Negative electrode composition, negative electrode sheet, method for manufacturing the same, battery, and energy storage device

Abstract

The application provides a negative electrode composition, a negative electrode sheet, a preparation method of the negative electrode sheet, a battery and an energy storage device. The application provides a negative electrode composition, which comprises a negative electrode active material, first carbon nanotubes and second carbon nanotubes, the diameter of the first carbon nanotubes is greater than the diameter of the second carbon nanotubes; and the quantity ratio of the first carbon nanotubes to the second carbon nanotubes ranges from 0.01 to 0.67.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to a negative electrode composition, a negative electrode sheet and its preparation method, a battery and an energy storage device. Background Technology

[0002] In sodium-ion batteries, hard carbon, the negative electrode active material, is usually used in combination with binders (styrene-butadiene rubber, SBR) and dispersants (polyacrylic acid PAA, sodium carboxymethyl cellulose CMC). Due to its high hardness, high elastic deformation (prone to slippage rather than densification during rolling) and low interparticle bonding force, the negative electrode sheet is prone to cracking, powder shedding, and even breakage after rolling under high rolling conditions. In addition, due to the low peel force, poor flexibility, and poor electrolyte wettability of the negative electrode sheet after rolling, the battery has problems such as low electronic conductivity, easy cracking and powder shedding of the negative electrode sheet after multiple charge and discharge processes, and rapid cycle degradation. Summary of the Invention

[0003] This application provides a negative electrode composition that, after being formed into a negative electrode active layer, has high peel strength and high electronic conductivity.

[0004] In a first aspect, this application provides a negative electrode composition comprising a negative electrode active material, a first carbon nanotube, and a second carbon nanotube, wherein the diameter of the first carbon nanotube is larger than the diameter of the second carbon nanotube; and the ratio of the number of the first carbon nanotube to the number of the second carbon nanotube ranges from 0.01 to 0.67.

[0005] Furthermore, the negative electrode composition also includes a binder, which is connected to the first carbon nanotube by intermolecular forces or chemical bonds.

[0006] Furthermore, the mass ratio of the binder to the first carbon nanotube in the negative electrode composition ranges from 15 to 170, and the mass fraction of the binder ranges from 1% to 3%.

[0007] Furthermore, the first carbon nanotube is a modified carbon nanotube, which includes polar groups, including at least one of carboxyl, hydroxyl, carbonyl, amino, amide, cyano, sulfonic acid, and phosphate groups.

[0008] Furthermore, the modified carbon nanotubes are modified by at least one of concentrated nitric acid, concentrated sulfuric acid, diethyl adipate, diethyl dimethylmalonate, diethyl octanoate, dimethyl malonate, dimethyl octanoate, methyl valerate, propyl butyrate, n-dodecyltrimethoxysilane, silane coupling agent, trimethylsilane, hexadecyltrimethyltetrafluoroborate ammonium, N-(cocoyl)-N,N,N-trimethylammonium sulfate, hexadecyltrimethylammonium nitrate, methacrylic acid, and maleic acid.

[0009] Furthermore, the mass fraction of the second carbon nanotube in the negative electrode composition ranges from 0.01% to 0.2%.

[0010] Furthermore, the diameter of the first carbon nanotube ranges from 10 nm to 50 nm.

[0011] Furthermore, the diameter of the second carbon nanotube ranges from 2 nm to 10 nm.

[0012] Furthermore, the average length of the first carbon nanotube ranges from 8 μm to 20 μm; the average length of the second carbon nanotube ranges from 8 μm to 20 μm.

[0013] Furthermore, the negative electrode composition further includes a negative electrode conductive agent, a first dispersant, and a second dispersant; the negative electrode conductive agent includes at least one of conductive carbon black, superconducting carbon black, Ketjen black, graphite, and graphene; the first dispersant includes at least one of sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide; the second dispersant includes at least one of polyacrylic acid and sodium carboxymethyl cellulose.

[0014] Secondly, embodiments of this application also provide a negative electrode sheet, the negative electrode sheet comprising: a negative electrode current collector and a negative electrode active layer, the negative electrode active layer being disposed on the surface of the negative electrode current collector, the negative electrode active layer being formed from the negative electrode composition described in the first aspect embodiment of this application.

[0015] Thirdly, embodiments of this application also provide a method for preparing a negative electrode sheet, the method comprising:

[0016] The first carbon nanotubes are mixed with a binder to obtain the first slurry;

[0017] The first slurry is mixed with the negative electrode active material and the second carbon nanotubes to obtain the second slurry; and

[0018] A negative electrode current collector is provided, and the second slurry is coated onto the negative electrode current collector. After drying and rolling, the negative electrode sheet is obtained. The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer. The negative electrode active layer includes a negative electrode active material, a first carbon nanotube, a second carbon nanotube, and a binder. The diameter of the first carbon nanotube is larger than the diameter of the second carbon nanotube, and the ratio of the number of the first carbon nanotube to the number of the second carbon nanotube is in the range of 0.01 to 0.67.

[0019] Fourthly, embodiments of this application also provide a battery, which includes: an electrolyte, a positive electrode, a separator, and the negative electrode described in the third aspect of this application.

[0020] Fifthly, embodiments of this application also provide an energy storage device, which includes:

[0021] Box; and

[0022] The battery described in the fourth aspect of this application is housed within the casing.

[0023] The negative electrode composition of this application includes a negative electrode active material, a first carbon nanotube, and a second carbon nanotube. The diameter of the first carbon nanotube is larger than the diameter of the second carbon nanotube, and the ratio of the number of the first carbon nanotube to the number of the second carbon nanotube ranges from 0.01 to 0.67. The second carbon nanotube has a smaller diameter. The smaller diameter (larger aspect ratio) of the second carbon nanotube has higher electronic conductivity and a larger effective contact area, which can improve the electronic conductivity of the negative electrode sheet using this negative electrode composition and promote electron transport. However, the second carbon nanotube with a smaller diameter has higher rigidity and stronger carbon-carbon bonds, resulting in a higher elastic modulus and stronger compression resistance. This leads to a lower packing density after battery coating, and a greater thickness after rolling under the same rolling conditions. The actual compaction density of the negative electrode sheet before the electrode assembly is placed in the shell is reduced, which not only limits the electron transport of the negative electrode sheet but also... Transmission also reduces the actual energy density of the battery. The larger diameter of the first carbon nanotube (smaller aspect ratio) results in a lower elastic modulus, making it easier to compress radially. This mitigates the rebound of the negative electrode sheet, resulting in a thinner sheet after rolling. This not only improves the peeling force of the negative electrode sheet, better preventing cracking and powder shedding, but also, compared to the smaller diameter of the second carbon nanotube, the larger diameter first carbon nanotube has higher ionic conductivity, promoting ion transport in the negative electrode sheet and further reducing battery polarization, thereby improving the battery's cycle and storage performance. This application, through the combined use of first and second carbon nanotubes of different diameters, allows the negative electrode composition to balance good radial compressibility and a high elastic modulus. This results in negative electrode sheets using this composition having higher electronic and ionic conductivity while reducing the risk of energy density reduction caused by high thickness rebound, thus enabling the battery to achieve both high energy density and high cycle capacity retention. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a scanning electron microscope image of a negative electrode composition according to an embodiment of this application.

[0026] Figure 2 This is a schematic diagram of the structure of the negative electrode sheet according to an embodiment of this application.

[0027] Figure 3 This is a schematic flowchart of a method for preparing a negative electrode sheet according to an embodiment of this application.

[0028] Figure 4 This is a schematic diagram of the preparation process of the first slurry according to an embodiment of this application.

[0029] Figure 5 This is a schematic diagram of the structure of a sodium battery according to an embodiment of this application.

[0030] Figure 6 This application describes a sodium battery according to an embodiment of the present application. Figure 5 A schematic diagram of the cross-sectional structure along the AA direction.

[0031] Figure 7 This is a schematic diagram of the structure of the positive electrode sheet according to an embodiment of this application.

[0032] Figure 8 This is a schematic diagram of the structure of an energy storage device according to an embodiment of this application.

[0033] Figure 9 This is a structural block diagram of an energy storage system according to an embodiment of this application.

[0034] Figure 10 This is an application scenario diagram of an energy storage system according to an embodiment of this application.

[0035] Explanation of reference numerals in the attached figures:

[0036] 100-Negative electrode sheet, 110-Negative current collector, 120-Negative active layer, 300-Battery, 310-Positive electrode sheet, 311-Positive current collector, 312-Positive active layer, 320-Separator, 340-Housing shell, 350-End cap assembly, 400-Energy storage device, 410-Box housing, 500-Energy storage system, 510-Power conversion device. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0038] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0039] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0040] It should be noted that, for ease of explanation, the same reference numerals denote the same components in the embodiments of this application, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0041] Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0042] Batteries are the smallest energy storage unit in energy storage devices and systems, and their performance directly affects the performance and application of these devices and systems. Batteries include lithium batteries (such as lithium-ion batteries) and sodium batteries (such as sodium-ion batteries).

[0043] In sodium-ion batteries, hard carbon, the negative electrode active material, is usually used in combination with binders (styrene-butadiene rubber, SBR) and dispersants (polyacrylic acid PAA, sodium carboxymethyl cellulose CMC). Due to its high hardness, high elastic deformation (prone to slippage rather than densification during rolling) and low interparticle bonding force, the negative electrode sheet is prone to cracking, powder shedding, and even breakage after rolling under high rolling conditions. In addition, due to the low peel force, poor flexibility, and poor electrolyte wettability of the negative electrode sheet after rolling, the battery has problems such as low electronic conductivity, easy cracking and powder shedding of the negative electrode sheet after multiple charge and discharge processes, and rapid cycle degradation.

[0044] Therefore, embodiments of this application provide a negative electrode composition, a negative electrode sheet, a method for preparing the same, a battery, and an energy storage device.

[0045] This application provides a negative electrode composition comprising a negative electrode active material, a first carbon nanotube, and a second carbon nanotube, wherein the diameter of the first carbon nanotube is larger than the diameter of the second carbon nanotube, and the ratio of the number of the first carbon nanotube to the number of the second carbon nanotube ranges from 0.01 to 0.67.

[0046] The negative electrode composition of this application embodiment is used to prepare the negative electrode active layer of the negative electrode sheet of a battery. Optionally, the battery of this application embodiment can be, but is not limited to, a lithium battery or a sodium battery. Optionally, a sodium battery can be at least one of a sodium-ion battery, a sodium metal battery, or a lithium-sodium hybrid battery. Optionally, a lithium battery can be at least one of a lithium-ion battery, a lithium metal battery, or a lithium-sodium hybrid battery. It is understood that the battery includes a negative electrode sheet. Optionally, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer, the negative electrode active layer being disposed on the surface of the negative electrode current collector. The negative electrode active layer is obtained by a negative electrode composition through processes such as slurry preparation, coating, drying, and rolling.

[0047] In this embodiment of the application, when the numerical range a to b is involved, unless otherwise specified, the numerical value can be any value between a and b, including the endpoint value a and the endpoint value b.

[0048] It should be noted that the diameters of the first and second carbon nanotubes in this application refer to their outer diameters.

[0049] Understandably, the ratio of the number of the first carbon nanotubes to the number of the second carbon nanotubes in the negative electrode composition ranges from 0.01 to 0.67.

[0050] Specifically, the ratio of the first carbon nanotubes to the second carbon nanotubes in the negative electrode composition can be, but is not limited to, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.13, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.67, etc. If the ratio of the first carbon nanotubes to the second carbon nanotubes is too small, the content of the first carbon nanotubes in the negative electrode composition will be too low, and the content of the second carbon nanotubes will be too high. If the content of the first carbon nanotubes is too low, the network support effect of the first carbon nanotubes in the negative electrode composition will be poor, and the effect on improving the peeling force of the negative electrode sheet will not be significant. In addition, the effect of reducing the thickness of the negative electrode sheet using this negative electrode composition is not significant, which reduces the conductivity of the negative electrode sheet and reduces the cycle performance of the negative electrode sheet. If the content of the second carbon nanotubes is too high, the negative electrode sheet using this negative electrode composition will have a large thickness after rolling, affecting the ion transport of the negative electrode sheet and thus affecting the energy density of the battery. If the ratio of the first carbon nanotubes to the second carbon nanotubes is too high, the content of the first carbon nanotubes in the negative electrode composition will be too high and the content of the second carbon nanotubes will be too low. If the content of the first carbon nanotubes is too high, the thickness of the negative electrode active layer after the negative electrode composition is formed into the negative electrode sheet will easily rebound, increasing the side reactions during battery cycling and reducing the battery cycle performance. In addition, when the first carbon nanotubes are mixed with the binder, the viscosity of the slurry increases, making stirring and processing difficult and reducing the dispersibility of the first carbon nanotubes. If the content of the second carbon nanotubes is too low, the electronic conductivity of the negative electrode sheet using this negative electrode composition will be reduced, thus reducing the rate performance of the battery.

[0051] Optionally, the first carbon nanotube can be, but is not limited to, at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0052] Optionally, the second carbon nanotube can be, but is not limited to, at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0053] It should be noted that the quantity and content of the first and second carbon nanotubes in the negative electrode composition can be tested using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). For example, a battery made from the negative electrode composition is placed at 25°C and subjected to charge-discharge cycles at a rate of 1P / 1P (1 times the rated power) for 5 cycles. After this, the fully charged battery (100% SOC) is disassembled, and the resulting negative electrode sheet is subjected to SEM testing. Twenty regions with magnifications from 5K to 20K are randomly selected, and the following steps are performed on each region: 1) Observe the carbon nanotubes in the region and label them one by one as 1#, 2#, and so on; 2) Magnify each labeled carbon nanotube to 300K to 500K and measure its diameter. Calculate the quantity of the first and second carbon nanotubes based on the diameter of each carbon nanotube. The SEM image of the negative electrode active layer of the negative electrode sheet is shown below. Figure 1 As shown.

[0054] The negative electrode composition of this application includes a negative electrode active material, a first carbon nanotube, and a second carbon nanotube. The diameter of the first carbon nanotube is larger than the diameter of the second carbon nanotube, and the ratio of the number of the first carbon nanotube to the number of the second carbon nanotube ranges from 0.01 to 0.67. The second carbon nanotube has a smaller diameter. The smaller diameter (larger aspect ratio) of the second carbon nanotube has higher electronic conductivity and a larger effective contact area, which can improve the electronic conductivity of the negative electrode sheet using this negative electrode composition and promote electron transport. However, the second carbon nanotube with a smaller diameter has higher rigidity and stronger carbon-carbon bonds, resulting in a higher elastic modulus and stronger compression resistance. This leads to a lower packing density after battery coating, and a greater thickness after rolling under the same rolling conditions. The actual compaction density of the negative electrode sheet before the electrode assembly is placed in the shell is reduced, which not only limits the electron transport of the negative electrode sheet but also... Transmission also reduces the actual energy density of the battery. The larger diameter of the first carbon nanotube (smaller aspect ratio) results in a lower elastic modulus, making it easier to compress radially. This mitigates the rebound of the negative electrode sheet, resulting in a thinner sheet after rolling. This not only improves the peeling force of the negative electrode sheet, better preventing cracking and powder shedding, but also, compared to the smaller diameter of the second carbon nanotube, the larger diameter first carbon nanotube has higher ionic conductivity, promoting ion transport in the negative electrode sheet and further reducing battery polarization, thereby improving the battery's cycle and storage performance. This application, through the combined use of first and second carbon nanotubes of different diameters, allows the negative electrode composition to balance good radial compressibility and a high elastic modulus. This results in negative electrode sheets using this composition having higher electronic and ionic conductivity while reducing the risk of energy density reduction caused by high thickness rebound, thus enabling the battery to achieve both high energy density and high cycle capacity retention.

[0055] In some embodiments, the negative electrode composition further includes a binder that is connected to the first carbon nanotube by intermolecular forces or chemical bonds.

[0056] It should be noted that when the negative electrode composition is made into a negative electrode slurry and coated onto the negative electrode current collector, the first carbon nanotube is first mixed with the binder to obtain a binder slurry (called the first slurry). The first slurry is then mixed with the negative electrode active material and the second carbon nanotube to obtain the negative electrode slurry (called the second slurry).

[0057] Optionally, the adhesive may be, but is not limited to, styrene-butadiene rubber (SBR).

[0058] In this embodiment, the first carbon nanotubes and the binder are connected by intermolecular forces or chemical bonds. This allows the first carbon nanotubes to be better encapsulated or adsorbed by the binder, forming a "CNT-SBR" composite unit. This effectively prevents the aggregation of the first carbon nanotubes and increases their dispersibility in the negative electrode composition. Furthermore, after the binder encapsulates the first carbon nanotubes, it also better prevents the first carbon nanotubes from being directly exposed, reducing side reactions during battery cycling and storage, and improving the battery's cycle performance. Moreover, it makes the current density distribution of the negative electrode sheet more uniform, and the density distribution of metal ions (such as sodium ions) more uniform, reducing battery polarization.

[0059] In some embodiments, the first carbon nanotube is a modified carbon nanotube, which includes polar groups, including at least one selected from carboxyl, hydroxyl, carbonyl, amino, amide, cyano, sulfonic acid, and phosphate groups.

[0060] In this embodiment, by modifying the carbon nanotubes to include polar groups, the first carbon nanotubes can be better connected to the binder through intermolecular forces or chemical bonds. This allows the first carbon nanotubes to be better encapsulated or adsorbed by the binder, forming a "CNT-SBR" composite unit. This effectively prevents the aggregation of the first carbon nanotubes and increases their dispersibility in the negative electrode composition. Furthermore, after the binder encapsulates the first carbon nanotubes, it also better prevents the first carbon nanotubes from being directly exposed, reducing side reactions during battery cycling and storage, and improving the battery's cycle performance. Moreover, it makes the current density distribution of the negative electrode sheet more uniform, and the density distribution of metal ions (such as sodium ions) more uniform, reducing battery polarization.

[0061] In some embodiments, the modified carbon nanotubes are modified by at least one of concentrated nitric acid, concentrated sulfuric acid, diethyl adipate, dimethyl dimethyl malonate, diethyl octanoate, dimethyl malonate, dimethyl octanoate, methyl valerate, propyl butyrate, n-dodecyltrimethoxysilane, silane coupling agent, trimethylsilane, hexadecyltrimethyltetrafluoroborate ammonium, N-(cocoyl)-N,N,N-trimethylammonium sulfate, hexadecyltrimethylammonium nitrate, methacrylic acid, and maleic acid.

[0062] In other words, the modified carbon nanotubes are obtained by modifying carbon nanotubes with a modifier, which includes at least one of concentrated nitric acid, concentrated sulfuric acid, diethyl adipate, diethyl dimethylmalonate, diethyl octanoate, dimethyl malonate, dimethyl octanoate, methyl valerate, propyl butyrate, n-dodecyltrimethoxysilane, silane coupling agent, trimethylsilane, hexadecyltrimethyltetrafluoroborate ammonium, N-(cocoyl)-N,N,N-trimethylammonium sulfate, methacrylic acid, and maleic acid.

[0063] In this embodiment, the modification of carbon nanotubes using these compounds can better increase the number of polar functional groups in the modified carbon nanotubes. This allows the modified first carbon nanotubes to be better connected with the binder through intermolecular forces or chemical bonds, promoting the uniform dispersion of the first carbon nanotubes in the binder emulsion. Consequently, the first carbon nanotubes can be better encapsulated or adsorbed by the binder to form "CNT-SBR" composite units, which can effectively prevent the aggregation of the first carbon nanotubes and increase their dispersibility in the negative electrode composition. In addition, after the binder encapsulates the first carbon nanotubes, it can better prevent the first carbon nanotubes from being directly exposed, reducing side reactions of the first carbon nanotubes during battery cycling and storage, and improving the cycle performance of the battery. Furthermore, it can make the current density distribution of the negative electrode sheet more uniform, and the density distribution of metal ions (such as sodium ions) more uniform, reducing the polarization phenomenon of the battery.

[0064] Optionally, the mass fraction of the negative electrode active material in the negative electrode composition ranges from 90% to 97%. Specifically, the mass fraction of the negative electrode active material in the negative electrode composition can be, but is not limited to, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc. If the mass fraction of the negative electrode active material in the negative electrode composition is too low, the energy density of the negative electrode sheet will be reduced; if the mass fraction of the negative electrode active material in the negative electrode composition is too high, the content of binders and other materials in the negative electrode composition will be reduced, which is not conducive to the adhesion between the negative electrode active materials, making the negative electrode sheet prone to cracking and powdering.

[0065] In some embodiments, the mass ratio of the binder to the first carbon nanotube in the negative electrode composition ranges from 15 to 170.

[0066] Specifically, the mass ratio of the binder to the first carbon nanotube in the negative electrode composition can be, but is not limited to, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, etc.

[0067] In this embodiment, if the mass ratio of the binder to the first carbon nanotube in the negative electrode composition is too low, the content of the binder in the negative electrode composition will be too low or the content of the first carbon nanotube will be too high. If the content of the binder is too low, the bonding between the negative electrode active materials in the negative electrode composition will be reduced, making the negative electrode sheet made from the negative electrode composition prone to powder shedding and reducing the cycle performance of the battery. If the content of the first carbon nanotube is too high, the thickness of the negative electrode active layer after the negative electrode composition is made into the negative electrode sheet will easily rebound, increasing the side reactions during battery cycling and reducing the cycle performance of the battery. In addition, when the first carbon nanotube is mixed with the binder, the viscosity of the slurry increases, making stirring and processing difficult and reducing the dispersibility of the first carbon nanotube. If the mass ratio of the binder to the first carbon nanotube in the negative electrode composition is too high, the content of the binder in the negative electrode composition will be too high or the content of the first carbon nanotube will be too low. If the content of the binder is too high, the proportion of the negative electrode active material in the negative electrode composition will be reduced, thus reducing the energy density of the negative electrode composition. If the content of the first carbon nanotube is too low, the network support effect of the first carbon nanotube in the negative electrode composition will be poor, and the effect on improving the peeling force of the negative electrode sheet will not be obvious. In addition, the effect on reducing the thickness of the negative electrode sheet using the negative electrode composition will not be obvious, thus reducing the conductivity of the negative electrode sheet and reducing the cycle performance of the negative electrode sheet.

[0068] In some embodiments, the adhesive has a mass fraction ranging from 1% to 3%.

[0069] Specifically, the mass fraction of the binder in the negative electrode composition can be, but is not limited to, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, etc.

[0070] In this embodiment, if the binder content is too low, the bonding between the negative electrode active materials in the negative electrode composition is reduced, making the negative electrode sheet made from the negative electrode composition prone to powder shedding and reducing the cycle performance of the battery. If the binder content is too high, the proportion of negative electrode active materials in the negative electrode composition is reduced, thus reducing the energy density of the negative electrode composition.

[0071] In some embodiments, the mass fraction of the second carbon nanotubes in the negative electrode composition ranges from 0.01% to 0.2%.

[0072] Specifically, the mass fraction of the second carbon nanotube in the negative electrode composition can be, but is not limited to, 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, etc.

[0073] In this embodiment, the second carbon nanotube has a smaller diameter. Smaller diameter second carbon nanotubes have higher electronic conductivity and a larger effective contact area, which can improve the electronic conductivity of the negative electrode sheet using this negative electrode composition and promote electron transport. If the content of the second carbon nanotube is too low, the electronic conductivity of the negative electrode sheet using this negative electrode composition is reduced, thus lowering the rate performance of the battery. The smaller diameter second carbon nanotube has higher rigidity and stronger carbon-carbon bonds, resulting in a higher elastic modulus and stronger compression resistance. Under the same rolling conditions, it has a larger thickness after rolling, affecting the ion transport of the negative electrode sheet and thus impacting the energy density of the battery. If the content of the second carbon nanotube is too high, the negative electrode sheet using this negative electrode composition will have a larger thickness after rolling, affecting the ion transport of the negative electrode sheet and thus impacting the energy density of the battery.

[0074] In some embodiments, the ratio of the diameter of the first carbon nanotube to the diameter of the second carbon nanotube ranges from 2 to 25.

[0075] Specifically, the ratio of the diameter of the first carbon nanotube to the diameter of the second carbon nanotube can be, but is not limited to, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 25, etc.

[0076] In this embodiment, if the ratio of the diameter of the first carbon nanotube to the diameter of the second carbon nanotube is too small, the difference between their diameters will be too small. This makes it difficult for the negative electrode to achieve a small thickness, high ionic conductivity, and high electronic conductivity simultaneously after the negative electrode composition is formed. This is detrimental to achieving both high kinetic performance and high cycle capacity retention in the battery. If the ratio of the diameter of the first carbon nanotube to the diameter of the second carbon nanotube is too large, the diameter of the first carbon nanotube will be too large, and the diameter of the second carbon nanotube will be too small. If the diameter of the first carbon nanotube is too large, the total contact area between the first carbon nanotube and the negative electrode active material will decrease, increasing the resistance of the negative electrode and reducing its kinetic performance. Furthermore, the larger contact angle of the first carbon nanotube network (enhanced hydrophobicity) reduces the wettability of the electrolyte, lowers the ionic conductivity of the negative electrode composition, and also reduces the kinetic performance of the negative electrode. If the diameter of the second carbon nanotube is too small, it will have higher rigidity and stronger carbon-carbon bonds, resulting in a higher radial elastic modulus and stronger radial compression resistance. Under the same rolling conditions, the thickness after rolling will be greater, increasing the ion transport path of the negative electrode sheet and thus affecting the energy density of the battery. In addition, if the diameter of the second carbon nanotube is too small, it will also increase the side reactions between the second carbon nanotube and the electrolyte, thereby reducing the electrical performance of the second carbon nanotube.

[0077] In some embodiments, the diameter of the first carbon nanotube ranges from 10 nm to 50 nm.

[0078] Specifically, the diameter of the first carbon nanotube can be, but is not limited to, 10nm, 12nm, 14nm, 16nm, 18nm, 10nm, 22nm, 24nm, 26nm, 28nm, 30nm, 32nm, 34nm, 36nm, 38nm, 40nm, 42nm, 44nm, 46nm, 48nm, 50nm, etc.

[0079] It should be noted that when the diameters of the first carbon nanotube and the second carbon nanotube are not equal at various positions, the diameter of the first carbon nanotube refers to the average diameter at various positions of the first carbon nanotube; the diameter of the second carbon nanotube refers to the average diameter at various positions of the second carbon nanotube.

[0080] In this embodiment, if the diameter of the first carbon nanotube is too small, it will have higher rigidity and stronger carbon-carbon bonds, resulting in a higher radial elastic modulus and stronger radial compression resistance. Under the same rolling conditions, it will have a larger thickness after rolling, increasing the ion transport path of the negative electrode sheet and thus affecting the energy density of the battery. In addition, a small diameter of the first carbon nanotube will also increase the side reactions between the first carbon nanotube and the electrolyte, thereby reducing the electrical performance of the first carbon nanotube. If the diameter of the first carbon nanotube is too large, the total contact area between the first carbon nanotube and the negative electrode active material will decrease, increasing the resistance of the negative electrode sheet and reducing its kinetic performance. Furthermore, a larger diameter first carbon nanotube network has a larger contact angle (enhanced hydrophobicity), reducing the wettability of the electrolyte and decreasing the ionic conductivity of the negative electrode sheet, which will also reduce its kinetic performance.

[0081] Furthermore, the diameter of the first carbon nanotube ranges from 14 nm to 30 nm. This allows the negative electrode to have better electrolyte wettability, a lower elastic modulus, and is easier to radially compress, resulting in a smaller thickness and a better shortening of the ion transport path.

[0082] In some embodiments, the diameter of the second carbon nanotube ranges from 2 nm to 10 nm.

[0083] Specifically, the diameter of the second carbon nanotube can be, but is not limited to, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, etc.

[0084] In this embodiment, if the diameter of the second carbon nanotube is too small, it will have higher rigidity and stronger carbon-carbon bonds, resulting in a higher radial elastic modulus and stronger radial compression resistance. Under the same rolling conditions, it will have a larger thickness after rolling, increasing the ion transport path of the negative electrode sheet and thus affecting the energy density of the battery. In addition, a small diameter of the second carbon nanotube will also increase the side reactions between the second carbon nanotube and the electrolyte, thereby reducing the electrical performance of the second carbon nanotube. If the diameter of the second carbon nanotube is too large, the total contact area between the second carbon nanotube and the negative electrode active material will decrease, increasing the resistance of the negative electrode sheet and reducing its kinetic performance. Furthermore, a larger diameter second carbon nanotube network has a larger contact angle (enhanced hydrophobicity), reducing the wettability of the electrolyte and decreasing the ionic conductivity of the negative electrode sheet, which will also reduce its kinetic performance.

[0085] In some embodiments, the average length of the first carbon nanotube ranges from 8 μm to 20 μm.

[0086] Specifically, the average length of the first carbon nanotube can be, but is not limited to, 8μm, 9μm, 10μm, 12μm, 16μm, 18μm, 20μm, etc.

[0087] In this embodiment, if the average length of the first carbon nanotube is too short, it will be detrimental to the formation of the conductive network in the negative electrode composition, reduce the electronic conductivity of the negative electrode composition, and reduce the dynamic performance of the battery; if the average length of the first carbon nanotube is too long, it will increase the preparation cost of the first carbon nanotube and increase the side reaction between the first carbon nanotube and the electrolyte, thus reducing the cycle performance of the battery.

[0088] In some embodiments, the average length of the second carbon nanotube ranges from 8 μm to 20 μm.

[0089] Specifically, the average length of the second carbon nanotube can be, but is not limited to, 8μm, 9μm, 10μm, 12μm, 16μm, 18μm, 20μm, etc.

[0090] In this embodiment, if the average length of the second carbon nanotube is too short, it will be detrimental to the formation of the conductive network in the negative electrode composition, reduce the electronic conductivity of the negative electrode composition, and reduce the dynamic performance of the battery; if the average length of the second carbon nanotube is too long, it will increase the preparation cost of the second carbon nanotube and increase the side reaction between the second carbon nanotube and the electrolyte, thus reducing the cycle performance of the battery.

[0091] Optionally, the average length of the first carbon nanotube is greater than the D50 particle size (i.e., median particle size) of the negative electrode active material. The average length of the second carbon nanotube is greater than the D50 particle size (i.e., median particle size) of the negative electrode active material.

[0092] In some embodiments, the negative electrode composition further includes a negative electrode conductive agent, a first dispersant, and a second dispersant; the negative electrode conductive agent includes at least one of conductive carbon black (SP), superconducting carbon black, Ketjen black, graphite, and graphene; the first dispersant includes at least one of sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide; the second dispersant includes at least one of polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC).

[0093] It should be noted that the first dispersant is used to be added to the binder slurry when the first carbon nanotubes are mixed with the binder to form a binder slurry (first slurry), in order to improve the dispersibility of the first carbon nanotubes in the first slurry.

[0094] In this embodiment, adding a negative electrode conductive agent to the negative electrode composition can improve the electronic conductivity of the negative electrode composition, thereby improving the kinetic performance of the negative electrode sheet; adding a first dispersant to the negative electrode composition can improve the stability and dispersibility of the first carbon nanotubes in the binder slurry. The first dispersant can reduce the surface energy of the binder slurry, and the steric hindrance effect and electrostatic repulsion of the first dispersant can promote the uniform dispersion of the first carbon nanotubes in the binder slurry; adding a second dispersant to the negative electrode composition can improve the dispersibility of the first carbon nanotube-binder (CNT-SBR) in the negative electrode composition, and improve the dispersibility of the negative electrode active material and the second carbon nanotube in the whole system.

[0095] Optionally, the mass fraction of the negative electrode conductive agent in the negative electrode composition ranges from 0.1% to 1.5%. Specifically, the mass fraction of the negative electrode conductive agent in the negative electrode composition can be, but is not limited to, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, etc. In this embodiment, if the mass fraction of the negative electrode conductive agent in the negative electrode composition is too low, the electronic conductivity of the negative electrode composition will be low, which is not conducive to improving the kinetic performance of the battery; if the mass fraction of the negative electrode conductive agent in the negative electrode composition is too high, the proportion of the negative electrode active material in the negative electrode composition will be reduced, the specific capacity of the negative electrode composition will be reduced, which is not conducive to improving the energy density of the battery.

[0096] Optionally, the mass of the first dispersant is 0.5% to 2.0% of the mass of the binder.

[0097] Understandably, in the negative electrode composition, the ratio of the mass of the first dispersant to the mass of the binder ranges from 0.5% (i.e., 0.5:100) to 2.0% (i.e., 2:100).

[0098] Specifically, the mass of the first dispersant can be, but is not limited to, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0% of the mass of the binder.

[0099] If the amount of the first dispersant added in the negative electrode composition is too low, it will not be conducive to the dispersion of the first carbon nanotubes in the binder slurry; if the amount of the first dispersant added is too high, it will reduce the proportion of binder in the first slurry, which will not be conducive to the adhesion between the negative electrode active materials in the negative electrode composition.

[0100] Optionally, the mass fraction of the second dispersant in the negative electrode composition ranges from 0.2% to 4%. Specifically, the mass fraction of the second dispersant in the negative electrode composition can be, but is not limited to, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, 2.3%, 2.5%, 2.8%, 3.3%, 3.5%, 3.8%, and 4%. If the mass fraction of the second dispersant in the negative electrode composition is too low, it will be detrimental to the dispersion of the negative electrode active material, the second carbon nanotube, and the first carbon nanotube-binder; if the mass fraction of the second dispersant in the negative electrode composition is too high, it will reduce the proportion of the negative electrode active material in the negative electrode composition, reduce the specific capacity of the negative electrode composition, and be detrimental to improving the energy density of the battery.

[0101] Optionally, the mass fraction of polyacrylic acid (second dispersant) in the negative electrode composition ranges from 0.2% to 2%. Specifically, the mass fraction of polyacrylic acid in the negative electrode composition can be, but is not limited to, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8%, etc. If the mass fraction of polyacrylic acid in the negative electrode composition is too low, it will be detrimental to the dispersion between the negative electrode active material, the second carbon nanotube, and the first carbon nanotube-binder; if the mass fraction of polyacrylic acid in the negative electrode composition is too high, it will reduce the proportion of the negative electrode active material in the negative electrode composition, reduce the specific capacity of the negative electrode composition, and be detrimental to improving the energy density of the battery.

[0102] Optionally, the mass fraction of sodium carboxymethyl cellulose (second dispersant) in the negative electrode composition ranges from 0.2% to 2%. Specifically, the mass fraction of sodium carboxymethyl cellulose in the negative electrode composition can be, but is not limited to, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, etc. If the mass fraction of sodium carboxymethyl cellulose in the negative electrode composition is too low, it is not conducive to the dispersion between the negative electrode active material, the second carbon nanotube, and the first carbon nanotube; if the mass fraction of sodium carboxymethyl cellulose in the negative electrode composition is too high, it reduces the proportion of the negative electrode active material in the negative electrode composition, reduces the specific capacity of the negative electrode composition, and is not conducive to improving the energy density of the battery.

[0103] Please see Figure 2 This application also provides a negative electrode sheet 100, which includes a negative electrode current collector 110 and a negative electrode active layer 120. The negative electrode active layer 120 is disposed on the surface of the negative electrode current collector 110 and is formed by the negative electrode composition described in this application embodiment.

[0104] It should be noted that the negative electrode active layer 120 can be disposed on at least one surface of the negative electrode current collector 110, such as one surface, two surfaces, three surfaces, etc. In the schematic diagram of the accompanying drawings of this application, the negative electrode active layer 120 is disposed on two opposite surfaces of the negative electrode current collector 110 as an example, and should not be construed as a limitation on the negative electrode sheet 100 and the negative electrode active layer 120 of the embodiments of this application.

[0105] Optionally, the negative electrode 100 includes a negative electrode current collector 110 and a negative electrode active layer 120.

[0106] Optionally, the negative current collector 110 can be, but is not limited to, at least one of copper foil, copper sheet, aluminum foil, and aluminum sheet.

[0107] Optionally, the negative electrode active material can be, but is not limited to, hard carbon or graphite.

[0108] The negative electrode 100 of this application embodiment can be prepared by the method described in the following embodiments of this application. In addition, it can also be prepared by other methods. The preparation method of this application embodiment is only one or more preparation methods of the negative electrode 100 of this application and should not be construed as a limitation on the negative electrode 100 provided in the embodiments of this application.

[0109] Please see Figure 3 This application provides a method for preparing a negative electrode sheet 100, the method comprising:

[0110] S201, the first carbon nanotube is mixed with a binder to obtain the first slurry;

[0111] S202, the first slurry is mixed with the negative electrode active material and the second carbon nanotube to obtain the second slurry; and

[0112] S203, a negative electrode current collector 110 is provided, the second slurry is coated on the negative electrode current collector 110, and after drying and rolling, the negative electrode sheet 100 is obtained. The negative electrode sheet 100 includes the negative electrode current collector 110 and the negative electrode active layer 120. The negative electrode active layer 120 includes a negative electrode active material, a first carbon nanotube, a second carbon nanotube, and a binder. The diameter of the first carbon nanotube is larger than the diameter of the second carbon nanotube, and the ratio of the number of the first carbon nanotube to the number of the second carbon nanotube is in the range of 0.01 to 0.67.

[0113] Understandably, the negative electrode active layer 120 is made of a negative electrode composition, which includes a negative electrode active material, a first carbon nanotube, a second carbon nanotube, and a binder. The diameter of the first carbon nanotube is larger than the diameter of the second carbon nanotube, and the ratio of the number of the first carbon nanotube to the number of the second carbon nanotube is in the range of 0.01 to 0.67.

[0114] For detailed descriptions of the first carbon nanotube, the second carbon nanotube, the negative electrode current collector 110, the negative electrode composition, and other aspects, please refer to the descriptions in the corresponding sections of the above embodiments, which will not be repeated here.

[0115] The method for preparing the negative electrode 100 of this application involves first mixing a first carbon nanotube with a binder to obtain a first slurry, and then mixing the first slurry with a negative electrode active material and a second carbon nanotube to obtain a second slurry. This allows the first carbon nanotube and the binder to be connected by intermolecular forces or chemical bonds, enabling the first carbon nanotube to be better encapsulated or adsorbed by the binder to form a "CNT-SBR" composite unit. This effectively prevents the aggregation of the first carbon nanotubes and increases their dispersibility in the negative electrode composition. Furthermore, after the binder encapsulates the first carbon nanotubes, it also better prevents the first carbon nanotubes from being directly exposed, reducing side reactions of the first carbon nanotubes during battery cycling and storage, and improving the cycle performance of the battery. Moreover, it makes the current density distribution of the negative electrode 100 more uniform, and the density distribution of metal ions (such as sodium ions) more uniform, reducing the polarization phenomenon of the battery. Furthermore, it can improve the dispersibility of the binder in the second slurry, allowing the binder to better bond the negative electrode active material and better prevent cracking and powdering of the negative electrode active layer 120 during use. Additionally, the diameter of the first carbon nanotube is larger than that of the second carbon nanotube, and the ratio of the number of the first carbon nanotube to the second carbon nanotube ranges from 0.01 to 0.67. The second carbon nanotube has a smaller diameter; a smaller diameter (larger aspect ratio) second carbon nanotube has higher electronic conductivity and a larger effective contact area, which can improve the electronic conductivity of the negative electrode sheet 100 using this negative electrode composition and promote electron transport. However, the smaller diameter second carbon nanotube has higher rigidity and stronger carbon-carbon bonds, resulting in a higher elastic modulus and stronger compression resistance. This leads to a lower packing density after battery coating, and under the same rolling conditions, a greater thickness after rolling. The actual compacted density of the negative electrode sheet 100 before the electrode assembly is installed in the casing is reduced, which not only limits the electron transport of the negative electrode sheet 100... This also reduces the actual energy density of the battery. The larger diameter of the first carbon nanotube (smaller aspect ratio) results in a lower elastic modulus, making it easier to compress radially. This can alleviate the rebound of the negative electrode 100, resulting in a smaller thickness of the negative electrode 100 after rolling. This not only improves the peeling force of the negative electrode 100 and better prevents cracking and powder shedding, but also, compared to the smaller diameter of the second carbon nanotube, the larger diameter of the first carbon nanotube has a higher ionic conductivity, which can promote ion transport in the negative electrode 100, further reducing battery polarization and thus improving the battery's cycle and storage performance.This application utilizes first and second carbon nanotubes of different diameters in combination to enable the negative electrode composition to achieve both good radial compressibility and high elastic modulus. As a result, the negative electrode sheet 100 using this negative electrode composition has higher electronic conductivity and ionic conductivity, while also reducing the risk of energy density reduction caused by high thickness rebound. This allows the battery to have both high energy density and high cycle capacity retention.

[0116] Please see Figure 4 Optionally, in S201, the first carbon nanotubes are mixed with a binder to obtain a first slurry; comprising:

[0117] S2011, the first carbon nanotubes are dispersed in water to obtain a suspension of the first carbon nanotubes; and

[0118] Optionally, carbon nanotubes with a diameter of 10 nm to 50 nm are modified with at least one of concentrated nitric acid (acidification treatment), concentrated sulfuric acid (acidification treatment), diethyl adipate, diethyl dimethylmalonate, diethyl octanoate, dimethyl malonate, dimethyl octanoate, methyl valerate, propyl butyrate, n-dodecyltrimethoxysilane, silane coupling agent, trimethylsilane, hexadecyltrimethyltetrafluoroborate ammonium, N-(cocoyl)-N,N,N-trimethylammonium sulfate, cocamidopropyl betaine, hexadecyltrimethylammonium acetate and hexadecyltrimethylammonium nitrate, methacrylic acid, and maleic acid, thereby giving the carbon nanotubes polar groups to obtain the first carbon nanotube; the first carbon nanotube is placed in water and ultrasonically dispersed using ultrasound to obtain a first carbon nanotube suspension.

[0119] Optionally, the power of the ultrasonic dispersion ranges from 200W to 500W; specifically, it can be, but is not limited to, 200W, 300W, 400W, 500W, etc.

[0120] Optionally, the ultrasonic dispersion time ranges from 0.5h to 2h; specifically, it can be, but is not limited to, 0.5h, 1h, 1.5h, 2h, etc.

[0121] Optionally, the mass fraction of the first carbon nanotubes in the first carbon nanotube suspension ranges from 8% to 13%; specifically, it can be, but is not limited to, 8%, 9%, 10%, 11%, 12%, 13%, etc.

[0122] For a detailed description of other aspects of the first carbon nanotube, please refer to the description of the corresponding section of the above embodiments, which will not be repeated here.

[0123] S2012, the first carbon nanotube suspension is mixed with a binder to obtain a first slurry.

[0124] Optionally, the first carbon nanotube suspension, the first dispersant, and the binder emulsion are stirred and mixed for a stirring time of 30 min to 240 min (e.g., but not limited to 30 min, 60 min, 90 min, 120 min, 150 min, 180 min, 210 min, 240 min, etc.) and a stirring rate of 500 rpm / min to 3000 rpm / min (e.g., but not limited to 500 rpm / min, 1000 rpm / min, 1500 rpm / min, 2000 rpm / min, 2500 rpm / min, 3000 rpm / min, etc.) to obtain the first slurry.

[0125] For a detailed description of other aspects of the first dispersant and binder, please refer to the description in the corresponding section of the above embodiments, which will not be repeated here.

[0126] In some embodiments, the first carbon nanotube suspension is directly mixed with a binder emulsion (such as an SBR emulsion). Furthermore, the first carbon nanotubes and the binder are bonded or connected through intermolecular forces. In other embodiments, the first carbon nanotube suspension is added during the synthesis of the binder, allowing the polar groups (e.g., -COOH) on the first carbon nanotubes to react during the binder synthesis process. This results in chemical bonds between the first carbon nanotubes and the binder, leading to a higher bonding strength and better dispersion of the first carbon nanotubes in the binder.

[0127] Optionally, the mass fraction of the binder in the first slurry ranges from 35% to 45%; further, the mass fraction of the binder in the first slurry ranges from 38% to 42%. Specifically, the mass fraction of the binder in the first slurry can be, but is not limited to, 35%, 36.5%, 38%, 40%, 42%, 45%, etc.

[0128] Optionally, the mass fraction of the first carbon nanotubes in the first slurry ranges from 0.4% to 3.0%; further, the mass fraction of the first carbon nanotubes in the first slurry ranges from 0.5% to 2.8%. Specifically, the mass fraction of the first carbon nanotubes in the first slurry can be, but is not limited to, 0.4%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, 2.3%, 2.5%, 2.8%, 3.0%, etc. In this embodiment, if the mass fraction of the first carbon nanotubes in the first slurry is too low, the network support effect of the first carbon nanotubes will be poor, the effect on improving the peeling force of the negative electrode 100 will not be significant, and the effect on reducing the thickness of the negative electrode 100 will not be significant, thus reducing the conductivity of the negative electrode 100 and the cycle performance of the negative electrode 100. If the mass fraction of the first carbon nanotube in the first slurry is too high, the thickness of the negative electrode active layer 120 after the negative electrode composition is made into the negative electrode active layer 120 of the negative electrode sheet 100 will easily rebound, the side reactions during the battery cycle will increase, and the battery cycle performance will be reduced. In addition, when the first carbon nanotube is mixed with the binder, the viscosity of the slurry will increase, making stirring and processing difficult and reducing the dispersibility of the first carbon nanotube.

[0129] In some embodiments, in S202, the first slurry is mixed with the negative electrode active material and the second carbon nanotube to obtain the second slurry;

[0130] Specifically, the first slurry, the negative electrode active material, the second carbon nanotube, the second dispersant, and the negative electrode conductive agent are placed in deionized water and mixed evenly to obtain the second slurry.

[0131] Optionally, the solid content of the second slurry is 40% to 70%. Specifically, the solid content of the second slurry can be, but is not limited to, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0132] Optionally, the mass fraction of the negative electrode active material in the solids content of the second slurry ranges from 90% to 97%. Specifically, the mass fraction of the negative electrode active material in the solids content of the second slurry can be, but is not limited to, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc.

[0133] Optionally, the mass fraction of the binder in the solids content of the second slurry ranges from 1% to 3%. Specifically, the mass fraction of the binder in the solids content of the second slurry can be, but is not limited to, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, etc.

[0134] Optionally, the mass fraction of polyacrylic acid (second dispersant) in the solids content of the second slurry ranges from 1% to 2%. Specifically, the mass fraction of the solids content in the second slurry can be, but is not limited to, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, etc.

[0135] Optionally, the mass fraction of sodium carboxymethyl cellulose (second dispersant) in the solids content of the second slurry ranges from 0.4% to 1%. Specifically, the mass fraction of sodium carboxymethyl cellulose in the solids content of the second slurry can be, but is not limited to, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0136] For detailed descriptions of other aspects of the negative electrode active material, the second carbon nanotube, the second dispersant, and the negative electrode conductive agent, please refer to the descriptions in the corresponding sections of the above embodiments, which will not be repeated here.

[0137] Please see Figure 5 and Figure 6 This application also provides a battery 300, which includes: an electrolyte, a positive electrode 310, a separator 320, and a negative electrode 100 as described in this application embodiment.

[0138] Optionally, the battery 300 can be, but is not limited to, a lithium battery or a sodium battery. Optionally, the sodium battery can be at least one of a sodium-ion battery, a sodium metal battery, or a lithium-sodium hybrid battery. Optionally, the lithium battery can be at least one of a lithium-ion battery, a lithium metal battery, or a lithium-sodium hybrid battery.

[0139] Optionally, the battery 300 may be, but is not limited to, at least one of cylindrical batteries, prismatic batteries, blade batteries, etc. The accompanying drawings of this application merely illustrate one or more possible configurations of the battery 300 and should not be construed as limiting the battery 300 of the embodiments of this application.

[0140] Understandably, the positive electrode 310 and the negative electrode 100 are located on opposite sides of the separator 320, that is, the separator 320 is located between the positive electrode 310 and the negative electrode 100, separating the positive electrode 310 and the negative electrode 100.

[0141] It should be noted that the positive electrode 310, the separator 320, and the negative electrode 100 are all at least partially immersed in the electrolyte.

[0142] Optionally, the electrolyte includes an electrolyte salt, an organic solvent, and a film-forming additive.

[0143] Optionally, the electrolyte salt may include, but is not limited to, sodium salts. Optionally, the sodium salt may be, but is not limited to, at least one of sodium hexafluorophosphate (NaPF6), NaClO4, sodium tetrafluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalatoborate), sodium difluorodioxalatophosphate, sodium difluorooxalatoborate, sodium difluorophosphate (NaPO2F2), and sodium trifluoromethanesulfonate (CF3SO3Na).

[0144] Optionally, the organic solvent may include at least one of cyclic carbonates and chain carbonates. Optionally, the cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (EC) and propylene carbonate (PC). Ethylene carbonate has a much higher dielectric constant than propylene carbonate, and can better promote the formation of a solid electrolyte interface membrane (SEI). Optionally, the chain carbonate may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Optionally, the organic solvent may also include at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, γ-butyrolactone, and 2,2-difluoroethyl acetate.

[0145] Optionally, the film-forming additive may include, but is not limited to, at least one of the following: propargylbenzenesulfonic acid, vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), methanedisulfonate (MMDS), butyl sulfonate lactone (BS), and 1,3-propenyl sulfonate lactone (PST).

[0146] Please see Figure 7 Optionally, the positive electrode 310 includes a positive current collector 311 and a positive active layer 312. The positive active layer 312 is disposed on the surface of the positive current collector 311.

[0147] It should be noted that the positive electrode active layer 312 can be disposed on at least one surface of the positive electrode current collector 311, such as one, two, or three surfaces. In the following embodiments and accompanying drawings of this application, the positive electrode sheet 310 is illustrated by way of having two positive electrode active layers 312 (i.e., the positive electrode current collector 311 has positive electrode active layers 312 on both opposite surfaces), and should not be construed as limiting the positive electrode sheet 310 of the embodiments of this application.

[0148] Optionally, the positive current collector 311 can be, but is not limited to, aluminum foil or aluminum sheet.

[0149] Optionally, the positive electrode active layer 312 includes a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, etc.

[0150] Optionally, the positive electrode active material can be, but is not limited to, sodium iron pyrophosphate, lithium iron phosphate, etc.

[0151] Optionally, the positive electrode conductive agent can be, but is not limited to, at least one of carbon nanotubes, conductive carbon black, superconducting carbon black, Ketjen black, acetylene black, carbon fiber, graphene, etc.

[0152] Optionally, the positive electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), and polyhexafluoropropylene.

[0153] Optionally, the diaphragm 320 may be, but is not limited to, at least one of polypropylene membrane (PP membrane), polyethylene membrane (PE membrane), ceramic diaphragm 320, and glass fiber diaphragm 320.

[0154] Please see again Figure 5 and Figure 6 Optionally, the battery 300 further includes a housing 340 and an end cap assembly 350, the housing 340 and the end cap assembly 350 forming a closed receiving cavity (not shown) for housing the electrolyte, the positive electrode 310, the separator 320, and the negative electrode 100. Understandably, the end cap assembly 350 electrically connects the positive electrode 310 and the negative electrode 100, respectively, leading out the positive electrode 310 and the negative electrode 100 for electrical connection to external devices or other batteries 300.

[0155] The negative electrode composition, negative electrode 100, and battery 300 of this application are further described below through specific embodiments.

[0156] Examples 1 to 14, Comparative Examples 1, 2, 4 to 5

[0157] (1) Preparation of negative electrode 100: I) Mix the first carbon nanotubes and water, and disperse them by ultrasonication to form a first carbon nanotube suspension emulsion; II) Mix the first carbon nanotube suspension emulsion, styrene-butadiene rubber (SBR, binder) and sodium dodecyl sulfonate (first dispersant), and stir to obtain a first slurry; III) Mix the first slurry, hard carbon (negative electrode active material), second carbon nanotubes, polyacrylic acid (second dispersant), sodium carboxymethyl cellulose (second dispersant), and conductive carbon black (negative electrode conductive agent) in water, and stir evenly to obtain a second slurry; IV) Coat the second slurry onto the copper foil of the negative electrode current collector 110, and after drying, cold pressing, slitting and cutting, obtain the negative electrode 100. In the negative electrode active layer 120, the mass fraction of conductive carbon black is 0.5%, the mass fraction of polyacrylic acid is 1%, the mass fraction of sodium carboxymethyl cellulose is 1%, the mass fraction of binder is 1.5%, the average length of the first carbon nanotube and the second carbon nanotube is 10 μm, and the mass fraction and related parameters of the first carbon nanotube and the second carbon nanotube are shown in Table 1 below, with the balance being hard carbon; the carbon nanotubes in each embodiment and comparative example are all single-walled carbon nanotubes.

[0158] (2) Preparation of positive electrode 310: The positive active material sodium iron pyrophosphate, conductive carbon black SP (positive conductive agent), and binder PVDF (positive binder) are dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:0.7:2.3 and mixed evenly to obtain positive electrode slurry; the positive electrode slurry is coated on the positive current collector 311 aluminum foil, and after drying, cold pressing, slitting and cutting, positive electrode 310 is obtained.

[0159] (3) Electrolyte preparation process: In an argon atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 1:1 to obtain a mixed solvent. Then, dried electrolyte salt NaClO4 is dissolved in the mixed solvent and stirred until completely dissolved and homogeneous. Fluoroethylene carbonate (FEC) and ethylene sulfate (PST) are added and mixed thoroughly to obtain the electrolyte. The molar concentration of NaClO4 in the electrolyte is 1 mol / L, which is 13 wt%.

[0160] (4) Preparation of diaphragm 320: Glass fiber diaphragm 320 is used as diaphragm 320.

[0161] (5) Assembly of battery 300: The positive electrode 310, separator 320 and negative electrode 100 are stacked in sequence to form an electrode assembly. After the electrode assembly is wound, a bare cell is obtained. After welding the tabs, the cell is assembled into the outer packaging. After injecting the prepared electrolyte, the cell is packaged, left to stand, formed, shaped and capacity tested, etc., and finally battery 300 is prepared.

[0162] Example 15

[0163] The difference between this embodiment and Embodiment 10 is that both the first carbon nanotube and the second carbon nanotube are multi-walled carbon nanotubes.

[0164] Comparative Example 3

[0165] The difference between Comparative Example 3 and Example 5 is that the first carbon nanotube, the second carbon nanotube, SBR, PAA, CMC, and hard carbon are added to water and mixed together in the same step to prepare the negative electrode slurry.

[0166] The following performance tests were performed on the negative electrode 100 and battery 300 of each embodiment and comparative example.

[0167] (1) Thickness of the negative electrode active layer 120: measured using a micrometer.

[0168] (2) Peel strength of negative electrode 100: One side of negative electrode 100 is attached to a steel plate with double-sided tape. The steel plate is installed on the fixed fixture at the bottom of the high-speed rail tensile testing machine. Confirm that the negative electrode 100 on the steel plate is firmly bonded to the steel plate. Tear about 1 cm along the interface between the negative electrode 100 and the double-sided tape at one end of the negative electrode 100 in the length direction. Clamp one corner of the torn negative electrode 100 on the movable fixture at the top of the high-speed rail tensile testing machine. The sample is ready. During the test: the tensile angle is 90° and the tensile speed is 20 mm / min until the interface between the negative electrode 100 and the double-sided tape is completely pulled apart. After pulling apart, the negative electrode active layer 120 is bonded to the surface of the double-sided tape. The other side of the pulled-out interface is the negative electrode 100 with at least partial exposure of the negative electrode current collector 110. Record the average load force (N) during the tensile process, divide it by the width of the negative electrode sheet 100 sample to obtain the peel strength between the negative electrode active layer 120 and the negative electrode current collector 110. Measure 5 parallel samples and then take the average value.

[0169] (3) First-cycle charge specific capacity, first-cycle discharge specific capacity, and 100-cycle capacity retention rate of the button cell: The battery 300 was placed in the Blue Electric test system for charge-discharge cycle testing at a test temperature of 25℃ and a rate of 0.1C (i.e., both the charge and discharge rates are 0.1C). The charge-discharge voltage range was 1.5V to 3.5V, yielding the first-cycle charge specific capacity and the first-cycle discharge specific capacity. The charge-discharge voltage range for the 2nd to 100th cycles was 1.5V to 3.5V, and the charge-discharge current was 1C. 100-cycle capacity retention rate = (100th-cycle discharge specific capacity - 2nd-cycle discharge specific capacity) / 2nd-cycle discharge specific capacity × 100%.

[0170] (4) The ratio of the number of first carbon nanotubes to second carbon nanotubes, A / a, was measured using SEM.

[0171] The performance parameters of the negative electrode 100 and battery 300 of each embodiment and comparative example are shown in Table 1 and Table 2 below.

[0172] Table 1 Performance parameters of negative electrode 100 and battery 300 in the embodiments and comparative examples.

[0173]

[0174]

[0175] Table 2 Performance parameters of negative electrode 100 and battery 300 in the embodiments and comparative examples

[0176]

[0177]

[0178] The test results from Examples 1 to 7, Comparative Examples 1 and 2 show that the negative electrode active layer 120 of Comparative Example 1 only includes the first carbon nanotube, resulting in a lower thickness of the negative electrode active layer 120 after rolling, lower peel strength of the negative electrode sheet 100, and lower first-cycle discharge specific capacity and 500-cycle capacity retention rate of the battery 300. The negative electrode active layer 120 of Comparative Example 2 only includes the second carbon nanotube, resulting in a larger thickness of the negative electrode active layer 120 after rolling. Although the peel strength of the negative electrode sheet 100 has increased, it is still low, and the first-cycle discharge specific capacity and 500-cycle capacity retention rate of the battery 300 are also low. The negative electrode active layer 120 of Examples 1 to 7 includes both the first and second carbon nanotubes, resulting in a negative electrode sheet 100 with greater peel strength, and the battery 300 with higher first-cycle discharge specific capacity and cycle capacity retention rate. Furthermore, the test results from Examples 1 to 7 show that when the lengths of the first carbon nanotube and the second carbon nanotube are equal, as the ratio of the number of the first carbon nanotube to the number of the second carbon nanotube increases, the thickness of the negative electrode active layer 120 gradually decreases, and the thickness rebound after two days of rolling gradually decreases; the peel strength of the negative electrode sheet 100 gradually decreases; and the first-cycle discharge specific capacity of the battery 300 gradually decreases, but the 500-cycle capacity retention rate of the battery 300 gradually increases.

[0179] As can be seen from the test results of Example 5 and Comparative Example 3, compared with Comparative Example 3, which directly mixes the first carbon nanotube and the second carbon nanotube to prepare the negative electrode slurry, the present application example first mixes the first carbon nanotube with the binder (SBR), and then mixes it with the second carbon nanotube and the negative electrode active material, etc. The resulting negative electrode active layer 120 has a smaller thickness after being rolled for 2 days, the negative electrode sheet 100 has a greater peel strength, and the battery 300 has a higher first-cycle discharge specific capacity and a higher 500-cycle capacity retention rate.

[0180] The test results from Examples 8 to 10 show that as the diameter of the second carbon nanotube increases, the thickness of the negative electrode active layer 120 after rolling for 2 days gradually decreases, the peel strength of the negative electrode sheet 100 first increases and then decreases, the first discharge specific capacity of the battery 300 gradually decreases, and the 500-cycle capacity retention rate of the battery 300 gradually increases.

[0181] The test results from Examples 11 to 14 show that as the diameter of the first carbon nanotube increases, the thickness of the negative electrode active layer 120 after rolling for 2 days gradually decreases, and the peel strength of the negative electrode sheet 100 is not significantly different; the first discharge specific capacity of the battery 300 gradually decreases, and the 500-cycle capacity retention rate of the battery 300 also gradually decreases.

[0182] The test results from Examples 5, 4, and 5 show that when the diameter of the first carbon nanotube is too large (Comparative Example 5), the peel strength of the negative electrode 100 decreases, and the first-cycle discharge specific capacity and the 500-cycle capacity retention rate of the battery 300 both decrease. When the diameter of the second carbon nanotube is too small (Comparative Example 4), the thickness of the negative electrode active layer 120 increases after rolling for 2 days, the peel strength of the negative electrode 100 decreases, and the first-cycle discharge specific capacity and the 500-cycle capacity retention rate of the battery 300 both decrease.

[0183] The test results of Examples 5 and 15 show that, compared with the scheme in which both the first and second carbon nanotubes are multi-walled carbon nanotubes (Example 15), the scheme in which both the first and second carbon nanotubes are single-walled carbon nanotubes (Example 5) has a lower thickness of the negative electrode active layer 120 after rolling for 2 days, and a higher peel strength of the negative electrode sheet 100; the first discharge specific capacity of the battery 300 and the 500-cycle capacity retention rate of the battery 300 are both higher.

[0184] Please see Figure 8 This application embodiment also provides an energy storage device 400, which includes a housing 410 and a battery 300 as described in this application embodiment, wherein the battery 300 is housed within the housing 410.

[0185] The energy storage device 400 of this application can be applied to, but is not limited to, energy storage on the generation side, energy storage on the grid side, and energy storage on the consumption side.

[0186] Optionally, the energy storage device 400 may include, but is not limited to, battery modules, battery packs, battery systems, energy storage boxes, energy storage cabinets, energy storage containers, etc. The actual application form of the energy storage device 400 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 400. The accompanying drawings of this application embodiment are only illustrative of the energy storage device 400 including multiple batteries 300, and should not be construed as limiting the energy storage device 400 of this application embodiment.

[0187] Optionally, the number of batteries 300 can be, but is not limited to, one or more. When there are multiple batteries 300, the multiple batteries 300 are stacked within the housing 410. It can be understood that the multiple batteries 300 can be arranged sequentially abutting each other, or the multiple batteries 300 can be arranged sequentially with intervals between them. Furthermore, the multiple batteries 300 can be stacked laterally (e.g., horizontally) or longitudinally (e.g., along the direction of gravity). The stacking method and direction of the multiple batteries 300 can be designed according to actual conditions, and this application does not impose specific limitations.

[0188] The term "multiple" refers to two or more.

[0189] Understandably, the multiple batteries 300 of the energy storage device 400 can be connected in parallel, or in series, or partially in parallel and partially in series (in other words, mixed connection). This application does not make specific limitations on the connection method of the multiple batteries 300 of the same energy storage device 400.

[0190] Understandably, the housing 410 has a receiving cavity in which one or more batteries 300 are received. In some embodiments, each receiving cavity receives one battery 300. In other embodiments, each receiving cavity receives multiple batteries 300.

[0191] Please see Figure 9 and Figure 10 This application also provides an energy storage system 500, which includes the energy storage device 400 described in this application embodiment; and an energy conversion device 510, wherein the energy conversion device 510 is electrically connected to the energy storage device 400, the energy conversion device 510 is used to convert other forms of energy into electrical energy, and the energy storage device 400 is used to store the electrical energy.

[0192] It should be noted that energy storage (i.e., energy storage) has a wide range of applications, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The energy storage system 500 in this application embodiment is described in detail using generation-side energy storage as an example. This should not be construed as limiting the energy storage system 500, nor should it be construed as limiting the energy storage device 400, battery 300, etc., in this application embodiment.

[0193] During operation, the power conversion device 510 converts other forms of energy into electrical energy and stores it in the energy storage device 400. The electrical energy stored in the energy storage device 400 can be used to supply electrical loads such as streetlights and household appliances during peak electricity prices, or to supply power when the power grid experiences a power outage. The electrical energy generated by the power conversion device 510 can also be supplied to the power grid through high-voltage cables to alleviate the power supply pressure on the power grid during peak periods.

[0194] Optionally, the power conversion device 510 can convert at least one other form of energy, such as solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy, into electrical energy.

[0195] Optionally, the number of power conversion devices 510 can be one or more. When there are multiple power conversion devices 510, the multiple power conversion devices 510 can be connected in series, in parallel or in a mixed manner. This application does not make specific limitations.

[0196] Optionally, the power conversion device 510 can be, but is not limited to, at least one of photovoltaic panels, wind power generation devices, hydropower generation devices, etc.

[0197] Optionally, the number of energy storage devices 400 can be one or more. When there are multiple energy storage devices 400, the multiple energy storage devices 400 can be connected in series or in parallel. This application does not make specific limitations.

[0198] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various locations throughout the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form yet another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0199] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A negative electrode composition, characterized in that, The negative electrode composition includes a negative electrode active material, a first carbon nanotube, and a second carbon nanotube, wherein the diameter of the first carbon nanotube is larger than the diameter of the second carbon nanotube; the quantity ratio of the first carbon nanotube to the second carbon nanotube ranges from 0.01 to 0.67; the negative electrode composition also includes a binder, wherein the mass ratio of the binder to the first carbon nanotube in the negative electrode composition ranges from 15 to 170, the diameter of the first carbon nanotube ranges from 10 nm to 50 nm, and the diameter of the second carbon nanotube ranges from 2 nm to 10 nm.

2. The negative electrode composition according to claim 1, characterized in that, The binder is connected to the first carbon nanotube through intermolecular forces or chemical bonds.

3. The negative electrode composition according to claim 2, characterized in that, The mass fraction of the adhesive ranges from 1% to 3%.

4. The negative electrode composition according to claim 2, characterized in that, The first carbon nanotube is a modified carbon nanotube, which includes polar groups, including at least one of carboxyl, hydroxyl, carbonyl, amino, amide, cyano, sulfonic acid, and phosphate groups.

5. The negative electrode composition according to claim 4, characterized in that, The modified carbon nanotubes are modified by at least one of the following: concentrated nitric acid, concentrated sulfuric acid, diethyl adipate, diethyl dimethyl malonate, diethyl octanoate, dimethyl malonate, dimethyl octanoate, methyl valerate, propyl butyrate, n-dodecyltrimethoxysilane, silane coupling agent, trimethylsilane, hexadecyltrimethyltetrafluoroborate ammonium, N-(cocoyl)-N,N,N-trimethylammonium sulfate, hexadecyltrimethylammonium nitrate, methacrylic acid, and maleic acid.

6. The negative electrode composition according to claim 1, characterized in that, The mass fraction of the second carbon nanotube in the negative electrode composition ranges from 0.01% to 0.2%.

7. The negative electrode composition according to claim 1, characterized in that, The average length of the first carbon nanotube ranges from 8 μm to 20 μm; the average length of the second carbon nanotube ranges from 8 μm to 20 μm.

8. The negative electrode composition according to any one of claims 1-7, characterized in that, The negative electrode composition further includes a negative electrode conductive agent, a first dispersant, and a second dispersant; the negative electrode conductive agent includes at least one of conductive carbon black, superconducting carbon black, Ketjen black, graphite, and graphene; the first dispersant includes at least one of sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide; the second dispersant includes at least one of polyacrylic acid and sodium carboxymethyl cellulose.

9. A negative electrode sheet, characterized in that, The negative electrode sheet includes: a negative current collector and a negative active layer, wherein the negative active layer is disposed on the surface of the negative current collector, and the negative active layer is formed by the negative electrode composition according to any one of claims 1-8.

10. A method for preparing a negative electrode sheet, characterized in that, The preparation method includes: The first carbon nanotubes are mixed with a binder to obtain the first slurry; The first slurry is mixed with the negative electrode active material and the second carbon nanotubes to obtain the second slurry; and A negative electrode current collector is provided. The second slurry is coated onto the negative electrode current collector, and after drying and rolling, the negative electrode sheet is obtained. The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer. The negative electrode active layer includes a negative electrode active material, a first carbon nanotube, a second carbon nanotube, and a binder. The diameter of the first carbon nanotube is larger than the diameter of the second carbon nanotube. The quantity ratio of the first carbon nanotube to the second carbon nanotube ranges from 0.01 to 0.

67. The mass ratio of the binder to the first carbon nanotube ranges from 15 to 170. The diameter of the first carbon nanotube ranges from 10 nm to 50 nm. The diameter of the second carbon nanotube ranges from 2 nm to 10 nm.

11. A battery, characterized in that, include: Electrolyte, positive electrode, separator, and negative electrode as described in claim 9.

12. An energy storage device, characterized in that, include: Box; as well as The battery of claim 11, wherein the battery is housed within the casing.

Images