CN113233443A - Preparation method of fluorinated spiral carbon nanotube and application of fluorinated spiral carbon nanotube in lithium primary battery - Google Patents
Preparation method of fluorinated spiral carbon nanotube and application of fluorinated spiral carbon nanotube in lithium primary battery Download PDFInfo
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Abstract
A preparation method of fluorinated helical carbon nano-tubes belongs to the technical field of preparation of carbon fluoride materials. Ferrous tartrate powder is used as a catalyst precursor, and polar molecules are introduced as a catalytic aid to improve the purity and yield of the spiral carbon nanotube; soaking the obtained compound of the spiral carbon nano tube and the catalyst particles in a nitric acid solution to remove the catalyst particles; and carrying out fluorination reaction to obtain the fluorinated spiral carbon nano tube. The shape of the spiral carbon nano tube is regulated and controlled through the preparation process, so that the quantity of the fluorination active sites is regulated and controlled, the fluorination reaction process is finally regulated and controlled, and the conductivity and discharge polarization effect of the material are improved. Meanwhile, the appearance, structure and fluorine-carbon ratio of the fluorinated spiral carbon nano tube are regulated and controlled by optimizing a fluorination process, so that the tube wall of the fluorinated carbon nano tube is cracked or even broken, a diffusion channel is provided for lithium ions, the polarization during discharge is reduced, and the lithium/fluorinated carbon primary battery anode material with high fluorine-carbon ratio and high specific capacity is obtained.
Description
Technical Field
The invention belongs to the technical field of lithium primary batteries and preparation of carbon fluoride nano materials, and particularly relates to a preparation method of a fluorinated spiral carbon nano tube and application of the fluorinated spiral carbon nano tube in a lithium primary battery.
Background
The helical carbon nanotube is a helical carbon nanomaterial obtained by periodically inserting a five-membered carbon ring and a seven-membered carbon ring into a linear carbon nanotube. The unique spiral structure determines that the material has unique properties in the aspects of optics, electrics, magnetics, microwave absorption, mechanics, chemistry and the like, and has great theoretical research and potential application values.
The lithium/carbon fluoride cell is a fluorinated Carbon (CF)x) Is a positive active material, and lithium metal is a negative material. Currently, lithium primary batteries include lithium/manganese dioxide batteries, lithium/sulfur dioxide batteries, lithium/thionyl chloride batteries, lithium/carbon fluoride batteries, and the like. Wherein the theoretical energy density of the lithium/carbon fluoride battery is the highest and is as high as 2180Wh/kg, and the practical specific energy can also reach 250-800 Wh/kg. In addition, the lithium/carbon fluoride battery has the characteristics of wide working temperature range, stable discharge platform, small self-discharge, no pollution and the like. The lithium/carbon fluoride battery is widely used for power supply of individual power source systems, power supply of active implanted medical instruments and the like, is expected to be used as a power supply of missiles and carrier rockets in the future, and has a wide development prospect. However, the major challenges currently limiting the application of lithium/fluorocarbon batteries are: 1. the low conductivity of the carbon fluoride causes the battery to have very large impedance and serious discharge polarization phenomenon; 2. there is an initial voltage delay effect on the discharge. The performance of the carbon fluoride primary battery can be improved by selecting a novel carbon source for fluorination and optimizing the fluorination process. For example, chinese patent 201711435109.8 discloses a lithium/carbon fluoride battery using fluorinated ketjen black as an active material, and the excellent conductivity of ketjen black improves the discharge plateau and rate capability of the battery. However, the above studies did not improve the batterySpecific capacity and voltage hysteresis effect. How to adjust and control the fluorination process to fluorinate a novel carbon source so as to optimize the performance of the lithium/fluorocarbon battery has become a popular research direction in recent years.
Disclosure of Invention
The invention aims to provide a preparation method of a fluorinated spiral carbon nanotube and application of the fluorinated spiral carbon nanotube in a lithium primary battery aiming at the defects in the background art. The method has simple process, and firstly, ferrous tartrate is taken as a catalytic precursor, the difference of carbon growth rates of different crystal faces of the catalyst caused by the catalytic anisotropy of iron nanoparticles generated after hydrogen reduction is utilized, and polar molecules are taken as a catalytic assistant to catalytically grow the carbon nanotube with a spiral structure; then, the five-membered ring and seven-membered ring structures which are periodically arranged are broken through the regulation and control of the fluorination process of the spiral carbon nano tube, cracks appear on the tube wall, and the carbon tube is cut off, so that a diffusion channel is provided for lithium ions, and the electrode reaction kinetics in the discharge process is improved. The spiral carbon nano tube obtained by the method has excellent structural characteristics and electrochemical performance, and the lithium/carbon fluoride primary battery based on the carbon fluoride nano tube has a stable discharge platform and high specific energy and has no obvious voltage hysteresis.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a preparation method of fluorinated helical carbon nanotubes is characterized by comprising the following steps:
step 1, ferrous tartrate powder is used as a catalyst precursor, and polar molecules (water vapor) are introduced to be used as a catalytic auxiliary agent so as to improve the purity and yield of the spiral carbon nanotube; the specific process is as follows:
firstly, weighing ferrous tartrate powder as a catalyst precursor, placing the catalyst precursor in a quartz boat, transferring the quartz boat into a tubular furnace, introducing inert gas as carrier gas into the tubular furnace, introducing water vapor as a catalytic assistant, and introducing hydrogen to form a reducing atmosphere, heating to 450-600 ℃ at a heating rate of 5-15 ℃/min, and preserving heat for 30-60 min to generate iron nanoparticles with catalytic anisotropy;
then, keeping the temperature of the tube furnace unchanged, stopping introducing hydrogen, introducing acetylene gas or mixed gas of acetylene and hydrogen into the tube furnace, and reacting for 30-60 min to catalytically grow the helical carbon nanotube;
finally, after the reaction is finished, naturally cooling the tubular furnace to room temperature, and taking out a product to obtain a compound of the spiral carbon nano tube and the catalyst particles;
step 2, soaking the compound of the spiral carbon nanotube and the catalyst particles obtained in the step 1 in a nitric acid solution for 12-48 hours to remove the catalyst particles, and performing suction filtration, washing and drying after soaking to obtain a purified spiral carbon nanotube (HCNT);
step 3, putting the spiral carbon nanotube obtained in the step 2 into a tube furnace as a precursor carbon source, heating to 600-900 ℃ under an inert gas atmosphere, and preserving heat for 2-6 h at 600-900 ℃; and then reducing the temperature to 200-400 ℃, stabilizing, and introducing fluorine gas with the gas flow of 100-200 mL/min to perform fluorination reaction for 2-6 h to obtain the fluorinated spiral carbon nanotube (F-HCNT).
Further, the gas flow of the inert gas in the step 1 is 50-100 mL/min; the air flow of the water vapor is 1-5 mL/h, and the temperature is 30-80 ℃; the flow rate of the hydrogen is 30-100 mL/min.
Further, the flow rate of the acetylene gas in the step 1 is 80-100 mL/min.
Further, in the mixed gas of acetylene and hydrogen in the step 1, the flow rate of hydrogen is 30-100 mL/min, and the flow rate of acetylene is 80-100 mL/min.
Further, the gas flow of the inert gas in the step 3 is 50-100 mL/min.
Further, in the nitric acid solution in the step 2, the volume ratio of the concentrated nitric acid to the water is (1-3): 1.
the invention also provides application of the fluorinated spiral carbon nano tube as a lithium/fluorinated carbon primary battery anode material.
The invention also provides a lithium/carbon fluoride battery taking the fluorinated spiral carbon nanotube as a positive active material, which comprises a fluorinated spiral carbon nanotube positive electrode, a lithium metal negative electrode, electrolyte and a diaphragm, wherein the fluorinated spiral carbon nanotube positive electrode is formed by coating the mixed slurry of the fluorinated spiral carbon nanotube, conductive carbon black and PVDF (polyvinylidene fluoride) on an aluminum foil current collector, and the mass ratio of the fluorinated spiral carbon nanotube to the conductive carbon black to the PVDF is (3-18): 1: 1.
the invention has the beneficial effects that:
the invention adopts spiral carbon nanotube material as a novel carbon source for fluorination and uses the material as the anode material of the lithium/carbon fluoride primary battery. On one hand, the shape of the spiral carbon nanotube is regulated and controlled by regulating and controlling preparation parameters (temperature, airflow and the like) of the spiral carbon nanotube, so that the quantity of fluorination active sites of the spiral carbon nanotube is regulated and controlled, the fluorination reaction process of the spiral carbon nanotube is finally regulated and controlled, the regulation and control of bond types such as carbon-fluorine semi-ionic bonds, covalent bonds and the like are realized, and the conductivity and discharge polarization effect of the material are improved. On the other hand, the morphology, the structure and the fluorine-carbon ratio of the fluorinated spiral carbon nano tube are regulated and controlled by optimizing a fluorination process, so that the tube wall of the fluorinated carbon nano tube is cracked or even broken, a diffusion channel is provided for lithium ions, the polarization generated during discharge is reduced, a high discharge platform and a smaller voltage hysteresis effect are provided, and the lithium/fluorinated carbon primary battery anode material with high fluorine-carbon ratio and high specific capacity is obtained. The fluorocarbon material obtained by the invention has the highest fluorocarbon ratio of 1.41 and the highest specific capacity of 796mAh g-1(the cut-off voltage is 1.5V), and the method has no obvious voltage hysteresis effect, and has important significance for improving the performance of the carbon fluoride battery, particularly improving the voltage hysteresis effect and promoting the application and popularization of the carbon fluoride battery.
Drawings
FIG. 1 is a TGA-DSC curve measured at a temperature rise rate of 5 ℃/min (temperature range of 30 to 800 ℃) in a nitrogen atmosphere of ferrous tartrate used in example 1;
FIG. 2 is an SEM image of the spiral carbon nanotubes obtained in step 2 of example 1(a), example 6(b) and comparative example (c);
FIG. 3 is SEM images of fluorinated helical carbon nanotubes obtained in example 1(a) and example 5 (b);
FIG. 4 is a TGA curve obtained by heating fluorinated helical carbon nanotubes obtained in example 1(F-HCNT-200), example 4(F-HCNT-350) and example 5(F-HCNT-400) at a temperature rising rate of 10 ℃/min under a nitrogen atmosphere;
FIG. 5 is a Raman spectrum of the Helical Carbon Nanotube (HCNT) obtained in step 2 of example 1, the fluorinated helical carbon nanotube (F-HCNT-200) obtained in example 1, the fluorinated helical carbon nanotube (F-HCNT-350) obtained in example 4, and the fluorinated helical carbon nanotube (F-HCNT-400) obtained in example 5;
FIG. 6 is the discharge curves at 0.01C rate for cells assembled with fluorinated helical carbon nanotubes from example 1(F-HCNT-200), example 4(F-HCNT-350) and example 5 (F-HCNT-400);
FIG. 7 is an EIS curve of fluorinated helical carbon nanotube assembled cells obtained in example 4(F-HCNT-350) and example 5 (F-HCNT-400).
Detailed Description
The technical scheme of the invention is detailed below by combining the accompanying drawings and the embodiment.
Example 1
A preparation method of fluorinated helical carbon nanotubes specifically comprises the following steps:
step 1, weighing 0.25g of ferrous tartrate powder as a catalyst precursor, placing the ferrous tartrate powder in a quartz boat, transferring the quartz boat into a tubular furnace, introducing argon with the gas flow of 50mL/min into the tubular furnace as a carrier gas, introducing water vapor with the gas flow of 2mL/h (50 ℃) as a catalytic assistant, simultaneously introducing hydrogen with the gas flow of 100mL/min to provide a reducing atmosphere, heating the tubular furnace to 550 ℃ at the heating rate of 10 ℃/min, and preserving the temperature at 550 ℃ for 60min to enable the catalyst precursor to generate iron nanoparticles with catalytic anisotropy under the induction of mixed gas; then, keeping the temperature of the tube furnace unchanged, stopping introducing hydrogen, introducing acetylene with the gas flow of 100mL/min into the tube furnace, and reacting for 60min to catalytically grow the helical carbon nanotube; after the reaction is finished, naturally cooling the tubular furnace to room temperature, and taking out a product to obtain a compound of the spiral carbon nano tube and the catalyst particles;
step 2, soaking the compound of the spiral carbon nanotube and the catalyst particles obtained in the step 1 in a nitric acid solution (the volume ratio of concentrated nitric acid to water in the nitric acid solution is 1: 1) for 24 hours for 3 times to remove the catalyst particles, and performing suction filtration, washing and drying after soaking to obtain a purified spiral carbon nanotube (HCNT);
step 3, putting the spiral carbon nano tube obtained in the step 2 into a tube furnace as a precursor carbon source, heating to 900 ℃ at the speed of 10 ℃/min under the argon atmosphere, and preserving heat for 2 hours at 900 ℃; then the temperature is reduced to 200 ℃ at the speed of 10 ℃/min, fluorine gas is introduced at the flow rate of 100mL/min after stabilization, and fluorination reaction is carried out for 2h, thus obtaining the fluorinated spiral carbon nanotube (F-HCNT).
Example 2
This example is different from example 1 in that:
the specific process of the step 3 is as follows: putting the spiral carbon nanotube obtained in the step 2 into a tube furnace as a precursor carbon source, heating to 900 ℃ at the speed of 10 ℃/min under the argon atmosphere, and preserving heat for 2h at 900 ℃; then the temperature is reduced to 250 ℃ at the speed of 10 ℃/min, fluorine gas is introduced at the flow rate of 100mL/min after stabilization, and fluorination reaction is carried out for 2h, thus obtaining the fluorinated spiral carbon nanotube (F-HCNT).
Example 3
This example is different from example 1 in that:
the specific process of the step 3 is as follows: putting the spiral carbon nanotube obtained in the step 2 into a tube furnace as a precursor carbon source, heating to 900 ℃ at the speed of 10 ℃/min under the argon atmosphere, and preserving heat for 2h at 900 ℃; then the temperature is reduced to 300 ℃ at the speed of 10 ℃/min, fluorine gas is introduced at the flow rate of 100mL/min after stabilization, and fluorination reaction is carried out for 2h, thus obtaining the fluorinated spiral carbon nanotube (F-HCNT).
Example 4
This example is different from example 1 in that:
the specific process of the step 3 is as follows: putting the spiral carbon nanotube obtained in the step 2 into a tube furnace as a precursor carbon source, heating to 900 ℃ at the speed of 10 ℃/min under the argon atmosphere, and preserving heat for 2h at 900 ℃; then the temperature is reduced to 350 ℃ at the speed of 10 ℃/min, fluorine gas is introduced at the flow rate of 100mL/min after stabilization, and fluorination reaction is carried out for 2h, thus obtaining the fluorinated spiral carbon nanotube (F-HCNT).
Example 5
This example is different from example 1 in that:
the specific process of the step 3 is as follows: putting the spiral carbon nanotube obtained in the step 2 into a tube furnace as a precursor carbon source, heating to 900 ℃ at the speed of 10 ℃/min under the argon atmosphere, and preserving heat for 2h at 900 ℃; then the temperature is reduced to 400 ℃ at the speed of 10 ℃/min, fluorine gas is introduced at the flow rate of 100mL/min after stabilization, and fluorination reaction is carried out for 2h, thus obtaining the fluorinated spiral carbon nanotube (F-HCNT).
Example 6
This example is different from example 1 in that:
the specific process of the step 1 is as follows: putting 0.25g of ferrous tartrate powder serving as a catalyst precursor into a quartz boat, putting the quartz boat into a tube furnace, introducing 2mL/h of water vapor (50 ℃) serving as a catalytic assistant and hydrogen with the gas flow of 30mL/min to form a reducing atmosphere by taking argon (50mL/min) as a carrier gas, heating the tube furnace to 550 ℃ at the heating rate of 10 ℃/min, and preserving the temperature at 550 ℃ for 60min to enable the catalyst precursor to generate iron nanoparticles with catalytic anisotropy under the induction of mixed gas; then, keeping the temperature of the tube furnace unchanged, stopping introducing hydrogen, introducing a mixed gas of acetylene with the gas flow rate of 80mL/min and hydrogen with the gas flow rate of 30mL/min into the tube furnace, and reacting for 60min to catalytically grow the helical carbon nanotube; and after the reaction is finished, naturally cooling the tubular furnace to room temperature, and taking out a product to obtain the compound of the spiral carbon nano tube and the catalyst particles.
Comparative example
The comparative example is different from example 1 in that:
the specific process of the step 1 is as follows: putting 0.25g of ferrous tartrate powder serving as a catalyst precursor into a quartz boat, putting the quartz boat into a tube furnace, introducing 2mL/h of water vapor (50 ℃) serving as a catalytic assistant and hydrogen with the gas flow of 30mL/min to form a reducing atmosphere by taking argon (50mL/min) as a carrier gas, heating the tube furnace to 525 ℃ at the heating rate of 10 ℃/min, and preserving the temperature at 525 ℃ for 60min to enable the catalyst precursor to generate iron nanoparticles with catalytic anisotropy under the induction of mixed gas; then, keeping the temperature of the tube furnace unchanged, stopping introducing hydrogen, introducing a mixed gas of acetylene with the gas flow rate of 45mL/min and hydrogen with the gas flow rate of 30mL/min into the tube furnace, and reacting for 60min to catalytically grow the helical carbon nanotube; and after the reaction is finished, naturally cooling the tubular furnace to room temperature, and taking out a product to obtain the compound of the spiral carbon nano tube and the catalyst particles.
FIG. 1 is a TGA-DSC curve obtained by measuring the temperature rise rate (temperature range of 30-800 ℃) of ferrous tartrate used in example 1 at 5 ℃/min under a nitrogen atmosphere; fig. 1 shows that ferrous tartrate is decomposed completely at 450 ℃ to generate iron nanoparticles with catalytic anisotropy, which is beneficial to the growth of spiral carbon nanotubes by subsequent catalytic induction reaction.
FIG. 2 is an SEM image of the spiral carbon nanotubes obtained in step 2 of example 1(a), example 6(b) and comparative example (c); as shown in fig. 2(a), the spiral carbon nanotube prepared by the gas induction method in example 1 has a long tube length, a substantially continuous spiral structure, and the highest spiral purity, and the tube diameter is about 92.5 nm. As can be seen from fig. 2(c), the spiral carbon nanotube tube prepared in the comparative example has a short length, and is mostly a straight carbon nanotube without a significant spiral structure. As can be seen from fig. 2(b), the helical carbon nanotube obtained in example 6 has high helical purity. Figure 2 shows that the conditions of example 1 are most favorable for the formation of helical carbon nanotube structures; and the effective regulation and control of the shape of the spiral carbon nano tube can be realized by regulating and controlling the reaction kinetic process during preparation and the components of the induced gas and the reaction gas, so that the C-F fluorinated active site and the C-F bond type on the surface of the spiral carbon nano tube can be regulated and controlled, and the method has important significance for improving the discharge performance of the lithium/carbon fluoride battery.
FIG. 3 is SEM images of fluorinated helical carbon nanotubes obtained in example 1(a) and example 5 (b); as can be seen from fig. 3(a), the spiral carbon nanotube in example 1 still has a certain spiral structure after fluorination, but cracks appear on the surface of the tube wall, which is caused by the carbon-carbon bond in the carbon material breaking to form a carbon-fluorine bond during the fluorination process, and the tube diameter of the fluorinated spiral carbon nanotube in fig. 3(a) is about 108.1nm, which is slightly increased compared with the spiral carbon nanotube. As shown in fig. 3(b), the number of cracks and gaps on the wall of the fluorinated spiral carbon nanotube obtained in example 5 is significantly increased compared to that of example 1, and the carbon tube has segmental fracture gaps along the spiral direction. This is because the high fluorination temperature leads to an increase in the degree of fluorination (F/C), and the destruction of the morphology of the helical carbon nanotube is more pronounced by the formation of more carbon-fluorine bonds and the cleavage of carbon-carbon bonds.
FIG. 4 is a TGA curve obtained by heating fluorinated helical carbon nanotubes obtained in example 1(F-HCNT-200), example 4(F-HCNT-350) and example 5(F-HCNT-400) at a temperature rising rate of 10 ℃/min under a nitrogen atmosphere; from this curve, the fluorine to carbon ratio (R) of the fluorinated material can be calculatedF/C) The calculation method is as follows:
wherein, WRIs the remaining mass percent (%) in the TGA curve, AR(F) And AR(C) The relative atomic masses of the fluorine atoms and carbon atoms, respectively.
It can be found by calculation that the sample obtained in example 1 has a fluorocarbon ratio of 0.22, the sample obtained in example 4 has a fluorocarbon ratio of 1.35, and the sample obtained in example 5 has a fluorocarbon ratio of 1.41. From the TGA curve, the fluorine-to-carbon ratio of each group of samples increased with the increase of the fluorination temperature, and the performance results are shown in Table 1.
TABLE 1
FIG. 5 shows the coiled carbon nanotube (HCNT) obtained in step 2 of example 1, the fluorinated coiled carbon nanotube (F-HCNT-200) obtained in example 1, the fluorinated coiled carbon nanotube (F-HCNT-350) obtained in example 4, and the likeRaman spectrum of fluorinated helical carbon nanotube (F-HCNT-400) obtained in example 5; by the D peak in the Raman curve (-1352 cm)-1) And peak G (. about.1588 cm)-1) Intensity ratio of (I)D/IGThe defect density of the carbon material can be judged. As can be seen from FIG. 5, I of the helical carbon nanotube before fluorinationD/IG0.92, I of fluorinated helical carbon nanotube in example 1D/IG1.39, indicating that fluorination increased defects in the helical carbon tube, resulting in ID/IGThe intensity ratio increases. Fig. 5 illustrates that the degree of fluorination (fluorocarbon ratio) of each sample increases with increasing fluorination temperature.
Assembling the battery:
preparing slurry from the fluorinated spiral carbon nanotube obtained in the embodiment 1-5, conductive agent carbon black and binder PVDF according to the mass ratio of 8:1:1, uniformly coating the slurry on a current collector aluminum foil, and performing vacuum drying at 80 ℃ for 12 hours to obtain a positive plate; and then, assembling the button cell in a glove box by taking the metal lithium as a negative electrode and the fluorinated spiral carbon nanotube electrode plate as a positive electrode, and standing for 24h for testing.
Fig. 6 is a discharge curve (cut-off voltage of 1.5V) of the button cell assembled by the fluorinated helical carbon nanotube obtained in examples 1, 4 and 5 at 0.01C rate. As can be seen from FIG. 6, the sample obtained in example 1 had a high capacity of 334mAh g-1The sample obtained in example 4 has higher specific capacity and highest discharge platform, and the specific capacity is 686mAh g-1The specific energy is 1544Wh kg-1. The sample obtained in example 5 has the highest specific capacity, up to 796mAh g-1The specific energy reaches 1848Wh kg-1. The samples obtained in examples 4 and 5 have high specific capacity and stable discharge platform (about 2.6V), and the samples obtained in examples 1, 4 and 5 have no obvious voltage hysteresis effect.
Fig. 7 is an impedance spectrum of button cell assembled by fluorinated spiral carbon nanotubes obtained in examples 4 and 5; in the figure, the diameter of the semicircle at the high frequency part represents the charge transfer resistance, and the slope of the straight line at the low frequency part represents the diffusion resistance of lithium ions. As can be seen from fig. 7, the sample obtained in example 5 has an increased charge transfer resistance and an increased diffusion resistance as compared with example 4. This is because the specific capacity of the sample increases with increasing fluorocarbon ratio at high fluorination temperatures, but the impedance increases accordingly.
Claims (7)
1. A preparation method of fluorinated helical carbon nanotubes is characterized by comprising the following steps:
step 1, preparing a compound of the spiral carbon nanotube and catalyst particles;
1.1 weighing ferrous tartrate powder, placing the ferrous tartrate powder in a tubular furnace, introducing inert gas serving as carrier gas, water vapor serving as catalytic aid and hydrogen into the tubular furnace to form a reducing atmosphere, heating to 450-600 ℃, and keeping the temperature for 30-60 min;
1.2, keeping the temperature of the tubular furnace unchanged, stopping introducing hydrogen, introducing acetylene gas or mixed gas of acetylene and hydrogen into the tubular furnace, and reacting for 30-60 min;
1.3 after the reaction is finished, naturally cooling to room temperature, and taking out to obtain a compound of the spiral carbon nanotube and the catalyst particles;
step 2, soaking the compound of the helical carbon nanotube and the catalyst particles obtained in the step 1 in a nitric acid solution for 12-48 h, and performing suction filtration, washing and drying to obtain a purified helical carbon nanotube;
step 3, putting the spiral carbon nano tube obtained in the step 2 into a tube furnace, heating to 600-900 ℃ under the inert gas atmosphere, and preserving heat for 2-6 hours at 600-900 ℃; and then reducing the temperature to 200-400 ℃, introducing fluorine gas with the gas flow of 100-200 mL/min, and carrying out fluorination reaction for 2-6 h to obtain the fluorinated helical carbon nanotube.
2. The method for preparing fluorinated helical carbon nanotubes according to claim 1, wherein the inert gas flow rate in step 1 is 50 to 100 mL/min; the air flow of the water vapor is 1-5 mL/h, and the temperature is 30-80 ℃; the flow rate of the hydrogen is 30-100 mL/min.
3. The method for preparing fluorinated helical carbon nanotubes according to claim 1, wherein the flow rate of the acetylene gas in step 1 is 80 to 100 mL/min.
4. The method for preparing fluorinated helical carbon nanotubes according to claim 1, wherein in the mixed gas of acetylene and hydrogen in step 1, the flow rate of hydrogen is 30-100 mL/min, and the flow rate of acetylene is 80-100 mL/min.
5. The method for preparing fluorinated helical carbon nanotubes according to claim 1, wherein the inert gas flow rate in step 3 is 50 to 100 mL/min.
6. The method for preparing fluorinated helical carbon nanotubes according to claim 1, wherein in the nitric acid solution of step 2, the volume ratio of concentrated nitric acid to water is (1-3): 1.
7. use of fluorinated helical carbon nanotubes obtained by the method of any one of claims 1 to 6 as a positive electrode material for lithium/fluorinated carbon primary batteries.
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