electrolyte salt may include lithium salt, such as lithium hexafluorophosphate (LiPF6), but is not limited thereto.

[0066] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. The separator in this embodiment of the invention can be a conventional separator in the art, for example, the separator includes a polypropylene membrane, but is not limited thereto.

[0067] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0068] The embodiments of the present invention can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked to obtain a stacked cell; then the cell is placed in a casing (outer packaging) and after conventional processes such as electrolyte injection and encapsulation, the battery is obtained.

[0069] This invention also provides an electrical device including the battery described above. This electrical device has advantages corresponding to the battery described above, which will not be described in detail here.

[0070] The present invention will be further described below through specific embodiments.

[0071] Unless otherwise specified, the Ni-containing CNTs used in the following examples and comparative examples have TEM images obtained by TEM testing, and ICP testing has confirmed the presence of nickel within the CNTs. The TEM images of the Ni-containing CNTs are shown below. Figure 2 ,from Figure 2 As can be seen, nickel (a nickel-containing compound) is present inside the CNT.

[0072] Example 1

[0073] 1. Preparation of negative electrode sheet

[0074] Artificial graphite, conductive carbon black (SP), thickener (CMC-Na), and binder (SBR) are mixed in a mass ratio of 96:1:1:2, and deionized water is added to prepare a first slurry for forming the first dressing layer (lower layer).

[0075] Artificial graphite, conductive agent, thickener (CMC), and binder (SBR) are mixed in a mass ratio of 96:1:1:2, and deionized water is added to prepare a second slurry for forming the second dressing layer (upper layer); wherein the conductive agent is CNT and SP, and the mass ratio of CNT and SP is 1:10 (i.e., CNT:SP = 1:10).

[0076] A double-layer coating process is used to simultaneously coat the first slurry and the second slurry onto the surface of a copper foil. After drying and rolling (rolling pressure of about 1.5 MPa), a positive electrode sheet is obtained. The positive and negative electrode coatings with the first coating layer and the second coating layer are formed on both the front and back surfaces of the copper foil, respectively.

[0077] Specifically, the structural diagram of the negative electrode is as follows: Figure 1 As shown, it includes a negative electrode current collector (copper foil), negative electrode coatings on both the front and back surfaces of the negative electrode current collector, and each side of the negative electrode coating includes a first coating layer and a second coating layer on the surface of the first coating layer facing away from the negative electrode current collector. The areal density ρ1 of the first coating layer and the areal density ρ2 of the second coating layer are the same (i.e., ρ 1 / ρ2=1), the mass ratio w1 of the conductive agent to artificial graphite (first negative electrode active material) in the first dressing layer is equal to the mass ratio w2 of the conductive agent to artificial graphite (second negative electrode active material) in the second dressing layer (i.e. w1 / w2=1), the diameter of the CNT in the second dressing layer is 40nm and the tube length is 2μm.

[0078] 2. Preparation of the positive electrode sheet

[0079] LiFePO4, SP, and PVDF were mixed in a mass ratio of 97:1:2, and the resulting powder was stirred evenly with NMP in a homogenizer to prepare a positive electrode slurry.

[0080] The positive electrode slurry is coated on both sides of the aluminum foil. After drying and rolling, a positive electrode coating is formed on both sides of the aluminum foil, thus producing a positive electrode sheet.

[0081] (2) Battery assembly

[0082] The positive electrode, separator (polypropylene membrane), and negative electrode are stacked to assemble a stacked cell; the stacked cell is placed in an aluminum-plastic film, and after processes such as electrolyte injection and encapsulation, it is assembled into a lithium-ion battery (the battery design capacity is 1.7Ah); the composition of the electrolyte used is as follows: the organic solvents are ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the volume ratio of EC, DMC, and EMC is 1:1:1, and the concentration of LiPF6 in the electrolyte is 1mol / L.

[0083] Comparative Examples 1 and Examples 2 to 19: The difference from Example 1 lies in the following: the mass ratio w1 of the conductive agent in the first dressing layer, the mass ratio w2 of the conductive agent in the second dressing layer to the artificial graphite (first negative electrode active material) in the second dressing layer (i.e., w1 / w2), and the ratio ρ1 of the areal density of the first dressing layer to ρ2 of the second dressing layer (i.e., ρ2 / ρ2). 1 / ρ2) The mass ratio of CNTs to artificial graphite (second negative electrode active material) in the second dressing layer, the diameter and length of the CNTs used, and the structure of the negative electrode coating are different. See Table 1 for details. Except for the differences shown in Table 1, the other conditions are the same as in Example 1.

[0084] The difference between Example 9 and Example 1 is that in the negative electrode sheet, the negative electrode coating only has a second coating layer (the first coating layer is not provided).

[0085] Comparative Example 2: The difference from Example 1 is that in the negative electrode sheet, the negative electrode coating only has a first coating layer (no second coating layer is provided).

[0086] The internal resistance (DCIR) of the batteries in each embodiment and comparative example was tested using the following procedure, and the results are shown in Table 1. The DCIR test (which mainly reflects the liquid absorption and retention capacity and conductivity of the conductive agent) was conducted using the following method:

[0087] (1) 25℃, 0.2C charge and discharge, calibrate the battery capacity;

[0088] (2) Charge at 0.2C to 50% SOC and 90% SOC;

[0089] (3) Set 2C charging for 30s, record the termination voltage and termination current of each process, and calculate DCIR.

[0090] Table 1. Relevant parameters of the negative electrode and DC internal resistance of the battery.

[0091]

[0092] As can be seen from Table 1, compared with Comparative Example 1 and Comparative Example 2, the introduction of CNTs containing Ni elements into the negative electrode coating in Examples 1 to 19 can reduce the DC impedance of the battery.

[0093] Furthermore, compared to Examples 8 and 9, the negative electrode in Example 1 is double-coated, and CNTs containing Ni are introduced into the second coating layer of the negative electrode, which can more significantly reduce the DC resistance of the battery.

[0094] Furthermore, as can be seen from Examples 1 to 7 and Example 19, compared with Examples 7 and 19, Examples 1 to 6 can further reduce the DC impedance of the battery by further controlling the diameter of the CNT within the range of 20 to 80 nm.

[0095] Furthermore, as can be seen from Examples 1, 10 and 11, compared with Example 11, Example 1 and Example 10 further control w1 / w2≥1, which can further reduce the DC impedance of the battery.

[0096] Furthermore, as can be seen from Examples 1, 12 and 13, compared with Example 13, Example 1 and Example 12 further control ρ1 / ρ2≤1, which can further reduce the DC impedance of the battery.

[0097] Furthermore, as can be seen from Examples 1 and 14 to 18, compared with Example 18, Examples 1 and 14 to 17 can further reduce the DC resistance of the battery by further controlling the mass ratio of CNT to graphite in the second dressing layer within the range of 0.09% to 3%.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode coating located on at least one side of the surface of the negative electrode current collector, the negative electrode coating comprising carbon nanotubes containing nickel.

2. The negative electrode sheet according to claim 1, characterized in that, The diameter of the carbon nanotubes is 20–80 nm.

3. The negative electrode sheet according to claim 2, characterized in that, The diameter of the carbon nanotubes is 30–60 nm.

4. The negative electrode sheet according to claim 1, characterized in that, The length of the carbon nanotubes is 0.5–20 μm.

5. The negative electrode sheet according to claim 1, characterized in that, The negative electrode coating includes a first dressing layer and a second dressing layer located on the side of the first dressing layer facing away from the negative electrode current collector, the second dressing layer including the carbon nanotubes.

6. The negative electrode sheet according to claim 5, characterized in that, The second dressing layer includes a second negative electrode active material, wherein the mass ratio of the carbon nanotubes in the second dressing layer to the second negative electrode active material is 0.09% to 3%.

7. The negative electrode sheet according to claim 5, characterized in that, The carbon nanotube content in the first dressing layer is 0.

8. The negative electrode sheet according to any one of claims 5-7, characterized in that, The second dressing layer includes a conductive agent, which includes a first conductive agent and a second conductive agent. The first conductive agent is the carbon nanotube, and the second conductive agent is a conductive material other than the carbon nanotube.

9. The negative electrode sheet according to claim 8, characterized in that, The mass ratio of the first conductive agent to the second conductive agent is 1:(1~20).

10. The negative electrode sheet according to claim 8, characterized in that, The second conductive agent includes one or more of conductive carbon black, graphene, carbon fiber materials, and nickel-free carbon nanotubes.

11. The negative electrode sheet according to any one of claims 5-7, characterized in that, The first dressing layer includes a first negative electrode active material and a conductive agent, and the second dressing layer includes a second negative electrode active material and a conductive agent. The conductive agent in the second dressing layer includes the carbon nanotubes. The mass ratio of the conductive agent in the first dressing layer to the first negative electrode active material is greater than or equal to the mass ratio of the conductive agent in the second dressing layer to the second negative electrode active material.

12. The negative electrode sheet according to any one of claims 5-7, characterized in that, The areal density of the first dressing layer is less than or equal to the areal density of the second dressing layer.

13. The negative electrode sheet according to any one of claims 5-7, characterized in that, The first dressing layer includes a first negative electrode active material, which includes one or more of natural graphite, artificial graphite, hard carbon, and silicon carbide. And / or, the second dressing layer includes a second negative electrode active material, which includes one or more of natural graphite, artificial graphite, hard carbon, and silicon carbide.

14. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-13.

15. An electrical appliance, characterized in that, Includes the battery as described in claim 14.

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