Preparation method of metal boride composite metal single element and sulfur composite nanomaterial and application thereof

Abstract

The application discloses a preparation method and application of a metal boride composite metal single element and sulfur composite nanomaterial, relates to the technical field of energy materials, and comprises the following steps: dissolving a metal salt in methanol, quickly adding a 2-methyl imidazole aqueous solution, and preparing a MOF precursor; dispersing the MOF precursor in a methanol deionized water solution, adding a reducing agent solution, and preparing a metal boride material; dispersing the metal boride material in a metal salt aqueous solution at room temperature, adding a sodium hydroxide solution, and calcining the product in an inert gas and a reducing gas atmosphere in sequence to obtain a metal boride@metal single element composite material; and mixing and calcining the obtained metal boride@metal single element composite material and elemental sulfur according to a mass ratio of 1:1-4. The material has good lithium polysulfide adsorption capacity, accelerates the kinetic conversion of polysulfides, and can improve the stability and actual service life of a lithium-sulfur battery.

Description

Technical Field

[0001] This invention belongs to the field of energy materials technology, specifically relating to a method for preparing metal boride composite metal elements and sulfur composite nanomaterials and their applications. Background Technology

[0002] With the development of the portable electronics industry, the demand for high-energy-density batteries is becoming increasingly urgent. Limited by the specific capacity of traditional materials such as lithium cobalt oxide and lithium manganese oxide, lithium-ion batteries can no longer meet the growing demand, making the search for a rechargeable battery with even higher specific capacity imperative. Lithium-sulfur batteries have attracted attention from researchers in recent years due to their high specific capacity (1675 mAh / g), low cost, wide availability of elemental sulfur, and non-toxicity, making them a promising next-generation commercially viable rechargeable battery system. However, a major problem that urgently needs to be solved in the commercialization of lithium-sulfur batteries is the easy solubility of lithium polysulfides, an intermediate product of discharge, in ether-based electrolytes (shuttle effect). This causes sulfur to migrate through the electrolyte to the negative electrode surface, reducing battery life.

[0003] The common approach to addressing the shuttle effect is to composite materials with elemental sulfur, encapsulating elemental sulfur and discharge intermediates within the material's pores. Carbon materials, being nonpolar molecules, form physical adsorption with lithium polysulfides, resulting in limited effectiveness in suppressing the shuttle effect. Polar metal compounds, with their chemical and physical adsorption properties, have become a hot topic for suppressing the shuttle effect; however, current research primarily focuses on whether the shuttle effect can be suppressed, with little consideration given to the reaction process during lithium-sulfur battery discharge. Summary of the Invention

[0004] To address the aforementioned shortcomings in the prior art, this invention provides a method for preparing metal boride composite metal elemental and sulfur composite nanomaterials and their applications. The material of this invention has excellent lithium polysulfide adsorption capacity, accelerates the kinetic conversion of polysulfides, and can improve the stability and actual service life of lithium-sulfur batteries.

[0005] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is: to provide a method for preparing metal boride composite metal elemental and sulfur composite nanomaterials, comprising the following steps:

[0006] (1) Dissolve the metal salt in methanol, then add 0.7-0.9 mol / L of 2-methylimidazole aqueous solution, stir for 5-15 min, let stand at room temperature for 10-15 h, and then centrifuge, wash and vacuum dry to obtain MOF precursor.

[0007] (2) The MOF precursor obtained in step (1) is dispersed in a 40-60 wt% methanol deionized water solution, then a reducing agent solution is added, and the mixture is stirred at 50-70℃ for 8-12 hours. After centrifugation, washing and vacuum drying, the metal boride material is obtained.

[0008] (3) Dissolve the metal salt in water, add the metal boride material obtained in step (2) at room temperature and stir to disperse, then add 4.5-5.5 mol / L sodium hydroxide solution, stir at 70-90℃ for 10-15 h, centrifuge, wash and vacuum dry, calcine at 300-400℃ for 1.5-2.5 h in an inert gas atmosphere, and then calcine at 500-600℃ for 1.5-2.5 h in a reducing gas atmosphere to obtain metal boride@metal element composite material;

[0009] (4) The metal boride@metal element composite material obtained in step (3) is mixed with elemental sulfur at a mass ratio of 1:1-4 and calcined at 150-180℃ for 12-24h to obtain metal boride composite metal element and sulfur composite nanomaterial.

[0010] Furthermore, in steps (1) and (3), the metal salt is independently selected from one of the following: iron salt, cobalt salt, nickel salt, molybdenum salt, and zinc salt.

[0011] Furthermore, the feature is that in step (1), the molar to volume ratio of the metal salt, methanol and 2-methylimidazole aqueous solution is 0.8-1.2 mmol: 20 mL: 50 mL.

[0012] Furthermore, in step (2), the concentration of sodium borohydride in the reducing agent solution is 5-7 mol / L, and the concentration of sodium hydroxide is 0.2-0.4 mol / L; the mass-volume ratio of MOF precursor, methanol deionized water solution and reducing agent solution is 150-250 mg: 30 mL: 30 mL.

[0013] Furthermore, in step (3), the mass-to-volume ratio of the metal salt, the metal boride material, the water, and the sodium hydroxide solution is 15-25 mg: 100 mg: 30 mL: 2 mL.

[0014] Furthermore, in step (3), the inert gas is argon or nitrogen, and the reducing gas is a hydrogen-argon mixture with a hydrogen gas fraction of 5%.

[0015] Further, wash with ethanol and deionized water.

[0016] The beneficial effects of this invention are as follows: This invention introduces a MOF precursor into the composite material. By adjusting the experimental temperature, solution mixing rate, and reagent concentration, the morphology of the MOF precursor can be controlled to be one of the following: nanowires, nanorods, nanospheres, nanosheets, nanoparticles, nanoarrays, nanoflowers, or nanocubes. Then, the MOF is partially borated to obtain a cobalt boride@MOF intermediate. Further impregnation and high-temperature reduction treatments reduce the free metal ions in the intermediate to elemental metals, thus preserving the morphology of the MOF precursor completely during subsequent reactions. The elemental metal in the material can be the same as or different from the metal ions in the metal boride, and the crystallinity and size of the elemental metal can be controlled by reaction time, reaction temperature, and gas flow rate. The metal boride composite metal element and sulfur composite nanomaterial prepared by this invention can accelerate the conversion process of lithium polysulfide to lithium sulfide during the discharge process of lithium flow battery. The metal boride can adsorb polysulfides and inhibit their shuttle, while the interfacial electronic interaction between the metal element and the metal boride can accelerate the kinetic conversion of polysulfides, thereby improving the cycle performance of lithium-sulfur battery.

[0017] This invention also provides a method for preparing metal boride composite metal elemental and sulfur composite nanomaterials, and the resulting metal boride composite metal elemental and sulfur composite nanomaterials.

[0018] This invention also provides the application of metal boride composite metal elements and sulfur composite nanomaterials in the cathode of lithium-sulfur batteries.

[0019] Furthermore, after mixing metal boride composite metal elements and sulfur composite nanomaterials, conductive agents and binders, and drying, lithium-sulfur battery cathode materials are obtained.

[0020] Furthermore, the mass fraction of the metal boride composite metal element and sulfur composite nanomaterial is 50%-80%, and the mass ratio of conductive agent to binder is 1:1.

[0021] In summary, the present invention has the following advantages:

[0022] 1. The metal boride composite metal element and sulfur composite nanomaterial of the present invention have a good adsorption capacity for lithium polysulfides, which can improve the stability of lithium-sulfur batteries.

[0023] 2. The metal boride composite metal element and sulfur composite nanomaterial of the present invention have excellent catalytic activity, which can promote the conversion of lithium polysulfides to lithium sulfides, catalyze the discharge process of lithium-sulfur batteries, and reduce the dissolution of lithium polysulfides.

[0024] 3. By using different calcination temperatures and times, the crystallinity and defect sites on the surface of the metal boride composite metal can be controlled, thereby controlling the overall performance of the lithium-sulfur battery.

[0025] 4. Compared with traditional metal boride composite metal element technology, the raw material cost of this invention is lower, the manufacturing process is simpler, and the preparation process is cleaner and more environmentally friendly. The overall preparation process is relatively energy-saving and has high commercial value. Attached Figure Description

[0026] Figure 1 This is a low-magnification SEM image of the Co@Co2B composite material of boride@metal element in Example 1 of the present invention;

[0027] Figure 2 This is a high-magnification SEM image of the Co@Co2B composite material of boride@metal element in Example 1 of the present invention;

[0028] Figure 3 The XRD patterns of Co2B and Co@Co2B in Embodiment 1 of the present invention are shown below.

[0029] Figure 4 This is a 0.5C discharge cycle curve of the metal boride composite metal element and sulfur composite nanomaterial of the present invention as the positive electrode of lithium-sulfur battery. Detailed Implementation

[0030] Example 1

[0031] A method for preparing cobalt boride composite cobalt and sulfur composite nanomaterials includes the following steps:

[0032] (1) Dissolve 1 mmol Co(NO3)2·6H2O in 20 mL of methanol, then quickly add 50 mL of 0.8 mol / L 2-methylimidazole aqueous solution, stir for 10 min, let stand at room temperature for 12 h, then centrifuge, wash, and vacuum dry to obtain MOF precursor (ZIF-67).

[0033] (2) 200 mg of MOF precursor (ZIF-67) was dispersed in 30 mL of 50 t% methanol deionized water, and then 30 mL of reducing agent solution was slowly added. The reducing agent solution included 0.2 mol of sodium borohydride and 0.01 mol of sodium hydroxide. After stirring at 60 °C for 10 h, the mixture was centrifuged, washed, and vacuum dried to obtain metal boride material (Co2B).

[0034] (3) Dissolve 20 mg Co(NO3)2·6H2O in 30 mL of water, add 100 mg of the metal boride material obtained in step (2) at room temperature and stir vigorously to disperse, then add 2 mL of 5 mol / L sodium hydroxide solution, stir at 60 °C for 12 h, centrifuge, wash, vacuum dry, calcine at 350 °C for 2 h under argon atmosphere, and then calcine at 550 °C for 2 h under 5% hydrogen-argon mixed atmosphere to obtain metal boride@metal element composite material (Co@Co2B);

[0035] (4) The metal boride@metal elemental composite material obtained in step (3) is mixed with elemental sulfur at a mass ratio of 1:4 and calcined at 155°C for 12 hours to obtain cobalt boride composite cobalt elemental and sulfur composite nanomaterials.

[0036] Example 2

[0037] A method for preparing nickel boride composite nickel and sulfur composite nanomaterials includes the following steps:

[0038] (1) Dissolve 0.8 mmol Ni(NO3)2·6H2O in 20 mL methanol, then quickly add 50 mL of 0.7 mol / L 2-methylimidazole aqueous solution, stir for 5 min, let stand at room temperature for 10 h, then centrifuge, wash, and vacuum dry to obtain MOF precursor (ZIF-74).

[0039] (2) 150 mg of the MOF precursor obtained in step (1) was dispersed in 30 mL of 40 t% methanol deionized water, and then 30 mL of reducing agent solution was slowly added. The reducing agent solution included 0.1 mol sodium borohydride and 0.01 mol sodium hydroxide. After stirring at 50 °C for 8 h, the mixture was centrifuged, washed, and vacuum dried to obtain the metal boride material.

[0040] (3) Dissolve 15mg Ni(NO3)2·6H2O in 30mL of water, add 100mg of the metal boride material obtained in step (2) at room temperature and stir vigorously to disperse, then add 2mL of 4.5mol / L sodium hydroxide solution, stir at 70℃ for 10, centrifuge, wash, vacuum dry, calcine at 300℃ for 1.5h under argon atmosphere, and then calcine at 500℃ for 1.5h under 5% hydrogen-argon mixed atmosphere to obtain metal boride@metal element composite material;

[0041] (4) The metal boride@metal elemental composite material obtained in step (3) is mixed with elemental sulfur at a mass ratio of 1:1 and calcined at 150°C for 12 hours to obtain nickel boride composite nickel elemental and sulfur composite nanomaterial.

[0042] Example 3

[0043] A method for preparing zinc boride composite zinc and sulfur composite nanomaterials includes the following steps:

[0044] (1) Dissolve 1.2 mmol Zn(NO3)2·6H2O in 20 mL methanol, then quickly add 50 mL of 0.9 mol / L 2-methylimidazole aqueous solution, stir for 15 min, let stand at room temperature for 15 h, then centrifuge, wash, and vacuum dry to obtain MOF precursor (ZIF-8).

[0045] (2) Disperse 250 mg of the MOF precursor obtained in step (1) in 30 mL of 60 t% methanol deionized water, and then slowly add 30 mL of reducing agent solution, which includes 0.3 mol sodium borohydride and 0.02 mol sodium hydroxide. After stirring at 70 °C for 12 h, centrifuge, wash, and vacuum dry to obtain metal boride material.

[0046] (3) Dissolve 25 mg Zn(NO3)2·6H2O in 30 mL of water, add 100 mg of the metal boride material obtained in step (2) at room temperature and stir vigorously to disperse, then add 2 mL of 5.5 mol / L sodium hydroxide solution, stir at 90 °C for 15 h, centrifuge, wash, vacuum dry, calcine at 400 °C for 2.5 h under nitrogen atmosphere, and then calcine at 600 °C for 2.5 h under 5% hydrogen-argon mixed atmosphere to obtain metal boride@metal element composite material;

[0047] (4) The metal boride@metal elemental composite material obtained in step (3) is mixed with elemental sulfur at a mass ratio of 1:4 and calcined at 180°C for 24 hours to obtain zinc boride composite zinc elemental and sulfur composite nanomaterial.

[0048] Example 4

[0049] A method for preparing iron boride composite iron and sulfur composite nanomaterials includes the following steps:

[0050] (1) Dissolve 0.9 mmol Fe(NO3)2·6H2O in 20 mL methanol, then quickly add 50 mL of 0.75 mol / L 2-methylimidazole aqueous solution, stir for 8 min, let stand at room temperature for 11 h, then centrifuge, wash, and vacuum dry to obtain MOF precursor (Fe-MOF);

[0051] (2) 180 mg of the MOF precursor obtained in step (1) was dispersed in 30 mL of 45 t% methanol deionized water, and then 30 mL of reducing agent solution was slowly added. The reducing agent solution included 0.15 mol of sodium borohydride and 0.012 mol of sodium hydroxide. After stirring at 55 °C for 9 h, the mixture was centrifuged, washed, and vacuum dried to obtain the metal boride material.

[0052] (3) Dissolve 18 mg Fe(NO3)2·6H2O in 30 mL of water, add 100 mg of the metal boride material obtained in step (2) at room temperature and stir vigorously to disperse, then add 2 mL of 4.8 mol / L sodium hydroxide solution, stir at 75 °C for 11 h, centrifuge, wash, vacuum dry, calcine at 330 °C for 1.8 h under argon atmosphere, and then calcine at 520 °C for 1.8 h under 5% hydrogen-argon mixed atmosphere to obtain metal boride@metal element composite material;

[0053] (4) The metal boride@metal elemental composite material obtained in step (3) is mixed with elemental sulfur at a mass ratio of 1:2 and calcined at 160°C for 15 hours to obtain boride iron composite iron elemental and sulfur composite nanomaterial.

[0054] Example 5

[0055] A method for preparing cobalt boride composite nickel and sulfur composite nanomaterials includes the following steps:

[0056] (1) Dissolve 1 mmol of metal salt in 20 mL of methanol, then quickly add 50 mL of 0.8 mol / L 2-methylimidazole aqueous solution, stir for 12 min, let stand at room temperature for 13 h, then centrifuge, wash, and vacuum dry to obtain MOF precursor (ZIF-67).

[0057] (2) 220 mg of the MOF precursor obtained in step (1) was dispersed in 30 mL of 55 t% methanol deionized water, and then 30 mL of reducing agent solution was slowly added. The reducing agent solution included 0.25 mol of sodium borohydride and 0.018 mol of sodium hydroxide. After stirring at 65 °C for 11 h, the mixture was centrifuged, washed, and vacuum dried to obtain the metal boride material.

[0058] (3) Dissolve 22 mg Ni(NO3)2·6H2O in 30 mL of water, add 100 mg of the metal boride material obtained in step (2) at room temperature and stir vigorously to disperse, then add 2 mL of 5.2 mol / L sodium hydroxide solution, stir at 85 °C for 11 h, centrifuge, wash, vacuum dry, calcine at 360 °C for 2.2 h under argon atmosphere, and then calcine at 580 °C for 2.2 h under 5% hydrogen-argon mixed atmosphere to obtain metal boride@metal element composite material;

[0059] (4) The metal boride@metal elemental composite material obtained in step (3) is mixed with elemental sulfur at a mass ratio of 1:3 and calcined at 160°C for 20 hours to obtain cobalt boride composite nickel elemental and sulfur composite nanomaterials.

[0060] Example 6

[0061] A method for preparing cobalt boride composite iron and sulfur composite nanomaterials includes the following steps:

[0062] (1) Dissolve 1 mmol of metal salt in 20 mL of methanol, then quickly add 50 mL of 0.8 mol / L 2-methylimidazole aqueous solution, stir for 10 min, let stand at room temperature for 12 h, then centrifuge, wash, and vacuum dry to obtain MOF precursor ZIF-67.

[0063] (2) Disperse 200 mg of the MOF precursor obtained in step (1) in 30 mL of 50 t% methanol deionized water, and then slowly add 30 mL of reducing agent solution, which includes 0.2 mol sodium borohydride and 0.01 mol sodium hydroxide. After stirring at 60 °C for 10 h, centrifuge, wash, and vacuum dry to obtain metal boride material.

[0064] (3) Dissolve 20 mg Fe(NO3)2·6H2O in 30 mL of water, add 100 mg of the metal boride material obtained in step (2) at room temperature and stir vigorously to disperse, then add 2 mL of 5 mol / L sodium hydroxide solution, stir at 80 °C for 12 h, centrifuge, wash, vacuum dry, calcine at 350 °C for 2 h under argon atmosphere, and then calcine at 550 °C for 2 h under 5% hydrogen-argon mixed atmosphere to obtain metal boride@metal element composite material;

[0065] (4) The metal boride@metal elemental composite material obtained in step (3) is mixed with elemental sulfur at a mass ratio of 1:3 and calcined at 160°C for 18 hours to obtain cobalt boride composite iron elemental and sulfur composite nanomaterials.

[0066] Example 7

[0067] A method for preparing nickel boride composite iron and sulfur composite nanomaterials includes the following steps:

[0068] (1) Dissolve 1 mmol Ni(NO3)2·6H2O in 20 mL methanol, then quickly add 50 mL of 0.8 mol / L 2-methylimidazole aqueous solution, stir for 10 min, let stand at room temperature for 12 h, then centrifuge, wash, and vacuum dry to obtain MOF precursor (Ni-MOF);

[0069] (2) Disperse 200 mg of the MOF precursor obtained in step (1) in 30 mL of 50 t% methanol deionized water, and then slowly add 30 mL of reducing agent solution, which includes 0.2 mol sodium borohydride and 0.01 mol sodium hydroxide. After stirring at 60 °C for 10 h, centrifuge, wash, and vacuum dry to obtain metal boride material.

[0070] (3) Dissolve 20 mg Fe(NO3)2·6H2O in 30 mL of water, add 100 mg of the metal boride material obtained in step (2) at room temperature and stir vigorously to disperse, then add 2 mL of 5 mol / L sodium hydroxide solution, stir at 80 °C for 12 h, centrifuge, wash, vacuum dry, calcine at 350 °C for 2 h under argon atmosphere, and then calcine at 550 °C for 2 h under 5% hydrogen-argon mixed atmosphere to obtain metal boride@metal element composite material;

[0071] (4) The metal boride@metal elemental composite material obtained in step (3) is mixed with elemental sulfur at a mass ratio of 1:4 and calcined at 160°C for 16 hours to obtain nickel boride composite iron elemental and sulfur composite nanomaterials.

[0072] Example 8

[0073] Application of a cobalt boride composite cobalt and sulfur composite nanomaterial in the cathode of a lithium-sulfur battery.

[0074] The application method involves mixing cobalt boride composite cobalt and sulfur composite nanomaterials, Super P and PVDF in a mass ratio of 8:1:1, coating the mixture onto aluminum foil, and drying it to serve as the positive electrode.

[0075] Then, using lithium metal as the negative electrode, a Celgard 2400 separator, 1 mol / L LiTFSI dissolved in DOL / DME (volume ratio 1:1) solvent as the electrolyte, and 1 mol / L LiNO3 as an additive, the cells were assembled into coin cells in a glove box.

[0076] Experimental Example 1

[0077] SEM images of the metal boride@metal elemental composite material Co@Co2B obtained in Example 1 at different magnifications are shown below. Figure 1 and Figure 2 As shown.

[0078] Depend on Figure 1 and Figure 2 It can be seen that Co@Co2B is a cubic material, and the morphology of the MOF precursor is completely preserved during the boronization and reduction processes.

[0079] The XRD patterns of Co2B and Co@Co2B obtained in Example 1 are as follows: Figure 3 As shown.

[0080] Depend on Figure 3 As can be seen from the spectrum, the presence of elemental cobalt in the cobalt boride sample can be confirmed, proving that the preparation method of the present invention successfully prepared the metal boride@metal element composite material.

[0081] The coin cells assembled in Example 8 were subjected to constant current charge-discharge tests using the Neware battery testing system. The charge-discharge voltage range was 1.7-2.8V. The 0.5C discharge cycle curves of the lithium-sulfur battery using metal boride composite metal elements and sulfur composite nanomaterials as the positive electrode are shown below. Figure 4 As shown.

[0082] Depend on Figure 4It is known that when the metal boride composite metal element and sulfur composite nanomaterial of the present invention are applied to the positive electrode of lithium-sulfur battery, the assembled coin cell has a higher capacity retention rate and better cycle stability after 100 cycles compared with the coin cell assembled with metal boride and sulfur composite nanomaterial.

[0083] Although specific embodiments of the present invention have been described in detail with reference to the accompanying drawings, this should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for preparing a metal boride composite metal element and sulfur composite nanomaterial, characterized in that, Includes the following steps: (1) Dissolve the metal salt in methanol, then add 0.7-0.9 mol / L of 2-methylimidazole aqueous solution, stir for 5-15 min, let stand at room temperature for 10-15 h, and then centrifuge, wash and vacuum dry to obtain MOF precursor; (2) The MOF precursor obtained in step (1) is dispersed in a 40-60 wt% methanol deionized water solution, and then a reducing agent solution is added. The mixture is stirred at 50-70℃ for 8-12 h, and then centrifuged, washed and vacuum dried to obtain the metal boride material. (3) Dissolve the metal salt in water, add the metal boride material obtained in step (2) at room temperature and stir to disperse, then add 4.5-5.5 mol / L sodium hydroxide solution, stir at 70-90℃ for 10-15 h, centrifuge, wash and vacuum dry, calcine at 300-400℃ for 1.5-2.5 h in an inert gas atmosphere, and then calcine at 500-600℃ for 1.5-2.5 h in a reducing gas atmosphere to obtain metal boride@metal element composite material; (4) The metal boride@metal element composite material obtained in step (3) is mixed with elemental sulfur at a mass ratio of 1:1-4 and calcined at 150-180℃ for 12-24 h to obtain metal boride composite metal element and sulfur composite nanomaterial. In step (1), the molar-to-volume ratio of the metal salt, methanol, and 2-methylimidazole aqueous solution is 0.8-1.2 mmol: 20 mL: 50 mL; In step (2), the concentration of sodium borohydride in the reducing agent solution is 5-7 mol / L, and the concentration of sodium hydroxide is 0.2-0.4 mol / L; the mass-volume ratio of the MOF precursor, the methanol deionized water solution, and the reducing agent solution is 150-250 mg: 30 mL: 30 mL. In step (3), the mass-volume ratio of the metal salt, the metal boride material, water, and sodium hydroxide solution is 15-25 mg: 100 mg: 30 mL: 2 mL.

2. The method for preparing the metal boride composite metal element and sulfur composite nanomaterial as described in claim 1, characterized in that, In steps (1) and (3), the metal salt is independently selected from one of the following: iron salt, cobalt salt, nickel salt, molybdenum salt, and zinc salt.

3. The method for preparing the metal boride composite metal element and sulfur composite nanomaterial as described in claim 1, characterized in that, In step (3), the inert gas is argon or nitrogen, and the reducing gas is a hydrogen-argon mixture with a hydrogen gas fraction of 5%.

4. The metal boride composite metal element and sulfur composite nanomaterial prepared by the method of any one of claims 1-3.

5. The application of the metal boride composite metal element and sulfur composite nanomaterial as described in claim 4 in the positive electrode of lithium-sulfur batteries.

6. The application as described in claim 5, characterized in that, The lithium-sulfur battery cathode material is prepared by mixing the metal boride composite metal element and sulfur composite nanomaterial, conductive agent and binder, and then drying.

7. The application as described in claim 6, characterized in that, The mass fraction of the metal boride composite metal element and sulfur composite nanomaterial is 50%-80%, and the mass ratio of conductive agent to binder is 1:1.

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