阅读说明：本技术 一种片状Fe基合金催化生长碳纳米管阵列的制备方法 (Preparation method of flaky Fe-based alloy catalytic growth carbon nanotube array ) 是由 简贤 吴龙伟 张兴中 李元勋 苏桦 舒剑 于 2021-01-21 设计创作，主要内容包括：一种片状Fe基合金催化生长碳纳米管阵列的制备方法,属于新材料技术、锂离子二次电池领域。包括以下步骤：1)片状Fe基合金置于CVD旋转炉内,通入氮气或者惰性气体；2)启动CVD旋转炉,炉内温度升至450～550℃,向炉内通入乙炔气体,反应30min后,停止乙炔气体的通入,得到长有碳纳米管阵列的Fe基合金；3)酸洗处理去除Fe基合金,得碳纳米管阵列。本发明通过控制工艺条件有效的调控碳纳米管阵列的生长,成功的实现了基底、缓冲层、催化剂层三合一制备出碳纳米管阵列；制备工艺条件温和,方法简单,有利于大规模的制备,具有很好的商业价值；制得的碳纳米管应用于锂离子电池负极,有良好的稳定性、较高的可逆比容量。(A preparation method for a flaky Fe-based alloy catalytic growth carbon nanotube array belongs to the field of new material technology and lithium ion secondary batteries. The method comprises the following steps: 1) placing the sheet Fe-based alloy in a CVD (chemical vapor deposition) rotary furnace, and introducing nitrogen or inert gas; 2) starting a CVD (chemical vapor deposition) rotary furnace, raising the temperature in the furnace to 450-550 ℃, introducing acetylene gas into the furnace, reacting for 30min, and stopping introducing the acetylene gas to obtain the Fe-based alloy with the carbon nanotube array; 3) and (4) removing the Fe-based alloy by acid washing to obtain the carbon nano tube array. The invention effectively regulates and controls the growth of the carbon nanotube array by controlling the process conditions, and successfully realizes the three-in-one preparation of the carbon nanotube array by the substrate, the buffer layer and the catalyst layer; the preparation process has mild conditions and simple method, is beneficial to large-scale preparation and has good commercial value; the prepared carbon nano tube is applied to the negative electrode of the lithium ion battery, and has good stability and higher reversible specific capacity.)

1. A preparation method of a flaky Fe-based alloy catalytic growth carbon nanotube array is characterized by comprising the following steps:

step 1, placing a sheet Fe-based alloy into a CVD (chemical vapor deposition) rotary furnace, and introducing nitrogen or inert gas with the gas flow of 30-60 ml/min into the furnace to evacuate air in the tube;

step 2, starting the CVD rotary furnace, and raising the temperature in the furnace to 450-550 ℃; then, introducing acetylene gas with the gas flow of 30-60 ml/min into the furnace, and reacting for 30 min; after the reaction is finished, stopping introducing the acetylene gas, naturally cooling to room temperature, and taking out to obtain the Fe-based alloy with the carbon nanotube array;

and 3, carrying out acid washing treatment on the Fe-based alloy with the carbon nanotube array grown in the step 2 to remove the Fe-based alloy, thus obtaining the carbon nanotube array.

2. The method for preparing the flaky Fe-based alloy catalytic growth carbon nanotube array according to claim 1, wherein the flaky Fe-based alloy in the step 1 is FeNiSi, FeNiCr, FeSiAl or FeCrMn.

3. The preparation method of the flaky Fe-based alloy catalytic growth carbon nanotube array according to claim 1, wherein the average particle size of the flaky Fe-based alloy in the step 1 is 70-100 μm, and the average thickness of the flaky Fe-based alloy is 1.5-2 μm.

4. The preparation method of the flaky Fe-based alloy catalytic growth carbon nanotube array according to claim 1, wherein the temperature in the furnace is increased to 450-550 ℃ in the step 2 at a temperature increase rate of 5-15 ℃/min.

5. The preparation method of the flaky Fe-based alloy catalytic growth carbon nanotube array according to claim 1, wherein the pickling treatment process in the step 3 specifically comprises the following steps: firstly, soaking a Fe-based alloy with a carbon nanotube array in a nitric acid solution for 48 hours, then diluting the Fe-based alloy with deionized water, and repeatedly performing suction filtration until the Fe-based alloy is neutral; then, drying and grinding the sample treated by the nitric acid, soaking the sample in hydrofluoric acid for 48 hours, and then repeatedly performing suction filtration by using deionized water until the sample is neutral; and finally, drying and grinding to obtain the carbon nano tube array.

6. Use of the carbon nanoarrays obtained by the method of any one of claims 1 to 5 in the negative electrode of a lithium ion battery.

Technical Field

The invention belongs to the field of new material technology and lithium ion secondary batteries, and particularly relates to a method for preparing a carbon nanotube array on the surface of Fe-based alloy by catalytic chemical vapor deposition and application of the carbon nanotube array in a lithium ion secondary battery.

Background

Since the discovery of carbon nanotubes, there has been a wide range of interest due to their unique geometry and electronic structure. Meanwhile, the material has the characteristics of good mechanical property, large length-diameter ratio, large specific surface area, high conductivity and the like, so that the material is widely applied to the fields of sensors, flat panel displays, supercapacitors, lithium ion batteries and the like. Particularly for the lithium ion battery, the maximum theoretical specific capacity of the graphite negative electrode material of the traditional lithium ion battery is only 372mAh g^-1For the electronic age developing rapidly at present, the performance of the anode material is not enough to meet the current demand, so that the anode material with simple preparation method, high stability and excellent performance is urgently needed. Although many negative electrode materials have been developed, including silicon negative electrode materials, metal oxide negative electrode materials, silicon-carbon composite negative electrode materials, metal alloy negative electrode materials, and the like, carbon materialsThe material is still an ideal material in the field of energy storage due to the characteristics of excellent performance, low price, simple preparation and the like. Among all carbon materials, the carbon nano tube has excellent conductivity and lithium storage performance, and has a very small diameter, so that lithium can be more conveniently inserted and removed, and the carbon nano tube becomes an especially important topic in replacing the traditional lithium ion battery cathode graphite material.

Compared with disordered carbon nanotubes, the carbon nanotube array is more ordered and more stable in length-diameter ratio, and has better performance when applied to lithium ion batteries, so that the preparation of the carbon nanotube array is an extremely hot topic. At present, the preparation methods of carbon nanotube arrays mainly include two methods: physical methods and chemical methods. The physical methods mainly include the conventional Arc discharge method (Arc discharge) and Laser Ablation (Laser Ablation), but the prepared carbon nanotubes are disordered and intertwined, and the directional arrangement of the carbon nanotubes needs to be realized by virtue of the specific properties (magnetism and self-assembly performance) of the carbon nanotubes. Due to the limitation of the physical method for preparing the carbon nanotube array, the synthesis process of the carbon nanotube is controlled to regularly and directionally grow, or the directionally ordered carbon nanotube array is directly obtained on the substrate, and even the controllability of the length, the pipe diameter, the density, the growth direction and the like of the carbon nanotube can be realized by changing the process parameters, so that the method becomes the hotspot of research of people gradually. The methods for preparing the oriented carbon nanotube array are generally called chemical methods, and mainly grow the ordered carbon nanotube array on a substrate directly by a Chemical Vapor Deposition (CVD) technology. The chemical method mainly comprises the following steps: template methods, Plasma Enhanced Chemical Vapor Deposition (PECVD), photo-assisted chemical vapor deposition, electric field induction, substrate methods, and the like. Among these methods, the substrate method is currently the most promising and widely used method, and can be classified into a solid catalyst method and a floating catalyst method according to the catalyst. The solid catalyst method is that a substrate is respectively coated with a buffer layer and a catalyst by the techniques of electron beam evaporation, magnetron sputtering, thermal evaporation and the like, and then the substrate is placed in a reaction furnace to prepare a carbon nano tube array; the floating catalyst method is to mix a catalyst and a liquid carbon source to be used as a precursor solution, introduce the precursor solution into a reaction chamber in a gas form, and perform catalytic pyrolysis to form the carbon nano tube. Generally, although there are many methods for preparing carbon nanotube arrays at present, there are some disadvantages, such as the preparation method is simple, but the prepared carbon nanotube arrays are intertwined and have a high degree of disorder, or the process for preparing the carbon nanotube arrays is too complicated, which is not suitable for mass preparation. Therefore, a method which is simple and low in cost and can be used for mass production of the carbon nanotube array is still an important research topic.

Disclosure of Invention

The invention aims to provide a preparation method for catalytically growing a carbon nanotube array on Fe-based alloy by a catalytic chemical vapor deposition method aiming at the defects in the background art. The invention adopts the sheet Fe-based alloy material to carry out carbon deposition by a Catalytic Chemical Vapor Deposition (CCVD) method, and realizes the three-in-one preparation of the carbon nanotube array with good compactness and good growth vigor by the substrate, the buffer layer and the catalyst layer. The large length-diameter ratio of the carbon nano tube enables the lithium ions to have small embedding depth, short stroke and many embedding positions (gaps, holes and the like between the inner layer and the interlayer of the tube), and simultaneously, the carbon nano tube has good conductivity, has good electron conductivity and ion transport capacity, and is suitable for being used as a lithium ion battery cathode material. Compared with the traditional graphite cathode, the performance of the graphite cathode is obviously improved, and the graphite cathode has a good application prospect in the application of lithium ion batteries.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a preparation method of a flaky Fe-based alloy catalytic growth carbon nanotube array is characterized by comprising the following steps:

step 1, placing the sheet Fe-based alloy in a CVD rotary furnace, introducing nitrogen or inert gas of 10-30 ml/min, and detecting the air tightness of the device, wherein if no problem exists, introducing nitrogen or inert gas with the gas flow of 30-60 ml/min into the furnace for 10min to exhaust the air in the tube.

Step 2, starting the CVD rotary furnace, and raising the temperature in the furnace to 450-550 ℃ at a temperature raising rate of 5-15 ℃/min under the atmosphere of nitrogen or inert gas; then, keeping the continuous introduction of nitrogen or inert gas, introducing acetylene gas with the gas flow of 30-60 ml/min into the furnace as a carbon source gas, and reacting for 30 min; and after the reaction is finished, keeping the continuous introduction of nitrogen or inert gas and stopping the introduction of acetylene gas, naturally cooling to room temperature, taking out the product, and finishing the catalytic growth of the sheet Fe-based alloy into the carbon nanotube array to obtain the Fe-based alloy material with the carbon nanotube array. Catalytic Chemical Vapor Deposition (CCVD) reaction mechanism: the principle is that carbon source gas contacts with catalyst particles and is cracked to obtain carbon atoms, the carbon atoms are dissolved in the catalyst particles, and when the dissolution limit is reached, the carbon nanotubes with tubular meshes are crystallized and separated on the surface of the catalyst particles.

And 3, carrying out acid washing treatment on the Fe-based alloy with the carbon nanotube array obtained in the step 2 to remove Fe-based alloy impurities: firstly, soaking the Fe-based alloy with the carbon nanotube array in a nitric acid solution with the concentration of 38% for 48 hours, then diluting the Fe-based alloy with deionized water, and repeatedly performing suction filtration until the Fe-based alloy is neutral; then, drying and grinding the sample treated by the nitric acid, soaking the sample in hydrofluoric acid for 48 hours, and then repeatedly performing suction filtration by using deionized water until the sample is neutral; and finally, drying and grinding to obtain the carbon nano tube array.

Further, the flaky Fe-based alloy in the step 1 is FeNiSi, FeNiCr, FeSiAl, FeCrMn or the like.

Furthermore, the average grain diameter of the flaky Fe-based alloy in the step 1 is 70-100 μm, and the average thickness is 1.5-2 μm.

Further, in the step 1, the inert gas is argon, nitrogen or inert gas is used as a protective gas, and the inert gas is continuously introduced from the beginning of heating to the end of the reaction.

The invention also provides the application of the carbon nanotube array prepared by the method, and the prepared carbon nanotube array has good stability and higher reversible specific capacity when being applied as the cathode of the lithium ion battery, and is a popular material for replacing the graphite cathode.

The invention provides a preparation method of a carbon nano tube array, which has the following principle: by utilizing the reaction mechanism of Catalytic Chemical Vapor Deposition (CCVD), carbon source gas contacts with hot catalyst particles and is cracked to obtain carbon atoms, the carbon atoms are dissolved in the catalyst particles, and when the dissolution limit is reached, the carbon atoms are crystallized and separated out to form the carbon nano tubes in a net tube shape on the surface of the catalyst particles. The carbon nanotube array prepared by the method has good growth vigor and compactness, and simultaneously has a large length-diameter ratio, so that the insertion path of lithium ions is effectively shortened, the insertion proportion of the lithium ions is increased, and the performance of the lithium ion battery is improved.

Compared with the prior art, the invention has the beneficial effects that:

the carbon nanotube array prepared by the method is realized by a Catalytic Chemical Vapor Deposition (CCVD), the growth of the carbon nanotube array can be effectively regulated and controlled by controlling the process conditions, and the carbon nanotube array is successfully prepared by three-in-one of the substrate, the buffer layer and the catalyst layer; the preparation process has mild conditions and simple preparation method, is beneficial to large-scale preparation and has good commercial value; meanwhile, the carbon nano tube prepared by the method is applied to the negative electrode of the lithium ion battery, and has good stability and higher reversible specific capacity.

Drawings

FIG. 1 is an SEM image of a carbon nanotube array catalytically grown by using a sheet Fe-based alloy FeSiAl as a catalyst in an embodiment of the present invention; wherein (a) is a sheet-shaped Fe-based alloy FeSiAl without a carbon nanotube array growing, (b) is the carbon nanotube array obtained in example 1, (c) is the carbon nanotube array obtained in example 2, and (d) is the carbon nanotube array obtained in example 3;

FIG. 2 is a Raman diagram of a sheet Fe-based alloy material grown with carbon nanotubes according to an embodiment of the present invention;

FIG. 3 is XRD patterns of a flake Fe-based alloy (a) with carbon nanotubes grown thereon before pickling and a carbon nanotube array (b) after pickling according to example 3 of the present invention;

fig. 4 is a CV curve of the carbon nanotube array prepared in example 3 of the present invention applied to a lithium ion battery;

fig. 5 is a first charge-discharge curve of the carbon nanotube array prepared in example 3 of the present invention at a current density of 50mAh/g when applied to a lithium ion battery;

fig. 6 is a constant current charge/discharge performance diagram at a current density of 50mAh/g when the carbon nanotube array prepared in embodiment 3 of the present invention is applied to a lithium ion battery;

fig. 7 is a constant current charge/discharge performance diagram of the carbon nanotube array prepared in example 3 of the present invention at a large current density of 1Ah/g when applied to a lithium ion battery.

Detailed Description

The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and examples.

Example 1

A method for preparing a carbon nanotube array by chemical vapor deposition comprises the following steps:

step 1, placing 5g of sheet Fe-based alloy FeSiAl in a CVD rotary furnace, opening an argon gas cylinder, introducing 20mL/min of argon gas, detecting the air tightness of the device, and if no problem exists, introducing 60mL/min of argon gas into the furnace for 10min to exhaust air in the tube.

Step 2, starting the CVD furnace, and raising the temperature in the furnace to 450 ℃ at a temperature rise rate of 10 ℃/min under the argon atmosphere; and then, keeping the continuous introduction of argon, introducing acetylene gas with the flow rate of 40mL/min into the furnace as reaction gas, reacting for 30min, stopping the introduction of the acetylene gas after the reaction is finished, naturally cooling to room temperature, and taking out a product to obtain the sheet Fe-based alloy material with the carbon nano tubes. Named Fe-based alloy FSA @ CNT-450 ℃;

and 3, carrying out acid washing treatment on the flaky Fe-based alloy material with the carbon nano tubes obtained in the step 2 to remove Fe-based alloy impurities: firstly, soaking the Fe-based alloy with the carbon nanotube array in a nitric acid solution with the concentration of 38% for 48 hours, then diluting the Fe-based alloy with deionized water, and repeatedly performing suction filtration until the Fe-based alloy is neutral; then, drying and grinding the sample treated by the nitric acid, soaking the sample in hydrofluoric acid with the concentration of 40% for 48 hours, and then repeatedly performing suction filtration by using deionized water until the sample is neutral; and finally, drying and grinding to obtain the carbon nano tube array after acid washing.

Example 2

This example is different from example 1 in that: in the step 2, the temperature in the furnace is increased to 500 ℃ at the temperature increase rate of 10 ℃/min; the rest of the procedure was the same as in example 1. The obtained Fe-based alloy material with the carbon nano tube is named as Fe-based alloy FSA @ CNT-500 ℃.

Example 3

This example is different from example 1 in that: in the step 2, the temperature in the furnace is increased to 550 ℃ at the temperature increasing rate of 10 ℃/min; the rest of the procedure was the same as in example 1. The obtained Fe-based alloy material with the carbon nano tube is named as Fe-based alloy FSA @ CNT-550 ℃.

FIG. 1 is an SEM image of a carbon nanotube array catalytically grown by using a sheet Fe-based alloy FeSiAl as a catalyst in an embodiment of the present invention; wherein (a) is a sheet-like Fe-based alloy fesai on which a carbon nanotube array is not grown, (b) is the carbon nanotube array obtained in example 1, (c) is the carbon nanotube array obtained in example 2, and (d) is the carbon nanotube array obtained in example 3. As shown in FIG. 1, the flaky Fe-based alloy FeSiAl has good catalytic effect, and the orderly-arranged carbon nanotube array is successfully prepared on the surface of the flaky Fe-based alloy.

FIG. 2 is a Raman diagram of a sheet Fe-based alloy material grown with carbon nanotubes according to an embodiment of the present invention; as is obvious from the figure, the Fe-based alloy after the carbon nanotube array is formed has two obvious characteristic peaks of the carbon nanotube, one is at 1300cm^-1Left and right D peak, the other at 1580cm^-1Left and right G peaks.

FIG. 3 is XRD patterns of a flake Fe-based alloy (a) with carbon nanotubes grown thereon before pickling and a carbon nanotube array (b) after pickling according to example 3 of the present invention; as can be seen from fig. 3, the diffraction peaks of the carbon nanotube array after acid washing appear at 26.12 ° and 44.12 ° 2 θ, which correspond to the (002) and (101) crystal planes of carbon, respectively, indicating that the carbon nanotubes after acid washing have good crystallinity and the obtained carbon nanotubes have high purity.

Assembling the battery:

taking the carbon nanotube array material obtained after acid cleaning as an active agent of a lithium ion battery negative electrode material, mixing the active agent with a conductive agent Keqin black and a binder PVDF (polyvinylidene fluoride) in a ratio of 8: 1: 1, then uniformly coating the slurry on a copper foil by using a film hanging device, placing the copper foil in a vacuum oven at 80 ℃ for 12 hours, and finally cutting and pressing to obtain a circular electrode plate with the diameter of 14 mm. And then, installing the battery in a glove box, wherein the battery is installed in the order of a positive electrode shell, a sample pole piece, a diaphragm, a lithium piece, a gasket, a spring piece and a negative electrode shell. The electrolyte is 1.0M lithium hexafluorophosphate (LiPF6) solution, wherein the solvent is a solvent with the volume ratio of 1: 1 Ethylene Carbonate (EC) and dimethyl carbonate (DMC), and a Celgard 2300 membrane is used as the membrane. It should be noted that the cell was installed in a glove box under argon atmosphere and the water oxygen content was all below 0.1ppm, and the half-cell finally obtained was allowed to stand for 24 hours.

Fig. 4 is a cyclic voltammetry test chart of a carbon nanotube array applied to a negative electrode of a lithium ion battery in embodiment 3 of the present invention; the scanning range is 0.01-3V, and the scanning speed is 0.1 mV/s. As can be seen from the figure, in the first scanning cycle, a large irreversible discharge peak is formed near the potential of 1.5V, which mainly corresponds to the formation of the SEI film and the decomposition of the electrolyte, and in the subsequent cycle, the discharge peak disappears, thus proving that in the first cycle, a stable SEI film is formed, which enables the battery to have good charge and discharge stability, and also in the subsequent cycle, the extraction and the insertion of lithium ions respectively correspond to 1.5V and 0.1V, and the CV curves are basically consistent, thus proving that the carbon nanotube has good stability as the negative electrode material of the lithium ion battery.

Fig. 5 is a first charge-discharge curve of the carbon nanotube array prepared in example 3 of the present invention at a current density of 50mAh/g when applied to a negative electrode of a lithium ion battery; as can be seen from the figure, the initial discharge specific capacity reaches 1356mAh/g, and the reversible specific capacity also reaches 447, which is higher than the maximum theoretical specific capacity 372mAh/g of the current commercial graphite cathode material.

Fig. 6 is a constant current charge/discharge performance diagram at a current density of 50mAh/g when the carbon nanotube array prepared in example 3 of the present invention is applied to a lithium ion battery cathode; it can be seen from the figure that when the carbon nanotube material is used as a negative electrode material of a lithium ion battery, the reversible specific capacity of each charge and discharge test is basically close (the specific capacity is maintained at about 440 mAh/g), and further, the material not only has the reversible specific capacity greater than that of the traditional graphite material, but also has excellent stability.

FIG. 7 is a diagram of constant current charging and discharging performance at a large current density of 1Ah/g when the carbon nanotube array prepared in example 3 of the present invention is applied to a lithium ion battery cathode; the result shows that even under large current density, the carbon nano tube array material still has considerable specific capacity as the lithium ion battery cathode material, and the coulombic efficiency is close to one hundred percent, so that the carbon nano tube array material has good cycling stability.