A molybdenum carbide / nitrogen-doped carbon composite material, a preparation method and application thereof

Abstract

The application relates to a molybdenum carbide / nitrogen-doped carbon composite material and a preparation method and application thereof, and belongs to the technical field of new energy materials and devices. Ammonium molybdate, glucose and g-C3N4 are uniformly mixed, and then subjected to hydrothermal treatment and high-temperature calcination treatment to obtain a composite material (Mo2C / NC) in which nano Mo2C electrocatalysts are dispersedly distributed in a nitrogen-doped carbon matrix. The nitrogen-doped carbon in the composite material has a hierarchical porous structure, which enhances electrolyte permeation and ion transmission capacity; the nitrogen-doped active sites not only enhance the adsorption performance of the porous carbon to polysulfides, but also can optimize the coordination structure of Mo2C to improve the catalytic activity of the Mo2C; the Mo2C can chemically adsorb and efficiently catalyze the reversible conversion of polysulfides, and improve the utilization rate of active substances. When the composite material is used as a positive electrode additive of a lithium-sulfur battery, the polysulfide dissolution and shuttling can be effectively inhibited, and the battery exhibits high specific capacity, rate performance and excellent cycle reversibility.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy materials and devices, and particularly relates to a molybdenum carbide / nitrogen-doped carbon composite material and a preparation method and application thereof. BACKGROUND

[0002] Under the background of the increasingly severe global energy crisis and the continuous improvement of environmental awareness, breakthrough progress in electrochemical energy storage technology has become the key to promoting efficient, clean and sustainable energy development. Among numerous new types of electrochemical energy storage technologies, lithium-sulfur (Li-S) batteries based on the multi-step and multi-electron reversible oxidation-reduction reaction of elemental sulfur have advantages such as high theoretical specific capacity (1675 mAh g-1), abundant sulfur resources and good environmental friendliness, and are considered as one of the most promising candidates for the next generation of electrochemical energy storage systems. -1

[0003] However, Li-S batteries still face the following main bottlenecks in performance improvement and commercialization: (1) Both sulfur and its discharge product lithium sulfide (Li2S) are insulators of electrons and lithium ions, resulting in slow battery redox kinetics and low active sulfur utilization; (2) The intermediate product lithium polysulfide (LiPSs) produced during charging and discharging will cause the "shuttle effect", which not only causes the continuous loss of active materials in the cycle, but also accelerates capacity decay and reduces coulombic efficiency due to the slow conversion kinetics of LiPSs; (3) The significant volume change of sulfur during charging and discharging easily leads to the detachment of active materials from the current collector, further affecting the structural stability of the battery. Therefore, it is crucial to explore effective strategies to regulate the conversion of LiPSs and inhibit the shuttle effect to improve the stability and performance of Li-S batteries.

[0004] To solve these problems, researchers have tried various strategies, such as designing composite conductive sulfur carriers, optimizing electrolytes, functional separators / interlayers, etc. to inhibit the dissolution and shuttle of LiPSs and accelerate the reversible conversion of LiPSs. Among the many candidate sulfur carriers, porous carbon materials are considered as ideal sulfur carrier materials due to their high electrical conductivity, excellent specific surface area and structural stability. However, due to the lack of polar active sites, the adsorption capacity of LiPSs is weak, and the catalytic conversion effect is limited. In contrast, polar metal compounds have good adsorption capacity for LiPSs, but their electrical conductivity is usually poor, which easily saturates the adsorption sites and is not conducive to the rapid conversion of LiPSs. Studies have shown that by introducing polar catalytic materials into porous carbon, the electrochemical performance of Li-S batteries can be significantly improved. Among them, metal carbides (such as molybdenum carbide) have excellent electrical conductivity, high chemical adsorption performance and catalytic activity, which can effectively promote the catalytic conversion of LiPSs, thereby significantly enhancing the electrochemical reaction activity and overall performance of Li-S batteries. SUMMARY ​

[0005] The present application aims at the deficiencies of the existing lithium-sulfur battery cathode material and its preparation technology, and provides a molybdenum carbide / nitrogen-doped carbon composite material, a preparation method and application thereof. The composite material can be used as a functional additive of a lithium-sulfur battery cathode, has excellent electrical conductivity and high efficient lithium polysulfide chemical adsorption and catalytic conversion capacity, thereby significantly improving the capacity, cycle stability and rate performance of the lithium-sulfur battery.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] The present application provides a molybdenum carbide / nitrogen-doped carbon composite material. In the composite material, fine Mo2C nanoparticles are uniformly dispersed in a nitrogen-doped carbon matrix.

[0008] The present application provides a preparation method of a molybdenum carbide / nitrogen-doped carbon composite material. g-C3N4 is used as a template, ammonium molybdate ((NH4)2MoO4·4H2O) is used as a molybdenum source, and glucose (C6H 12 O6) is used as a carbon source. After being uniformly mixed, the mixture is subjected to hydrothermal treatment and high-temperature calcination to obtain the molybdenum carbide / nitrogen-doped carbon composite material (Mo2C / NC).

[0009] As a preferred technical scheme of the present application, the specific steps of the preparation method are as follows:

[0010] (1) 20-25 g of urea is placed in a tube furnace for high-temperature calcination to obtain g-C3N4. The calcination atmosphere is air, the temperature is 520-560℃, the holding time is 3-4 h, and the heating rate is 3-5℃ / min;

[0011] (2) 0.1-0.2 g of (NH4)2MoO4·4H2O and 0.4-0.6 g of C6H 12 O6 are dissolved in 20 mL of deionized water at room temperature, and 0.1-0.2 g of g-C3N4 is ultrasonically dispersed in the solution, and stirred for 8-12 h to obtain a milky white solution;

[0012] (3) the mixed solution prepared in step (2) is placed in a reaction kettle for hydrothermal reaction at a temperature of 120-150℃ for 8-12 h; then the reaction product is suction filtered and dried for use;

[0013] (4) the product obtained in step (3) is subjected to high-temperature calcination treatment in an inert atmosphere. The calcination atmosphere is argon, the temperature is 800-850℃, the holding time is 2-3 h, and the heating rate is 2-4℃ / min to obtain Mo2C / NC;

[0014] (5) The Mo2C / NC prepared in step (4) is mixed with Ketjen black (KB) in a certain proportion to obtain a conductive carrier (KB / Mo2C / NC), wherein the mass ratio of Mo2C / NC is 2% to 8%; the conductive carrier is combined with active sulfur by a molten sulfur infiltration process to obtain a composite sulfur cathode material (KB / Mo2C / NC-S) for lithium-sulfur batteries.

[0015] The application also provides application of the Mo2C / NC composite material in a lithium-sulfur battery cathode material. The composite sulfur cathode material (KB / Mo2C / NC-S) for lithium-sulfur batteries, a conductive agent and a binder are mixed in a mass ratio of 8:1:1 to obtain a slurry. The slurry is uniformly coated on an aluminum foil, vacuum dried at 70℃ for 24h and cut to obtain a lithium-sulfur battery cathode sheet, wherein the active sulfur area loading is 1.5 to 2.0 mg / cm2. 2 The Mo2C / NC composite material can be used as a functional additive of a lithium-sulfur battery cathode to effectively improve the utilization rate of active sulfur.

[0016] Compared with the prior art, the application has the following beneficial effects:

[0017] The Mo2C / NC composite material prepared in the application is used as a functional additive of a lithium-sulfur battery cathode, mixed with Ketjen black (KB) and used as a conductive carrier (KB / Mo2C / NC) of active sulfur and a sulfur molten composite to obtain a composite cathode material (KB / Mo2C / NC-S) for lithium-sulfur batteries. The nano Mo2C electrocatalyst is dispersedly distributed in the nitrogen-doped carbon matrix. The nitrogen-doped carbon has a hierarchical porous structure, which enhances the electrolyte permeation and ion transmission capacity; the nitrogen-doped active sites not only enhance the adsorption performance of the porous carbon to polysulfides, but also can improve the catalytic activity of Mo2C by optimizing the coordination structure of Mo2C; Mo2C can chemically adsorb and efficiently catalyze the reversible conversion of polysulfides, thereby improving the utilization rate of active substances. The composite material used as a functional additive of a lithium-sulfur battery cathode can effectively inhibit the dissolution and shuttle of polysulfides, and significantly improve the capacity, rate performance and cycle life of the battery.

[0018] In addition, the preparation process of the composite material is simple, easy to operate and has high yield, which is conducive to industrialization and expansion, and provides a new way for preparing lithium-sulfur battery cathode additive materials. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The XRD curve of g-C3N4 in Example 1.

[0020] Figure 2 The XRD curve of the Mo2C / NC composite material (Mo2C / NC) in Example 1.

[0021] Figure 3 SEM morphology of g-C3N4 in Example 1.

[0022] Figure 4 SEM morphology of molybdenum carbide / nitrogen-doped carbon composite (Mo2C / NC) in Example 1.

[0023] Figure 5 (a) TEM and (b) HRTEM morphology of molybdenum carbide / nitrogen-doped carbon composite (Mo2C / NC) in Example 1.

[0024] Figure 6 (a) N2 adsorption-desorption isotherm and (b) DFT pore size distribution of molybdenum carbide / nitrogen-doped carbon composite (Mo2C / NC) in Example 1 (the inset part is the curve graph of pore size distribution ≤ 2 nm).

[0025] Figure 7 XPS full spectrum (a) and XPS high-resolution spectrum of C1s (b), Mo3d (c), N 1s (d) elements of molybdenum carbide / nitrogen-doped carbon composite (Mo2C / NC) in Example 1.

[0026] Figure 8 Thermogravimetric analysis of molybdenum carbide / nitrogen-doped carbon composite (Mo2C / NC) in Example 1.

[0027] Figure 9 The results of the constant current charge-discharge cycle test of lithium-sulfur batteries prepared in Example 1 and Comparative Example 1 at 0.5C rate.

[0028] Figure 10 The performance test results of lithium-sulfur batteries prepared in Example 1 and Comparative Example 1 at different rates. DETAILED DESCRIPTION

[0029] The molybdenum carbide / nitrogen-doped carbon composite (Mo2C / NC) and the preparation method and application thereof provided by the present application are further described in detail below in combination with the examples and the accompanying drawings.

[0030] Example 1

[0031] The present example provides a molybdenum carbide / nitrogen-doped carbon composite, which is prepared by using g-C3N4 as a template, ammonium molybdate ((NH4)2MoO4·4H2O) as a molybdenum source, and glucose (C6H 12 O6) as a carbon source, uniformly mixing them, and then performing hydrothermal treatment and high-temperature calcination to obtain the molybdenum carbide / nitrogen-doped carbon composite (Mo2C / NC). The specific steps are as follows:

[0032] (1) 20 g urea was placed in a tube furnace for high-temperature calcination to obtain g-C3N4, wherein the calcination atmosphere was air, the temperature was 550°C, the holding time was 4 h, and the heating rate was 5°C / min.

[0033] (2) 0.12 g (NH4)2MoO4·4H2O and 0.5 g C6H 12 O6 were dissolved in 20 mL deionized water at room temperature, and 0.13 g g-C3N4 was weighed and ultrasonically dispersed in the solution, and stirred for 8 h to obtain a milky white solution.

[0034] (3) The mixed solution prepared in step (2) was placed in a reaction kettle for hydrothermal reaction at a temperature of 120°C for 10 h; then the reaction product was suction filtered and dried for use.

[0035] (4) The product obtained in step (3) was placed in an inert atmosphere for high-temperature calcination, wherein the calcination atmosphere was argon, the temperature was 800°C, the holding time was 3 h, and the heating rate was 2°C / min, to obtain Mo2C / NC.

[0036] (5) The Mo2C / NC prepared in step (4) was fully ground and mixed with KB in a certain proportion to obtain a conductive carrier (KB / Mo2C / NC), wherein the mass ratio of Mo2C / NC was 3%. The conductive carrier was compounded with active sulfur by a molten sulfur infiltration process to obtain a composite sulfur positive electrode material (KB / Mo2C / NC-S) for lithium-sulfur batteries.

[0037] The application of the molybdenum carbide / nitrogen-doped carbon composite material in the positive electrode material of a lithium-sulfur battery, the KB / Mo2C / NC-S, a conductive agent Super P, and a binder polyvinylidene fluoride PVDF were fully ground and mixed in a mass ratio of 8:1:1 to obtain a slurry. The obtained slurry was uniformly coated on an aluminum foil, vacuum dried at 70°C for 24 h, and cut to obtain a lithium-sulfur battery positive electrode sheet, wherein the active sulfur area loading was 1.6 mg / cm 2 .

[0038] Please refer to Figure 1 , which is the XRD curve of the g-C3N4 prepared in the embodiment. It can be known from Figure 3 that the carbon matrix has a wrinkled sheet-like disordered stacking structure, which can greatly increase the specific surface area of the composite material, is conducive to enhancing the adsorption performance of the carbon matrix on polysulfides, and can enhance the infiltration and penetration of the electrolyte.

[0039] Please refer to Figure 2 , which is the XRD curve of the molybdenum carbide / nitrogen-doped carbon composite material (Mo2C / NC). It can be known from Figure 4 and Figure 5It is known that fine Mo2C nanoparticles are dispersed in a nitrogen-doped carbon matrix. Mo2C can chemically adsorb and efficiently catalyze the reversible transformation of polysulfides, enhancing electrochemical reaction kinetics and improving the utilization rate of active materials. Furthermore, combined with… Figure 6 It can be seen that the specific surface area of ​​this composite material is 184.82 m². 2 / g, the high specific surface area can provide abundant adsorption and catalytic polysulfide reaction sites.

[0040] Please see Figure 7 The figure shows the XPS full spectrum (a) and high-resolution XPS spectra of C1s (b), Mo 3d (c), and N 1s (d) elements of the molybdenum carbide / nitrogen-doped carbon composite material (Mo2C / NC). The Mo2C / NC composite material contains four elements: C, N, O, and Mo. Figure 7 a) where the O element mainly originates from the adsorption of moisture from the air and surface oxidation of the sample. In the high-resolution C1s spectrum ( Figure 7 b) Three features are present: including C-Mo bonds (285.0 eV), CC / C=C bonds (284.2 eV), and CN bonds (287.5 eV); in the high-resolution spectrum of Mo 3d ( Figure 7 c) There are six characteristic peaks: the characteristic peaks at 227.8 eV and 230.9 eV correspond to Mo. 2+ 3D 5 / 2 and Mo 2+ 3D 3 / 2 The binding energies, with peaks at 228.9 eV and 233.3 eV corresponding to Mo, are shown. 4+ 3D 5 / 2 and Mo 4+ 3D 3 / 2 The peaks at 231.8 eV and 235.6 eV correspond to Mo. 6+ 3D 5 / 2 and Mo 6+ 3D 3 / 2 The binding energy of Mo 6+ and Mo 4+ This is due to the surface oxidation of Mo2C; in the high-resolution N1s spectrum ( Figure 8 d) Three characteristic peaks are present: including pyridine-N bond (397.2 eV), graphite-N bond (400.4 eV), and Mo 3p. 3 / 2 (393.6 eV). XPS results indicate that molybdenum, nitrogen, and carbon are bonded together in the molybdenum carbide / nitrogen-doped carbon composite (Mo2C / NC). Nitrogen-doped active sites not only enhance the adsorption performance of porous carbon for polysulfides, but also improve its catalytic activity by optimizing the coordination structure of Mo2C.

[0041] Please see Figure 9The figure is a thermogravimetric analysis curve of molybdenum carbide / nitrogen-doped carbon composite (Mo2C / NC), the temperature range is 0-700℃, and the atmosphere is air. Mo2C is oxidized to MoO3 at about 150℃, and the carbon material disappears by burning in air at about 350℃. The content of Mo2C is calculated to be 34wt%.

[0042] The KB / Mo2C / NC conductive carrier prepared in the example is fused with active sulfur as a positive electrode material, lithium sheet as a negative electrode; Celgard 2500 type polypropylene film is used as a separator; lithium bis(trifluoromethylsulfonate) imide (LiTFSI) is used as a solute, 1,3-dioxolane DOL and dimethyl ether DME in a volume ratio of 1:1 are used as solvents, a solution with a concentration of 1mol·L -1 -1 is prepared and 1wt% LiNO3 is added as an electrolyte; finally, a 2032 button lithium-sulfur battery is assembled and charge-discharge test is carried out, and the test voltage window is 1.7-2.8V.

[0043] Comparative Example 1

[0044] In order to illustrate the influence of the Mo2C / NC positive electrode additive for lithium-sulfur batteries provided by the present application on the electrochemical performance of lithium-sulfur batteries, the preparation of lithium-sulfur batteries in Comparative Example 1 is basically the same as in Example 1, except that the battery is assembled with a positive electrode material without adding Mo2C / NC and charge-discharge test is carried out.

[0045] The KB / S electrode material prepared in the comparative example is used as a working electrode, lithium sheet is used as a counter electrode; Celgard 2500 type polypropylene film is used as a separator; lithium bis(trifluoromethylsulfonate) imide (LiTFSI) is used as a solute, 1,3-dioxolane DOL and dimethyl ether DME in a volume ratio of 1:1 are used as solvents, a solution with a concentration of 1mol·L -1 -1 is prepared and 1wt% LiNO3 is added as an electrolyte; finally, a 2032 button lithium-sulfur battery is assembled and charge-discharge test is carried out, and the test voltage window is 1.7-2.8V.

[0046] Please refer to Figure 10Figure 2 is a graph showing the results of the constant current charge-discharge cycle test of the lithium-sulfur battery prepared in Example 1 and Comparative Example 1 at a rate of 0.5C. As shown in the figure, the lithium-sulfur battery assembled in Example 1 has an initial discharge capacity of 978.9 mAh / g at a current density of 0.5C, and the reversible capacity remains 632.5 mAh / g after 500 cycles, with a decay rate of about 0.071% per cycle and a capacity retention rate of 64.6%, showing good cycle stability. The lithium-sulfur battery assembled in Comparative Example 1 has an initial discharge capacity of 822.3 mAh / g at 0.5C, and the capacity decreases to 334.1 mAh / g after 500 cycles, with a capacity retention rate of only 40.6% and an average capacity decay rate of 0.12% per cycle. Compared with Comparative Example 1, the cathode material in Example 1 is added with Mo2C / NC, so that the capacity and cycle stability of the lithium-sulfur battery assembled are both significantly improved.

[0047] Referring to ​ Figure 3 is a graph showing the results of the rate performance test of the lithium-sulfur battery in Example 1 and Comparative Example 1, with charge-discharge at 0.1C, 0.2C, 0.5C, 1C and 2C, respectively. The lithium-sulfur battery prepared in Example 1 has a discharge capacity of 1210.9 mAh / g at a low rate of 0.1C, and a discharge capacity of 657.7 mAh / g at a high rate of 2C. In comparison, the lithium-sulfur battery assembled in Comparative Example 1 has a discharge capacity of 901.5 mAh / g at a low rate of 0.1C, and a discharge capacity of only 124.5 mAh / g at a high rate of 2C, indicating that the rate performance of the lithium-sulfur battery in Comparative Example 1 is significantly lower than that in Example 1.

[0048] The above battery performance test results show that when the carbonized molybdenum / nitrogen-doped carbon composite material (Mo2C / NC) provided by the present application is used as a functional additive for the cathode of a lithium-sulfur battery, the electrochemical performance of the lithium-sulfur battery is significantly improved, mainly due to the following reasons: the nitrogen-doped carbon has a hierarchical porous structure, which enhances the electrolyte penetration and ion transport capacity; the nitrogen-doped active sites not only enhance the adsorption performance of the porous carbon for polysulfides, but also improve the catalytic activity of Mo2C by optimizing the coordination structure of Mo2C; Mo2C can chemically adsorb and efficiently catalyze the reversible conversion of polysulfides, improving the utilization rate of active materials. When the composite material is used as a functional additive for the cathode of a lithium-sulfur battery, it can effectively inhibit the dissolution and shuttling of polysulfides, significantly improving the capacity, rate performance and cycle stability of the battery.

[0049] Example 2

[0050] The preparation method of this example is the same as that of Example 1, except that glucose (C6H 12The mass of O6) is adjusted to 0.7 g, and other conditions remain unchanged. Compared with the Mo2C / NC composite material prepared in Example 1, the content of the carbon source is increased in this example, which leads to a decrease in the specific surface area of the prepared Mo2C / NC composite material, is not conducive to the construction of a stable porous connected structure, reduces the infiltration and penetration of the electrolyte to the active material, and reduces the electrochemical reaction kinetics. The lithium-sulfur battery assembled in this example has a decrease in the electrochemical performance such as capacity and cycle stability compared with Example 1: the initial discharge capacity is 704.4 mAh / g at 0.5C, the capacity is 357.2 mAh / g after 500 cycles, and the capacity retention rate is 50.71%.

[0051] Example 3

[0052] The preparation method of this example is the same as that of Example 1, except that the ammonium molybdate ((NH4)2MoO4·4H2O) in step (2) is adjusted to 0.08 g, and other conditions remain unchanged. Compared with the Mo2C / NC composite material prepared in Example 1, the content of the molybdenum source is reduced in this example, which leads to a lower Mo2C content in the prepared Mo2C / NC composite material. The lithium-sulfur battery assembled in this example has a decrease in the electrochemical performance such as capacity and cycle stability compared with Example 1: the initial discharge capacity is 824.4 mAh / g at 0.5C, the capacity is 271.2 mAh / g after 500 cycles, and the capacity retention rate is 32.9%.

[0053] Example 4

[0054] The preparation method of this example is the same as that of Example 1, except that the high-temperature calcination time in step (4) is reduced to 1 h, and other conditions remain unchanged. Compared with Example 1, the active material Mo2C content in the Mo2C / NC composite material is lower due to the reduction of the high-temperature calcination time of the Mo2C / NC composite material in this example, and the electrochemical performance decreases obviously. The lithium-sulfur battery assembled in this example has a decrease in the electrochemical performance such as capacity and cycle stability compared with Example 1: the initial discharge capacity is 724.4 mAh / g at 0.5C, the capacity is 327.2 mAh / g after 500 cycles, and the capacity retention rate is 45.2%.

[0055] The above is only an example and description of the concept of the present application, and various modifications or supplements or the use of similar ways to replace can be made by those skilled in the art to the described specific examples, as long as they do not deviate from the concept of the present application or exceed the scope defined by the present claims, which shall belong to the protection scope of the present application.

Claims

1. A method for producing a molybdenum carbide / nitrogen-doped carbon composite material, characterized by, The specific steps are as follows: (1) 20-25 g of urea is placed in a tube furnace for high-temperature calcination to obtain g-C3N4, wherein the calcination atmosphere is air, the temperature is 520-560°C, the holding time is 3-4 h, and the heating rate is 3-5°C / min; (2) 0.1-0.2 g (NH4)2MoO4*4H2O and 0.4-0.6 g C6H 12 O6 were dissolved in 20 mL deionized water, while 0.1-0.2 g g-C3N4 was ultrasonically dispersed in the solution, and stirred for 8-12 h to prepare a milky white solution; (3) The mixed solution prepared in step (2) is placed in a reaction kettle for hydrothermal reaction, the temperature is 120-150°C, and the time is 8-12 h; then the reaction product is filtered and dried for use; (4) The product obtained in step (3) is subjected to high-temperature calcination treatment in an inert atmosphere, wherein the calcination atmosphere is argon, the temperature is 800-850°C, the holding time is 2-3 h, the heating rate is 2-4°C / min, and Mo2C / NC is prepared; (5) Mo2C / NC prepared in step (4) and KB are fully ground and mixed in a certain proportion to obtain a conductive carrier (KB / Mo2C / NC), wherein the mass ratio of Mo2C / NC is 2%-8%; the conductive carrier is combined with active sulfur by a molten sulfur infiltration process to obtain a composite sulfur positive electrode material (KB / Mo2C / NC-S) for lithium-sulfur batteries, wherein fine Mo2C nanoparticles are uniformly dispersed in the nitrogen-doped carbon matrix.

2. The use of the molybdenum carbide / nitrogen-doped carbon composite material prepared by the method of claim 1 in a lithium-sulfur battery cathode material, characterized in that, The composite sulfur positive electrode material (KB / Mo2C / NC-S) for lithium-sulfur batteries prepared using the molybdenum carbide / nitrogen-doped carbon composite material, a conductive agent, and a binder are fully ground and mixed in a mass ratio of 8:1:1 to obtain a slurry; the obtained slurry is uniformly coated on an aluminum foil, vacuum dried at 70°C for 24 h, and cut to obtain a lithium-sulfur battery positive electrode sheet, wherein the molybdenum carbide / nitrogen-doped carbon composite material serves as a functional additive for lithium-sulfur battery positive electrodes and can effectively improve the utilization rate of active sulfur.

3. Use according to claim 2, wherein the compound is ###0002### The prepared lithium-sulfur battery positive electrode sheet has an active sulfur area loading of 1.5-2.0 mg / cm 2 .

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