CN114751395A - Nitrogen-doped porous carbon sphere/S composite material, preparation method thereof and application thereof in lithium-sulfur battery - Google Patents

Nitrogen-doped porous carbon sphere/S composite material, preparation method thereof and application thereof in lithium-sulfur battery Download PDF

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CN114751395A
CN114751395A CN202210567983.1A CN202210567983A CN114751395A CN 114751395 A CN114751395 A CN 114751395A CN 202210567983 A CN202210567983 A CN 202210567983A CN 114751395 A CN114751395 A CN 114751395A
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porous carbon
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CN114751395B (en
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程年才
俞立跃
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Fuzhou University
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • H—ELECTRICITY
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    • H—ELECTRICITY
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    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
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Abstract

The invention discloses a nitrogen-doped porous carbon sphere/S composite material, a preparation method thereof and application thereof in a lithium-sulfur battery, wherein the preparation of the nitrogen-doped porous carbon sphere/S composite material comprises the following steps: mixing the solution A and the solution B, and reacting in a specific temperature range; separating the solid phase product, washing with deionized water, and drying to obtain white powder; the solution A comprises zinc salt and deionized water; the solution B comprises 2-methylimidazole and deionized water; carbonizing the dried sample to obtain a nitrogen-doped porous carbon sphere material; and then uniformly mixing the nitrogen-doped porous carbon spheres with the sublimed sulfur and carrying out heat treatment to obtain the nitrogen-doped porous carbon sphere/S composite material. According to the invention, the water system ZIF coordination behavior is regulated and controlled at low temperature, the nitrogen-doped porous carbon sphere material obtained by heat treatment has good physical and chemical adsorption effects and large specific surface area on polysulfide, the shuttle effect of polysulfide can be effectively inhibited, the electron transfer resistance of the anode is reduced, the volume change of charge and discharge products is relieved, the sulfur utilization rate is improved, and finally the long-cycle stability lithium-sulfur battery is obtained.

Description

Nitrogen-doped porous carbon sphere/S composite material, preparation method thereof and application thereof in lithium-sulfur battery
Technical Field
The invention belongs to the technical field of batteries, and particularly relates to a nitrogen-doped porous carbon sphere/S composite material, a preparation method thereof and application thereof in a lithium-sulfur battery.
Background
With the continuous development of human society, the demand for energy is increasing day by day, and the traditional fossil energy cannot meet the green and sustainable development concept of the current society due to the defects of non-regeneration, environmental pollution and the like. Therefore, the development of clean and efficient energy acquisition and storage technology is a common pursuit of the whole human society. The lithium-sulfur battery has high theoretical specific capacity of 1675 mAh g-1And theoretical energy density 2600 Wh.Kg-1And is considered to be one of the most promising energy storage systems in the new generation of battery systems. Meanwhile, in the lithium-sulfur battery, the sulfur anode material has the advantages of abundant reserves, low price, environmental friendliness and the like, so that the lithium-sulfur battery is widely concerned and researched by numerous scholars at home and abroad. However, although Li-S batteries have attractive application prospects, there are still several problems that hinder the practical application of Li-S batteries:
(1) shuttle effect: polysulfide as intermediate product of redox reaction is dissolved in common ether-base organic electrolyte, and under the action of concentration gradient, polysulfide diffuses to Li metal cathode and reacts with Li in cathode +Combine to form Li2S, causing loss of active substances, attenuation of specific capacity of the battery and reduction of coulombic efficiency;
(2) volume expansion: due to Li2S(1.66g cm−3) And S (2.03g cm)−3) Density difference between them, so that the discharge product Li2S can generate volume expansion to influence the structure of the anode matrix;
(3) poor conductivity of the active material: sulfur and discharge product Li2S/Li2S2The insulating property of (2) results in low utilization of the active material.
The water system ZIF has the advantages of simple preparation, low cost and the like. But its micron-scale size makes it difficult to have a high specific surface area and porosity. One aqueous ZIF preparation strategy at room temperature, as disclosed in patent CN 110876961B, has monomer sizes on the order of microns, making it difficult to obtain large specific surface areas. This is disadvantageous for lithium sulfur battery anodes that require a high electrical contact area.
In order to overcome the problems, the nitrogen-doped porous carbon spheres with high specific surface area and porosity are obtained by regulating the preparation behavior of the water system ZIF at low temperature. The positive electrode of the lithium-sulfur battery is provided by compounding the nitrogen-doped porous carbon spheres and sulfur, meets the characteristics of polysulfide adsorption, capacity of accommodating volume change of charge and discharge products, high conductivity and the like, and shows excellent charge and discharge performance when applied to the lithium-sulfur battery.
Disclosure of Invention
The invention aims to provide a nitrogen-doped porous carbon sphere/S composite material, a preparation method thereof and application thereof in a lithium sulfur battery.
In order to realize the purpose, the technical scheme of the invention is as follows:
the preparation method of the nitrogen-doped porous carbon sphere/S composite material comprises the following steps:
(1) weighing zinc salt, adding the zinc salt into deionized water, and stirring until the zinc salt is completely dissolved to prepare a solution A;
(2) weighing 2-methylimidazole, adding into deionized water, and stirring until the 2-methylimidazole is completely dissolved to prepare a solution B;
(3) mixing the solution A and the solution B, and stirring and reacting uniformly in a specific temperature range;
(4) centrifugally separating the reaction solution obtained in the step (3) to obtain a solid-phase product, washing the solid-phase product with deionized water, and drying the washed solid-phase product to obtain white powder;
(5) putting the white powder obtained in the step (4) into a quartz boat, and carbonizing the white powder in a nitrogen atmosphere to obtain nitrogen-doped porous carbon spheres;
(6) and adding the obtained nitrogen-doped porous carbon spheres and sublimed sulfur into a carbon disulfide solution, uniformly mixing, drying to constant weight, and carrying out heat treatment in a nitrogen atmosphere to obtain the nitrogen-doped porous carbon sphere/S composite material.
Further, the concentration of zinc salt in the solution A in the step (1) is 0.002-2 mol/L; the zinc salt is one or more of Zn (NO3)2, ZnSO4, (CH3COO)2Zn and ZnCl 2.
Further, the concentration of 2-methylimidazole in the solution B in the step (2) is 0.05-5 mol/L.
Further, the reaction temperature in the step (3) is 0-20 ℃, and the reaction time is 2-9 h.
Further, the temperature of carbonization in the step (5) is 700-.
Further, the temperature of the heat treatment in the step (6) was 155 ℃.
Further, in the step (6), the mass ratio of the nitrogen-doped porous carbon spheres to the sublimed sulfur is 3:7-1: 9.
The second purpose of the invention is to disclose a lithium-sulfur battery, which comprises a positive electrode and a negative electrode, wherein a diaphragm and an electrode solution are arranged between the positive electrode and the negative electrode, and the positive electrode comprises the nitrogen-doped porous carbon sphere/S composite material.
Further, the positive electrode also includes an aluminum foil.
Further, the negative electrode is metallic lithium.
Further, the separator is a single-layer separator composed of polypropylene (PP).
Further, the positive electrode is a nitrogen-doped porous carbon sphere/S-aluminum foil composite positive electrode, and the preparation process comprises the following steps:
(1) dispersing the obtained nitrogen-doped porous carbon sphere/S composite material, a conductive agent and a binder in N-methylpyrrolidone according to the mass ratio of 8:1:1, uniformly mixing, wherein the conductive agent can be Super p Li or carbon nanotube powder, and the binder is polyvinylidene fluoride;
(2) Coating the slurry obtained in the step (1) on the surface of an aluminum foil;
(3) drying in a vacuum drying oven at 30-60 deg.C for 12-36 hr.
The carbon-sulfur composite lithium-sulfur battery positive electrode material obtained by the invention has the following advantages:
(1) the nitrogen-doped porous carbon spheres prepared by the method have rich nitrogen-doped sites and porous structures, have strong chemical and physical adsorption capacity on polysulfide, and effectively inhibit shuttle effect;
(2) the porous structure on the surface of the nitrogen-doped porous carbon sphere can buffer the volume change in the charging and discharging process;
(3) the high-temperature carbonized nitrogen-doped porous carbon spheres have excellent conductivity and have a high electrical contact area with active substances, so that the polarization phenomenon in the charge-discharge process, particularly under high current density, can be effectively reduced, and the high sulfur utilization rate can be realized under high magnification.
Drawings
FIG. 1 is an SEM representation of nitrogen-doped porous carbon spheres prepared in example 1;
FIG. 2 is an SEM representation of nitrogen-doped porous carbon spheres prepared in example 2;
fig. 3 is an SEM characterization of nitrogen-doped porous nanoplates prepared in comparative example 1;
FIG. 4 is the non-carbonized XRD patterns of example 1 and comparative example 1;
FIG. 5 is N of nitrogen-doped porous carbon spheres prepared in example 1 2Adsorption and desorption curves and aperture distribution maps;
FIG. 6 is N of nitrogen-doped porous nanoplatelets prepared according to comparative example 12Adsorption and desorption curves and aperture distribution maps;
fig. 7 is a cyclic voltammogram of the lithium sulfur batteries prepared in example 1 and comparative example 1;
fig. 8 is an electrochemical impedance spectrum of the lithium sulfur batteries prepared in example 1 and comparative example 1;
FIG. 9 is a graph of the cycle performance at 1C for the lithium sulfur battery prepared in example 1;
fig. 10 is a graph of cycle performance at 1C for the lithium sulfur battery prepared in comparative example 1.
Detailed Description
The following examples are given to illustrate the present invention but not to limit the scope of the present invention.
Example 1
Step 1: preparation of positive electrode sulfur carrier nitrogen-doped porous carbon sphere of lithium-sulfur battery
(1) Weighing a proper amount of zinc nitrate hexahydrate, adding the zinc nitrate hexahydrate into deionized water, and preparing 0.012 mol/L zinc nitrate aqueous solution to obtain solution A;
(2) weighing a proper amount of 2-methylimidazole, adding into deionized water, and preparing 0.12 mol/L2-methylimidazole water solution to obtain a solution B;
(3) mixing the solution A and the solution B, controlling the temperature of the reaction solution to be 10 ℃, and stirring for reaction for 3 hours;
(4) transferring the reaction solution obtained in the step (3) into a centrifuge tube, separating a solid-phase product by using a centrifuge at 7000rpm/min, washing with deionized water, and freeze-drying to obtain white powder;
(5) Putting the white powder obtained in the step (4) into a quartz boat, and carbonizing at 900 ℃ in a nitrogen atmosphere to obtain nitrogen-doped porous carbon spheres;
and 2, step: preparation of nitrogen-doped porous carbon sphere/S composite material
(6) Adding the obtained nitrogen-doped porous carbon spheres and sublimed sulfur into a carbon disulfide solution according to the mass ratio of 2:8, uniformly mixing, drying to constant weight, and carrying out heat treatment at 155 ℃ for 12 hours in a nitrogen atmosphere to obtain the nitrogen-doped porous carbon sphere/S composite material;
and step 3: preparation of nitrogen-doped porous carbon sphere/S-aluminum foil composite anode
(1) Dispersing the obtained nitrogen-doped porous carbon sphere/S composite material, a conductive agent and a binder in N-methylpyrrolidone according to the mass ratio of 8:1:1, uniformly mixing, wherein the conductive agent can be Super p Li or carbon nanotube powder, and the binder is polyvinylidene fluoride;
(2) coating the slurry obtained in the step (1) on the surface of an aluminum foil;
(3) drying in a vacuum drying oven at 40-60 deg.C for 12-36 hr.
And 4, step 4: lithium sulfur battery assembly
Using the nitrogen-doped porous carbon sphere/S-aluminum foil composite anode prepared in the step 3 as an anode, and using metalPlacing a commercial PP diaphragm between a positive electrode and a negative electrode as a negative electrode, placing the diaphragm in a battery case, dropwise adding electrolyte on two sides of the diaphragm, and pressurizing and packaging to complete the assembly of the lithium-sulfur battery, wherein the electrolyte is 1M LiTFSI-DME/DOL (the volume ratio of DME to DOL is = 1: 1) and contains 1 wt% LiNO 3。
Example 2
Step 1: preparation of positive electrode sulfur carrier nitrogen-doped porous carbon sphere of lithium-sulfur battery
(1) Weighing a proper amount of zinc nitrate hexahydrate, adding the zinc nitrate hexahydrate into deionized water, and preparing a 0.012 mol/L zinc nitrate aqueous solution to prepare a solution A;
(2) weighing a proper amount of 2-methylimidazole, adding into deionized water, and preparing 0.12 mol/L2-methylimidazole water solution to obtain a solution B;
(3) mixing the solution A and the solution B, controlling the temperature of the reaction solution to be 20 ℃, and stirring for reaction for 3 hours;
(4) transferring the reaction solution obtained in the step (3) into a centrifuge tube, separating a solid-phase product by using a centrifuge at 7000rpm/min, washing with deionized water, and freeze-drying to obtain white powder;
(5) putting the white powder obtained in the step (4) into a quartz boat, and carbonizing at 900 ℃ in a nitrogen atmosphere to obtain nitrogen-doped porous carbon spheres;
step 2: preparation of nitrogen-doped porous carbon sphere/S composite material
(6) Adding the obtained nitrogen-doped porous carbon spheres and sublimed sulfur into a carbon disulfide solution according to the mass ratio of 2:8, uniformly mixing, drying to constant weight, and carrying out heat treatment at 155 ℃ for 12 hours in a nitrogen atmosphere to obtain the nitrogen-doped porous carbon sphere/S composite material;
and step 3: preparation of nitrogen-doped porous carbon sphere/S-aluminum foil composite anode
(1) Dispersing the obtained nitrogen-doped porous carbon sphere/S composite material, a conductive agent and a binder in N-methylpyrrolidone according to the mass ratio of 8:1:1, uniformly mixing, wherein the conductive agent can be Super p Li or carbon nanotube powder, and the binder is polyvinylidene fluoride;
(2) Coating the slurry obtained in the step (1) on the surface of an aluminum foil;
(3) drying in a vacuum drying oven at 40-60 deg.C for 12-36 hr.
And 4, step 4: lithium sulfur battery assembly
And 3, taking the nitrogen-doped porous carbon sphere/S-aluminum foil composite positive electrode prepared in the step 3 as a positive electrode, taking metal lithium as a negative electrode, placing a commercial PP diaphragm between the positive electrode and the negative electrode, placing the diaphragm in a battery case, dropwise adding electrolyte on two sides of the diaphragm, and pressurizing and packaging to complete the assembly of the lithium-sulfur battery, wherein the electrolyte is 1M LiTFSI-DME/DOL (the volume ratio of DME to DOL = 1: 1) and contains 1 wt% of LiNO 3. Comparative example 1
Step 1: preparation of positive electrode sulfur carrier nitrogen-doped porous nanosheet of lithium-sulfur battery
(1) Weighing a proper amount of zinc nitrate hexahydrate, adding the zinc nitrate hexahydrate into deionized water, and preparing 0.012 mol/L zinc nitrate aqueous solution to obtain solution A;
(2) weighing 2-methylimidazole, adding into deionized water, and preparing 0.12 mol/L2-methylimidazole water solution to obtain solution B;
(3) mixing the solution A and the solution B, controlling the temperature of the reaction solution to be 25 ℃, and stirring for 3 hours;
(4) transferring the reaction solution obtained in the step (3) into a centrifuge tube, separating a solid-phase product by using a centrifuge at 7000rpm/min, washing with deionized water, and freeze-drying to obtain white powder;
(5) Putting the white powder obtained in the step (4) into a quartz boat, and carbonizing at 900 ℃ in a nitrogen atmosphere to obtain a nitrogen-doped porous nanosheet;
and 2, step: preparation of nitrogen-doped porous nanosheet/S composite material
(6) Adding a carbon disulfide solution into the obtained nitrogen-doped porous nanosheet and sublimed sulfur according to the mass ratio of 2:8, uniformly mixing, drying to constant weight, and carrying out heat treatment at 155 ℃ for 12 hours in a nitrogen atmosphere to obtain the nitrogen-doped porous nanosheet/S composite material;
and 3, step 3: preparation of nitrogen-doped porous nanosheet/S-aluminum foil composite positive electrode
(1) Dispersing the obtained nitrogen-doped porous nanosheet/S composite material, a conductive agent and a binder in a mass ratio of 8:1:1 in N-methylpyrrolidone, uniformly mixing, wherein the conductive agent can be Super p Li or carbon nanotube powder, and the binder is polyvinylidene fluoride;
(2) coating the slurry obtained in the step (1) on the surface of an aluminum foil;
(3) drying in a vacuum drying oven at 30-60 deg.C for 12-36 hr.
And 4, step 4: lithium sulfur battery assembly
And 3, taking the nitrogen-doped porous nanosheet/S-aluminum foil composite positive electrode prepared in the step 3 as a positive electrode and metal lithium as a negative electrode, placing a commercial PP diaphragm between the positive electrode and the negative electrode, placing the diaphragm into a battery shell, dropwise adding electrolyte on two sides of the diaphragm, and pressurizing and packaging to complete the assembly of the lithium-sulfur battery, wherein the electrolyte is 1M LiTFSI-DME/DOL (the volume ratio of DME to DOL is = 1: 1) and contains 1 wt% of LiNO 3。
Fig. 1 and 2 are SEM images of nitrogen-doped porous carbon spheres prepared in examples 1 and 2, and it can be seen from the SEM images that the nitrogen-doped porous carbon spheres have a rough surface, which is formed due to volatilization of Zn during high-temperature carbonization, which provides a large number of adsorption sites for polysulfides, contributing to improvement of cycle stability of a lithium-sulfur battery. Fig. 3 is an SEM image of nitrogen-doped porous nanosheets prepared in comparative example 1, from which it can be seen that the nitrogen-doped porous nanosheets are platelet-shaped structures having a thickness of about 200 nm. According to the characterization result of SEM, the microstructure of the water system ZIF derivative can be effectively controlled by regulating and controlling the reaction temperature, and the small-size nano nitrogen-doped porous carbon material is obtained.
To further demonstrate the regulatory effect of reaction temperature on aqueous ZIF profiling behavior, XRD tests were performed on samples of example 1 and comparative example 1 that were not carbonized. As shown in fig. 4, the two have distinct crystal structures, and the diffraction peak of comparative example 1 has an extremely strong peak, which indicates that comparative example 1 has excellent crystallinity and intact crystal planes. While example 1 shows only one large broad peak between 10 and 20 degrees, and three characteristic peaks belonging to ZnO between 30 and 40 degrees, the peak strength of which is much weaker than that of comparative example 1 and has weaker crystallinity, and the crystal structures of the two show larger difference. This is because, under low temperature conditions, part of the crystal plane coordination of the aqueous ZIF is suppressed, resulting in incomplete coordination during the reaction. It is because the unsaturated coordination of example 1 makes the crystal face of the sample partially incomplete or not formed to cause it to form a spherical structure.
FIG. 5 shows example 1N2Adsorption and desorption curve and pore diameterDistribution diagram, from which N of example 1 can be seen2The adsorption and desorption curve is a typical IV-type isotherm, which is N typical of the porous carbon material2Adsorption and desorption curve types. Example 1 has a large number of microporous structures with pore diameters of less than 1nm and simultaneously has a mesoporous structure with pore diameters of 20-30nm, demonstrating that example 1 has a porous structure. FIG. 6 is N of comparative example 12The absorption and desorption curves and the pore size distribution diagram show that the micro-mesoporous structure and the mesoporous structure of the comparative example 1 are obviously reduced compared with the micro-mesoporous structure and the mesoporous structure of the example 1. More porous structures can effectively improve the adsorption capacity of the carrier to polysulfide, thereby inhibiting the shuttle effect.
To demonstrate the acceleration effect of nitrogen-doped porous carbon spheres on sulfur redox kinetics, a half-cell cyclic voltammetry test was performed on nitrogen-doped porous carbon spheres/S, as shown in fig. 7. Compared with the comparative example 1, the two reduction peaks in the example 1 in the figure have higher potential and current response, which shows that the nitrogen-doped porous carbon spheres can accelerate the reaction kinetics of the sulfur reduction process, and the oxidation peaks also show higher current response, which proves that the nitrogen-doped porous carbon spheres can effectively reduce the reaction energy barrier of the sulfur redox kinetics. To further prove the influence of the nitrogen-doped porous carbon spheres on the sulfur redox kinetics, a half-cell electrochemical impedance spectrum test is performed on the nitrogen-doped porous carbon spheres/S, the impedance spectrum shown in fig. 8 consists of charge transfer impedance (Rct) and diffusion impedance of a high-frequency region, while the embodiment 1 has a smaller impedance value, and the nitrogen-doped porous carbon spheres are also proved to be capable of effectively promoting the sulfur redox kinetics.
Fig. 9 is a long cycle performance test of example 1, and it can be seen that the battery has good cycle stability.
Fig. 10 is a long cycle performance test of the nitrogen-doped porous nanosheet/S, and it can be seen that the cycle stability of the battery is significantly reduced compared to the nitrogen-doped porous carbon sphere/S composite positive electrode prepared in example 1.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims (10)

1. The preparation method of the nitrogen-doped porous carbon sphere/S composite material is characterized by comprising the following steps of:
(1) weighing zinc salt, adding the zinc salt into deionized water, and stirring until the zinc salt is completely dissolved to prepare a solution A;
(2) weighing 2-methylimidazole, adding into deionized water, and stirring until the 2-methylimidazole is completely dissolved to obtain a solution B;
(3) mixing the solution A and the solution B, and stirring and reacting uniformly in a specific temperature range;
(4) centrifugally separating the reaction solution obtained in the step (3) to obtain a solid-phase product, washing the solid-phase product with deionized water, and drying the washed solid-phase product to obtain white powder;
(5) Putting the white powder obtained in the step (4) into a quartz boat, and carbonizing in a nitrogen atmosphere to obtain nitrogen-doped porous carbon spheres;
(6) and adding the obtained nitrogen-doped porous carbon spheres and sublimed sulfur into a carbon disulfide solution, uniformly mixing, drying to constant weight, and carrying out heat treatment in a nitrogen atmosphere to obtain the nitrogen-doped porous carbon sphere/S composite material.
2. The method for preparing the nitrogen-doped porous carbon sphere/S composite material according to claim 1, wherein the method comprises the following steps: the concentration of zinc salt in the solution A in the step (1) is 0.002-2 mol/L; the zinc salt being Zn (NO)3)2、ZnSO4、(CH3COO)2Zn and ZnCl2One or more of them.
3. The method for preparing the nitrogen-doped porous carbon sphere/S composite material according to claim 1, wherein the method comprises the following steps: the concentration of the 2-methylimidazole in the solution B in the step (2) is 0.05-5 mol/L.
4. The method for preparing a nitrogen-doped porous carbon sphere/S composite material according to claim 1, wherein the method comprises the following steps: the reaction temperature in the step (3) is 0-20 ℃, and the reaction time is 2-9 h.
5. The method for preparing a nitrogen-doped porous carbon sphere/S composite material according to claim 1, wherein the method comprises the following steps: the carbonization temperature in the step (5) is 700-1300 ℃, and the heating rate is 1-10 ℃/min.
6. The method for preparing a nitrogen-doped porous carbon sphere/S composite material according to claim 1, wherein the method comprises the following steps: the temperature of the heat treatment in the step (6) was 155 ℃.
7. The method of manufacturing a positive electrode for a lithium-sulfur battery according to claim 1, wherein: in the step (6), the mass ratio of the nitrogen-doped porous carbon spheres to the sublimed sulfur is 3:7-1: 9.
8. A nitrogen-doped porous carbon sphere/S composite material prepared by the preparation method according to any one of claims 1 to 7.
9. Use of the nitrogen-doped porous carbon sphere/S composite of claim 8 in a lithium sulfur battery.
10. Use according to claim 9, characterized in that: the nitrogen-doped porous carbon sphere/S composite material is used for preparing the anode of the lithium-sulfur battery, and the preparation method comprises the following steps:
1) dispersing the nitrogen-doped porous carbon sphere/S composite material, the conductive agent and the binder in a mass ratio of 8:1:1 into N-methylpyrrolidone, and uniformly mixing to obtain slurry;
2) coating the slurry obtained in the step 1) on the surface of an aluminum foil;
3) and (3) drying in a vacuum drying oven at the temperature of 30-60 ℃ for 12-36 hours to obtain the nitrogen-doped porous carbon sphere/S-aluminum foil composite anode.
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