CN111900390B

CN111900390B - Metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material and preparation method and application thereof

Info

Publication number: CN111900390B
Application number: CN202010474902.4A
Authority: CN
Inventors: 曹琪; 王栋; 黄田柳; 敬波; 彭细桂
Original assignee: Hunan Xibei New Material Technology Co ltd; Xiangtan University
Current assignee: Hunan Xibei New Material Technology Co ltd; Xiangtan University
Priority date: 2020-05-29
Filing date: 2020-05-29
Publication date: 2022-04-01
Anticipated expiration: 2040-05-29
Also published as: CN111900390A

Abstract

The invention provides a metallic tin and carbon nano tube co-doped lithium-sulfur battery intermediate layer material, a preparation method and application thereof. The preparation process comprises the following steps: adding a conductive polymer into a solvent, continuously stirring to dissolve the conductive polymer, sequentially adding a carbon nano tube and a tin salt into the solution, uniformly mixing, and continuously stirring to obtain a spinning solution; carrying out electrostatic spinning operation on the spinning solution in a dry environment to obtain a spinning fiber membrane; and carrying out pre-oxidation treatment and carbonization treatment on the spinning fiber film to obtain the intermediate layer material codoped by the metal tin and the carbon nano tube. The interlayer material prepared by the invention can well improve the overall conductivity of the positive electrode and play a good role in inhibiting the shuttle effect, and can effectively improve the electrochemical performance of the lithium-sulfur battery.

Description

Metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of lithium-sulfur batteries, and particularly relates to a metallic tin and carbon nanotube co-doped lithium-sulfur battery intermediate layer material, and a preparation method and application thereof.

Background

With the increasing demand of high-energy storage systems in the actual production and living needs of society, lithium-sulfur batteries are receiving more and more extensive attention due to various advantages of the lithium-sulfur batteries. The lithium-sulfur battery is a lithium battery with sulfur as the positive electrode and metal lithium as the negative electrode. The lithium-sulfur battery using sulfur as the positive electrode material has higher theoretical specific capacity (1675mAh/g) and energy density (2600Wh/kg), and the theoretical energy density is about 5 times of that of the traditional lithium-ion battery. In addition, sulfur is a byproduct of the petroleum industry, is inexpensive and environmentally friendly, and thus a lithium sulfur battery is a very promising lithium battery.

However, the inherent defects of the lithium-sulfur battery greatly limit the development, wherein the outstanding problems are the 'shuttle effect', polysulfide dissolves in electrolyte and shuttles between a positive electrode and a negative electrode, thereby causing the accelerated loss of the battery capacity, in addition, the lower conductivity of the active substance sulfur also forms a barrier in the discharging process, and a series of problems cause the electrochemical performance of the lithium-sulfur battery to be reduced, thereby influencing the large-scale commercial application of the lithium-sulfur battery.

The invention patent CN 108039462a discloses a method for manufacturing an intermediate layer of a conductive polymer composite of a lithium-sulfur battery, comprising the steps of: (1) growing and preparing a conductive high polymer nanorod array on graphene oxide; (2) preparing a porous carbon nanotube; (3) and (3) preparing the lithium-sulfur battery with the conductive polymer-graphene oxide-porous carbon nanotube composite as the middle layer. According to the invention, the conductive polymer-graphene oxide-porous carbon nanotube composite is used as the middle layer, a large number of nano microporous structures on the surface of the porous carbon nanotube and the conductive polymer nanorod array grown on the graphene oxide film are utilized, so that the transmission capability of electrons in the charging and discharging processes of the battery is greatly enhanced, and the porous structure of the composite can maintain the transmission capability of lithium ions, thereby improving the utilization rate of the positive active material; in addition, the nitrogen-containing functional group of the conductive high polymer and the oxygen-containing functional group on the surface of the graphene oxide can effectively adsorb migration and dissolution of polysulfide formed in the discharging process to an electrolyte solution, so that the cycling stability of the battery is greatly improved.

The intermediate layer material prepared in the comparison document has more raw materials, complex preparation process and difficult control of experimental conditions; the product is greatly influenced by external conditions such as temperature, stirring speed and the like, and the shape of the material is difficult to accurately control; the product is formed by vacuum filtration and external force extrusion, so that the material is not easy to be uniformly distributed, and the instability of the final electrochemical performance is easily caused; after the lithium sulfur battery is prepared, the discharge specific capacity of the battery cycle performance is lower after 100 cycles.

Disclosure of Invention

In order to overcome the problems in the prior art, the application provides a metallic tin and carbon nanotube co-doped lithium-sulfur battery intermediate layer material, and a preparation method and application thereof.

In order to achieve the purpose, the invention is realized by the following technical scheme:

the intermediate layer material has a three-dimensional cobweb structure formed by interweaving carbon nanotubes and carbon nanofibers, the carbon nanotubes are attached to the surfaces of the crosslinked carbon nanofibers, and metallic tin nanoparticles are loaded on the surfaces or inside the carbon nanofibers.

A preparation method of a metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material comprises the following steps:

s1: adding a conductive polymer into a solvent, and continuously stirring to dissolve the conductive polymer;

s2, sequentially adding the carbon nano tube and the tin salt into the solution prepared in the step S1, uniformly mixing, and continuously stirring to obtain a spinning solution;

s3, carrying out electrostatic spinning operation on the spinning solution prepared in the step S2 in a dry environment to obtain a spinning fiber membrane;

s4, carrying out pre-oxidation treatment and carbonization treatment on the spinning fiber film prepared in the step S3 to obtain the intermediate layer material co-doped with metal tin and carbon nano tubes.

Further, the mass ratio of the conductive polymer to the tin salt to the carbon nanotube is 10:10: 1-10: 2: 1.

Further, the tin salt is at least one of tin chloride, tin sulfate and tin nitrate.

Further, the stirring speed in step S1 and step S2 is 550 to 660r/min, and more preferably 600 to 650 r/min.

Further, the stirring temperature in step S1 and step S2 is 50 to 70 ℃, and more preferably 60 to 65 ℃.

Further, the stirring time in step S1 and step S2 is 2 to 4 hours, and more preferably 2.5 to 3 hours.

Further, the carbon nanotubes added in step S2 are pre-acidified, and the treatment steps are as follows: placing the carbon nano tube in concentrated nitric acid, refluxing for 10-14 h at 45-65 ℃, and then drying for 10-14 h in a vacuum drying oven at 55-65 ℃ to obtain the acidified carbon nano tube. The acidification is used for removing impurities in the carbon nano tubes and purifying the carbon nano tubes.

Further, the working voltage of the electrostatic spinning treatment in the step S3 is 20-24 kV, and the distance between the bottom of the needle tube and the receiver is 14-16 cm.

Further, the pre-oxidation processing in step S4 is as follows: the method is carried out in an air atmosphere, the temperature is 250-300 ℃, the heating rate is 2-3 ℃/min, and the heat preservation time is 1.5-2 h. In the pre-oxidation process, excessive solvent is removed by heating treatment in air due to reaction with oxygen and nanofibers co-doped with tin oxide and carbon nanotubes are formed.

Further, the carbonization processing in step S4 is as follows: the carbonization is carried out in an argon atmosphere, the carbonization temperature is 650-700 ℃, the heating rate is 4-6 ℃/min, and the heat preservation time is 2-3 h. During carbonization, tin oxide is reduced to metallic tin by a carbon species in an Ar atmosphere.

The lithium-sulfur battery comprises the metal tin and carbon nanotube co-doped lithium-sulfur battery interlayer material.

The conductive polymer may be various conductive polymers commonly used in the art, for example, polyacrylonitrile, polyethylene oxide, polyvinylpyrrolidone. Preferably, the conductive polymer is polyacrylonitrile.

The solvent is a variety of solvents commonly used in the art. Preferably, the solvent in this application is N, N-dimethylformamide.

The carbon nanotube in the application is one or two of a multi-wall carbon nanotube and a single-wall carbon nanotube.

The conductive polymer is used as a precursor of a carbon-based structure to form carbon nanofibers after an electrostatic spinning process, wherein a three-dimensional cobweb-shaped structure formed by mutually interweaving carbon nanotubes and carbon nanofibers is tightly stacked to form a special three-dimensional conductive network, the carbon nanotubes are attached to the surface of the crosslinked carbon nanofibers, and metal tin nanoparticles are loaded on the surface and inside of the carbon nanofibers. The surface of the fibers is created with a rich pore structure including micropores, mesopores and macropores (according to the international association of pure and applied chemistry (iupac) definition, micropores are called with a pore diameter of less than 2 nm, macropores are called with a pore diameter of more than 50 nm, and mesopores are called with a pore diameter of between 2 and 50 nm).

The invention has the following beneficial effects:

(1) the metal tin and carbon nanotube co-doped intermediate layer material prepared by the invention is characterized in that the carbon nanofibers which are mutually interwoven and the carbon nanotubes attached to the surfaces of the fibers are used as a conductive framework, and the existence of a porous structure can form a crossed rapid channel, so that more channels are provided for the transmission of ions, and the implementation of a charging and discharging process is facilitated.

(2) The intermediate layer material co-doped with the metal tin and the carbon nano tube, prepared by the invention, has a higher specific surface area, provides more reaction sites for the contact of polar metal tin and polysulfide, can anchor the polysulfide more effectively, further accelerates the transformation of the polysulfide, effectively inhibits the shuttle of the polysulfide between a positive electrode and a negative electrode, effectively improves the electrochemical performance of the lithium-sulfur battery, has an abundant pore structure, can effectively deposit the polysulfide, and thus reduces the loss of the electrochemical performance of the battery caused by the shuttle effect.

(3) The metal tin has strong capability of catalyzing polysulfide conversion and has adsorption performance, polysulfide has strong interaction, and after the metal tin is added into interlayer pores, the metal tin has obvious adsorption behavior and can accelerate the catalytic capability of polysulfide conversion. Other transition metals with strong chemical activity are not favorable for forming ideal electrospinning solution when used in large amounts.

Drawings

FIG. 1 is a scanning electron micrograph of an interlayer material prepared according to example 1;

FIG. 2 is a high power scanning electron micrograph of an interlayer material prepared according to example 1;

FIG. 3 is a transmission electron micrograph of an interlayer material prepared according to example 1;

FIG. 4 is a high resolution transmission electron microscope image of an interlayer material prepared in example 1;

FIG. 5 is an X-ray diffraction pattern of an interlayer material prepared in example 1;

FIG. 6 shows the structure of the nitrogen adsorption/desorption curve and pore size distribution curve of the interlayer material prepared in example 1;

FIG. 7 is a thermogravimetric analysis of the interlayer material prepared in example 1;

FIG. 8 is a scanning electron micrograph of an interlayer material prepared according to example 2;

FIG. 9 is a scanning electron micrograph of an interlayer material prepared according to example 3;

FIG. 10 is a graph of rate performance of a lithium sulfur cell assembled using the interlayer material prepared in example 1;

FIG. 11 is a graph of long cycle performance of a lithium sulfur cell assembled using the interlayer material prepared in example 1;

FIG. 12 is a cyclic voltammogram of a lithium sulfur cell assembled using the interlayer material prepared in example 1;

FIG. 13 is a graph of cycle performance of a lithium sulfur cell assembled with an interlayer material prepared in example 1 in accordance with the present invention;

FIG. 14 is a graph of cycle performance of a lithium sulfur cell assembled using the interlayer material prepared in example 2;

FIG. 15 is a graph of cycle performance of a lithium sulfur cell assembled using the interlayer material prepared in example 3;

FIG. 16 is a graph of cycle performance of a lithium sulfur cell assembled using an interlayer material prepared in comparative example 1;

fig. 17 is a graph of cycle performance of a lithium sulfur battery assembled using the interlayer material prepared in comparative example 2.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments.

Preparation of metallic tin and carbon nano tube co-doped lithium-sulfur battery intermediate layer material and anode

Example 1

The multi-wall carbon nano-tube and concentrated nitric acid are refluxed for 12 hours at 50 ℃. And (3) after refluxing for 12h, drying for 12h in a vacuum drying oven at 60 ℃ to obtain the purified multi-wall carbon nano tube. Then, 0.01g of polyvinylpyrrolidone and 400ml of deionized water are mixed and stirred continuously, and after dissolution, 0.03mol of sodium thiosulfate pentahydrate is added and stirred for 60min to dissolve the sodium thiosulfate pentahydrate, so that a uniform and transparent solution is obtained. And then 4ml of concentrated hydrochloric acid is dripped into the transparent solution, the mixture is stirred for 5 hours at 50 ℃, the obtained product is filtered and washed for many times by deionized water, and finally the product is dried for 12 hours in vacuum at 60 ℃ to prepare the sulfur powder. Grinding the purified multi-walled carbon nano-tube and the prepared sulfur powder for 30min according to the mass ratio of 1:3, then putting the mixture into a tube furnace, and heating for 12h at 155 ℃ by using argon to obtain the multi-walled carbon nano-tube/sulfur composite material. Weighing 0.07g of multi-walled carbon nanotube/sulfur composite material, adding 0.02g of acetylene black and 0.01g of polyvinylidene fluoride, uniformly grinding, adding N-methylpyrrolidone (NMP) to prepare slurry, uniformly coating the slurry on a current collector aluminum foil by using a 250 mu m scraper, performing vacuum drying at 60 ℃ for about 12 hours to prepare a positive electrode film, cutting a wafer with the diameter of 10mm, and weighing to obtain the positive electrode of the lithium-sulfur battery.

0.5g of polyacrylonitrile is put into 5ml of N, N-dimethylformamide solution, stirring is carried out for 3h at the temperature of 60 ℃ to obtain transparent solution, then 0.25g of tin tetrachloride pentahydrate and 0.05g of purified multi-walled carbon nano-tubes are simultaneously added into the solution, and stirring is carried out for 12h at the temperature of 60 ℃ to obtain spinning solution. The electrostatic spinning process was carried out at a high voltage of 20kV, with a distance of 15cm between the tip and the collector. During the electrospinning process, the flow rate of the solution was 0.6 ml/h. Next, the fiber film was peeled off from the receiving sheet, and subjected to a pre-oxidation treatment: air is introduced into the tube furnace, the heating rate is 2 ℃/min to 250 ℃, and the heating time is kept for 2 h. And then carbonizing: introducing argon into the tubular furnace, and carbonizing for 2 hours at the temperature rising rate of 5 ℃/min to 650 ℃ to obtain the metal tin and carbon nano tube co-doped electrostatic spinning fiber membrane material. Finally, it was cut into a circular piece having a diameter of 19mm and used as an interlayer material.

Example 2

Example 2 differs from example 1 in that: adding 0.5g of polyacrylonitrile into 5ml of N, N-dimethylformamide solution, stirring for 3 hours at 60 ℃ to obtain a transparent solution, then simultaneously adding 0.5g of tin tetrachloride pentahydrate and 0.05g of purified multi-walled carbon nanotubes into the solution, and stirring for 12 hours at 60 ℃ to obtain the spinning solution. The rest of the preparation method and conditions were the same as in example 1.

Example 3

Example 3 differs from example 1 in that: adding 0.5g of polyacrylonitrile into 5ml of N, N-dimethylformamide solution, stirring for 3 hours at 60 ℃ to obtain a transparent solution, then simultaneously adding 0.1g of tin tetrachloride pentahydrate and 0.05g of purified multi-walled carbon nanotubes into the solution, and stirring for 12 hours at 60 ℃ to obtain the spinning solution. The rest of the preparation method and conditions were the same as in example 1.

Comparative example 1

Comparative example 1 differs from example 1 in that: tin tetrachloride pentahydrate is not added in the preparation of the interlayer material. The rest of the preparation method and conditions were the same as in example 1.

Comparative example 2

Comparative example 2 differs from example 1 in that: tin tetrachloride pentahydrate and multi-walled carbon nanotubes are not added in the preparation of the interlayer material. The rest of the preparation method and conditions were the same as in example 1.

Assembly of lithium-sulfur battery

The metallic tin and carbon nanotube co-doped electrostatic spinning material prepared in examples 1 to 3 as the intermediate layer and the prepared positive plate, and the intermediate layer material and the positive plate prepared in comparative examples 1 to 2 were assembled into a 2025 type cell for testing to perform electrochemical performance testing: wherein the electrolyte consists of 1, 2-dimethoxyethane and 1, 3-dioxacycloalkane in a volume ratio of 1:1, 0.1mol/L lithium nitrate and 1mol/L bis (trifluoromethane) sulfonimide salt. A lithium metal sheet was used as the negative electrode, and a Celgard2400 separator was used. And packaging the battery in a glove box in an argon atmosphere, standing for 3 hours, and then testing the charge and discharge performance of the battery. Wherein the charge-discharge cut-off voltage range is 1.8-2.8V.

Third, performance test

1. Performance test of intermediate layer material co-doped with metallic tin and carbon nano tube

Scanning Electron Microscope (SEM) tests were performed on the intermediate layer material co-doped with metallic tin and carbon nanotubes prepared in example 1, and the test results are shown in fig. 1 and fig. 2, where fig. 1 is a low-magnification scanning electron microscope image and fig. 2 is a high-magnification scanning electron microscope image. It can be seen that the intermediate layer material co-doped with the metal tin and the carbon nanotubes has an obvious cross-linked spider-web structure, and the carbon nanofibers are overlapped with each other to form a three-dimensional conductive framework.

The Transmission Electron Microscope (TEM) and High Resolution Transmission Electron Microscope (HRTEM) tests were performed on the intermediate layer material co-doped with metallic tin and carbon nanotubes prepared in example 1, and the results are shown in fig. 3 and 4, respectively, for further characterizing the surface state of the intermediate layer. The figure shows that the metal tin is uniformly distributed on the nano-fiber, and the winding of multi-wall carbon nano-tubes on the surface of the fiber can be obviously observed.

When the metallic tin and carbon nanotube co-doped interlayer material prepared in example 1 was subjected to X-ray diffraction, as shown in fig. 5, characteristic peaks (PDF #04-0673) of tin (Sn) appeared on an X-ray diffraction (XRD) pattern, and no other distinct peaks appeared, indicating that metallic tin was successfully generated in the interlayer and was substantially free of impurities.

The nitrogen adsorption and desorption curve test and the pore size distribution test were performed on the intermediate layer material co-doped with metallic tin and carbon nanotubes prepared in example 1, and the test results are shown in fig. 6. As can be seen from the nitrogen sorption and desorption curves of fig. 6, the rapid increase in the low pressure region indicates the presence of micropores, while the presence of a significant hysteresis loop in the high and high pressure regions indicates the presence of mesoporous and macroporous structures. Furthermore, as can be seen from the pore size distribution curve of FIG. 6, the particle size distribution and the formation of many large pores are mainly attributed to the high-temperature calcination, and the relative BET surface area of the intermediate layer is 321.2m²/g。

Thermogravimetric analysis (TGA) was performed on the metallic tin and carbon nanotube co-doped interlayer material prepared in example 1, and the test results are shown in fig. 7.

Scanning Electron Microscope (SEM) tests were performed on the metallic tin and carbon nanotube co-doped interlayer material prepared in example 2, and the test results are shown in fig. 8. As can be seen from fig. 8, the intermediate layer material co-doped with metallic tin and carbon nanotubes has a significant cross-linked structure in a spider-web shape, and the carbon nanofibers are overlapped with each other to form a three-dimensional conductive skeleton.

Scanning Electron Microscope (SEM) tests were performed on the metallic tin and carbon nanotube co-doped interlayer material prepared in example 3, and the test results are shown in fig. 9. As can be seen from fig. 9, the intermediate layer material co-doped with metal tin and carbon nanotubes has a significant cross-linked structure in a spider-web shape, and the carbon nanofibers are overlapped with each other to form a three-dimensional conductive skeleton.

The material of the carbon nanotube-doped interlayer prepared in comparative example 1 was physically characterized, and the result was the same as that of metallic tin in example 1Similar to the result of the carbon nano tube co-doped intermediate layer material, the carbon nano tube co-doped intermediate layer material has an obvious cobweb-shaped cross-linking structure, and carbon nano fibers are overlapped to form a three-dimensional structure and have a rich pore structure. But the relative surface area of the carbon nanotube-doped interlayer material was 371.2m²The concentration is 50m higher than that of the intermediate layer material co-doped with the metallic tin and the carbon nano tube²In the vicinity of/g, this is probably due to the fact that the surface-generated metallic tin particles block part of the pores, thereby reducing the specific surface area. Under the same conditions, the specific surface area is certainly more favorable to be greatly increased, but in the application, the specific surface of the comparative example 1 is increased, but the increase range is smaller, and when the specific surface is more or less than the increase range, whether the adsorption and the catalytic capability of the metal tin particles are sufficient or not is more important, and of course, the adsorption effect is too strong due to too many metal tin particles, so that the sulfide is adsorbed too much, the lithium ion channel is blocked, and the performance is influenced.

2. Performance testing of lithium-sulfur batteries

The lithium sulfur batteries prepared in examples 1 to 3 and comparative examples 1 to 2 were numbered 1 to 5, respectively.

The rate performance curve of the No. 1 battery is shown in FIG. 10, and the battery shows good discharge capacity under all current densities of 0.1-2C, and the capacities of the battery are 1293.5, 1159.0, 1080.2, 984.7 and 855.2mAh/g respectively. When the current density was restored to 0.1C, the lithium-sulfur battery still had a specific discharge capacity of 1129.2 mAh/g. The electrostatic spinning interlayer material codoped by the metal tin and the carbon nano tube can provide good specific discharge capacity for the lithium-sulfur battery under different current densities when being applied to the lithium-sulfur battery, and has excellent rate performance.

The long cycle performance curve of the battery No. 1 under the high current density is shown in fig. 11, the initial discharge specific capacity under 1C is 1021.7mAh/g, even if the battery is cycled for 400 times, the reversible discharge specific capacity of the lithium-sulfur battery can still maintain 654.1mAh/g, the attenuation rate is as low as 0.088%, and the result shows that when the electrostatic spinning interlayer material codoped by metal tin and carbon nanotubes is applied to the lithium-sulfur battery, the battery still has excellent discharge capacity under the high current density.

The cyclic voltammogram of cell No. 1 is shown in fig. 12. As can be seen from fig. 12, the lithium-sulfur battery using the metal tin and carbon nanotube co-doped electrospinning material as the intermediate layer has good cycle stability and reversibility.

The batteries of nos. 1 to 5 were subjected to battery cycle performance tests, the test results are shown in fig. 13 to 17, and the results are summarized in table 1:

TABLE 1

As can be seen from table 1, the initial capacity of the No. 1-3 lithium-sulfur battery using the interlayer materials prepared in examples 1-3 was as high as 1100mAh/g or more at a current density of 0.2C, and the specific discharge capacity of 900mAh/g or more was still obtained even after 100 cycles, wherein the No. 1 battery had a specific discharge capacity of 1041.9mAh/g, and compared with the No. 4 and No. 5 batteries, the initial capacity at a current density of 0.2C was only 970mAh/g and 713.2mAh/g, and the capacity was attenuated to 857.3mAh/g and 501mAh/g after 100 cycles, and the capacity retention rate was low.

In conclusion, the electrostatic spinning material co-doped with metal tin and the carbon nano tube prepared by the invention has excellent electrochemical performance. In the invention, the electrospinning interlayer material is composed of carbon nano-fibers which are co-doped with metal tin particles and multi-walled carbon nano-tubes. When the sulfur content is as high as 72.6%, the material can have high initial specific discharge capacity of 1123.1mAh/g at 0.2C, the retention rate is 92.8% after 100 cycles, the material is hardly attenuated, the high initial specific discharge capacity of 1021.7mAh/g still can be displayed at the large current density of 1C, and the average attenuation rate of the capacity within 400 circles is as low as 0.088%, so that the material fully shows that the material of the intermediate layer can play a good role in inhibiting the shuttle-through effect, and the utilization rate of active substances is greatly improved. The excellent rate performance of the material also shows that the intermediate layer material co-doped with the metal tin and the carbon nano tube has good conductivity, so that the internal resistance of the electrode is reduced. In addition, their nearly overlapping cyclic voltammograms highlight the excellent cyclic stability of the lithium sulfur cell provided by the interlayer material.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and is not intended to limit the practice of the invention to these embodiments. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims

1. The lithium-sulfur battery interlayer material co-doped with metallic tin and carbon nano tubes is characterized in that the interlayer material has a three-dimensional cobweb structure formed by interweaving the carbon nano tubes and carbon nano fibers, the carbon nano tubes are attached to the surfaces of the crosslinked carbon nano fibers, and metallic tin nano particles are loaded on the surfaces or the interiors of the carbon nano fibers.

2. A preparation method of a metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material is characterized by comprising the following steps:

s4, carrying out pre-oxidation treatment and carbonization treatment on the spinning fiber membrane prepared in the step S3 to obtain a metal tin and carbon nano tube co-doped intermediate layer material;

wherein the carbonization treatment process is as follows: the carbonization is carried out in an argon atmosphere, the carbonization temperature is 650 ℃, the heating rate is 4-6 ℃/min, and the heat preservation time is 2-3 h.

3. The preparation method of the metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material as claimed in claim 2, wherein,

the mass ratio of the conductive polymer to the tin salt to the carbon nano tube is 10:10: 1-10: 2: 1.

4. The preparation method of the metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material as claimed in claim 2, wherein,

in step S2, the tin salt is at least one of tin chloride, tin sulfate, and tin nitrate.

5. The preparation method of the metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material as claimed in claim 2, wherein,

in the step S1 and the step S2, the stirring speed is 550-660 r/min, the temperature is 50-70 ℃, and the stirring time is 2-4 h.

6. The preparation method of the metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material as claimed in claim 2, wherein,

the carbon nanotubes added in step S2 are pre-acidified, and the treatment steps are as follows: placing the carbon nano tube in concentrated nitric acid, refluxing for 10-14 h at 45-65 ℃, and then drying for 10-14 h in a vacuum drying oven at 55-65 ℃ to obtain the acidified carbon nano tube.

7. The preparation method of the metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material as claimed in claim 2, wherein,

in the step S3, the working voltage of the electrostatic spinning treatment is 20-24 kV, and the distance between the bottom of the needle tube and the receiver is 14-16 cm.

8. The preparation method of the metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material as claimed in claim 2, wherein,

the pre-oxidation process in step S4 is as follows: the method is carried out in an air atmosphere, the temperature is 250-300 ℃, the heating rate is 2-3 ℃/min, and the heat preservation time is 1.5-2 h.

9. A lithium-sulfur battery comprising the metallic tin and carbon nanotube co-doped lithium-sulfur battery interlayer material of claim 1.