Modified carbon nanotube, method for modifying the same, electrode sheet, energy storage device, and electric device

Abstract

The application discloses modified carbon nanotubes, a modification method thereof, an electrode sheet, an energy storage device and an electric device. The modified carbon nanotube comprises a carbon nanotube body and an acylhydrazone compound group, and the acylhydrazone compound group is connected with the carbon nanotube body through a covalent bond.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry, specifically relating to modified carbon nanotubes and their modification methods, electrode sheets, energy storage devices, and electrical devices. Background Technology

[0002] Currently, developing high-energy-density batteries and improving electrode capacity utilization remain challenging technological hurdles. Taking lithium batteries as an example, their positive electrode active materials are mostly transition metal oxides or transition metal phosphates, which are semiconductors or insulators with poor conductivity, requiring the addition of conductive agents to improve conductivity. Meanwhile, the negative electrode graphite material has slightly better conductivity, but during repeated charge and discharge cycles, the expansion and contraction of graphite material can reduce the contact between graphite particles, increase the gaps, and even cause some to detach from the current collector, becoming dead active material that no longer participates in the electrode reaction. Therefore, conductive agents are also needed to maintain the stability of the conductivity of the negative electrode material during cycling. Summary of the Invention

[0003] This invention is primarily based on the following problems and findings: Theoretically, carbon nanotubes (CNTs) possess a perfect graphite-like surface structure with excellent stability and chemical inertness. However, numerous defects exist at their ends and bends. These defective sites are easily oxidized to generate carboxyl and hydroxyl groups, which can then react with other chemical reagents. These factors reduce the conductivity of CNTs, decrease their effective surface area, and make it difficult for nanoparticles to be loaded onto their surface, leading to agglomeration and thus affecting the applications of CNTs. The inventors discovered that primordial defects such as five- or seven-membered ring pairs, sp³ hybridization defects, and lattice vacancies in nanotubes can easily leave voids through the oxidative damage of strong acids on the tube walls, thereby connecting functional groups. However, current CNT functionalization methods generally involve oxidizing the openings with concentrated acid, cutting the tubes into short sections, and attaching carboxyl groups to the defect sites at the ends and / or sidewalls before further modification. This process can significantly damage the structure and properties of CNTs. Furthermore, non-covalent functionalization methods introduce additives such as surfactants or polymers that are difficult to completely remove, which aid in the dispersion of carbon nanotubes and reduce the electrical and thermal transport properties of the carbon nanotube network. Simultaneously, the strong van der Waals forces (~500 Ev / μm) and large aspect ratios (>1000) between single-walled carbon nanotubes often lead to the formation of large bundles, making dispersion difficult and significantly limiting the realization of their superior properties and practical applications. Commonly used solvent exfoliation methods typically employ solvents with high toxicity, high boiling points, and low dispersion efficiency. Therefore, effectively dispersing carbon nanotubes in common solvents while maintaining structural integrity and avoiding additives remains a significant problem and challenge in the research and application of single-walled carbon nanotubes.

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide modified carbon nanotubes and their modification methods, electrode plates, energy storage devices, and electrical devices. The modified carbon nanotubes exhibit good electrochemical performance and good dispersibility; using them as conductive agents in electrode plates helps reduce impedance and improve cycle performance.

[0005] In a first aspect, the present invention provides a modified carbon nanotube. The modified carbon nanotube comprises a carbon nanotube body and an acylhydrazone compound group, wherein the acylhydrazone compound group is covalently bonded to the carbon nanotube body.

[0006] The modified carbon nanotubes according to the above embodiments of the present invention have at least the following beneficial effects: 1) Compared with unmodified carbon nanotubes, the modified carbon nanotubes, by introducing acylhydrazone compounds as functional groups, are beneficial to improving the port defects of carbon nanotubes, which not only improves the conductivity but also has better dispersibility; 2) The modification process does not require the introduction of surfactants or other additives; 3) Using them as conductive agents in electrode plates is beneficial to reducing impedance and improving cycle performance.

[0007] In addition, the modified carbon nanotubes according to the above embodiments of the present invention may also have the following additional technical features: In some embodiments of the present invention, the covalent bond includes an amide bond and / or an ester bond.

[0008] In some embodiments of the present invention, the acylhydrazone compound group includes at least one substituent, the substituent including an amino group and / or a halogen.

[0009] In some embodiments of the present invention, the content of the acylhydrazone compound groups is ≥65wt%, based on the total mass of the carbon nanotubes.

[0010] In some embodiments of the present invention, the nitrogen content is ≥6wt% based on the total mass of the acylhydrazone compound groups.

[0011] In some embodiments of the present invention, the acylhydrazone group includes ketoacylhydrazone groups and / or enol acylhydrazone groups.

[0012] In some embodiments of the present invention, the acylhydrazone group includes monoacylhydrazone group and / or polyacylhydrazone group.

[0013] In some embodiments of the present invention, the carbon nanotube body includes single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0014] In a second aspect, the present invention provides a method for modifying carbon nanotubes. The method includes: Carbon nanotubes were pretreated to obtain carbon nanotubes containing the first functional group. An acylhydrazone compound containing a second functional group is mixed with a carbon nanotube containing a first functional group, allowing the second and first functional groups to react and achieve a covalent bond between the acylhydrazone compound and the carbon nanotube.

[0015] The modified carbon nanotube method of the above embodiments of the present invention has at least the following beneficial effects: 1) no additives such as surfactants are required during the modification process; 2) compared with unmodified carbon nanotubes, this method can introduce acylhydrazone compounds as functional groups to improve the port defects of carbon nanotubes, and the modified carbon nanotubes obtained not only have improved electrical conductivity, but also have better dispersibility; 3) using the obtained modified carbon nanotubes as conductive agents in electrode plates is beneficial to reducing impedance and improving cycle performance.

[0016] In some embodiments of the present invention, the first functional group includes a carboxyl group and / or an acyl halide group, and the second functional group includes a functional group capable of reacting with the carboxyl group and / or a functional group capable of reacting with the acyl halide group.

[0017] In some embodiments of the present invention, the pretreatment includes: performing a carboxylation reaction on the carbon nanotubes to obtain carbon nanotubes containing carboxyl groups.

[0018] In some embodiments of the present invention, the pretreatment further includes: converting the carboxyl groups in the carbon nanotubes containing carboxyl groups into acyl halide groups to obtain carbon nanotubes containing acyl halide groups.

[0019] In some embodiments of the present invention, the carbon nanotubes are subjected to a carboxylation reaction using a mixed acid solution composed of sulfuric acid and hydrogen peroxide. The mixed acid solution is obtained by mixing concentrated sulfuric acid with a concentration of not less than 98% and hydrogen peroxide solution with a mass concentration of 30wt%, and the mass ratio of the concentrated sulfuric acid to the hydrogen peroxide is (2~4):1.

[0020] In some embodiments of the present invention, the carboxylation reaction is carried out under ultrasonic conditions for a duration of ≤10 min.

[0021] In some embodiments of the present invention, the mass ratio of the carbon nanotubes to the acylhydrazone compound is 1:(2~7).

[0022] In some embodiments of the present invention, the mass ratio of the carbon nanotubes to the acylhydrazone compound is 1:(5~7).

[0023] In a third aspect, the present invention provides an electrode electrode. The electrode electrode includes a current collector and an active material layer, the active material layer being disposed on at least one side of the current collector, and the active material layer comprising the aforementioned modified carbon nanotubes or modified carbon nanotubes prepared using the aforementioned modified carbon nanotube method. This electrode electrode possesses all the features and effects of the aforementioned modified carbon nanotubes and the aforementioned modified carbon nanotube method, which will not be elaborated further here. In general, this electrode electrode exhibits both low impedance and good cycle performance.

[0024] In some embodiments of the present invention, the content of the modified carbon nanotubes is 1wt% to 2.5wt% based on the total mass of the active material layer.

[0025] In some embodiments of the present invention, the electrode plates include: a positive electrode plate and / or a negative electrode plate.

[0026] In a fourth aspect, the present invention provides an energy storage device. This energy storage device includes the aforementioned electrode plates. The energy storage device possesses all the features and effects of the aforementioned electrode plates, which will not be repeated here. In general, this energy storage device combines low internal resistance with good cycle performance.

[0027] In a fifth aspect, the present invention provides an electrical device. According to an embodiment of the invention, the electrical device includes the aforementioned energy storage device. This electrical device possesses all the features and effects of the aforementioned energy storage device, which will not be elaborated further here.

[0028] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart of a method for modifying carbon nanotubes according to an embodiment of the present invention.

[0030] Figure 2 This is a flowchart of a method for modifying carbon nanotubes according to another embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram of an energy storage device according to an embodiment of the present invention.

[0032] Figure 4 This is a comparison chart showing the effect of different (ultrasonic) carboxylation reaction times on the conductivity of modified carbon nanotubes in Examples 1, 5-7 and Comparative Example 1 of the present invention.

[0033] Figure 5These are comparative graphs of the electrochemical impedance spectroscopy curves of the batteries prepared in Examples 8-11 of this invention.

[0034] Figure 6 This is a comparison chart of the cycle capacity retention rates obtained in Example 9 and Comparative Example 3 of the present invention. Detailed Implementation

[0035] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0036] In a first aspect, the present invention provides a modified carbon nanotube. The modified carbon nanotube comprises a carbon nanotube body and an acylhydrazone group, wherein the acylhydrazone group is covalently bonded to the carbon nanotube body.

[0037] According to embodiments of the present invention, by introducing acylhydrazone compounds to form covalent bonds with carbon nanotubes, not only can nitrogen doping be introduced to improve the electrical conductivity of carbon nanotubes, but also the dispersion of carbon nanotubes can be improved. Nitrogen atoms have one more electron than carbon atoms and possess higher electron affinity. In nitrogen-doped carbon materials, carbon atoms adjacent to nitrogen heteroatoms have a high positive charge density. Simultaneously, there is a conjugation effect between the lone pair electrons of nitrogen atoms and the large π bonds in the carbon lattice. After nitrogen heteroatoms are incorporated into the carbon nanotube lattice, they can act as electron donors, significantly improving the conductivity of carbon nanotubes. Furthermore, nitrogen doping increases lattice defects in carbon nanotubes, leading to an increase in the Fermi surface density of states, thereby improving the electrical conductivity of carbon nanotubes. Therefore, the modified carbon nanotubes of the above embodiments of the present invention have at least the following beneficial effects: 1) Compared with unmodified carbon nanotubes, the modified carbon nanotubes, by introducing acylhydrazone compounds as functional groups, are beneficial to improving the port defects of carbon nanotubes, which not only improves the conductivity but also has better dispersibility; 2) The modification process does not require the introduction of surfactants or other additives; 3) Using them as conductive agents in electrode plates is beneficial to reducing impedance and improving cycle performance.

[0038] It should be noted that, in this invention, the acylhydrazone compounds refer to acylhydrazone compounds and / or derivatives of acylhydrazone compounds. The acylhydrazone compound group refers to the compound group obtained after the reaction of the acylhydrazone compound and / or its derivative with the carboxyl groups on the surface of carbon nanotubes. The acylhydrazone compound can be unsubstituted or substituted with any group, and the acylhydrazone compound derivative refers to an acylhydrazone compound derivative having an acylhydrazone bond structure. The conditions for the reaction of the acylhydrazone compound and / or its derivative with the carboxyl groups on the surface of carbon nanotubes include, but are not limited to, acidic conditions.

[0039] In some embodiments of the present invention, the covalent bond may include an amide bond and / or an ester bond. Using either an amide bond or an ester bond is advantageous for achieving covalent bonding between the acylhydrazone group and the carbon nanotube bulk. For example, as specific examples, when preparing modified functional groups, the carbon nanotube can first undergo a carboxylation reaction to carry a carboxyl group. Optionally, the carboxyl group carried by the carbon nanotube can be further converted into an acyl halide group, such as an acyl chloride. Reacting the carbon nanotube with a carboxyl group or an acyl halide group with an acylhydrazone compound containing an amino group yields modified carbon nanotubes in which the acylhydrazone group and the carbon nanotube bulk are linked by an amide bond. Alternatively, reacting the carbon nanotube with a carboxyl group or an acyl halide group with an acylhydrazone compound containing a hydroxyl group yields modified carbon nanotubes in which the acylhydrazone group and the carbon nanotube bulk are linked by an ester bond. Furthermore, the covalent bond may include an amide bond, wherein the acylhydrazone compound group is connected to the carbon nanotube body via an amide bond, which not only further increases the nitrogen doping content but also increases the nitrogen content entering the carbon nanotube lattice, thus improving the conductivity of the carbon nanotube. As some specific examples, the covalent bond may include an acylhydrazone bond.

[0040] In some embodiments of the present invention, the acylhydrazone group may include at least one substituent. The acylhydrazone group may be substituted or unsubstituted. When the acylhydrazone group contains a substituent, the substituent may include, but is not limited to, one or more conventional substituents such as amino, halogen, hydroxyl, carboxyl, hydrocarbon, alkoxy, phenyl, and phenoxy. As some specific examples, the substituent may include amino and / or halogen substituents; that is, the acylhydrazone group may include one or more amino groups, and / or, the acylhydrazone group may include one or more halogen substituents. Acylhydrazone groups containing amino groups are beneficial for further increasing the nitrogen doping content introduced into the modified carbon nanotubes, thereby further improving the conductivity of the modified carbon nanotubes. In addition, halogens may include, but are not limited to, fluorine. Halogen substitution has a positive effect on suppressing the collapse of the active material structure during charge-discharge cycles, which is beneficial for improving the cycle performance of the electrode and the battery. Taking fluorine substitution as an example, the fluorine substituent F- can exhibit higher oxidation stability, which is beneficial for improving the cycle stability of the battery. It should be noted that the amino group in the acylhydrazone compound having an amino group refers to a substituent that is different from the -NHNH= group. As some specific examples, the amino group can be connected to a carbon element, such as the amino group being connected to a carbon element on a benzene ring, a hydrocarbon group, or a hydrocarbon chain.

[0041] In some embodiments of the present invention, based on the total mass of carbon nanotubes, the content of acylhydrazone groups can be ≥65wt%, for example, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, etc. The content of acylhydrazone groups reflects, to some extent, the degree to which the surface of the carbon nanotubes is replaced by corresponding functional groups. Increasing the content of acylhydrazone groups can further increase the nitrogen doping content introduced into the modified carbon nanotubes, thereby further improving the conductivity of the modified carbon nanotubes. Therefore, ensuring that the content of acylhydrazone groups in the modified carbon nanotubes meets the above-mentioned range is beneficial for obtaining further improved conductivity.

[0042] In some embodiments of the present invention, based on the total mass of the acylhydrazone compound groups, the nitrogen content can be ≥6 wt%, for example, ≥6 wt%, 8 wt%, 10 wt%, 12.5 wt%, 15 wt%, 18 wt%, 20 wt%, etc. Increasing the nitrogen content in the acylhydrazone compound groups also helps to increase the nitrogen doping amount in the modified carbon nanotubes, thereby further improving the conductivity of the carbon nanotubes. Therefore, ensuring that the nitrogen content in the modified carbon nanotubes meets the above-mentioned ranges is beneficial for obtaining further improved conductivity.

[0043] In some embodiments of the present invention, the specific type of acylhydrazone compound group is not particularly limited, and those skilled in the art can flexibly select it according to actual needs. For example, the acylhydrazone compound group may include ketoacylhydrazone compound groups and / or enol acylhydrazone compound groups. As some specific examples, when the acylhydrazone compound group includes ketoacylhydrazone compound groups, the modified carbon nanotube may include... Structure; when the acylhydrazone group includes an enol acylhydrazone group, the modified carbon nanotube may include In this structure, R1 can be a hydrogen atom or other groups, such as a carbonyl group forming an ester bond (e.g., the structure can be covalently bonded between the carbonyl group and the carbon nanotube body). Unless otherwise stated, in this invention, " "" indicates the connecting part between the same or different atoms or end parts of a chemical formula.

[0044] In some embodiments of the present invention, the acylhydrazone group may include monoacylhydrazone groups and / or polyacylhydrazone groups. Both monoacylhydrazone groups and polyacylhydrazone groups can introduce nitrogen doping into carbon nanotubes. It is understood that the monoacylhydrazone groups and the polyacylhydrazone groups may also be independently substituted or unsubstituted acylhydrazone groups, and if substituents are present, their respective substituents may independently include amino groups and / or halogen groups. As some specific examples, the acylhydrazone groups may include polyacylhydrazone groups, for example, they may include only polyacylhydrazone groups, or they may include both monoacylhydrazone groups and polyacylhydrazone groups. Choosing polyacylhydrazone groups is also beneficial for increasing the nitrogen doping content introduced into the modified carbon nanotubes, thereby further improving the conductivity of the modified carbon nanotubes. As some specific examples, when the acylhydrazone compound group is a monoacylhydrazone compound group, it may further include at least one amino substitution and / or at least one halogen substitution.

[0045] In some embodiments of the present invention, as specific examples, the acylhydrazone compound group may include at least one of amino and halogen.

[0046] In some embodiments of the present invention, the acylhydrazone compounds forming the acylhydrazone compound groups may include, but are not limited to, those that form the acylhydrazone compound groups. and / or Among them, R1, R2, R3, R4, R5, R6, R7, and R8 can be independently selected from substituents such as amino, hydrocarbon, halogen (e.g., F), and H. The above acylhydrazone compounds can react with the carboxyl groups on the surface of carbon nanotubes to form covalent bonds.

[0047] In some embodiments of the present invention, the carbon nanotube body includes single-walled carbon nanotubes and / or multi-walled carbon nanotubes. For example, the carbon nanotube body may include only single-walled carbon nanotubes or multi-walled carbon nanotubes, or it may include both single-walled and multi-walled carbon nanotubes. Those skilled in the art can choose flexibly according to actual needs. As some specific examples, the carbon nanotube body may be single-walled carbon nanotubes.

[0048] In some embodiments of the present invention, the modified carbon nanotubes can be prepared by mixing carbon nanotubes having a first functional group and an acylhydrazone compound having a second functional group, thereby reacting the second functional group with the first functional group to achieve a covalent bond between the acylhydrazone compound group and the carbon nanotube body. Optionally, the first functional group may include a carboxyl group and / or an acyl halide group, and the second functional group may include an amino group and / or a hydroxyl group. Preferably, the acylhydrazone compound may include an amino-substituted acylhydrazone compound, wherein the amino group can react with the carboxyl group or acyl halide group on the carbon nanotube to achieve an amide bond between the acylhydrazone compound group and the carbon nanotube body. Carbon nanotubes with carboxyl groups can be obtained by carboxylating the carbon nanotubes with an acid solution, and carbon nanotubes containing acyl halide groups can be obtained by further converting the carboxyl groups on the carbon nanotubes, for example, by using thionyl chloride (SOCl2) to convert the carboxyl groups on the carbon nanotubes into acyl chlorides.

[0049] Based on the same inventive concept, in a second aspect, this invention proposes a method for modifying carbon nanotubes. (See reference...) Figure 1 The method comprises: pretreating carbon nanotubes to obtain carbon nanotubes containing a first functional group; mixing an acylhydrazone compound containing a second functional group with the carbon nanotubes containing the first functional group, thereby reacting the second and first functional groups to achieve covalent bonding between the acylhydrazone compound and the carbon nanotubes. This method has at least the following advantages: 1) no additives such as surfactants are needed during the modification process; 2) compared to unmodified carbon nanotubes, this method introduces acylhydrazone compounds as functional groups to improve the port defects of carbon nanotubes, resulting in modified carbon nanotubes with improved conductivity and better dispersibility; 3) using the modified carbon nanotubes as conductive agents in electrode plates helps reduce impedance and improve cycle performance.

[0050] The following is for reference. Figures 1-2 The above-mentioned method for modifying carbon nanotubes is described in detail.

[0051] S1: Pretreatment of carbon nanotubes to obtain carbon nanotubes containing the first functional group. In some embodiments of the present invention, the first functional group may include a carboxyl group and / or an acyl halide group, and the second functional group may include a functional group capable of reacting with a carboxyl group and / or a functional group capable of reacting with an acyl halide group. Optionally, the acyl halide group may include, but is not limited to, an acyl chloride group. Optionally, the second functional group may include an amino group and / or a hydroxyl group, thereby facilitating the formation of covalent bonds between acylhydrazone compound groups and carbon nanotubes via amide bonds and / or ester bonds to obtain modified carbon nanotubes.

[0052] In some embodiments of the present invention, the pretreatment may include: performing a carboxylation reaction on the carbon nanotubes to obtain carbon nanotubes containing carboxyl groups. By performing a carboxylation reaction on the carbon nanotubes, a large number of -COOH groups can be formed at the ends and gaps of the carbon nanotubes, providing modification sites for the introduction of acyl chloride compound groups.

[0053] In this invention, the reaction conditions for the carboxylation reaction of carbon nanotubes can be either conventionally chosen in the art or can meet the following conditions: In some specific examples, a mixed acid solution consisting of sulfuric acid and hydrogen peroxide can be used to perform a carboxylation reaction on carbon nanotubes. This mixed acid solution can be obtained by mixing concentrated sulfuric acid with a concentration of not less than 98% and a hydrogen peroxide solution with a mass concentration of 30 wt%. The mass ratio of concentrated sulfuric acid to hydrogen peroxide can be (2~4):1, such as 2 / 1, 2.5 / 1, 3 / 1, 3.5 / 1, or 4 / 1. Using this method to cut carbon nanotubes can create more defect sites, thereby forming a large number of -COOH groups at the ends and gaps of the carbon nanotubes, providing sites for functional modification by introducing acylhydrazone groups.

[0054] In some specific examples, the carboxylation reaction can be carried out under ultrasonic conditions. The modification sites for introducing acylhydrazone groups onto the carbon nanotube surface can be controlled by adjusting the duration of the ultrasonication. Furthermore, the ultrasonication time during the carboxylation reaction can be ≤10 min, for example, 1 min, 2 min, 5 min, 8 min, 10 min, etc. The inventors have found that the conductivity of the final modified carbon nanotubes first increases and then decreases with increasing ultrasonication time. Controlling the ultrasonication time to within 10 min allows the final modified carbon nanotubes to have better conductivity. Additionally, conventional ultrasonic equipment in the field can be used for the carboxylation reaction, with frequencies ranging from 40 kHz to 50 kHz.

[0055] In some embodiments of the present invention, the pretreatment may further include: converting the carboxyl groups in the carboxyl-containing carbon nanotubes into acyl halide groups to obtain carbon nanotubes containing acyl halide groups. For example, thionyl chloride can be reacted with the carboxyl-containing carbon nanotubes to obtain carbon nanotubes containing acyl chloride groups. The reaction conditions for converting the carboxyl groups in the carboxyl-containing carbon nanotubes into acyl halide groups can be conventionally selected in the art and are not particularly limited here.

[0056] In some embodiments of the present invention, the acylhydrazone compound may satisfy at least one of the following conditions: the acylhydrazone compound may include one or more substituents, the substituents may include amino groups and / or halogens, such as including multiple amino groups and / or multiple halogen substituents; the nitrogen content in the acylhydrazone compound may be ≥6 wt%; the acylhydrazone compound groups may include ketoacylhydrazone groups and / or enol acylhydrazone groups; the acylhydrazone compound groups may include monoacylhydrazone groups and / or polyacylhydrazone groups. Optionally, the carbon nanotube bulk comprises single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The beneficial effects of these features have been described in detail in the foregoing sections and will not be repeated here.

[0057] S2: An acylhydrazone compound containing a second functional group is mixed with a carbon nanotube containing a first functional group, allowing the second and first functional groups to react and achieve covalent bonding between the acylhydrazone compound and the carbon nanotube. According to embodiments of the present invention, reacting the second functional group with the first functional group can successfully introduce nitrogen doping into carbon nanotubes. Simultaneously, the introduction of acylhydrazone compounds improves both conductivity and the dispersibility of the resulting modified carbon nanotubes. As described above, the first functional group may include carboxyl groups and / or acyl halide groups, and the second functional group may include amino groups and / or hydroxyl groups.

[0058] In some embodiments of the present invention, the mass ratio of carbon nanotubes to acylhydrazone compounds can be 1:(2~7), for example, 1 / 2, 1 / 3, 1 / 4, 1 / 5, 1 / 6, or 1 / 7. Increasing the amount of acylhydrazone compounds is beneficial for replacing as many modification sites (such as carboxyl groups and / or acyl halide groups) on the surface of carbon nanotubes as possible. Controlling the mass ratio of carbon nanotubes to acylhydrazone compounds to meet the given range requirements can result in higher acylhydrazone compound and nitrogen doping content in the modified carbon nanotubes, thereby facilitating further improvement in conductivity. Furthermore, the mass ratio of carbon nanotubes to acylhydrazone compounds can be 1:(5~7). Meeting the given conditions is beneficial for further replacing as many modification sites on the surface of carbon nanotubes as possible, thereby facilitating better conductivity.

[0059] In some embodiments of the present invention, reference is made to Figure 2 It is understood that methods for modifying carbon nanotubes can further include: S3: Clean the modified carbon nanotubes to remove unreacted acylhydrazone compounds from their surface.

[0060] According to embodiments of the present invention, when an excess of acylhydrazone compounds is used, unreacted acylhydrazone compounds on the surface of the modified carbon nanotubes can also be removed by washing. The method of washing the modified carbon nanotubes and the washing solution used are not particularly limited, and those skilled in the art can choose flexibly according to actual needs. As some specific examples, the crude modified carbon nanotubes can be washed once or multiple times with a cold methanol solution, and then the washed crude product can be recrystallized in ethanol, thereby removing unreacted acylhydrazone compounds and obtaining pure modified carbon nanotubes.

[0061] It should be noted that the modified carbon nanotube method of the above embodiments of the present invention and the modified carbon nanotube described above are based on the same inventive concept. All the features and effects described above for the modified carbon nanotube are also applicable to the modified carbon nanotube method or the modified carbon nanotubes prepared by the modified carbon nanotube method, and will not be described in detail here.

[0062] In a third aspect, the present invention provides an electrode electrode. This electrode electrode includes a current collector and an active material layer, the active material layer being disposed on at least one side of the current collector. The active material layer includes the aforementioned modified carbon nanotubes or modified carbon nanotubes prepared using the aforementioned modified carbon nanotube method. This electrode electrode possesses all the features and effects of the aforementioned modified carbon nanotubes and the aforementioned modified carbon nanotube method, which will not be elaborated further here. In general, this electrode electrode exhibits both low impedance and good cycle performance.

[0063] In some embodiments of the present invention, the content of modified carbon nanotubes can be 1 wt% to 2.5 wt%, based on the total mass of the active material layer, for example, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, etc. Modified carbon nanotubes can be used as conductive agents in the active material layer of the electrode. The inventors have found that as the content of modified carbon nanotubes in the positive electrode active material layer increases, the impedance of the electrode first decreases and then increases. By controlling the content of modified carbon nanotubes in the active material layer to meet the given range, the electrode can obtain a lower electrochemical impedance.

[0064] In some embodiments of the present invention, the electrode sheet may include a positive electrode sheet and / or a negative electrode sheet. The modified carbon nanotubes can be used as a conductive agent for both the positive and negative electrode sheets, and can be flexibly selected according to actual needs.

[0065] It should be noted that in an electrode sheet, the active material layer typically includes an active material, a conductive agent, and a binder. The active material layer and binder can be selected from conventional active materials and binders within the relevant field, depending on the specific type of the electrode sheet (positive or negative). The conductive agent can include the aforementioned modified carbon nanotubes. In some specific examples, for positive electrodes, the active material can include, but is not limited to, layered transition metal oxides such as nickel-cobalt-manganese, olivine-type transition metal oxides such as lithium iron phosphate, etc., and the binder can be polyvinylidene fluoride, etc. For negative electrodes, the active material can include, but is not limited to, artificial graphite, soft carbon, hard carbon, silicon-carbon composite materials, etc., and the binder can be styrene-butadiene rubber, sodium carboxymethyl cellulose, etc.

[0066] In a fourth aspect, the present invention provides an energy storage device. This energy storage device includes the aforementioned electrode plates. The energy storage device possesses all the features and effects of the aforementioned electrode plates, which will not be repeated here. In general, this energy storage device combines low internal resistance with good cycle performance.

[0067] It should be noted that the present invention does not impose any particular limitation on the specific type of energy storage device, and those skilled in the art can flexibly choose according to the actual situation, for example, referring to... Figure 3 It is understood that the energy storage device may include a battery, which may include a positive electrode, a negative electrode, a separator, and an electrolyte. At least one of the positive and negative electrodes may be the aforementioned electrode. The present invention does not impose any particular limitation on the specific composition of the separator and the electrolyte; conventional choices in the art can be used. For example, the separator may include at least one of polypropylene (PP), polyethylene (PE), and ceramic separators. The electrolyte may include electrolyte salts and organic solvents, and the specific types and compositions of the electrolyte salts and organic solvents are not particularly limited; those skilled in the art can select them according to actual needs. Furthermore, the present invention does not impose any particular limitation on the specific type of battery; those skilled in the art can flexibly choose according to actual conditions. For example, the battery may be a prismatic battery or a cylindrical battery. For another example, the battery may be a liquid battery or a semi-solid battery. Yet another example is that the battery may be a lithium battery or a sodium battery.

[0068] In a fifth aspect, the present invention provides an electrical device. According to an embodiment of the invention, the electrical device includes the aforementioned energy storage device. This electrical device possesses all the features and effects of the aforementioned energy storage device, which will not be repeated here. In general, the electrical device offers better performance. It should be noted that the present invention does not impose any particular limitation on the specific type of electrical device; those skilled in the art can flexibly select one according to actual circumstances. For example, the electrical device may include, but is not limited to, electronic devices, vehicles, aircraft, and household appliances.

[0069] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0070] Example 1 Benzoylhydrazide (2 mmol) and 4-aminoacetophenone (3 mmol) were added to anhydrous ethanol (10 mL), and the mixture was heated under reflux for 4 hours in the presence of acetic acid. The solvent was removed by vacuum distillation, and the crude product was washed repeatedly with cold methanol solution. The washed crude product was recrystallized in ethanol to give pure aminohydrazone.

[0071]

[0072] A mixed acid solution was prepared by mixing 98 wt% H2SO4 solution and 30 wt% H2O2 at a mass ratio of 4:1. Carbon nanotubes (CNTs) were then subjected to ultrasonic treatment using the mixed acid solution for 5 min to obtain carboxylated modified carbon nanotubes. SOCl2 was used to convert the -COOH in the carboxylated carbon nanotubes into acyl chlorides, and the carbon nanotubes with acyl chlorides were condensed with the aminohydrazones at a mass ratio of 1:6.

[0073] The modified carbon nanotubes were cleaned using methanol as a solvent to obtain the modified carbon nanotubes.

[0074] Examples 2-4 The difference between Examples 2-4 and Example 1 is that the carbon nanotubes containing acyl chlorides were condensed with aminohydrazones at mass ratios of 1:4, 1:5, and 1:7, respectively.

[0075] (a) Observe whether there is any aminohydrazone residue in Examples 1-4: In Examples 1-4, after the condensation reaction of carbon nanotubes with acyl chlorides and aminohydrazones was completed, the modified crude carbon nanotubes were initially washed using methanol as a solvent. During the washing process, the solvent containing the modified crude carbon nanotubes was rotated. When the mass ratio of carbon nanotubes to aminohydrazones was 1:6 and 1:7, aminohydrazone residue was clearly observed during solvent rotation. This phenomenon was not observed when the mass ratio was 1:4 and 1:5. In actual operation, the mass ratio of carbon nanotubes to aminohydrazones can be controlled at 1:(5-6). A slight excess of aminohydrazones helps ensure that all carboxylation modification sites of the carbon nanotubes are substituted with acylhydrazones.

[0076] Examples 5-7 and Comparative Example 1 The difference between Examples 5-7 and Example 1 is that the ultrasonic treatment time of carbon nanotubes using mixed acid solution is 2 min, 8 min, and 10 min, respectively.

[0077] The difference between Comparative Example 1 and Example 1 is that no modification was made to the carbon nanotubes.

[0078] (b) Test the conductivity improvement effect of the modified carbon nanotubes prepared in Examples 1, 5-7 and the carbon nanotubes in Comparative Example 1.

[0079] Test method: Using carbon nanotubes as a conductive agent, LiFePO4, PVDF, and CNTs were mixed in a mass ratio of 96:2.5:1.5 and dissolved in N-methylpyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was coated onto the surface of aluminum foil to form an active material layer, thus obtaining a positive electrode film. The surface resistance of the active material layer was tested under the same compaction density. The test results are as follows: Figure 4 As shown.

[0080] from Figure 4 As can be seen, the resistance of the active material layer first decreases and then increases with the extension of ultrasonic time. In particular, the resistance of the active material layer in Example 1 is relatively lower. This indicates that, compared with other examples, the amount of nitrogen doping that can be introduced into the defect sites created on the surface of carbon nanotubes after 5 minutes of ultrasonication has the greatest effect on improving the conductivity of carbon nanotubes.

[0081] Examples 8-11 and Comparative Examples 2-3 A positive electrode sheet was prepared using the carbon nanotubes obtained in Example 1 and Comparative Example 1, and a battery was assembled.

[0082] Positive electrode sheet: LiFePO4, PVDF, and CNTs are mixed in a mass ratio of 96:2.5:1.5 and dissolved in N-methylpyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is filtered through a 150-mesh filter and coated onto an aluminum foil surface to form a positive electrode sheet. After drying, it is pressed to a density of 1.7 g / cm³ using a roller press. 3 This yields the positive electrode sheet for a lithium-ion battery. Negative electrode sheet: Artificial graphite, sodium carboxymethyl cellulose, superconducting carbon black (Super-P), and styrene-butadiene rubber are dispersed in deionized water at a mass ratio of 96:2:1:1. After stirring evenly, a negative electrode slurry is obtained, which is then coated onto the surface of aluminum foil to form a negative electrode sheet. After drying, the sheet is rolled using a roller press until the compaction of the negative electrode reaches 3.7 g / cm³. 3 This yields the negative electrode sheet for lithium-ion batteries.

[0083] Electrolyte: Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare the electrolyte.

[0084] Separating membrane: A standard uncoated polypropylene film with a thickness of 13μm is used.

[0085] Following the conventional lithium-ion battery assembly steps, a 3.2Ah soft-pack cell is prepared by winding the positive electrode, negative electrode, and separator, and then injecting electrolyte while maintaining a consistent electrolyte retention coefficient for each cell.

[0086] In Examples 8-11, the modified carbon nanotubes obtained in Example 1 were used to prepare the positive electrode sheets. In Comparative Examples 2 and 3, the carbon nanotubes in Comparative Example 1 were used to prepare the positive electrode sheets. The difference between Examples 8-11 is that the mass ratio of LiFePO4, PVDF, and CNTs in the positive electrode sheets is different, as detailed in Table 1. In Comparative Example 2, the mass ratio of LiFePO4, PVDF, and CNTs is the same as in Example 8; in Comparative Example 3, the mass ratio of LiFePO4, PVDF, and CNTs is the same as in Example 9.

[0087] Table 1

[0088] (c) Verify the dispersibility of the carbon nanotubes prepared in Example 1 When preparing the battery, the slurry was filtered using a 150-mesh filter screen during discharge, and the presence of particle residue on the filter screens in Examples 8-11 and Comparative Example 2 was observed.

[0089] In Comparative Example 2, a small amount of particles remained on the filter screen, while in Examples 8-11, no particles remained on the filter screen, indicating that the dispersibility of the modified carbon nanotubes obtained by the method of the above embodiments of the present invention has been improved.

[0090] (d) The resistance of the positive electrode sheets prepared in Example 8 and Comparative Example 2 were compared, and the specific resistance of the positive electrode active material layer was tested (multiple measurements were taken in different regions to obtain the average value). The test results are shown in Table 2. Table 2 shows that the conductivity of the carbon nanotubes modified using the method of the above embodiments of the present invention is significantly improved. Furthermore, by comparing the fluctuation range between the resistance measured in different regions of the positive electrode sheets prepared in Example 8 and Comparative Example 2 and their respective specific resistances, it can be seen that the resistance values ​​measured in different regions of the positive electrode sheet prepared in Example 8 fluctuate less, which further illustrates that the dispersibility of the modified carbon nanotubes obtained using the method of the above embodiments of the present invention is improved.

[0091] Table 2

[0092] (e) Test the AC impedance of the batteries obtained in Examples 8-11 At 25°C, the batteries prepared in Examples 8-11 were connected to an electrochemical workstation, and the electrochemical impedance spectroscopy curves were obtained by scanning from a high frequency of 800 kHz to a low frequency of 50 mHz with an AC amplitude of 10 mV. See the comparison diagram for details. Figure 5 , Figure 5 The impedance spectrum curves shown for 2.5%, 2%, 1.5%, and 1% addition amounts correspond to the batteries obtained in Examples 8, 9, 10, and 11, respectively.

[0093] from Figure 5 As can be seen, in the positive electrode sheet, the resistance is lowest when the amount of modified carbon nanotubes added to the positive electrode active material layer is 2wt%. When the amount of added carbon nanotubes is further increased to 2.5wt%, the electrochemical resistance increases. The reason for this may be that the larger amount of modified CNTs added also increases the difficulty of dispersion.

[0094] (d) Cycle capacity retention of the batteries obtained from Example 9 and Comparative Example 2 Batteries prepared in Examples 8-9 and Comparative Examples 2-3 were subjected to charge-discharge cycle tests at a rate of 1.0C at 45°C to compare the capacity retention rate over 250 cycles.

[0095] Test results show that the cycle energy retention rate of Example 8 is better than that of Comparative Example 2, and the cycle energy retention rate of Example 9 is better than that of Comparative Example 3. Among them, Figure 6The changes in capacity retention of the batteries prepared in Example 9 and Comparative Example 3 during 250 charge-discharge cycles at a 1.0C rate are shown. Figure 6 As can be seen, the cycle energy retention rate of the battery is significantly improved after using modified CNTs in the positive electrode.

[0096] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0097] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A modified carbon nanotube, characterized in that, include: The carbon nanotube body and the acylhydrazone compound group are covalently connected to the carbon nanotube body. The covalent bonds include amide bonds and / or ester bonds; The acylhydrazone groups include ketoacylhydrazone groups and / or enolacylhydrazone groups; Based on the total mass of the carbon nanotubes, the content of the acylhydrazone compound groups is ≥65wt%.

2. The modified carbon nanotube according to claim 1, characterized in that, The acylhydrazone compound group includes at least one substituent, which includes an amino group and / or a halogen.

3. The modified carbon nanotube according to claim 1, characterized in that, Based on the total mass of the acylhydrazone compound groups, the nitrogen content is ≥6wt%.

4. The modified carbon nanotubes according to any one of claims 1 to 3, characterized in that, At least one of the following conditions must be met: The acylhydrazone groups include monoacylhydrazone groups and / or polyacylhydrazone groups; The carbon nanotube body includes single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

5. A method for modifying carbon nanotubes, characterized in that, include: Carbon nanotubes were pretreated to obtain carbon nanotubes containing the first functional group. An acylhydrazone compound containing a second functional group is mixed with a carbon nanotube containing a first functional group, so that the second functional group and the first functional group react to achieve a covalent bond between the acylhydrazone compound and the carbon nanotube. The covalent bonds include amide bonds and / or ester bonds; The acylhydrazone groups include ketoacylhydrazone groups and / or enolacylhydrazone groups; The mass ratio of the carbon nanotubes to the acylhydrazone compound is 1:(2~7).

6. The method according to claim 5, characterized in that, The first functional group includes a carboxyl group and / or an acyl halide group, and the second functional group includes a functional group capable of reacting with the carboxyl group and / or a functional group capable of reacting with the acyl halide group.

7. The method according to claim 6, characterized in that, The pretreatment includes: performing a carboxylation reaction on the carbon nanotubes to obtain carbon nanotubes containing carboxyl groups.

8. The method according to claim 7, characterized in that, At least one of the following conditions must be met: The pretreatment further includes: converting the carboxyl groups in the carbon nanotubes containing carboxyl groups into acyl halide groups to obtain carbon nanotubes containing acyl halide groups; The carbon nanotubes were subjected to a carboxylation reaction using a mixed acid solution composed of sulfuric acid and hydrogen peroxide. The mixed acid solution was obtained by mixing concentrated sulfuric acid with a concentration of not less than 98% and hydrogen peroxide solution with a mass concentration of 30wt%. The mass ratio of the concentrated sulfuric acid to the hydrogen peroxide was (2~4):

1. The carboxylation reaction is carried out under ultrasonic conditions, and the ultrasonic time is ≤10 min. The second functional group includes amino and / or hydroxyl groups.

9. The method according to any one of claims 5 to 8, characterized in that, The mass ratio of the carbon nanotubes to the acylhydrazone compound is 1:(5~7).

10. An electrode sheet, characterized in that, It includes a current collector and an active material layer, wherein the active material layer is disposed on at least one side of the current collector, and the active material layer includes modified carbon nanotubes according to any one of claims 1 to 4 or modified carbon nanotubes prepared by any one of claims 5 to 9.

11. The electrode sheet according to claim 10, characterized in that, Based on the total mass of the active material layer, the content of the modified carbon nanotubes is 1wt%~2.5wt%; And / or, The electrode plates include: positive electrode plates and / or negative electrode plates.

12. An energy storage device, characterized in that, Includes the electrode sheet as described in claim 10 or 11.

13. An electrical appliance, characterized in that, Includes the energy storage device as described in claim 12.

Images