Negative electrode sheet and secondary battery, battery module, battery pack and electric device containing the same

Abstract

The present application provides a single-layer coated negative electrode sheet, which improves the diffusion capacity of lithium ions in the negative electrode film layer and improves the charging performance of the battery by limiting the mass fraction of carbon microtubes and conductive agents in the negative electrode film layer to satisfy a certain relationship. The present application also provides a double-layer coated negative electrode sheet, which improves the charging performance of the battery by including carbon microtubes in at least one layer of the first film layer and the second film layer. In addition, the present application also relates to secondary batteries, battery modules, battery packs and electrical devices comprising the above-mentioned single-layer coated and double-layer coated negative electrode sheets.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a single-layer coated negative electrode sheet and a double-layer coated negative electrode sheet, as well as a secondary battery, a battery module, a battery pack and an electrical device containing the same. Background Art

[0002] In recent years, as the application scope of secondary batteries becomes wider and wider, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] However, in a secondary battery having a thick coating weight (e.g., at least 9 mg / cm 2 ) electrodes, the fast charging performance of the battery is low; the internal polarization of the battery cell increases, the battery cell life deteriorates, and factors such as lithium deposition that cause safety hazards appear. Therefore, the electrochemical performance of secondary batteries with thick coatings still needs to be improved, especially to improve their fast charging performance. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode sheet that can improve the charging capacity of a secondary battery, and to provide a secondary battery, a battery module, a battery pack and an electrical device including the negative electrode sheet of the present application.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a single-layer coated negative electrode plate, which includes a current collector and a negative electrode film layer arranged on at least one surface of the current collector, the negative electrode film layer contains a negative electrode active material and carbon microtubes, and optionally contains a conductive agent; wherein the mass fraction W1 of the carbon microtubes in the negative electrode film layer and the mass fraction W2 of the conductive agent in the negative electrode film layer satisfy: when 0.2%≤W1≤2%, then W1+W2≤2%; when W1>2%, then 0≤W2≤0.5%, based on the total weight of the negative electrode film layer.

[0006] The present application improves the liquid retention capacity of the negative electrode film layer and promotes the diffusion capacity of lithium ions in the negative electrode film layer by adding carbon microtubes into the negative electrode film layer and limiting the mass fractions of the carbon microtubes and the conductive agent in the negative electrode film layer to satisfy a certain relationship, thereby improving the charging performance of the secondary battery.

[0007] In any embodiment, in the single-layer coated negative electrode sheet, the mass fraction W1 of carbon microtubes in the negative electrode film layer is 0.2% to 5%, thereby further optimizing the components of the negative electrode film layer and improving the charging performance of the secondary battery.

[0008] In any embodiment, in a single-layer coated negative electrode sheet, the inner diameter of the carbon microtube is 0.2 μm to 12 μm, optionally 2 μm to 10 μm; optionally, the aspect ratio is 2-20; further optionally, the wall thickness of the carbon microtube is 0.01 μm to 1 μm. By limiting the specifications of the carbon microtube, the carbon microtube can fully play its role of storing and retaining liquid in the negative electrode film layer, improve the liquid phase diffusion capacity, thereby fully utilizing the active substances of the negative electrode film layer and improving the charging performance of the battery.

[0009] In any embodiment, in a single-layer coated negative electrode sheet, the negative electrode active material includes at least one of artificial graphite, natural graphite, and silicon-based materials; optionally, the conductive agent includes at least one of conductive agent sp, KS-6, conductive graphite, carbon nanotubes, graphene, and carbon fiber VGCF.

[0010] The second aspect of the present application provides a double-layer coated negative electrode plate, which includes a current collector, a first film layer and a second film layer; wherein the first film layer is arranged on at least one surface of the current collector, and the second film layer is arranged on the outer surface of the first film layer; the first film layer is located between the current collector and the second film layer; and the first film layer contains a first negative electrode active material, and the second film layer contains a second negative electrode active material; at least one of the first film layer and the second film layer contains carbon microtubes; and the first film layer and the second film layer are different in at least one of the negative electrode active material and whether they include carbon microtubes.

[0011] The present application introduces carbon microtubes into the film layer of the double-layer coated negative electrode plate, thereby improving the liquid storage capacity of the film layer, ensuring the diffusion of lithium ions in the entire film layer, and achieving the purpose of fully utilizing the active substances in the film layer, thereby improving the electrochemical performance of the secondary battery, especially the charging performance.

[0012] In any embodiment, in the double-layer coated negative electrode sheet, the first film layer does not contain carbon microtubes, and the second film layer contains carbon microtubes. Thus, by further limiting the distribution of carbon microtubes, the second film layer (upper layer) is provided with sufficient electrolyte, thereby promoting the diffusion of lithium ions to the first film layer (lower layer) to fully utilize the negative electrode active material.

[0013] In any embodiment, in the double-layer coated negative electrode plate, both the first film layer and the second film layer contain carbon microtubes, thereby increasing the liquid retention capacity of the two film layers, and the lithium ion channel runs through the entire film layer to further enhance the diffusion capacity of lithium ions.

[0014] In any embodiment, in the double-layer coated negative electrode sheet, the total mass fraction W3 of the carbon microtubes in the first film layer and the second film layer is 0.2% to 5%, based on the total weight of the first film layer and the second film layer. Thus, the mass fraction of the carbon microtubes in the double film layer is further limited to optimize the electrochemical performance of the negative electrode sheet, thereby improving the charging capacity of the battery.

[0015] In any embodiment, in the double-layer coated negative electrode sheet, the first film layer and the second film layer optionally further include a conductive agent, and the total mass fraction W3 of the carbon microtubes and the total mass fraction W4 of the conductive agent satisfy: when 0.2% ≤ W3 ≤ 2%, then W3 + W4 ≤ 2%; when W3> 2%, then 0 ≤ W4 ≤ 0.5%, based on the total mass of the first film layer and the second film layer. When the total mass fraction of the carbon microtubes and the conductive agent satisfies a specific relationship, a balance between the amount of the load (carbon microtubes and the conductive agent), the energy density and the charging performance can be achieved, and the fast charging capability is improved.

[0016] In any embodiment, in the double-layer coated negative electrode sheet, the mass of the carbon microtubes in the second film layer is 50-100% relative to the total mass of the carbon microtubes. The carbon microtubes are all or mostly present in the second film layer, which is conducive to more lithium ion-containing electrolytes diffusing to the upper layer, so as to provide sufficient lithium ions to reach the interface between the upper layer and the lower layer, and the interface between the lower layer and the current collector, so as to achieve the purpose of fully utilizing the active material in the lower layer.

[0017] In any embodiment, in the double-layer coated negative electrode sheet, the diameter of the carbon microtube is 0.2 μm to 12 μm, and can be 2 μm to 10 μm; the aspect ratio is 2-20; the wall thickness of the carbon microtube is 0.01 μm to 1 μm. By limiting the carbon microtubes of appropriate specifications, the uniformity of the pore size distribution is achieved, the liquid storage and retention capacity of the membrane layer is enhanced, and the lithium ion diffusion capacity is improved.

[0018] In any embodiment, in a double-layer coated negative electrode plate, under the condition that only the first film layer contains carbon microtubes, the first film layer and the second film layer optionally further contain a conductive agent; the mass fraction of the carbon microtubes in the second film layer is 0.4% to 10%, and the mass fraction of the conductive agent is 0% to 4%, optionally 0% to 1.6%, based on the weight of the second film layer; the mass fraction of the conductive agent in the first film layer is 0% to 4%, optionally 0% to 2%, based on the weight of the first film layer.

[0019] In any embodiment, in a double-layer coated negative electrode plate, under the condition that both the first and second film layers contain carbon microtubes, the first film layer and the second film layer optionally further contain a conductive agent; the mass fraction of the carbon microtubes in each film layer is 0.2% to 5%, and the mass fraction of the conductive agent in each film layer is 0% to 2%, based on the weight of each film layer.

[0020] By further limiting the mass content of carbon microtubes and conductive agents in each film layer, the composition and structure of the negative electrode film layer can be optimized to achieve the best fast charging capability.

[0021] In any embodiment, in the double-layer coated negative electrode sheet, under the condition that both the first and second film layers contain carbon microtubes, the mass fraction ratio of the carbon microtubes in the second film layer to the first film layer is 10:3 to 1:1.

[0022] In any embodiment, in the double-layer coated negative electrode plate, the weight ratio of the second film layer to the first film layer is 1:4 to 4:1. Thus, the diffusion performance of the upper layer and the lower layer reaches the best ratio, further improving the fast charging capability of the battery.

[0023] In any embodiment, in the double-layer coated negative electrode sheet, the first and second negative electrode active materials may be the same or different, including at least one of artificial graphite, natural graphite, and silicon-based materials.

[0024] In any embodiment, in the double-layer coated negative electrode plate, the conductive agent in the first film layer and the second film layer may be the same or different, including at least one of conductive agent sp, KS-6, conductive graphite, carbon nanotubes, graphene, and carbon fiber VGCF.

[0025] The third aspect of the present application provides a secondary battery, which includes the single-layer coated negative electrode plate described in the first aspect of the present application and the double-layer coated negative electrode plate described in the second aspect of the present application.

[0026] A fourth aspect of the present application provides a battery module, which includes the secondary battery described in the third aspect of the present application.

[0027] The fifth aspect of the present application provides a battery pack, which includes the battery module described in the fourth aspect of the present application.

[0028] The sixth aspect of the present application provides an electrical device, which includes at least one of the secondary battery described in the third aspect of the present application, the battery module described in the fourth aspect of the present application, or the battery pack described in the fifth aspect of the present application.

[0029] The present application improves the fast charging capability of the secondary battery by using carbon microtubes in the negative electrode of the secondary battery and limiting the mass fraction of the carbon microtubes and the conductive agent to satisfy a certain relationship. Accordingly, the battery pack, battery module and power device provided by the present application have improved fast charging capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of a single-layer coated negative electrode sheet according to one embodiment of the present application.

[0031] Figure 2 Schematic diagram of a double-layer coated negative electrode sheet according to an embodiment of the present application

[0032] Figure 3 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0033] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0034] Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0035] Figure 6 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0036] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0037] Figure 8 It is a schematic diagram of an electric device for a secondary battery according to one embodiment of the present application.

[0038] Description of reference numerals:

[0039] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly; 6 current collector; 7 single-layer negative electrode film layer; 8 first film layer; 9 second film layer. DETAILED DESCRIPTION

[0040] Below, the negative electrode sheet and its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0041] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-6. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0044] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0045] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0046] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0047] With the rapid development of new energy, the requirements for lithium-ion batteries are getting higher and higher. While pursuing energy density, in order to alleviate users' mileage anxiety, it is necessary to improve the charging capacity of lithium-ion batteries. For the current system, liquid phase diffusion is the bottleneck of fast charging, so significantly improving liquid phase diffusion is crucial to improving charging capacity.

[0048] Existing methods to improve fast charging capabilities include drilling and pore making technology, as well as carbon nanotube technology, but all of them have problems such as large energy density loss, small liquid storage and retention effects, large specific surface area, and many side reactions.

[0049] The inventors have discovered that by introducing carbon microtubes into the negative electrode film layer, the liquid storage and liquid retention functions can be fully utilized, thereby improving the liquid phase diffusion capacity and enabling lithium ions to penetrate the entire negative electrode film layer, so as to fully utilize the negative electrode active material, especially the negative electrode active material close to the current collector, to achieve the purpose of improving the charging capacity of the battery.

[0050] [Negative electrode]

[0051] The first aspect of the present application provides a single-layer coated negative electrode plate, which includes a current collector and a negative electrode film layer arranged on at least one surface of the current collector, wherein the negative electrode film layer contains a negative electrode active material and carbon microtubes, and optionally contains a conductive agent; wherein the mass fraction W1 of the carbon microtubes in the negative electrode film layer and the mass fraction W2 of the conductive agent in the negative electrode film layer satisfy: when 0.2%≤W1≤2%, then W1+W2≤2%; when W1>2%, 2%<W1<5.8% can be selected, then 0≤W2≤0.5%, based on the total weight of the negative electrode film layer.

[0052] By adding carbon microtubes to the negative electrode film layer of the present application, the liquid retention capacity of the negative electrode film layer can be improved, liquid phase diffusion can be promoted, and active substances can be fully utilized; at the same time, the mass fraction ratio of carbon microtubes and conductive agent in the negative electrode film layer is limited, so that the battery has a good energy density and the charging capacity of the battery is improved. Figure 1 shown.

[0053] In some embodiments, the mass fraction W1 of the carbon microtubes in the negative electrode film layer is 0.2-5%. By further limiting the mass fraction of the carbon microtubes in the negative electrode film layer, the components of the negative electrode film layer are optimized to improve the fast charging capability of the battery.

[0054] In some embodiments, the inner diameter of the carbon microtube (i.e., the diameter of the hollow inner cavity) is 0.2 μm to 12 μm, and optionally 2 μm to 10 μm; optionally, the aspect ratio (i.e., the ratio of the length of the carbon nanotube to the inner diameter) is 2-20; further optionally, the wall thickness of the carbon microtube is 0.01 μm to 1 μm. The inner diameter of the carbon microtube can also be 1 μm to 12 μm, or 2 μm to 4 μm.

[0055] The carbon microtubes of the above specifications are similar to through holes, and their advantages are that they can give full play to the role of liquid storage and liquid retention, improve the liquid phase diffusion capacity, and thus make full use of the active substances in the negative electrode membrane layer, and improve the fast charging capacity of the battery; moreover, compared with the pore-making and punching technology used in the prior art (with an inner diameter of tens of microns), the inner diameter of the carbon microtubes of the present application is smaller, even a few microns, and its advantage is that the distance between the carbon microtubes is small and evenly distributed, which can improve the consistency of the pore size distribution, so that the polarization distribution inside the battery cell is uniform, avoiding the phenomenon of local lithium precipitation, and also effectively playing the role of liquid retention, improving the overall charging capacity, and reducing the energy density loss. Compared with the carbon nanotube technology used in the prior art, the carbon microtubes of the present application have a smaller inner diameter, can play the role of liquid storage and liquid retention, and improve the diffusion capacity of lithium ions.

[0056] In some embodiments, the negative electrode active material contained in the negative electrode film layer includes at least one of artificial graphite, natural graphite, and silicon-based materials, and is optionally selected from artificial graphite; the conductive agent includes at least one of conductive agent sp, KS-6, conductive graphite, carbon nanotubes, graphene, and carbon fiber VGCF, and the conductive agent sp is optionally selected.

[0057] In the single-layer coated negative electrode plate of the present application, further optionally, the negative electrode film layer contains carbon microtubes with an inner diameter of 2μm to 4μm, and the mass fraction W1 of the carbon microtubes in the negative electrode film layer and the mass fraction W2 of the conductive agent in the negative electrode film layer satisfy: when 1.5%≤W1≤2%, then 1.6%≤W1+W2≤2%; when 2.5%≤W1≤3%, then 0≤W2≤0.5%, based on the total weight of the negative electrode film layer.

[0058] The second aspect of the present application provides a double-layer coated negative electrode plate, which includes a current collector, a first film layer and a second film layer, wherein the first film layer is arranged on at least one surface of the current collector, and the second film layer is arranged on the outer surface of the first film layer; the first film layer is located between the current collector and the second film layer; and the first film layer contains a first negative electrode active material; the second film layer contains a second negative electrode active material; at least one of the first film layer and the second film layer contains carbon microtubes; and the first film layer and the second film layer are different in at least one of the negative electrode active material and whether they include carbon microtubes.

[0059] In the present application, optionally, an intermediate coating is also included between the current collector and the first film layer. The intermediate coating is used to enhance the bonding force between the negative electrode active material and the current collector, strengthen the transmission of electrons, and reduce polarization. The thickness of the intermediate coating is not more than 6 μm, and includes a conductive agent and a binder. Among them, the conductive agent includes at least one of conductive agent sp, KS-6, conductive graphite, carbon nanotubes, graphene, and carbon fiber VGCF, and the binder includes at least one of styrene-butadiene rubber (SBR), polyacrylate, ethylene-propylene rubber, nitrile rubber, and polyvinylidene fluoride (PVDF).

[0060] In the present application, a double-layer coating process is used to form a negative electrode film layer having a double-layer structure of a first film layer and a second film layer, such as Figure 2 The total thickness of the negative electrode film layer is 25-110 μm.

[0061] It should be noted that the “first film layer”, “first film layer” and “lower layer” used in this application have the same meaning, referring to the layer containing active substances close to the current collector; the “second film layer”, “second film layer” and “upper layer” have the same meaning, referring to the layer containing active substances far from the current collector; the “double-layer film layer” refers to the first film layer and the second film layer; and the “total mass” refers to the total mass of a substance in the first film layer and the second film layer.

[0062] In the present application, in the double-layer coated negative electrode sheet, especially with a thick coating weight (at least 9 mg / cm 2 ) by adding carbon microtubes to the negative electrode sheet, which is beneficial to improving the fast charging capability of the secondary battery.

[0063] In some embodiments, in the double-layer coated negative electrode sheet, the first film layer does not contain carbon microtubes, and the second film layer contains carbon microtubes. This is conducive to enhancing the storage capacity of the electrolyte in the second film layer, so that the second film layer (upper layer) has sufficient electrolyte, thereby improving the diffusion capacity of lithium ions to the first film layer (lower layer), promoting the diffusion of lithium ions to the film layer on the surface of the current collector, achieving the purpose of fully utilizing the negative electrode active material and improving the charging capacity of the battery.

[0064] In some embodiments, in the double-layer coated negative electrode sheet, the first film layer and the second film layer both contain carbon microtubes. Thus, a smooth lithium ion channel is formed in the double-layer film layer of the negative electrode sheet, ensuring the lithium ion diffusion path from the upper layer / electrolyte interface to the lower layer / current collector interface, further improving the diffusion depth and diffusion speed of lithium ions from the upper layer to the lower layer, thereby making full use of the negative electrode active material and improving the charging capacity of the battery.

[0065] In some embodiments, in the double-layer coated negative electrode sheet, in the double-layer film layer composed of the first film layer and the second film layer, the total mass fraction W3 of the carbon microtubes is 0.2% to 5%, optionally 1.5% to 3%, and further optionally 1.8% to 2.6%, based on the total weight of the first film layer and the second film layer. Thus, the charging capacity of the double-layer coated negative electrode sheet is further improved.

[0066] In some embodiments, in a double-layer coated negative electrode plate, the first film layer and the second film layer optionally further contain a conductive agent; in the double-layer film layer composed of the first film layer and the second film layer, the total mass fraction W3 of the carbon microtubes and the total mass fraction W4 of the conductive agent satisfy: when 0.2%≤W3≤2%, then W3+W4≤2%; when W3>2%, then 0≤W4≤0.5%, based on the total mass of the first film layer and the second film layer.

[0067] By limiting the total mass fraction of carbon microtubes and conductive agent in the double-layer film to meet a specific relationship, the secondary battery can improve the fast charging capability without compromising the energy density. In other words, a balance is achieved between the amount of load (carbon microtubes and conductive agent), energy density and charging performance.

[0068] In some embodiments, in the double-layer coated negative electrode sheet, the mass of the carbon microtubes in the second film layer is 50-100% relative to the total mass of the carbon microtubes. Thus, the carbon microtubes can be present entirely or mostly in the second film layer, which is conducive to more lithium ion-containing electrolyte diffusing to the upper layer and then reaching the lower layer, so as to improve the lithium ion diffusion capacity of the lower layer and achieve the purpose of fully utilizing the active material in the lower layer.

[0069] In some embodiments, in the double-layer coated negative electrode sheet, the inner diameter of the carbon microtube is 0.2 μm to 12 μm, or 1 μm to 12 μm, optionally 2 μm to 10 μm, and further optionally 2 μm to 4 μm; its aspect ratio is 2-20, and the tube wall thickness is 0.01 μm to 1 μm.

[0070] By selecting carbon microtubes of specific specifications, the liquid storage and retention functions of carbon microtubes are further optimized, the diffusion of electrolyte is promoted, and the negative electrode active material is more fully utilized, and the deintercalation of lithium ions is accelerated, so as to further improve the fast charging capacity of the battery. In particular, the inner diameter of the carbon microtube is limited to 0.2μm to 12μm, so that the distance between the carbon microtubes is small and evenly distributed, thereby ensuring the uniformity of the pore size distribution and the uniform polarization distribution inside the battery cell, avoiding the phenomenon of local lithium precipitation, and the energy density loss is small, and the charging capacity is further improved.

[0071] In some embodiments, in a double-layer coated negative electrode sheet, under the condition that only the second film layer contains carbon microtubes, and the first film layer and the second film layer optionally also contain a conductive agent, the mass fraction of the carbon microtubes in the second film layer is 0.4% to 10%, and the mass fraction of the conductive agent is 0% to 4%, optionally 0% to 1.6%, based on the weight of the second film layer; the mass fraction of the conductive agent in the first film layer is 0% to 4%, optionally 0% to 2%, and optionally 0.4% to 2%, based on the weight of the first film layer.

[0072] In some embodiments, in the double-layer coated negative electrode sheet, carbon microtubes are included in both the first film layer and the second film layer, and the first film layer and the second film layer optionally further include a conductive agent, the mass fraction of the carbon microtubes in each film layer is 0.2% to 5%, and the mass fraction of the conductive agent in each film layer is 0% to 2%, based on the weight of each film layer. Thus, the composition and structure of the negative electrode sheet are optimized to optimize the fast charging capability of the secondary battery.

[0073] Optionally, the mass fraction ratio of the carbon microtubes in the negative electrode sheet in the second film layer to that in the first film layer is 10:3 to 1:1. By further limiting the mass fraction ratio of the carbon microtubes in the two film layers, the diffusion depth of the electrolyte in the direction toward the current collector is increased, and the liquid retention effect is effectively exerted, thereby achieving the purpose of fully utilizing the negative electrode active material and improving the fast charging capability of the battery.

[0074] Optionally, the weight ratio of the second film layer to the first film layer in the negative electrode plate is 1:4 to 4:1. The weight ratio refers to the ratio of the coating weight of the second film layer to the first film layer. This further optimizes the structure of the negative electrode plate, makes the coating process simple and easy to operate, and improves the fast charging capability of the battery.

[0075] In some embodiments, in the first film layer and the second film layer, the first and second negative electrode active materials may be the same or different, including at least one of artificial graphite, natural graphite, and silicon-based materials; optionally, the first negative electrode active material in the first film layer may be artificial graphite a, with a median particle size DV50 of 20-25 μm, and the second negative electrode active material in the second film layer may be artificial graphite b, with a median particle size DV50 of 10-14 μm.

[0076] In some embodiments, in the first film layer and the second film layer, under the condition that a conductive agent is optionally included, the conductive agent may be the same or different, including at least one of conductive agent sp, KS-6, conductive graphite, carbon nanotubes, graphene, and carbon fiber VGCF.

[0077] In the present application, the current collector is not particularly limited, and a metal foil or a composite current collector may be used. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0078] In the present application, the negative electrode film layer, the first film layer and the second film layer may further include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylate, ethylene-propylene rubber, nitrile rubber and polyvinylidene fluoride (PVDF), and styrene-butadiene rubber may be selected. This is conducive to obtaining better bonding performance.

[0079] In the present application, the negative electrode film layer, the first film layer and the second film layer may further optionally include a dispersant. The dispersant may include at least one of sodium carboxymethyl cellulose (CMC-Na), methyl cellulose and ethyl cellulose; optionally, sodium carboxymethyl cellulose. This is conducive to obtaining better dispersion performance.

[0080] Preparation method

[0081] In this application, the preparation method of carbon microtubes is as follows:

[0082] A precursor solution containing polystyrene is electrospun to obtain nanofiber filaments, and the nanofiber filaments are uniformly dispersed in a hydrochloric acid solution containing pyrrole and the like, wherein the mass ratio of pyrrole to nanofiber filaments is 0.8:1 to 1.2:1, and ammonium persulfate is added to carry out polymerization reaction, wherein the mass of ammonium persulfate is 1.1-1.3 times that of the nanofiber filaments, to obtain nanofiber filaments with a surface coated with a polymer, and then tetrahydrofuran is added to the above-mentioned surface-coated polymer nanofiber filaments, wherein the mass of tetrahydrofuran is 8-22 times that of the nanofiber filaments, and the mixture is fully stirred to dissolve the polystyrene, thereby obtaining a hollow polymer tube, and the nanofiber is pre-sintered at 280-320°C for 1-3h and carbonized at 1100-1300°C for 3-5h, and then cooled to obtain a micron-sized carbon tube.

[0083] Among them, by using different mass ratios of tetrahydrofuran and nanofiber filaments, the carbon microtubes with different inner diameters described in the present application can be obtained.

[0084] In the present application, single-layer coated and double-layer coated negative electrode sheets are prepared according to conventional methods in the art.

[0085] The single-layer coated negative electrode sheet is prepared by a conventional single-layer coating process, and the specific method is as follows:

[0086] S1: adding raw material components of the negative electrode film layer, such as negative electrode active material, conductive agent, binder, dispersant and / or carbon microtubes, to a solvent (such as water or deionized water) in a certain proportion, and stirring to form a negative electrode slurry;

[0087] S2: coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and after drying and compacting, a single-layer coated negative electrode sheet of the present application is obtained.

[0088] Among them, the layer formed by the above-mentioned negative electrode slurry is called the negative electrode film layer.

[0089] Optionally, an intermediate coating may be included between the negative electrode current collector and the negative electrode film layer. The intermediate coating is formed before step S2 by mixing a conductive agent (Sp, KS-6 or carbon nanotubes) with a binder (styrene-butadiene rubber (SBR), polyacrylate, ethylene-propylene rubber, nitrile rubber or polyvinylidene fluoride (PVDF)) in a certain proportion to form a slurry, which is then coated on at least one surface of the current collector to obtain the intermediate coating, and the thickness of the intermediate coating is not more than 6 μm.

[0090] In the present application, the double-layer coated negative electrode plate is prepared by a conventional double-layer coating process, and the specific method is as follows:

[0091] P1: adding the raw material components for preparing the first film layer, such as the first negative electrode active material, the conductive agent, the binder, the dispersant and / or the carbon microtubes, to a solvent (water or deionized water) in a certain proportion and mixing them, and stirring them evenly to form a slurry of the first film layer, also called the lower layer slurry;

[0092] P2: Add the raw material components for preparing the second film layer, such as the negative electrode active material, the conductive agent, the binder, the dispersant and / or the carbon microtubes, into the solvent (water or deionized water) in a certain proportion and mix them, and then stir them evenly to form the slurry of the second film layer, also called the upper slurry;

[0093] P3: The lower layer slurry prepared in P1 is coated on at least one surface of the negative electrode current collector to form a first film layer (lower layer). Then the upper layer slurry prepared in P2 is coated on the surface of the first film layer, and after drying and compaction, a second film layer (upper layer) is obtained. Thus, the double-layer coated negative electrode sheet of the present application is prepared.

[0094] Optionally, an intermediate coating may be included between the negative electrode current collector and the first film layer. The intermediate coating is formed before step P3 by mixing a conductive agent (Sp, KS-6 or carbon nanotubes) with a binder (styrene-butadiene rubber (SBR), polyacrylate, ethylene-propylene rubber, nitrile rubber or polyvinylidene fluoride (PVDF)) in a certain proportion to form a slurry, which is then coated on at least one surface of the current collector to obtain the intermediate coating, and the thickness of the intermediate coating is not more than 6 μm.

[0095] It should be understood that the negative electrode plate of the present application can be used not only in secondary batteries, but also in any other battery, battery module, battery pack or electrical device that needs to improve the fast charging capability.

[0096] Secondary battery

[0097] The secondary battery, battery module, battery pack and electric device of the present application are described below.

[0098] Secondary battery

[0099] In one embodiment of the present application, a secondary battery is provided, comprising the negative electrode plate of the present application.

[0100] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, 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 set 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.

[0101] [Positive electrode]

[0102] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0103] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0104] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0105] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0106] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0107] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0108] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0109] [Electrolytes]

[0110] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte).

[0111] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0112] In some embodiments, the electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0113] In some embodiments, the solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0114] In some embodiments, the electrolyte may also optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature performance, etc.

[0115] [Isolation film]

[0116] In some embodiments, the secondary battery further includes a separator. The separator is disposed between the positive electrode plate and the negative electrode plate to serve as a separator. The present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0117] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0118] [Outer packaging]

[0119] In some embodiments, the secondary battery may include an outer package for packaging the positive electrode sheet, the negative electrode sheet and the electrolyte. As an example, the positive electrode sheet, the negative electrode sheet and the separator may be stacked or wound to form a stacked structure battery cell or a wound structure battery cell, and the battery cell is packaged in the outer package; the electrolyte may be an electrolyte, and the electrolyte is infiltrated in the battery cell. The number of batteries in the secondary battery may be one or more, which can be adjusted according to demand.

[0120] In one embodiment, the present application provides an electrode assembly. In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly by a winding process or a lamination process. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

[0121] In some embodiments, the outer packaging of the secondary battery may be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc. In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.

[0122] Method for preparing secondary battery

[0123] In one embodiment, the present application provides a method for preparing a secondary battery, wherein the negative electrode sheet described in the first aspect and / or the second aspect of the present application is used.

[0124] The preparation of the secondary battery may also include the step of assembling the negative electrode sheet, the positive electrode sheet and the electrolyte of the present application to form a secondary battery. In some embodiments, the positive electrode sheet, the separator and the negative electrode sheet may be wound or stacked in sequence, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, thereby obtaining a battery cell. The battery cell is placed in an outer package, and the electrolyte is injected and sealed to obtain a secondary battery.

[0125] In some embodiments, the preparation of the secondary battery may further include the step of preparing a positive electrode sheet. As an example, the positive electrode active material, the conductive agent and the binder may be dispersed in a solvent (e.g., N-methylpyrrolidone, referred to as NMP) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, a positive electrode sheet is obtained.

[0126] In some embodiments, the preparation of a secondary battery includes the step of preparing a negative electrode sheet according to the method described in the present application.

[0127] Power-consuming device, battery module or battery pack

[0128] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 3 The secondary battery 5 is a square structure as an example.

[0129] In some embodiments, reference Figure 4, the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0130] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0131] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0132] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0133] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0134] Figure 6 and Figure 7 1 is a battery pack 1 as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0135] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0136] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0137] Figure 8 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0138] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0139] Example

[0140] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in the art or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are conventional products that are commonly used in the art and can be obtained commercially. The content of each component in the embodiments of the present application, if not otherwise specified, is based on the mass without crystal water.

[0141] The following descriptive terms: "the negative electrode sheet of Example A1" refers to the negative electrode sheet used in the preparation process of the lithium ion battery of Example A1; "the positive electrode sheet of Example A1" refers to the positive electrode sheet used in the preparation process of the lithium ion battery of Example A1; "the electrolyte of Example A1" refers to the electrolyte used in the preparation process of the lithium ion battery of Example A1; "the isolation membrane of Example A1" refers to the isolation membrane used in the preparation process of the lithium ion battery of Example A1; "the lithium ion battery of Example A1" refers to a lithium ion battery prepared by the positive electrode, isolation membrane, negative electrode and electrolyte of Example A1.

[0142] In this application, coating weights are all dry weights.

[0143] The sources of raw materials involved in the embodiments of this application are as follows:

[0144] Nickel-cobalt-manganese ternary material (LiMO2, M is Ni-Co-Mn solid solution, the specific proportion of which is detailed in each embodiment)

[0145] Artificial graphite a (Guangdong Kaijin New Energy Technology Co., Ltd., DV50 = 22 μm);

[0146] Artificial graphite b (Guangdong Kaijin New Energy Technology Co., Ltd., DV50 = 12 μm);

[0147] N-Methylpyrrolidone (NMP, CAS: 872-50-4, Shanghai MacLean Biotechnology Co., Ltd.)

[0148] Polyvinylidene fluoride (CAS: 24937-79-9, Shanghai MacLean Biotechnology Co., Ltd.)

[0149] Acetylene black (Guangdong Kaijin New Energy Technology Co., Ltd.)

[0150] Acrylate (CAS: 25067-02-1, Shanghai MacLean Biotechnology Co., Ltd.)

[0151] Dimethyl carbonate (DMC, CAS: 616-38-6, Shanghai MacLean Biotechnology Co., Ltd.)

[0152] Carbon microtubes were prepared according to the following method:

[0153] Electrospinning (voltage 20Kv, flow rate 50mL / min) of a nanofiber precursor solution containing 15% (mass percentage) of polystyrene (N-methylpyrrolidone as solvent) was performed to obtain nanofibers; the nanofibers were evenly dispersed in a 1M hydrochloric acid solution containing 15% (mass percentage) of pyrrole, with the mass ratio of pyrrole to nanofibers being 1:1; then ammonium persulfate was added for polymerization reaction, the mass of ammonium persulfate being 1.2 times that of the nanofibers, to obtain nanofibers with a surface coated with a polymer, and tetrahydrofuran was added to the above-mentioned surface coated polymer nanofibers, the mass of tetrahydrofuran being 16 times that of the nanofibers; at 25°C, the mixture was stirred for 6h to dissolve the polystyrene, to obtain a hollow polymer tube, which was pre-sintered at 300°C for 2h and carbonized at 1200°C for 4h, and then cooled to obtain a micron-sized carbon tube;

[0154] The carbon microtubes thus obtained had an inner diameter of 2.5 μm, a wall thickness of 0.05 μm and a length of 15 μm.

[0155] The above implementation process was repeated, and the mass ratio of tetrahydrofuran to nanofiber filaments was changed to 20, 19, 17, 14, 13, 12, and 10, respectively, to obtain carbon microtubes with inner diameters of 0.2, 1, 2, 4, 6, 10, and 12 μm, respectively.

[0156] Example A1

[0157]

Preparation of negative electrode slurry

[0158] The components of the raw materials: negative electrode active material artificial graphite b (median particle size DV50 = 12 μm), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose CMC, conductive agent sp, carbon microtubes are mixed in a mass fraction of 95%: 1.8%: 1.2%: 0.2%: 1.8% (based on the total weight of the raw materials), deionized water is added, and a negative electrode slurry with a solid component mass fraction of 50% is obtained under the action of a vacuum mixer; the carbon microtubes used have an inner diameter of 2.5 μm, a wall thickness of 0.05 μm, and a length of 15 μm.

[0159]

Preparation of negative electrode sheet

[0160] The negative electrode slurry prepared above was 2 The coating weight (dry weight) is evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm; the copper foil is then dried at room temperature and transferred to a 120° C. oven for drying for 1 hour, and then cold pressed and cut to obtain the negative electrode sheet.

[0161]

Preparation of positive electrode

[0162] The positive electrode active material nickel cobalt manganese ternary material (LiNi 0.8 Co 0.1 Mn 0.1 O2), binder polyvinylidene fluoride, and conductive agent acetylene black are mixed in a mass ratio of 8:1:1, and solvent NMP is added to obtain positive electrode slurry under the action of a vacuum mixer; the positive electrode slurry is uniformly coated on a positive electrode current collector aluminum foil with a thickness of 13 μm according to a certain coating weight (according to N / P=1.05, N / P refers to the ratio of the negative electrode surface capacity per unit area to the positive electrode surface capacity per unit area); the aluminum foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the positive electrode sheet.

[0163]

Preparation of electrolyte

[0164] In an argon atmosphere glove box with a water content of <10 ppm, EC and EMC were mixed in a beaker at a mass ratio of 3:7, and LiPF6 was added to form an electrolyte, in which the mass content of LiPF6 was 12.5%.

[0165]

Isolation film

[0166] The isolation membrane was purchased from Cellgard, model number is cellgard2400.

[0167]

Preparation of lithium-ion batteries

[0168] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell; the bare cell with a capacity of 4.3Ah is placed in an outer packaging foil, and the 8.6g electrolyte prepared above is injected into the dried battery, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained. The outer packaging is 33mm (width) × 220mm (length) × 97mm (height), and the thickness of the shell is 0.6mm; the battery group margin is 90%.

[0169] Examples A2-A5 and A15-A16

[0170] The preparation process of the lithium-ion battery is generally similar to that of Example A1, except that the inner diameter of the carbon microtube is changed during the preparation of the negative electrode slurry. The specific values ​​are shown in Table 1.

[0171] Examples A6-A12

[0172] The preparation process of the lithium-ion battery is generally similar to that of Example A1, except that, in the preparation of the negative electrode slurry, the mass fractions of the conductive agent sp and the carbon microtubes in the raw materials are changed, as shown in Table 1.

[0173] Comparative Example 1

[0174] The preparation process of the lithium-ion battery is generally referred to Example A1, except that in the preparation of the negative electrode slurry, the mass fractions of the carbon microtubes and the conductive agent sp in the raw material are changed to 1.8% and 2%, respectively, as shown in Table 1.

[0175] Comparative Example 2

[0176] The preparation process of the lithium-ion battery is generally similar to that of Example A1, except that no conductive agent is added in the preparation of the negative electrode slurry, and the mass fraction of the carbon microtubes is 6%, as shown in Table 1.

[0177] Comparative Example 3

[0178] The preparation process of the lithium-ion battery is generally similar to that of Example A1, except that no carbon microtubes are added during the preparation of the negative electrode sheet, as shown in Table 1.

[0179] In Examples A2-A16 and Comparative Examples 1-3, the mass fractions of the carbon microtubes and the conductive agent used to prepare the slurry in the raw materials are the mass fractions of the carbon microtubes and the conductive agent in the negative electrode film layer shown in Table 1; for the remaining components used to prepare the slurry, the negative electrode active material artificial graphite, the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 95:1.8:1.2.

[0180] Example B1

[0181] The preparation process of the lithium-ion battery is generally similar to that of Example A1, except for the preparation process of the negative electrode:

[0182] [Preparation of slurry for the first film layer]

[0183] The raw material components: the first negative electrode active material artificial graphite a (median particle size Dv50 = 22), the conductive agent sp, the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are mixed according to the mass fraction of 96%: 1%: 1.8%: 1.2% (based on the total weight of the raw materials), deionized water is added, and a negative electrode slurry with a solid component mass fraction of 50% is obtained under the action of a vacuum mixer; the lower layer of the negative electrode film layer, that is, the layer close to the current collector, is prepared.

[0184] [Preparation of slurry for the second film layer]

[0185] The raw material components: the second negative electrode active material artificial graphite b (median particle size Dv50=12), the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose CMC, and the carbon microtubes are mixed according to the mass fraction of 94%: 1.8%: 1.2%: 3% (based on the total weight of the raw materials), and deionized water is added to obtain a negative electrode slurry with a solid component mass fraction of 50% under the action of a vacuum mixer; the upper layer of the negative electrode film layer, i.e., a layer away from the current collector, does not contain carbon microtubes.

[0186]

Preparation of negative electrode sheet

[0187] The slurry of the first film layer prepared above was prepared at 7 mg / cm 2 The coating weight of (dry weight) was evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm, and dried to obtain the first film layer (i.e., the lower layer of the negative electrode film layer) used in this embodiment; 7 mg / cm 2 The coating weight of (dry weight) is evenly coated with the slurry of the second film layer prepared above; the copper foil is then dried at room temperature and transferred to a 120° C. oven for drying for 1 hour, and then cold pressed and cut to obtain the negative electrode sheet.

[0188] The inner diameter of the carbon microtube used is 2.5 μm, the wall thickness is 0.05 μm, and the length is 15 μm. The coating weight ratio of the first film layer to the second film layer is 1:1, that is, the weight ratio of the first film layer to the second film layer.

[0189] Examples B2-B5 and B15-B16

[0190] The preparation process of the lithium-ion battery is generally similar to that of Example B1, except that the inner diameter of the carbon microtubes is changed in the preparation of the slurry for the first and second membrane layers. The specific values ​​are shown in Table 2.

[0191] Examples B6 and B17-B18

[0192] The preparation process of the lithium-ion battery is generally referred to Example B1, except that, in the slurry preparation of the first film layer, the mass fractions of the conductive agent sp of the raw material are as shown in Table 2, and the remaining components, the first negative electrode active material artificial graphite a (median particle size Dv50 = 22), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 96:1.8:1.2;

[0193] In the slurry preparation of the second membrane layer, the raw material also includes a conductive agent sp. The mass fractions of the carbon microtubes and the conductive agent sp in the raw material are shown in Table 2. The remaining components, the second negative electrode active material artificial graphite b (median particle size Dv50=12), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 94:1.8:1.2.

[0194] Examples B7-B12

[0195] The preparation process of the lithium-ion battery is generally referred to Example B1, except that, in the slurry preparation of the first film layer, the mass fractions of the conductive agent sp of the raw material are as shown in Table 2, and the remaining components, the first negative electrode active material artificial graphite a (median particle size Dv50 = 22), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 96:1.8:1.2;

[0196] In the preparation of the slurry for the second membrane layer, the mass fraction of the carbon microtubes in the raw materials was changed as shown in Table 2; the remaining components, the second negative electrode active material artificial graphite b (median particle size Dv50=12), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose were added in a mass ratio of 94:1.8:1.2.

[0197] Examples B13-B14

[0198] The preparation process of the lithium-ion battery is generally referred to Example B1, except that, in the slurry preparation of the first film layer, the mass fractions of the conductive agent sp of the raw material are as shown in Table 2, and the remaining components, the first negative electrode active material artificial graphite a (median particle size Dv50 = 22), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 96:1.8:1.2;

[0199] In the preparation of the negative electrode sheet, the coating ratio of the first film layer to the second film layer was changed, as shown in Table 2.

[0200] Examples B19-B20

[0201] The preparation process of the lithium-ion battery is generally referred to Example B1, except that, in the slurry preparation of the first film layer, the mass fractions of the conductive agent sp of the raw material are as shown in Table 2, and the remaining components, the first negative electrode active material artificial graphite a (median particle size Dv50 = 22), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 96:1.8:1.2;

[0202] In the preparation of the slurry for the second membrane layer, the raw material of Example B20 also contains a conductive agent sp. The mass fractions of the carbon microtubes and the conductive agent sp in the raw material are shown in Table 2, respectively. The remaining components, the second negative electrode active material artificial graphite b (median particle size Dv50=12), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 94:1.8:1.2.

[0203] In the preparation of the negative electrode sheet, the weight ratio of the first film layer to the second film layer was changed, as shown in Table 2.

[0204] Comparative Example 4

[0205] The preparation process of the lithium-ion battery is generally similar to that of Example B1, except that in the preparation of the second film layer, the slurry of the second film layer does not contain carbon microtubes, but contains a conductive agent with a mass fraction of 3%, as shown in Table 2.

[0206] Example C1

[0207] The preparation process of the lithium ion battery is generally referred to Example A1, except for the following preparation process:

[0208] [Preparation of slurry for the first film layer]

[0209] The raw material components: the first negative electrode active material artificial graphite a (median particle size Dv50 = 22), the conductive agent sp, the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose, and the carbon microtubes are mixed according to a mass fraction of 95.3%: 0.8%: 1.5%: 1.2%: 1.2% (based on the total weight of the raw materials), deionized water is added, and a negative electrode slurry with a solid component mass fraction of 50% is obtained under the action of a vacuum mixer; the lower layer of the negative electrode film layer, that is, a layer close to the current collector, is prepared.

[0210] [Preparation of slurry for the second film layer]:

[0211] The raw material components: the second negative electrode active material artificial graphite b (median particle size Dv50=12), the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose, and the carbon microtubes are mixed according to the mass fraction of 93.3%: 1.5%: 1.2%: 4% (based on the total weight of the raw materials), deionized water is added, and a negative electrode slurry with a solid component mass fraction of 50% is obtained under the action of a vacuum mixer; the upper layer of the negative electrode film layer, that is, the layer away from the current collector, is prepared.

[0212]

Preparation of negative electrode sheet

[0213] The slurry of the first film layer prepared above was prepared at 6 mg / cm 2 The coating weight of (dry weight) was evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm, and dried to obtain the first film layer (i.e., the lower layer of the negative electrode film layer) used in this embodiment; 6 mg / cm 2 The coating weight of (dry weight) is evenly coated with the slurry of the second film layer prepared above; the copper foil is then dried at room temperature and transferred to a 120° C. oven for drying for 1 hour, and then cold pressed and cut to obtain the negative electrode sheet.

[0214] The inner diameter of the carbon microtube used is 2.5 μm, the wall thickness is 0.05 μm, and the length is 15 μm. The coating weight ratio of the first film layer to the second film layer is 1:1, that is, the weight ratio of the first film layer to the second film layer.

[0215] Examples C2-C5 and C15-C16

[0216] The preparation process of the lithium-ion battery is generally similar to that of Example C1, except that the inner diameter of the carbon microtubes is changed in the preparation of the slurry for the first and second membrane layers. The specific values ​​are shown in Table 3.

[0217] Examples C6-C12 and C17-C18

[0218] The preparation process of the lithium ion battery is generally similar to that of Example C1, except that:

[0219] In the preparation of the slurry of the first film layer, the raw material optionally contains a conductive agent sp, and the mass fractions of the carbon microtubes and the conductive agent sp in the raw material are shown in Table 3, respectively. The remaining components, the first negative electrode active material artificial graphite a (median particle size Dv50=22), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 95.3:1.5:1.2;

[0220] In the slurry preparation of the second membrane layer, the raw material optionally contains a conductive agent sp. The mass fractions of the carbon microtubes and the conductive agent sp in the raw material are shown in Table 3, respectively. The remaining components, the second negative electrode active material artificial graphite b (median particle size Dv50=12), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 93.3:1.5:1.2.

[0221] C13-C14 and C19-C20

[0222] The preparation process of the lithium ion battery is generally similar to that of Example C1, except that:

[0223] In the slurry preparation of the first film layer, the mass fractions of carbon microtubes and conductive agent sp in the raw materials are shown in Table 3, and the remaining components, the first negative electrode active material artificial graphite a (median particle size Dv50 = 22), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose, are added in a mass ratio of 95.3:1.5:1.2;

[0224] In the preparation of the slurry of the second membrane layer, the raw material also includes a conductive agent sp, and the mass fractions of the carbon microtubes and the conductive agent sp in the raw material are shown in Table 3, respectively. The remaining components, the second negative electrode active material artificial graphite b (median particle size Dv50=12), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 93.3:1.5:1.2;

[0225] In the preparation of the negative electrode sheet, the weight ratio of the first film layer to the second film layer was changed, as shown in Table 3.

[0226] Comparative Example 5

[0227] The preparation process of the lithium-ion battery is generally similar to that of Example C1, except that in the preparation of the negative electrode sheet, the slurries of the first and second film layers do not contain carbon microtubes, and the mass fraction of the conductive agent in the raw materials is 1%, as shown in Table 3;

[0228] The remaining components in the slurry prepared by the first film layer, the first negative electrode active material artificial graphite a (median particle size Dv50=22), the binder styrene butadiene rubber, and the dispersant sodium carboxymethyl cellulose were added in a mass ratio of 96.3:1.5:1.2; the remaining components in the slurry prepared by the second film layer, the first negative electrode active material artificial graphite b (median particle size Dv50=12), the binder styrene butadiene rubber, and the dispersant sodium carboxymethyl cellulose were added in a mass ratio of 96.3:1.5:1.2.

[0229]

Related parameters and battery performance test

[0230] 1. Determination method of carbon microtubes

[0231] In the present application, the length, inner diameter and wall thickness of the carbon microtubes can be tested by using a scanning electron microscope (ZEISS Sigma 300). The sample preparation is as follows: the pole piece is cut into a sample of 8 mm × 3 mm size, placed on the sample stage, and tested by a scanning electron microscope (ZEISS Sigma 300) at a magnification of 10K, the carbon microtubes can be observed, and the length, inner diameter and wall thickness of the carbon microtubes can be measured.

[0232] 2. Method for determining the structure of the negative electrode film

[0233] In this application, the structure of the negative electrode film layer can be tested by using a scanning electron microscope (ZEISS Sigma 300) at a magnification of 10K. The sample preparation is as follows: first, the negative electrode sheet is cut into a sample of 2cm×2cm size, and the negative electrode sheet is fixed on the sample stage by paraffin. Then the sample stage is placed in the sample holder and locked and fixed, and the argon ion cross-section polisher (IB-19500CP) is turned on and vacuumed (10 -4 Pa), set the argon flow rate (0.15MPa), voltage (8KV) and polishing time (2 hours), adjust the sample stage to the swing mode and start polishing. The sample test was carried out according to JY / T010-1996.

[0234] 3.Battery fast charging capability test

[0235] At 25°C, the batteries of the above embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour), specifically including: charging the battery at a constant current of 1C to a voltage of 4.25V, then charging at a constant voltage to a current of ≤0.05C, standing for 5 minutes, and then discharging at a constant current of 0.33C to a voltage of 2.8V, and recording its actual capacity as C0.

[0236] Then the battery is charged with 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, constant current to the full battery charge cut-off voltage of 4.25V or 0V negative electrode cut-off potential (whichever is reached first). After each charge, it is necessary to discharge with 1C0 to the full battery discharge cut-off voltage of 2.8V. Record the SOC (State of Charge) at different charge rates to 10%, 20%, 30%, ..., 80% The charge rate-negative electrode potential curve under different SOC states is drawn, and the charge rate corresponding to the negative electrode potential of 0V under different SOC states is obtained after linear fitting. The charge rate is the charging window under the SOC state, which is recorded as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC respectively. The charging time T of the battery from 10%SOC to 80%SOC is calculated according to the formula (60 / C20%SOC+60 / C30%SOC+60 / C40%SOC+60 / C50%SOC+60 / C60%SOC+60 / C70%SOC+60 / C80%SOC)×10%, in min. The shorter the time, the better the fast charging performance of the battery. Initial discharge DCR (Direct Current Resistance) test

[0237] The lithium ion batteries of the embodiment and the comparative example were tested according to the above process, and the specific values ​​are shown in Tables 1 to 3.

[0238] Table 1: Effects of relevant parameters for preparing single-layer coated negative electrode sheets on battery performance

[0239]

[0240]

[0241]

[0242]

[0243]

[0244] Compared with the comparative examples, the embodiments of the present application can be seen from Table 1 that when the mass fractions of carbon microtubes and conductive agent in the single-layer coated negative electrode film layer satisfy a specific relationship, the fast charging capability of the battery can be significantly improved; as can be seen from Tables 2-3, when the double-layer coated negative electrode plate contains carbon microtubes, the charging capacity of the battery is significantly improved.

[0245] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A single-layer coated negative electrode plate, characterized in that: The single-layer coated negative electrode sheet comprises a current collector and a negative electrode film layer disposed on at least one surface of the current collector, wherein the negative electrode film layer comprises a negative electrode active material and carbon microtubes, and optionally comprises a conductive agent; The mass fraction W1 of the carbon microtubes in the negative electrode film layer and the mass fraction W2 of the conductive agent in the negative electrode film layer satisfy: when 0.2%≤W1≤2%, then W1+W2≤2%; when W1>2%, then 0≤W2≤0.5%, based on the total weight of the negative electrode film layer.

2. The single-layer coated negative electrode sheet according to claim 1, characterized in that: The mass fraction W1 of the carbon microtubes in the negative electrode film layer is 0.2% to 5%.

3. The single-layer coated negative electrode sheet according to claim 1 or 2, characterized in that: The inner diameter of the carbon microtube is 0.2 μm to 12 μm.

4. The single-layer coated negative electrode sheet according to claim 1 or 2, characterized in that: The inner diameter of the carbon microtube is 2 μm to 10 μm.

5. The single-layer coated negative electrode sheet according to claim 1 or 2, characterized in that: The aspect ratio of the carbon microtube is 2-20.

6. The single-layer coated negative electrode sheet according to claim 1 or 2, characterized in that: The wall thickness of the carbon microtube is 0.01 μm to 1 μm.

7. The single-layer coated negative electrode sheet according to claim 1 or 2, characterized in that: The negative electrode active material includes at least one of artificial graphite, natural graphite and silicon-based material.

8. The single-layer coated negative electrode sheet according to claim 1 or 2, characterized in that: The conductive agent includes at least one of conductive agent sp, KS-6, conductive graphite, carbon nanotubes, graphene, and carbon fiber VGCF.

9. A double-layer coated negative electrode plate, characterized in that: The double-layer coated negative electrode sheet comprises a current collector, a first film layer and a second film layer, wherein the first film layer is arranged on at least one surface of the current collector, and the second film layer is arranged on the outer surface of the first film layer; the first film layer is located between the current collector and the second film layer; Among them, the first film layer contains a first negative electrode active material; the second film layer contains a second negative electrode active material; at least one of the first film layer and the second film layer contains carbon microtubes; and the first film layer and the second film layer are different in at least one of the negative electrode active material and whether they include carbon microtubes.

10. The double-layer coated negative electrode sheet according to claim 9, characterized in that: The first film layer does not contain carbon microtubes, and the second film layer contains carbon microtubes.

11. The double-layer coated negative electrode plate according to claim 9, characterized in that: The first film layer and the second film layer both contain carbon microtubes.

12. The double-layer coated negative electrode sheet according to any one of claims 9 to 11, characterized in that: In the first film layer and the second film layer, the total mass fraction W3 of the carbon microtubes is 0.2% to 5%, based on the total weight of the first film layer and the second film layer.

13. The double-layer coated negative electrode plate according to claim 9, characterized in that: The first film layer and the second film layer optionally further include a conductive agent, and the total mass fraction W3 of the carbon microtubes and the total mass fraction W4 of the conductive agent satisfy: when 0.2%≤W3≤2%, then W3+W4≤2%; when W3>2%, then 0≤W4≤0.5%, based on the total mass of the first film layer and the second film layer.

14. The double-layer coated negative electrode sheet according to any one of claims 9 to 11, characterized in that: The mass of the carbon microtubes in the second film layer is 50-100% relative to the total mass of the carbon microtubes.

15. The double-layer coated negative electrode sheet according to any one of claims 9 to 11, characterized in that: The inner diameter of the carbon microtube is 0.2 μm to 12 μm.

16. The double-layer coated negative electrode sheet according to any one of claims 9 to 11, characterized in that: The inner diameter of the carbon microtube is 2 μm to 10 μm.

17. The double-layer coated negative electrode sheet according to any one of claims 9 to 11, characterized in that: The aspect ratio of the carbon microtube is 2-20.

18. The double-layer coated negative electrode sheet according to any one of claims 9 to 11, characterized in that: The wall thickness of the carbon microtube is 0.01 μm to 1 μm.

19. The double-layer coated negative electrode plate according to claim 10, characterized in that: The first film layer and the second film layer optionally also contain a conductive agent; the mass fraction of the carbon microtubes in the second film layer is 0.4% to 10%, and the mass fraction of the conductive agent is 0% to 4%, based on the weight of the second film layer; the mass fraction of the conductive agent in the first film layer is 0% to 4%, based on the weight of the first film layer.

20. The double-layer coated negative electrode plate according to claim 19, characterized in that: The mass fraction of the conductive agent in the second film layer is 0% to 1.6%, based on the weight of the second film layer.

21. The double-layer coated negative electrode plate according to claim 19, characterized in that: The mass fraction of the conductive agent in the first film layer is 0% to 2%, based on the weight of the first film layer.

22. The double-layer coated negative electrode plate according to claim 11, characterized in that: The first film layer and the second film layer optionally further contain a conductive agent; when the first film layer and the second film layer both contain the carbon microtubes, the mass fraction of the carbon microtubes in each film layer is 0.2% to 5%, and the mass fraction of the conductive agent in each film layer is 0% to 2%, based on the weight of each film layer.

23. The double-layer coated negative electrode plate according to claim 22, characterized in that: The mass fraction ratio of the carbon microtubes in the second film layer to that in the first film layer is 10:3 to 1:

1.

24. The double-layer coated negative electrode sheet according to any one of claims 9-11, 13 and 19-23, characterized in that: The weight ratio of the second film layer to the first film layer is 1:4 to 4:

1.

25. The double-layer coated negative electrode sheet according to any one of claims 9-11, 13 and 19-23, characterized in that: The first negative electrode active material and the second negative electrode active material are the same, and include at least one of artificial graphite, natural graphite, and silicon-based materials.

26. The double-layer coated negative electrode sheet according to any one of claims 9-11, 13 and 19-23, characterized in that: The first negative electrode active material and the second negative electrode active material are different and include at least one of artificial graphite, natural graphite, and silicon-based materials.

27. The double-layer coated negative electrode sheet according to any one of claims 13 and 19-23, characterized in that: The conductive agent is the same in the first film layer and the second film layer, and includes at least one of conductive agent sp, KS-6, conductive graphite, carbon nanotubes, graphene, and carbon fiber VGCF.

28. The double-layer coated negative electrode sheet according to any one of claims 13 and 19-23, characterized in that: The conductive agent is different in the first film layer and the second film layer, and includes at least one of conductive agent sp, KS-6, conductive graphite, carbon nanotubes, graphene, and carbon fiber VGCF.

29. A secondary battery, characterized in that: A single-layer coated negative electrode sheet according to any one of claims 1 to 8, or a double-layer coated negative electrode sheet according to any one of claims 9 to 28.

30. A battery module, characterized in that: Includes the secondary battery as claimed in claim 29.

31. A battery pack, characterized in that: A battery module comprising the battery module described in claim 30.

32. An electrical device, characterized in that: Includes at least one selected from the secondary battery of claim 29, the battery module of claim 30, or the battery pack of claim 31.

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