CN111099577A - Nitrogen-doped carbon nanotube material - Google Patents

Nitrogen-doped carbon nanotube material Download PDF

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CN111099577A
CN111099577A CN201811262167.XA CN201811262167A CN111099577A CN 111099577 A CN111099577 A CN 111099577A CN 201811262167 A CN201811262167 A CN 201811262167A CN 111099577 A CN111099577 A CN 111099577A
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nitrogen
carbon nanotube
reaction
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dispersion
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CN111099577B (en
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郭金
廖莎
张会成
王少军
凌凤香
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Sinopec Dalian Petrochemical Research Institute Co ltd
China Petroleum and Chemical Corp
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China Petroleum and Chemical Corp
Sinopec Dalian Research Institute of Petroleum and Petrochemicals
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Abstract

A nitrogen-doped carbon nanotube material is prepared through cross-linking formaldehyde with melamine to form nitrogen-doped precursor, hydrothermal reaction to make the nitrogen-doped precursor and carbon nanotubes interact and fuse uniformly, and microwave reaction without solvent to synthesize high-nitrogen content doped carbon nanotubes. The nitrogen-doped carbon nanotube material provided by the invention avoids the loss caused by sublimation of a nitrogen-doped precursor in a heating process in the traditional nitrogen-doping process in the preparation process, improves the nitrogen-doping efficiency, and realizes uniform fusion of the nitrogen-doped precursor and the carbon nanotube through interaction under mild to strong reaction conditions. The prepared nitrogen-doped carbon nanotube material has good stability, is not easy to denature in air, is easy to store, has a large specific surface area, is used as a lithium ion battery cathode material, provides a good channel for lithium ion transmission, and shows large specific capacity and good cycling stability.

Description

Nitrogen-doped carbon nanotube material
Technical Field
The invention relates to a nitrogen-doped carbon nanotube material, in particular to a high-nitrogen-content doped carbon nanotube lithium battery cathode material and a preparation method thereof, belonging to the technical field of nano composite materials and application thereof.
Background
The carbon nanotube is a hollow cylinder formed by rolling graphite layers, and the bonding mode of the carbon nanotube is mainly a deformed Sp2 orbit. When the graphite layer is rolled into the carbon nanotube, partial deformation of Sp2 hybridization occurs, so Sp2 tends to form re-hybridization of Sp3, and the re-hybridization structure and the two-orbital confinement characteristics can endow the carbon nanotube with excellent force, heat, electricity, light, magnetism and chemical properties. Therefore, the carbon nanotube has higher mechanical strength, better electric heat conduction performance and higher chemical and biological activity than graphene.
With the development of Carbon Nanotubes (CNTs) and carbon nanotubes doped with different elements, carbon tubes have attracted attention because of their unique structures and their excellent properties, and when doped with different elements, the structures of six rings of carbon nanotubes are changed to some extent so that their properties are changed or improved. Carbon nanotube materials have wide applications in electronic and optical devices, electrochemistry, thermal conduction, and the like. Nitrogen atoms are doped into the crystal lattice of the carbon nano tube, so that the stability of the CNT structure is reduced, the periphery of N atoms in the structure is in a multi-electron state, ionic bonds between N-C atoms are enhanced, the covalency is weakened, the surface alkalinity is enhanced, and the adsorption performance of the surface of the carbon nano tube is changed: the high electron cloud density of nitrogen atoms doped in the carbon nanotube lattice also results in unique properties of the carbon nanotube in terms of electrons, materials and electrochemistry, and creates good conditions for improving electron transport and mass transport of the CNT material.
The existing techniques for preparing nitrogen-doped carbon nanotubes mainly include high-temperature solid-phase reaction, chemical vapor deposition, arc discharge, hydrothermal method, high-temperature thermal decomposition and the like. CN 104176724B provides a preparation method of a nitrogen-doped carbon nanotube, which comprises the steps of firstly, uniformly mixing oxalic acid, water and metal salt to obtain a first mixed solution, then, mixing the obtained first mixed solution with melamine to obtain a second mixed solution, then, refluxing to obtain a suspension of a compound of melamine oxalate and metal oxalate, finally, carrying out suction filtration, washing and drying to obtain a precursor compound, then, carrying out calcination treatment at 600-900 ℃ under a nitrogen atmosphere to obtain a primary product, and finally, removing metal impurities introduced in the preparation process through acid treatment to obtain the nitrogen-doped carbon nanotube.
CN 108190862 a provides a Microwave Plasma Chemical Vapor Deposition (MPCVD) method for preparing nitrogen-doped carbon nanotube material. And doping plasmas generated by exciting the introduced nitrogen gas into the carbon nano tube, exciting reaction gas by using the nitrogen gas as a nitrogen source and generating the plasmas by using microwaves, and nitriding the carbon nano tube on the platinum substrate to finally obtain the nitrogen-doped carbon nano tube material with different contents.
However, these methods generally have many steps, long time consumption, difficult control of reaction time and degree, low nitrogen doping efficiency and easy introduction of impurity elements. Resulting in difficulty in preparing a carbon nanotube material doped with high nitrogen content, thereby limiting the wide application of nitrogen-doped carbon nanotubes.
Disclosure of Invention
In order to solve the problems of complex equipment, complex process, complex and time-consuming operation, low product utilization rate, low nitrogen doping content caused by the loss of a large amount of nitrogen doping precursors in the nitrogen doping process and the like in the preparation of the nitrogen-doped carbon nanotube material in the prior art, the invention provides a method for efficiently, quickly and massively synthesizing the high-nitrogen-content doped carbon nanotube material.
In order to achieve the above technical objects, a first aspect of the present invention provides a method for preparing a nitrogen-doped carbon nanotube material, comprising the steps of:
(1) dispersing the acidified carbon nano tube in a formaldehyde aqueous solution to obtain a dispersion liquid A;
(2) dispersing melamine into deionized water to obtain a dispersion liquid B;
(3) mixing the dispersion liquid A and the dispersion liquid B, heating to 50-80 ℃ for reaction for 10-60min, adjusting the pH of the reaction liquid to 7-9, heating in a sealed environment to 100-200 ℃ for hydrothermal reaction for 5-30 h, filtering, and drying to obtain black solid powder;
(4) and (4) placing the black solid powder obtained in the step (3) in a microwave reaction cavity, and heating for 1-60min at the microwave power of 300-1200W to obtain the nitrogen-doped carbon nanotube material.
In the above-mentioned production method, the concentration of the aqueous formaldehyde solution in the step (1) is not particularly limited, and in a preferred embodiment of the present invention, the concentration of formaldehyde is 37% to 40% by mass. Mixing the acidified carbon nano tube with formaldehyde solution according to the solid-to-liquid ratio of 1g (10-100) mL. Preferably, the mixture is uniformly mixed and dispersed in an ultrasonic mode, and the ultrasonic time is 5-30 min.
In the above preparation method, it should be understood by those skilled in the art that the acidified carbon nanotube is obtained by acidifying and modifying a carbon nanotube with a strong acid, and the acidifying and modifying of the carbon nanotube are well known to those skilled in the art, so long as the purpose of changing the kind and concentration of the functional group on the surface of the carbon nanotube to improve the water solubility thereof can be achieved, thereby satisfying the requirements of the present invention for the acidified carbon nanotube. For example, the carbon nanotubes are subjected to an acidification modification treatment with mixed acids (concentrated sulfuric acid and concentrated nitric acid, concentrated nitric acid and concentrated hydrochloric acid).
Among them, as a more specific embodiment, carbon nanotubes having the following properties are preferable in the selection of materials: diameter of 10-300nm, length of 2-30 μm, and specific surface area>100m2Per g, conductivity>100s/cm。
In the above production method, the dispersion liquid a and the dispersion liquid B are mixed in the step (3), and the dispersion liquid a is preferably poured into the dispersion liquid B. Mixing the acidified carbon nanotubes in the dispersion A and the melamine in the dispersion B in a ratio of 1:1-20 by weight. After mixing, the mixture is preferably mixed and dispersed uniformly in an ultrasonic mode, and the ultrasonic time is 5-30 min.
In the above preparation method, the pH of the reaction solution in the step (3) may be adjusted by using an organic base or an inorganic base, and as a more specific embodiment, the pH is selected from one or more of methylamine, ethylamine, ethylenediamine, propylamine, isopropylamine, triethanolamine, aniline, cyclohexylamine, o-aminophenol, 2-chlorophenol, potassium carbonate, sodium bicarbonate, potassium hydroxide, and sodium hydroxide.
In the preparation method, the hydrothermal reaction temperature in the step (3) is preferably 120-160 ℃, and the time is preferably 12-18 h.
In the preparation method, the power of the microwave reaction in the step (4) is preferably 600-1000W, and the time is preferably 10-30 min.
In the preparation method, the microwave reaction cavity is purged by nitrogen or inert gas before and during the microwave reaction, and preferably, argon is used for purging.
The technical purpose of the second aspect of the invention is to provide the nitrogen-doped carbon nanotube material prepared by the above method. In the preparation process of the method, formaldehyde and melamine are mixed firstly to generate moderate crosslinking reaction to form a water-soluble nitrogen-doped precursor, and then hydrothermal reaction is carried out to carry out nitrogen doping on the carbon nano tube, so that the nitrogen-doped precursor and the carbon nano tube are easy to interact, conditions are created for uniformly fusing the composite material, and the nitrogen-doped process is more favorably realized; the subsequent microwave reaction has high heating speed and uniform heating, the nitrogen-doped precursor is heated and decomposed, and the carbon nano tube and the nitrogen-doped precursor are uniformly fused together in the previous preparation process, so that the nitrogen doping of the carbon nano tube is more uniform, and the synthesis of the high-content nitrogen-doped carbon nano tube is facilitated.
The technical purpose of the third aspect of the invention is to provide application of the nitrogen-doped carbon nanotube material, wherein the material can be used as a lithium ion battery cathode material and shows good cycle stability and rate capability.
Compared with the prior art, the invention has the following advantages:
(1) according to the invention, formaldehyde is used as a bridge in the preparation process of the nitrogen-doped carbon nanotube material, so that the formaldehyde and melamine are properly crosslinked to form the nitrogen-doped precursor, and the problem of low nitrogen-doping efficiency caused by large loss of the nitrogen-doped precursor due to strong sublimation of the nitrogen-doped precursor in the heating process in the traditional solid nitrogen-doping reaction is solved.
(2) In the preparation process, the formaldehyde and the melamine are subjected to a cross-linking reaction to form the water-soluble nitrogen-doped precursor, so that the nitrogen-doped precursor and the carbon nano tube are interacted and uniformly fused in the subsequent hydrothermal reaction, and the preparation of the high-nitrogen-content doped carbon nano tube material is realized.
(3) In the microwave reaction stage in the preparation process, the heating speed is high, the heating is uniform, on one hand, the loss caused by sublimation of the nitrogen-doped precursor due to slow temperature rise in the traditional reaction can be avoided, on the other hand, the nitrogen-doped precursor is heated and decomposed under the microwave condition, and as the carbon nano tubes and the nitrogen-doped precursor are uniformly fused together in the previous hydrothermal reaction process, the nitrogen doping of the carbon nano tubes is more uniform, and the synthesis of the high-nitrogen-content doped carbon nano tubes is more facilitated.
(4) The microwave reaction in the preparation process adopts a solvent-free treatment mode, so that the post-treatment processes of washing, separating, drying and the like of the product are omitted, and the production process is simplified.
(5) The nitrogen-doped carbon nanotube material prepared by the method has good stability, is not easy to denature in air, is easy to store, has a large specific surface area, is used as a lithium ion battery cathode material, provides a good channel for lithium ion transmission, and shows a large specific capacity and a good cycling stability performance.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
FIG. 1 is an SEM image of acidified carbon nanotubes prepared according to the present invention;
FIG. 2 is an SEM image of nitrogen-doped carbon nanotube material prepared in example 8;
FIG. 3 shows the current density of 100mA g for the N-doped carbon nanotube material of example 8-1Time charge and discharge cycle curve.
Detailed Description
The following non-limiting examples are presented to enable those of ordinary skill in the art to more fully understand the present invention and are not intended to limit the invention in any way.
The acidified carbon nanotubes used in the following examples were prepared by the following method:
the carbon nanotubes used had the following properties: the carbon nanotube has a diameter of 10-300nm, a length of 2-30 μm, and a specific surface area>100m2Per g, conductivity>100s/cm。
Preparing acidified carbon nanotubes: filling 1g of carbon nanotube and 200mL of concentrated sulfuric acid into a three-neck flask, ultrasonically dispersing uniformly, slowly dropwise adding 60mL of concentrated nitric acid with the concentration of 70%, refluxing and stirring for 1h at 60 ℃, naturally cooling to room temperature, adding a large amount of deionized water for dilution, standing for layering, removing supernatant, dialyzing black precipitate at the bottom by using deionized water, replacing small molecules in the black precipitate, balancing the surface of the black precipitate, and obtaining the carbon nanotube aqueous dispersion which can be stably and uniformly dispersed for a long time. Freeze-drying the carbon nanotube aqueous dispersion to obtain acidified carbon nanotube powder, and placing the acidified carbon nanotube powder in a dryer for later use. The SEM image is shown in figure 1, the one-dimensional carbon nanotube structure can be clearly seen, the carbon nanotube wall after acidification treatment is smoother, the length of the tube is more than 3 mu m, and the tube diameter is 50nm-300 nm.
The nitrogen-doped carbon nanotube material of the present invention was prepared in examples 1 to 8:
example 1
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 20mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed to obtain dispersion A.
(2) 3.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) Mixing the dispersion A and the dispersion B, heating in water bath to 60 ℃, and stirring for 10 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 8.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 120 ℃ for reaction for 12 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating for 10min with the microwave power of 600W to obtain the nitrogen-doped carbon nanotube material.
Example 2
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed to obtain dispersion A.
(2) 5.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) Mixing the dispersion A and the dispersion B, heating in water bath to 60 ℃, and stirring for 10 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 8.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 120 ℃ for reaction for 12 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating for 10min with the microwave power of 600W to obtain the nitrogen-doped carbon nanotube material.
Example 3
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed to obtain dispersion A.
(2) 10.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) Mixing the dispersion A and the dispersion B, heating in water bath to 70 ℃, and stirring for 10 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 8.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 120 ℃ for reaction for 12 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. And heating for 20min at the microwave power of 600W to obtain the nitrogen-doped carbon nanotube material.
Example 4
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed to obtain dispersion A.
(2) 10.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) Mixing the dispersion A and the dispersion B, heating in water bath to 70 ℃, and stirring for 20 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 8.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 120 ℃ for reaction for 12 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating for 30min with the microwave power of 600W to obtain the nitrogen-doped carbon nanotube material.
Example 5
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed to obtain dispersion A.
(2) 10.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) Mixing the dispersion A and the dispersion B, heating in water bath to 70 ℃, and stirring for 20 min. And then adding potassium hydroxide into the reaction liquid, adjusting the pH value of a reaction liquid system to 9.0, carrying out ultrasonic mixing uniformly, then pouring the reaction liquid into a high-pressure reaction kettle, and heating to 120 ℃ for reaction for 12 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating for 10min with the microwave power of 800W to obtain the nitrogen-doped carbon nanotube material.
Example 6
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed to obtain dispersion A.
(2) 10.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) Mixing the dispersion A and the dispersion B, heating in water bath to 80 ℃, and stirring for 30 min. And then adding potassium hydroxide into the reaction liquid, adjusting the pH value of a reaction liquid system to 9.0, carrying out ultrasonic mixing uniformly, then pouring the reaction liquid into a high-pressure reaction kettle, and heating to 140 ℃ for reaction for 15 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating for 10min with the microwave power of 800W to obtain the nitrogen-doped carbon nanotube material.
Example 7
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed to obtain dispersion A.
(2) 10.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) Mixing the dispersion A and the dispersion B, heating in water bath to 80 ℃, and stirring for 30 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 9.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 160 ℃ for reaction for 15 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating for 10min with the microwave power of 800W to obtain the nitrogen-doped carbon nanotube material.
Example 8
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed to obtain dispersion A.
(2) 10.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) Mixing the dispersion A and the dispersion B, heating in water bath to 80 ℃, and stirring for 30 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 9.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 160 ℃ for reacting for 18 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. And heating for 30min at the microwave power of 1000W to obtain the nitrogen-doped carbon nanotube material.
The SEM image of the nitrogen-doped carbon nanotube material obtained in example 8 is shown in fig. 2, which clearly shows that the one-dimensional carbon nanotube structure has a curled nitrogen-doped carbon nanotube, the length of the tube is greater than 2 μm, and the tube diameter is 50nm to 300 nm.
Comparative example 1
In the step (1), formaldehyde solution is not used, and deionized water is used for replacing:
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 30mL of deionized water, and placed in an ultrasonic instrument to be uniformly dispersed, and the dispersion A was recorded.
(2) 10.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) Mixing the dispersion A and the dispersion B, heating in water bath to 80 ℃, and stirring for 30 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 9.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 160 ℃ for reacting for 18 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating the substrate for 30min at the microwave power of 1000W to obtain the comparative nitrogen-doped carbon nanotube material.
Comparative example 2
And (3) adjusting the pH value of the reaction solution without adding alkali liquor, and directly carrying out hydrothermal reaction after uniformly mixing the dispersion solution A and the dispersion solution B:
(1) 1.0g of acidified carbon nanotubes was weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed to obtain dispersion A.
(2) 10.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.
(3) And mixing the dispersion liquid A and the dispersion liquid B, uniformly mixing by ultrasonic waves, pouring the reaction liquid into a high-pressure reaction kettle, and heating to 160 ℃ for reacting for 18 hours. And (4) carrying out suction filtration and vacuum drying to obtain black solid powder.
(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating the substrate for 30min at the microwave power of 1000W to obtain the comparative nitrogen-doped carbon nanotube material.
The materials of examples 1-8, comparative example 1 and comparative example 2 were used as negative electrode materials for lithium ion batteries. The synthesized nitrogen-doped carbon nanotube is used as an active component, a 2016 type battery shell, a metal lithium sheet (phi 16 mm multiplied by 1mm) and 1.0M LiPF are selected6The mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DEC) (volume ratio of 1:1) is used as electrolyte, and Celgard2300 microporous polypropylene coal membrane is used as battery diaphragm. The materials are assembled into a button cell in a glove box filled with Ar gas, and the test is carried out after the working electrode is fully soaked by the electrolyte. The method comprises the following five steps:
(1) size mixing
The material used has a large specific surface and is easy to adsorb moisture in the air, so the material for preparing the electrode is firstly dried fully in a vacuum drying oven at 120 ℃ to remove the surface moisture. Then adding an active substance, a conductive additive (acetylene black) and a binder (PVDF) into the dispersant according to the mass percentage of 80:10:10N-methylpyrrolidone (NMP) mixed grinding, resulting in uniform mixing of the materials, making a viscous slurry.
(2) Coating film
The resulting viscous paste was uniformly coated on a copper foil (thickness of about 100 μm). The specific operation is as follows: 1) the copper foil of moderate size is cut and laid flat on a table top. 2) Removing stains on the surface of the copper foil. 3) The slurry was dispersed on a copper foil and uniformly spread on the copper foil using a die. 4) The copper foil coated with the slurry was dried in a vacuum drying oven at 120 ℃ for 12 hours.
(3) Roller compaction
After the completion of drying, the copper foil coated with the slurry was rolled with a small-sized rolling machine to prevent the electrode material from falling off from the surface of the copper foil.
(4) Tabletting
And cutting the rolled film into a plurality of circular electrode slices with the diameter of 12mm by using a manual slicer. In order to prevent the coating film from falling off during charge and discharge cycles, it was pressed into a sheet by an oil press. And taking out and weighing after drying, and waiting for battery loading.
(5) Assembled battery
The process of assembling the button cells was carried out in a glove box filled with Ar gas. The battery is assembled according to the sequence of negative battery shell/electrolyte/working electrode plate/electrolyte/diaphragm/lithium plate/positive battery shell. And standing for 24 hours, and carrying out electrochemical test after the electrolyte is fully soaked.
And carrying out charge and discharge tests on the assembled button type simulation battery. The material of example 8 was used at a voltage in the range of 0.01 to 3.0V and at a current of 100mA g-1The results of the cycle stability test at the current density of (a) are shown in fig. 3. The nitrogen content in the electrode materials of examples 1-8 and comparative examples 1-2, the corresponding first charge-discharge capacity and the discharge capacity after 100 charge-discharge tests are shown in table 1. Wherein the content of nitrogen element is determined by element analysis.
The test data show that the invention improves the nitrogen doping content in the carbon nano tube, and the nitrogen content can reach 5.1 percent at most; secondly, the specific capacity of the button cell for the first discharge is increased, and the first discharge capacity in the embodiment 8 can reach 417.2 mAh.g-1Compared with the comparative example 1, the reversible capacity retention rate is increased by about 15.4%, compared with the comparative example 2, the reversible capacity retention rate is increased by about 13.2%, and the reversible capacity is still kept high after 100 times of circulation, the reversible capacity retention rate exceeds 80.0% and is up to 90.7%, which shows that the material prepared by the invention has high reversible capacity and good cycle performance.
TABLE 1
Figure DEST_PATH_IMAGE001

Claims (10)

1. A preparation method of a nitrogen-doped carbon nanotube material comprises the following steps:
(1) dispersing the acidified carbon nano tube in a formaldehyde aqueous solution to obtain a dispersion liquid A;
(2) dispersing melamine into deionized water to obtain a dispersion liquid B;
(3) mixing the dispersion liquid A and the dispersion liquid B, heating to 50-80 ℃ for reaction for 10-60min, adjusting the pH of the reaction liquid to 7-9, heating in a sealed environment to 100-200 ℃ for hydrothermal reaction for 5-30 h, filtering, and drying to obtain black solid powder;
(4) and (4) placing the black solid powder obtained in the step (3) in a microwave reaction cavity, and heating for 1-60min at the microwave power of 300-1200W to obtain the nitrogen-doped carbon nanotube material.
2. The preparation method according to claim 1, wherein the acidified carbon nanotubes are mixed with the aqueous formaldehyde solution in the step (1) at a solid-to-liquid ratio of 1g to 10-100 mL.
3. The method according to claim 1, wherein the dispersion A and the dispersion B are mixed in the step (3) by pouring the dispersion A into the dispersion B.
4. The method according to claim 1, wherein the dispersion liquid A and the dispersion liquid B are mixed in the step (3), and the ratio of the acidified carbon nanotubes in the dispersion liquid A to the melamine in the dispersion liquid B is 1:1-20 by weight.
5. The method according to claim 1, wherein an organic base or an inorganic base is used for adjusting the pH of the reaction solution in the step (3).
6. The method of claim 1, wherein the base is selected from one or more of methylamine, ethylamine, ethylenediamine, propylamine, isopropylamine, triethanolamine, aniline, cyclohexylamine, o-aminophenol, 2-chlorophenol, potassium carbonate, sodium bicarbonate, potassium hydroxide, and sodium hydroxide.
7. The preparation method according to claim 1, wherein the hydrothermal reaction in the step (3) is carried out at a temperature of 120 to 160 ℃ for 12 to 18 hours.
8. The preparation method according to claim 1, wherein the microwave reaction in the step (4) has a power of 600-1000W and a time of 10-30 min.
9. The nitrogen-doped carbon nanotube material prepared by the method of any one of claims 1 to 8.
10. Use of the nitrogen-doped carbon nanotube material of claim 9 as a negative electrode material for a lithium ion battery.
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