Negative electrode sheet, battery, and electric device

Abstract

The present application provides a negative electrode sheet, a battery, and an electric device. The negative electrode sheet comprises a negative electrode current collector and a negative electrode coating located on the surface of at least one side of the negative electrode current collector; the negative electrode coating comprises carbon nanotubes; and the carbon nanotubes contain nickel. The present application can reduce the internal resistance of batteries and improve the fast charging performance of the batteries.

Description

Negative electrode sheet, battery and electric device

[0001] The present application claims priority to the Chinese patent application No. 202411340955.1, filed on September 24, 2024, and entitled "Negative electrode sheet, battery and electric device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the field of electrochemical devices, in particular to a negative electrode sheet, a battery and an electric device. BACKGROUND

[0003] Secondary batteries are widely used in electric vehicles (such as electric cars, electric motorcycles), aerospace and other fields. With the development of technology, there is an increasingly high demand for the fast charging (fast charging) performance of batteries. However, in the related art, the internal resistance of the battery is large, which is not conducive to its fast charging performance. For example, in order to improve the energy density of the battery, the area density of the electrode sheet (such as the negative electrode sheet) usually needs to be increased, but this will increase the impedance of the battery, which will deteriorate the fast charging (fast charging) performance of the battery. SUMMARY

[0004] The present application provides a negative electrode sheet, a battery and an electric device, which can reduce the internal resistance and improve the fast charging performance of the battery, effectively overcoming the defects existing in the prior art.

[0005] In one aspect of the present application, a negative electrode sheet is provided, comprising a negative current collector and a negative coating layer located on at least one side surface of the negative current collector, the negative coating layer comprising carbon nanotubes, the carbon nanotubes containing a nickel element.

[0006] According to an embodiment of the present application, the tube diameter of the carbon nanotubes is 20-80 nm.

[0007] According to an embodiment of the present application, the tube diameter of the carbon nanotubes is 30-60 nm.

[0008] According to an embodiment of the present application, the length of the carbon nanotubes is 0.5-20 μm.

[0009] According to an embodiment of the present application, the negative coating layer comprises a first coating layer and a second coating layer located on the side surface of the first coating layer away from the negative current collector, the second coating layer comprising the carbon nanotubes.

[0010] According to an embodiment of the present application, the second coating layer comprises a second negative active material, and the mass ratio of the carbon nanotubes to the second negative active material in the second coating layer is 0.09%-3%.

[0011] According to an embodiment of the present application, the content of the carbon nanotubes in the first coating layer is 0.

[0012] According to an embodiment of the present application, the second coating layer comprises a conductive agent, the conductive agent in the second coating layer comprises 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.

[0013] According to an embodiment of the present application, the mass ratio of the first conductive agent to the second conductive agent is 1:(1-20).

[0014] According to an embodiment of the present application, the second conductive agent comprises one or more of conductive carbon black, graphene, carbon fiber material, and carbon nanotube without nickel element.

[0015] According to an embodiment of the present application, the first coating layer comprises a first negative active material and a conductive agent, the second coating layer comprises a second negative active material and a conductive agent, the conductive agent in the second coating layer comprises the carbon nanotube; the mass ratio of the conductive agent in the first coating layer to the first negative active material is greater than or equal to the mass ratio of the conductive agent in the second coating layer to the second negative active material.

[0016] According to an embodiment of the present application, the areal density of the first coating layer is less than or equal to the areal density of the second coating layer.

[0017] According to an embodiment of the present application, the first coating layer comprises a first negative active material, the first negative active material comprises one or more of natural graphite, artificial graphite, hard carbon, and silicon-carbon; and / or, the second coating layer comprises a second negative active material, the second negative active material comprises one or more of natural graphite, artificial graphite, hard carbon, and silicon-carbon.

[0018] According to another aspect of the present application, a battery is provided, comprising the above negative electrode sheet.

[0019] According to another aspect of the present application, an electric device is provided, comprising the above battery.

[0020] According to the embodiments of the present application, at least the following beneficial effects are achieved: by introducing carbon nanotubes containing nickel elements into the negative electrode coating layer, a conductive network is formed in the negative electrode coating layer, which can reduce the impedance of the negative electrode sheet, and further reduce the internal resistance of the battery, and improve the fast charging performance of the battery, while maintaining a high energy density of the negative electrode sheet and the battery, and further ensuring the electrochemical performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a schematic view of a negative electrode sheet structure according to an embodiment of the present application;

[0022] FIG. 2 is an electron microscope image of the CNT containing the nickel element in the embodiment.

[0023] Legend: 1, negative current collector; 2, negative coating; 21, first coating layer; 22, second coating layer. DETAILED DESCRIPTION

[0024] To make the technical personnel in the art better understand the scheme of the present application, the present application is further described in detail below. The specific embodiments listed below are only to describe the principles and characteristics of the present application, and the examples are only used to explain the present application, and do not limit the scope of the present application. Based on the embodiments of the present application, all other embodiments obtained by the ordinary skilled person in the art without creative labor are within the scope of protection of the present application.

[0025] The embodiment of the present application provides a negative electrode sheet, as shown in FIG. 1, which comprises a negative current collector 1 and a negative coating 2 on at least one side surface of the negative current collector 1, wherein the negative coating 2 comprises carbon nanotubes (CNT) containing a nickel (Ni) element.

[0026] According to the research of the inventor, by introducing CNT containing a nickel element into the negative coating to form a conductive network in the negative coating, the impedance of the negative electrode sheet can be reduced, thereby reducing the internal resistance of the battery and improving the fast charging performance of the battery, etc. At the same time, the high energy density of the negative electrode sheet and the battery can be maintained, and the electrochemical performance of the battery is further ensured.

[0027] Generally, the Ni element in the CNT exists in the form of a nickel compound, which is dispersed in the inside of the CNT.

[0028] In the embodiment of the present application, the CNT can be commercially available or self-made by conventional methods in the art. For example, the CNT can be prepared by a moving bed or fixed bed growth process, wherein the CNT containing the Ni element can be CNT synthesized by a nickel-based catalyst, for example, the CNT is grown by a fixed bed process using a nickel-based catalyst, and the synthesized CNT contains the Ni element, which exists in the form of a compound in the inside of the CNT.

[0029] In some embodiments, the CNT containing the nickel element can have a tube diameter of 20-80 nm. For example, the CNT can have a tube diameter 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 a range formed by any two of them.

[0030] According to the research of the inventor, by introducing the CNT with the tube diameter of 20-80 nm in the negative electrode coating 2, the CNT has a more suitable size, which can improve the compaction performance of the negative electrode sheet, improve the energy density of the negative electrode sheet, and at the same time, connect the conductive path in the negative electrode coating 2, improve the active ion diffusion capacity of the negative electrode coating 2, reduce the negative electrode sheet impedance and the battery internal resistance. Therefore, by controlling the tube diameter of the CNT within the above range (20-80 nm), it is beneficial to further maintain the high compaction density of the negative electrode coating 2, and then maintain the high energy density of the negative electrode sheet and the battery, and at the same time, further reduce the impedance of the negative electrode sheet, and then reduce the battery internal resistance, and improve the fast charging performance of the battery.

[0031] Further research shows that the tube diameter of the CNT containing nickel element can be 30-60 nm. According to the research of the inventor, under the negative electrode sheet structure system of the embodiment of the application, by introducing the CNT with the tube diameter of 30-60 nm in the negative electrode coating 2, the CNT has a smaller bending degree, which is beneficial to build a good conductive network in the negative electrode coating 2, and is beneficial to the diffusion of active ions in the negative electrode coating 2, reduces the negative electrode sheet impedance, and at the same time basically does not affect the compaction density of the negative electrode coating 2, can maintain the high energy density of the negative electrode sheet, thereby can reduce the battery internal resistance, improve the fast charging performance of the battery, and at the same time, improve the capacity and other performances of the battery.

[0032] In addition, the length (tube length) of the CNT containing nickel element 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 a range formed by any two of them, which is beneficial to reduce the battery impedance and improve the fast charging performance and other performances of the battery.

[0033] Generally, the negative electrode coating 2 includes a negative electrode active material, a conductive agent and a binder, and can also include a thickening agent. Among them, the conductive agent includes the CNT containing nickel element, and the CNT containing nickel element in the negative electrode coating 2 as a conductive agent can build a good conductive network between the negative electrode active material particles, and at the same time, can improve the liquid absorption and liquid retention energy of the negative electrode sheet to the electrolyte, improve the electrolyte wettability of the negative electrode sheet, promote the diffusion of active ions in the negative electrode sheet, reduce the impedance of the negative electrode sheet, and then reduce the battery internal resistance, and improve the fast charging performance and other performances of the battery.

[0034] Specifically, the negative electrode active material can include a carbon-based negative electrode active material and / or a silicon-based negative electrode active material, the carbon-based negative electrode active material includes graphite and / or hard carbon for example, the graphite can include natural graphite and / or artificial graphite, and the silicon-based negative electrode active material includes silicon-carbon material and the like for example.

[0035] In some embodiments, the negative active material includes one or more of natural graphite, artificial graphite, hard carbon, silicon-carbon.

[0036] The embodiments of the present application can adopt a conventional negative current collector 1 in the art, for example, the negative current collector 1 includes a copper foil.

[0037] In the embodiments of the present application, the negative coating layer 2 can be a single-layer structure (for example, the second coating layer 22 described below), or a double-layer or more-layer structure.

[0038] In some embodiments, as shown in FIG. 1, the negative coating layer 2 includes a first coating layer 21 (lower layer) and a second coating layer 22 (upper layer) located on the side surface of the first coating layer 21 away from the negative current collector 1, and the second coating layer 22 includes the CNT containing nickel element described above. Through the design of the double-layer structure and the introduction of the CNT containing nickel element in the upper layer, a good conductive network is built while a good void structure is formed in the upper layer, which promotes the reaction uniformity of the negative sheet during the charging and discharging process of the battery, and is beneficial to further reduce the impedance of the negative sheet, thereby reducing the internal resistance of the battery and improving the performance of the battery such as fast charging.

[0039] Specifically, the first coating layer and the second coating layer each include a negative active material (the negative active material in the first coating layer is referred to as a first negative active material, and the negative active material in the second coating layer is referred to as a second negative active material), and the first negative active material and the second negative active material can be the same or different.

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

[0041] In some embodiments, the second negative active material includes one or more of natural graphite, artificial graphite, hard carbon, silicon-carbon.

[0042] In some embodiments, the mass ratio of the carbon nanotubes in the second coating layer 22 to the second negative active material in the second coating layer 22 is 0.09% to 3%, for example, 0.09%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or a range consisting of any two of them, which is beneficial to reduce the internal resistance of the battery and improve the performance of the battery such as fast charging.

[0043] In addition, the content of the CNT containing nickel element in the first coating layer 21 is 0, that is, the first coating layer 21 does not contain the CNT containing nickel element described above, and the first coating layer 21 can include other conductive materials (hereinafter referred to as a third conductive agent) other than the CNT containing nickel element, for example, one or more of conductive carbon black (SP), graphene, carbon fiber material, and carbon nanotubes not containing nickel element.

[0044] Specifically, the conductive agent in the second coating layer 22 can include a first conductive agent and a second conductive agent, the first conductive agent being a carbon nanotube containing a nickel element, and the second conductive agent being another conductive material other than the carbon nanotube containing a nickel element, and the second conductive agent can specifically include one or several of conductive carbon black (SP), graphene, carbon fiber material, and carbon nanotube not containing a nickel element.

[0045] Specifically, the above-mentioned carbon nanotube not containing a nickel element can be a thin tube with a tube diameter less than 15 nm.

[0046] In some embodiments, the mass ratio of the first conductive agent to the second conductive agent can be 1:(1-20), for example, 1:1, 1:3, 1:5, 1:8, 1:10, 1:13, 1:15, 1:18, 1:20, or a range consisting of any two of them.

[0047] In addition, the mass ratio w1 of the conductive agent to the first negative active material in the first coating layer 21 can be greater than or equal to the mass ratio w2 of the conductive agent to the second negative active material in the second coating layer 22 (i.e., w1 / w2≥1).

[0048] In addition, the area density p1 of the first coating layer 21 can be less than or equal to the area density p2 of the second coating layer 22 (i.e., p1 / p2≤1).

[0049] In the embodiments of the present application, the area density of the negative electrode coating 2 and different regions (such as the first coating layer 21 and the second coating layer 22) of the negative electrode coating 2 can be tested by a scanning electron microscope (SEM), and the tube diameter and tube length of the CNT can be measured by a scanning electron microscope (SEM) and a transmission electron microscope (TEM), and the test standard can refer to the standard GB / T 30544.13-2018.

[0050] In a specific implementation, the negative electrode sheet can be placed in an HCl solution of a certain concentration, and the dissolution process can be accelerated by stirring or ultrasonic treatment to remove the negative current collector 1 (such as a copper foil), the binder (such as SBR) in the coating layer, the thickening agent (such as CMC), and the SEI film in the negative active material and the conductive agent (such as graphite, CNT, and other carbon materials) in the negative electrode sheet. Then, the obtained solution and the insoluble components are subjected to solid-liquid separation by filtration or centrifugation, etc. to obtain the insoluble components (i.e., the solid phase, mainly the negative active material and the conductive agent). The insoluble components are dried and ground into fine particles of a certain size, and then mixed with an appropriate amount of solvent or dispersant, placed in an ultrasonic bath or subjected to ultrasonic treatment using an ultrasonic probe to form a uniform suspension. During the ultrasonic treatment, due to the different characteristics of the negative active material (such as graphite) and CNT, there will be a phenomenon of slight aggregation and dispersion. After the ultrasonic treatment, centrifugation is performed, and the centrifugal speed is adjusted to separate the CNT and the negative active material, and physical property tests are performed respectively. For example, after the CNT is separated from the negative electrode sheet through the process, the tube diameter and tube length of the CNT can be tested according to the standard GB / T 30544.13-2018.

[0051] Specifically, the conductive agent in the negative electrode coating can be directly characterized by FIB-SEM, such as whether the carbon nanotubes are contained in each region of the negative electrode coating, and the tube diameter and tube length of the carbon nanotubes.

[0052] In the embodiments of the present application, whether the CNT contains Ni elements can be detected by TEM and inductively coupled plasma (ICP) tests. In a specific implementation, the TEM image of the CNT can be obtained by TEM test, and the qualitative analysis of the elements in the CNT is performed by ICP auxiliary test to detect whether there is a nickel element inside the CNT.

[0053] Specifically, based on the total mass of the first coating 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 coating layer 21) can be 70% to 99%, such as 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or a range consisting of any two of these values, the mass fraction of the conductive agent (i.e., the ratio of the total mass of the conductive agent in the first coating layer 21 to the total mass of the first coating layer 21) can be 0.3% to 15%, such as 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range consisting of any two of these values, the mass fraction of the binder can be 0.3% to 15%, such as 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range consisting of any two of these values, the mass fraction of the thickening agent can be 0.3% to 15%, such as 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range consisting of any two of these values.

[0054] Further, based on the total mass of the second coating 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 coating layer 22) can be 70% to 99%, such as 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or a range consisting of any two of these values, the mass fraction of the conductive agent (i.e., the ratio of the total mass of the conductive agent in the second coating layer 22 to the total mass of the second coating layer 22) can be 0.3% to 15%, such as 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range consisting of any two of these values, the mass fraction of the binder can be 0.3% to 15%, such as 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range consisting of any two of these values, the mass fraction of the thickening agent can be 0.3% to 15%, such as 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range consisting of any two of these values.

[0055] In the embodiments of the present application, the binder in the negative electrode coating layer 2 (the first coating layer 21 and the second coating layer 22) can be a conventional binder in the art. For example, the binder in the negative electrode coating layer 2 can include one or more of sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. The thickening agent can be a conventional thickening agent in the art. For example, the thickening agent includes a CMC-based thickening agent, such as a CMC salt, e.g., CMC-Na, and the like.

[0056] In the embodiments of the present application, the negative electrode coating layer 2 (the positive electrode active material layer) can be provided on one side surface of the negative electrode current collector 1, or both side surfaces of the negative electrode current collector 1 in the thickness direction can each be provided with the negative electrode coating layer 2 (as shown in FIG. 1). When both side surfaces of the negative electrode current collector 1 are each provided with the negative electrode coating layer 2, the negative electrode coating layer 2 on one side surface can be the negative electrode coating layer 2 containing the CNTs containing nickel elements described above, or both side surfaces of the negative electrode current collector 1 can each be provided with the negative electrode coating layer 2 containing the CNTs containing nickel elements described above.

[0057] In the embodiments of the present application, the negative electrode sheet can be prepared by a conventional coating method in the art. Specifically, the components for forming the negative electrode coating layer 2, such as the negative electrode active material, the conductive agent, and the binder, can be dispersed in a first solvent, such as water (deionized water can be used specifically), to prepare a first slurry for forming the first coating layer 21 and a second slurry for forming the second coating layer 22, respectively. Then, the second slurry and the first slurry are coated on the surface of the negative electrode current collector 1 by a double-layer coating process, and the positive electrode sheet is prepared after drying, rolling, and other processes. The coating, drying, rolling, and other processes involved are conventional operations for preparing the negative electrode sheet by the coating method, and are not particularly limited.

[0058] The embodiments of the present application also provide a battery including the negative electrode sheet described above, which has advantages corresponding to the negative electrode sheet and will not be described herein.

[0059] The battery according to the embodiments of the present application can be a lithium ion battery, but is not limited thereto.

[0060] Generally, the battery includes an electrolyte, an electrode core, and a shell encapsulating the electrode core. The electrolyte is injected into the electrode core in the shell. The electrode core includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet. The electrode core can be a laminated electrode core, i.e., the electrode core is formed by stacking the positive electrode sheet, the separator, and the negative electrode sheet.

[0061] Specifically, the positive electrode sheet includes a positive electrode current collector, and a positive electrode coating layer on at least one side surface of the positive electrode current collector. Specifically, the positive electrode coating layer can be provided on one side surface of the positive electrode current collector, or positive electrode coating layers can be respectively provided on opposite side surfaces (front and back side surfaces) of the positive electrode current collector in the thickness direction of the positive electrode current collector.

[0062] Specifically, the positive electrode coating layer (positive electrode active material layer) can include a positive electrode active material, a conductive agent, and a binder, which can all be conventional materials in the art. For example, the positive electrode active material can include a lithium-containing positive electrode active material for a lithium ion battery, such as one or more of lithium iron phosphate (LiFePO4), lithium cobaltate, a positive electrode ternary material, etc., such as a nickel-cobalt-manganese ternary material and / or a nickel-cobalt-aluminum ternary material; the conductive agent can include one or more of conductive carbon black (SP), carbon nanotubes (CNT), acetylene black, graphene, ketjen black, carbon fibers; and the binder can 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, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, etc.

[0063] Based on the total mass of the positive electrode coating layer, 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 layer) can be 70% to 99%, such as 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or a range defined by any two of these values, the mass fraction of the conductive agent can be 0.5% to 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range defined by any two of these values, and the mass fraction of the binder can be 0.5% to 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range defined by any two of these values.

[0064] Embodiments of the present application can employ a conventional positive electrode current collector in the art, such as an aluminum foil.

[0065] In embodiments of the present application, the positive electrode sheet can be prepared by a conventional method in the art, such as by a coating method. Specifically, the components for forming the positive electrode coating layer, such as the positive electrode active material, the conductive agent, and the binder, can be dispersed in a second solvent, such as N-methyl pyrrolidone (NMP), to prepare a positive electrode slurry, which can then be coated on the surface of the positive electrode current collector, and the positive electrode sheet can be prepared after drying, rolling, etc.

[0066] The electrolyte of the embodiments of the present application can be a conventional electrolyte in the art, for example, the electrolyte is a non-aqueous electrolyte, which specifically can include an organic solvent and an electrolyte salt, the organic solvent for example includes one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC), and the electrolyte salt can include a lithium salt, for example, the lithium salt includes lithium hexafluorophosphate (LiPF6) and the like, but is not limited thereto.

[0067] In the embodiments of the present application, the separator is used to separate the positive electrode sheet and the negative electrode sheet to avoid short circuit caused by contact between the positive electrode sheet and the negative electrode sheet, and the embodiments of the present application can use a conventional separator in the art, for example, the separator includes a polypropylene film, but is not limited thereto.

[0068] In the embodiments of the present application, a conventional shell material in the art can be used to package the battery cell, for example, the shell includes a soft packaging material such as an aluminum plastic film, but is not limited thereto.

[0069] The embodiments of the present application can assemble the components such as the positive electrode sheet, the separator, and the negative electrode sheet into a battery through a conventional method in the art, for example, the positive electrode sheet, the separator, and the negative electrode sheet can be stacked to obtain a stacked sheet type battery cell; then the battery cell is placed in a shell (outer package), and after conventional processes such as liquid injection (i.e., injection of electrolyte) and packaging, a battery is obtained.

[0070] The embodiments of the present application also provide a power consuming device including the above-mentioned battery, which has advantages corresponding to the above-mentioned battery, and details are not described herein.

[0071] The present application is further described below through specific embodiments.

[0072] In the following examples and comparative examples, unless otherwise specified, the CNT containing Ni element is measured by TEM test to obtain a TEM image, and combined with ICP test to measure that the CNT contains nickel element inside, wherein the TEM image of the CNT containing Ni element is shown in FIG. 2, and from FIG. 2, it can be seen that the nickel element (nickel-containing compound) exists inside the CNT.

[0073] Example 1

[0074] 1. Preparation of the negative electrode sheet

[0075] The artificial graphite, conductive carbon black (SP), thickening agent (CMC-Na), and binder (SBR) are mixed according to a mass ratio of 96:1:1:2, and deionized water is added to prepare a first slurry for forming a first coating layer (lower layer);

[0076] The artificial graphite, the conductive agent, the thickening agent (CMC), and the binder (SBR) are mixed according to a mass ratio of 96:1:1:2, and deionized water is added to prepare a second slurry for forming a second coating layer (upper layer); wherein the conductive agent is CNT and SP, and the mass ratio of CNT to SP is 1:10 (i.e., CNT:SP = 1:10).

[0077] The first slurry and the second slurry are simultaneously coated on the surface of the copper foil by using a double-layer coating process, and after drying and rolling (the rolling pressure is about 1.5 MPa), a positive electrode sheet is prepared; wherein the positive and negative surfaces of the copper foil are respectively formed with the negative electrode coating layer having the first coating layer and the second coating layer.

[0078] Specifically, the structure of the negative electrode sheet is shown in FIG. 1, which includes a negative electrode current collector (copper foil) and a negative electrode coating layer on the positive and negative surfaces of the negative electrode current collector. Each side of the negative electrode coating layer includes a first coating layer and a second coating layer on the side surface of the first coating layer away from the negative electrode current collector. The surface density p1 of the first coating layer and the surface density p2 of the second coating layer are the same (i.e., p1 / p2 = 1). The mass ratio w1 of the conductive agent to the artificial graphite (first negative electrode active material) in the first coating layer is equal to the mass ratio w2 of the conductive agent to the artificial graphite (second negative electrode active material) in the second coating layer (i.e., w1 / w2 = 1). The tube diameter of CNT in the second coating layer is 40 nm, and the tube length is 2 pm. 1 / p2 = 1), the mass ratio w1 of the conductive agent to the artificial graphite (first negative electrode active material) in the first coating layer is equal to the mass ratio w2 of the conductive agent to the artificial graphite (second negative electrode active material) in the second coating layer (i.e., w1 / w2 = 1), and the tube diameter of CNT in the second coating layer is 40 nm, and the tube length is 2 pm.

[0079] 2. Preparation of the positive electrode sheet

[0080] LiFePO4, SP, and PVDF are mixed according to a mass ratio of 97:1:2, and the obtained powder and NMP are stirred uniformly in a homogenizer to prepare a positive electrode slurry.

[0081] The positive electrode slurry is coated on the positive and negative surfaces of the aluminum foil, and after drying and rolling, a positive electrode coating layer is formed on the positive and negative surfaces of the aluminum foil to prepare a positive electrode sheet.

[0082] (2) Assembly of the battery

[0083] The positive electrode sheet, the separator (polypropylene film), and the negative electrode sheet are stacked to assemble a laminated cell. The laminated cell is placed in an aluminum plastic film, and after processes such as liquid injection and packaging, a lithium ion battery (the designed capacity of the battery is 1.7 Ah) is assembled. The composition of the electrolyte used is as follows: the organic solvent is ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC), and the volume ratio of EC, DMC, and EMC is 1:1:1. The concentration of LiPF6 in the electrolyte is 1 mol / L.

[0084] 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.

[0085] 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).

[0086] 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).

[0087] 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:

[0088] (1) 25℃, 0.2C charge and discharge, calibrate the battery capacity;

[0089] (2) Charge at 0.2C to 50% SOC and 90% SOC;

[0090] (3) Set 2C charging for 30s, record the termination voltage and termination current of each process, and calculate DCIR.

[0091] Table 1. Relevant parameters of the negative electrode and DC internal resistance of the battery.

[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] Further, from the examples 1-6 and 19, it can be seen that, compared with the examples 7 and 19, the examples 1-6 can further reduce the direct current impedance of the battery by further controlling the tube diameter of the CNTs in the range of 20-80 nm.

[0095] Further, from the examples 1, 10 and 11, it can be seen that, compared with the example 11, the examples 1 and 10 can further reduce the direct current impedance of the battery by further controlling w1 / w2≥1.

[0096] Further, from the examples 1, 12 and 13, it can be seen that, compared with the example 13, the examples 1 and 12 can further reduce the direct current impedance of the battery by further controlling ρ1 / ρ2≤1.

[0097] Further, from the examples 1, 14-18, it can be seen that, compared with the example 18, the examples 1, 14-17 can further reduce the direct current impedance of the battery by further controlling the mass ratio of the CNTs to the graphite in the second coating layer in the range of 0.09%-3%.

[0098] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the examples of the present application.

Claims

1. A negative electrode sheet, wherein, The negative electrode sheet includes a negative electrode current collector and a negative electrode coating layer on at least one side surface of the negative electrode current collector, and the negative electrode coating layer includes carbon nanotubes containing a nickel element.

2. The negative electrode sheet according to claim 1, wherein The carbon nanotubes have a tube diameter of 20-80 nm.

3. The negative electrode sheet according to claim 2, wherein The carbon nanotubes have a tube diameter of 30-60 nm.

4. The negative electrode sheet according to claim 1, wherein The carbon nanotubes have a length of 0.5-20 μm.

5. The negative electrode sheet according to claim 1, wherein The negative electrode coating layer includes a first coating layer and a second coating layer on a side surface of the first coating layer away from the negative electrode current collector, and the second coating layer includes the carbon nanotubes.

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

7. The negative electrode sheet according to claim 5, wherein The content of the carbon nanotubes in the first coating layer is 0.

8. The negative electrode sheet according to any one of claims 5 to 7, wherein The second coating layer includes a conductive agent, and the conductive agent in the second coating layer includes a first conductive agent and a second conductive agent, the first conductive agent is the carbon nanotubes, and the second conductive agent is a conductive material other than the carbon nanotubes.

9. The negative electrode sheet according to claim 8, wherein A 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, wherein The second conductive agent includes one or more of conductive carbon black, graphene, carbon fiber material, and carbon nanotubes not containing a nickel element.

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

12. The negative electrode sheet according to any one of claims 5 to 7, wherein A surface density of the first coating layer is less than or equal to a surface density of the second coating layer.

13. The negative electrode sheet according to any one of claims 5 to 7, wherein The first coating layer includes a first negative electrode active material, and the first negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, and silicon-carbon.

14. The negative electrode sheet according to any one of claims 5 to 7, wherein The second coating layer includes a second negative electrode active material, and the second negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, and silicon-carbon.

15. A battery, wherein, The negative electrode sheet includes the negative electrode sheet according to any one of claims 1-14.

16. An electrical device, comprising: The battery includes the battery according to claim 15.

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