A self-supporting nano-sulfur positive electrode material for lithium-sulfur batteries, and a preparation method and applications thereof

Abstract

The application relates to a lithium-sulfur battery self-supporting nano-sulfur positive electrode material, and belongs to the technical field of lithium-sulfur batteries. The positive electrode material takes a second component as an intermediate interlayer, and takes first components covering the two sides of the second component as upper and lower interlayers to form a sandwich interlayer network structure. The first component is graphene or heteroatom-doped graphene, and the mass of the first component accounts for 10-50% of the total mass of the first component and the second component. The second component is V2O5 nanobelt-wrapped spherical nano-sulfur particles, and the mass of the spherical nano-sulfur particles accounts for 30-80% of the total mass of the first component. Compared with the prior art, the graphene in the application has a self-supporting structure, the aluminum foil current collector used in the traditional process can be saved, the mass energy density of the positive electrode material is improved, the V2O5 nanobelt can adsorb polysulfides on one hand and can also relieve the volume expansion of the spherical nano-sulfur particles on the other hand, so that the cycle stability of the lithium-sulfur battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery technology, specifically to a self-supporting nano-sulfur cathode material for lithium-sulfur batteries, its preparation method, and its application. Background Technology

[0002] Currently, with the increasing demand for high-energy-density energy storage devices from electric vehicles and portable electronic devices, lithium-sulfur batteries are considered one of the most promising next-generation battery systems due to their extremely high theoretical specific capacity (1675 mAh / g) and energy density (2600 Wh / kg), as well as their abundant sulfur resources and environmental friendliness. However, the commercial application of lithium-sulfur batteries still faces many challenges. Among them, the poor conductivity of sulfur cathode materials, the dissolution shuttle effect of intermediate lithium polysulfides during charge and discharge, and the volume expansion of sulfur during cycling (approximately 80%) severely restrict the development of their electrochemical performance and the improvement of cycle life.

[0003] Traditional lithium-sulfur battery cathodes are typically prepared by mechanically mixing sulfur with a conductive agent (such as carbon materials) and then coating it onto a current collector (such as aluminum foil). While this method is simple, the contact between sulfur and the conductive substrate is not tight, resulting in poor conductive network stability and difficulty in effectively suppressing the dissolution and shuttle movement of polysulfides. This leads to low utilization of active materials, decreased coulombic efficiency, and rapid capacity decay. Furthermore, the introduction of inactive materials (such as binders and current collectors) reduces the overall energy density of the battery.

[0004] In recent years, researchers have focused on developing novel sulfur cathode structures to address the aforementioned problems. Among these, self-supporting cathode structures have attracted widespread attention due to their ability to achieve high sulfur loading, good conductive network continuity, and structural stability without the need for traditional current collectors and binders. In particular, the effective combination of sulfur with nanomaterials (such as three-dimensional conductive frameworks constructed from carbon nanotubes, graphene, and porous carbon) can significantly enhance electron / ion transport kinetics, physically confine and chemically adsorb polysulfides, while also buffering volume changes to some extent. However, existing methods for preparing self-supporting sulfur cathodes often involve complex templates, high-temperature treatments, or expensive raw materials, resulting in poor process repeatability and difficulty in large-scale production, thus limiting their practical applications. More importantly, while most carbon-based three-dimensional frameworks can provide conductive pathways and physical confinement, their chemical adsorption capacity for polysulfides is limited. Furthermore, during long-term cycling, the volume expansion of sulfur can still easily lead to local breakage or contact failure of the conductive framework, thereby affecting structural integrity and electrochemical stability. Summary of the Invention

[0005] While most existing carbon-based three-dimensional frameworks provide conductive pathways and physical confinement, their chemisorption capacity for polysulfides is limited. Furthermore, during long-term cycling, the volume expansion of sulfur can easily lead to localized breakage or contact failure of the conductive framework, affecting structural integrity and electrochemical stability. This invention provides a self-supporting nano-sulfur cathode material for lithium-sulfur batteries, its preparation method, and its applications. The V₂O₅ nanoribbon design employed in this invention achieves strong chemisorption of polysulfides through its abundant polar sites. Simultaneously, its one-dimensional ribbon structure and good mechanical adaptability effectively encapsulate and mitigate the volume expansion of spherical nano-sulfur particles during charge and discharge, thus overcoming the shortcomings of existing carbon-based frameworks in adsorption and buffering functions.

[0006] The objective of this invention can be achieved through the following technical solutions: One of the objectives of this invention is to provide a self-supporting nano-sulfur cathode material for lithium-sulfur batteries. This cathode material uses a second component as an intermediate interlayer, and a first component covering both sides of the second component as an upper interlayer and a lower interlayer, respectively, to form a sandwich interlayer network structure. The first component is graphene or heteroatom-doped graphene, and its mass accounts for 10-50% of the total mass of the first and second components; the second component is V2O5 nanoribbons encapsulating nano-sulfur particles, and the mass of the nano-sulfur particles accounts for 30-80% of the total mass of the second component.

[0007] Furthermore, the heteroatoms in the heteroatom-doped graphene include one or more of B atoms, N atoms, O atoms, S atoms, and P atoms.

[0008] Furthermore, the nano-sulfur particles are spherical nano-sulfur particles with a diameter of 100-500 nm.

[0009] Furthermore, the thickness of the positive electrode material is 10-100 μm.

[0010] The second objective of this invention is to provide a method for preparing the self-supporting nano-sulfur cathode material for lithium-sulfur batteries as described above, comprising the following steps: A1. Mix Na2S2O3 aqueous solution with polyvinylpyrrolidone at room temperature to obtain a first mixture. While stirring, add concentrated hydrochloric acid to the first mixture. After centrifugation, obtain spherical sulfur nanoparticles and redisperse them in polyvinylpyrrolidone aqueous solution to obtain a spherical sulfur nanoparticle dispersion. A2. Mix V2O5 with 30 mL of deionized water, then add H2O2 dropwise, stir until an orange solution is formed, carry out a hydrothermal reaction, and obtain V2O5 nanoribbons after centrifugation and washing. A3. Mix the spherical sulfur nanoparticle dispersion obtained in A1 and the V2O5 nanobelt dispersion obtained in A2 evenly to obtain V2O5 nanobelts that encapsulate spherical sulfur nanoparticles, denoted as S@V2O5 core-shell structured nanoparticles. A4. Mix the S@V2O5 core-shell structured nanoparticle solution with the graphene dispersion evenly, wash and dry to obtain a self-supporting nano-sulfur cathode material for lithium-sulfur batteries.

[0011] Furthermore, in A1, The concentration of Na2S2O3 in the Na2S2O3 aqueous solution is 0.02-0.06 M, preferably 0.04 M; The mass fraction of polyvinylpyrrolidone in the first mixture is 0.01-0.05 wt%, preferably 0.02 wt%. The concentration of concentrated hydrochloric acid is 10M; The mass fraction of polyvinylpyrrolidone in the aqueous solution is 0.01-0.10 wt%, preferably 0.05 wt%.

[0012] Furthermore, in A2, The mass-to-volume ratio of V2O5 to H2O2 is (0.1-0.5) g: (1-10) mL, preferably 0.36 g: 5 mL; H2O2 is 30% H2O2; The hydrothermal reaction is carried out at a temperature of 170-250ºC, preferably 200ºC, for a time of 3-7 h, preferably 5 h.

[0013] Furthermore, in A3, the mass ratio of the spherical sulfur nanoparticle dispersion to the V2O5 nanoribbon dispersion is (1-4):1, preferably 2:1.

[0014] Furthermore, in A4, the mass ratio of the S@V2O5 core-shell structured nanoparticle solution to the graphene dispersion is (3-10):3, preferably 7:3.

[0015] The third objective of this invention is to provide a lithium-sulfur battery, which includes the self-supporting nano-sulfur cathode material for lithium-sulfur batteries as described above.

[0016] Compared with existing technologies, the lithium-sulfur battery cathode material of the present invention uses graphene as the upper and lower sandwich layers, and V2O5 nanoribbons encapsulating spherical nano-sulfur particles as the middle sandwich layer. In order to improve the electrochemical activity of graphene, heteroatom-doped graphene can be used, including at least one or two of B atoms, N atoms, O atoms, S atoms, and P atoms. Furthermore, graphene has a self-supporting structure, which can eliminate the need for aluminum foil current collectors used in traditional processes and improve the mass energy density of the cathode material. V2O5 nanoribbons can adsorb polysulfides on the one hand, and alleviate the volume expansion of spherical nano-sulfur particles on the other hand, thereby improving the cycle stability of lithium-sulfur batteries. Attached Figure Description

[0017] Figure 1 These are SEM images of graphene from the embodiments; Figure 2 These are TEM images of V2O5 nanoribbons in the examples; Figure 3 This is a SEM image of spherical sulfur nanoribbons coated with V2O5 nanoribbons in the example; Figure 4 This is a front-side SEM image of the self-supporting conductive network structure formed by graphene and V2O5 nanoribbons coating spherical sulfur nanoparticles in Example 1. Figure 5 This is a cross-sectional SEM image of the self-supporting conductive network structure formed by graphene and V2O5 nanoribbons coating spherical sulfur nanoparticles in Example 1. Figure 6 This is the long-cycle curve of the lithium-sulfur battery in Example 1; Figure 7 This is a SEM image of the self-supporting conductive network formed by graphene and nano-sulfur in Comparative Example 1. Figure 8 This is the long-cycle curve of the lithium-sulfur battery in Comparative Example 1. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0019] Example 1 This embodiment provides a method for preparing a self-supporting nano-sulfur cathode material for lithium-sulfur batteries, including the following steps: A1: The synthesis steps for spherical sulfur nanoparticles are as follows: Na₂S₂O₃ aqueous solution (100 ml, 0.04 M) was mixed with polyvinylpyrrolidone (PVP, molecular weight = 55,000, 0.05 wt%) at room temperature. Subsequently, 0.8 mL of concentrated hydrochloric acid (HCl, 10 M) was added to the Na₂S₂O₃ / PVP solution under magnetic stirring. Sulfur nanoparticles were obtained by centrifugation and redispersed in PVP aqueous solution (20 ml, 0.05 wt%) to obtain a sulfur nanosphere dispersion.

[0020] A2: The synthesis steps of V2O5 nanoribbons are as follows: 0.36 g of V2O5 powder was mixed with 30 mL of deionized water to obtain a slurry. Then, 5 mL of 30% H2O2 solution was added dropwise to the slurry, and the mixture was stirred for 10 minutes to form an orange mixed solution. Subsequently, the mixed solution was placed in a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 200ºC for 5 hours to generate V2O5 nanoribbons. Finally, the V2O5 nanoribbons were collected by centrifugation and washed multiple times with distilled water.

[0021] A3: The synthesis steps of the S@V2O5 core-shell structure are as follows: The V2O5 nanoribbons obtained in A2 are dispersed in pure water to obtain a V2O5 nanoribbon dispersion; the sulfur nanosphere dispersion and the V2O5 nanoribbon dispersion are mixed under stirring conditions at a mass ratio of 2:1 of the dispersed mass in the dispersion to obtain a nanoparticle solution of V2O5 nanoribbons encapsulating nano-sulfur particles, denoted as the S@V2O5 core-shell structure nanoparticle solution.

[0022] A4: The synthesis steps of the self-supporting S@V2O5-RGO nano-sulfur cathode material are as follows: 1g of graphene was dissolved in 99g of water to form a graphene dispersion with a mass fraction of 1%. The S@V2O5 core-shell structured nanoparticle solution and the graphene dispersion were stirred for 2 hours at a mass ratio of 7:3. The resulting composite was washed with deionized water, filtered through a 5.0 μm cellulose membrane, and dried at 60ºC under vacuum.

[0023] The self-supported nano-sulfur cathode material for lithium-sulfur batteries prepared in this example was observed using a scanning electron microscope, and the results are as follows: Figure 3-5 As shown, V2O5 nanoribbons are wrapped around the surface of nano-sulfur to form spheres, while graphene is uniformly wrapped around the surface of the S@V2O5 core-shell structure. The three form an overall self-supporting structure that can be directly used as a cathode material for lithium-sulfur batteries.

[0024] Performance testing: Figure 6The chart shows the long-cycle curves of a lithium-sulfur battery using this material directly as the positive electrode and matched with a lithium metal anode. It demonstrates that this material can be directly used as the positive electrode material in lithium-sulfur batteries, and the cycle stability of the lithium-sulfur battery is significantly improved, with an initial capacity of 838.5 mAh g at a 2C current density. -1 After 400 cycles, the capacity of the lithium-sulfur battery is 627.6 mAh g. -1 .

[0025] Comparative Example 1 In this invention, V2O5 nanoribbons can not only coat the surface of nano-sulfur to alleviate the volume expansion of sulfur during charging and discharging, but also adsorb polysulfides formed during charging and discharging, reducing the shuttle effect of polysulfides. In order to verify the role of V2O5 nanoribbons, V2O5 nanoribbons are not used in this comparative example.

[0026] The specific preparation method of the self-supporting nano-sulfur cathode material for lithium-sulfur batteries in this comparative example includes: A1: The synthesis steps for spherical sulfur nanoparticles are as follows: Na₂S₂O₃ aqueous solution (100 ml, 0.04 M) was mixed with polyvinylpyrrolidone (PVP, molecular weight = 55,000, 0.02 wt%) at room temperature. Subsequently, 0.8 mL of concentrated hydrochloric acid (HCl, 10 M) was added to the Na₂S₂O₃ / PVP solution under magnetic stirring. Sulfur nanoparticles were obtained by centrifugation and redispersed in PVP aqueous solution (20 ml, 0.05 wt%).

[0027] A2: The synthesis steps of the self-supporting S-RGO nano sulfur cathode material are as follows: the sulfur nanosphere solution and the graphene dispersion are stirred for 2 hours at a mass ratio of 7:3. The resulting composite is washed with deionized water, filtered through a cellulose membrane, and dried at 60ºC under vacuum.

[0028] The self-supported nano-sulfur cathode material for lithium-sulfur batteries prepared in this example was observed using a scanning electron microscope, and the results are as follows: Figure 7 As shown, nano-sulfur and graphene form a disordered integrated structure. Specifically, nano-sulfur and graphene combine to form a highly integrated disordered structure. This structure can effectively construct a three-dimensional conductive network, but it also places higher demands on the stability of the structure: on the one hand, the drastic volume changes of highly dispersed nano-sulfur during charging and discharging can easily disrupt its interfacial contact with graphene; on the other hand, although the integrated disordered structure is conducive to electron transport, its physical confinement ability is limited, making it difficult to completely suppress the dissolution and shuttle of polysulfides.

[0029] Therefore, the V₂O₅ nanoribbons introduced in Example 1 of this invention play a crucial synergistic stabilizing role. The V₂O₅ nanoribbons not only coat the surface of the sulfur nanoribbons, effectively buffering their volume expansion during charge and discharge, and maintaining close contact between the sulfur nanoribbons and the graphene substrate, thus ensuring the integrity of the conductive network; simultaneously, their abundant polar sites can effectively adsorb polysulfides generated during charge and discharge, significantly reducing the shuttle effect. These two functions work together to compensate for the shortcomings of the disordered integrated structure of "sulfur nanoribbons-graphene" in terms of mechanical confinement and chemical adsorption. Therefore, the V₂O₅ nanoribbons and the graphene matrix together constitute a dual stabilizing mechanism that combines rigidity and flexibility, physical confinement and chemical anchoring, enabling this disordered integrated structure to achieve high conductivity while also realizing excellent structural stability and cycling performance.

[0030] Figure 8 The chart shows the long-cycle curves of a lithium-sulfur battery using this material directly as the positive electrode and matched with a lithium metal anode. It demonstrates that this material can be directly used as the positive electrode material in lithium-sulfur batteries, and the cycle stability of the lithium-sulfur battery is significantly improved, with an initial capacity of 822.7 mAh g⁻¹ at a 2C current density. -1 After 300 cycles, the capacity of the lithium-sulfur battery is 298.6 mAh g. -1 .

[0031] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A self-supporting nano-sulfur cathode material for lithium-sulfur batteries, characterized in that, The cathode material uses the second component as the middle interlayer, and the first component covering both sides of the second component as the upper and lower interlayers to form a sandwich interlayer network structure. The first component is graphene or heteroatom-doped graphene, and its mass accounts for 10-50% of the total mass of the first and second components; the second component is V2O5 nanoribbons encapsulating nano-sulfur particles, and the mass of the nano-sulfur particles accounts for 30-80% of the total mass of the second component.

2. The self-supporting nano-sulfur cathode material for lithium-sulfur batteries according to claim 1, characterized in that, The heteroatoms in the heteroatom-doped graphene include one or more of B atoms, N atoms, O atoms, S atoms, and P atoms.

3. The self-supporting nano-sulfur cathode material for lithium-sulfur batteries according to claim 1, characterized in that, The sulfur nanoparticles are spherical sulfur nanoparticles with a diameter of 100-500 nm.

4. The self-supporting nano-sulfur cathode material for lithium-sulfur batteries according to claim 1, characterized in that, The thickness of the positive electrode material is 10-100 μm.

5. A method for preparing a self-supporting nano-sulfur cathode material for lithium-sulfur batteries as described in any one of claims 1-4, characterized in that, Includes the following steps: A1. Mix Na2S2O3 aqueous solution with polyvinylpyrrolidone at room temperature to obtain a first mixture. While stirring, add concentrated hydrochloric acid to the first mixture. After centrifugation, obtain spherical sulfur nanoparticles and redisperse them in polyvinylpyrrolidone aqueous solution to obtain a spherical sulfur nanoparticle dispersion. A2. Mix V2O5 with 30 mL of deionized water, then add H2O2 dropwise, stir until an orange solution is formed, carry out a hydrothermal reaction, and obtain V2O5 nanoribbons after centrifugation and washing. A3. Mix the spherical sulfur nanoparticle dispersion obtained in A1 and the V2O5 nanobelt dispersion obtained in A2 evenly to obtain V2O5 nanobelts that encapsulate spherical sulfur nanoparticles, denoted as S@V2O5 core-shell structured nanoparticles. A4. Mix the S@V2O5 core-shell structured nanoparticle solution with the graphene dispersion evenly, wash and dry to obtain a self-supporting nano-sulfur cathode material for lithium-sulfur batteries.

6. The method for preparing a self-supporting nano-sulfur cathode material for lithium-sulfur batteries according to claim 5, characterized in that, In A1, The concentration of Na2S2O3 in the Na2S2O3 aqueous solution is 0.02-0.06 M, preferably 0.04 M; The mass fraction of polyvinylpyrrolidone in the first mixture is 0.01-0.05 wt%, preferably 0.02 wt%. The concentration of concentrated hydrochloric acid is 10M; The mass fraction of polyvinylpyrrolidone in the aqueous solution is 0.01-0.10 wt%, preferably 0.05 wt%.

7. The method for preparing a self-supporting nano-sulfur cathode material for lithium-sulfur batteries according to claim 5, characterized in that, In A2, The mass-to-volume ratio of V2O5 to H2O2 is (0.1-0.5) g: (1-10) mL, preferably 0.36 g: 5 mL; H2O2 is 30% H2O2; The hydrothermal reaction is carried out at a temperature of 170-250ºC, preferably 200ºC, for a time of 3-7 h, preferably 5 h.

8. The method for preparing a self-supporting nano-sulfur cathode material for lithium-sulfur batteries according to claim 5, characterized in that, In A3, the mass ratio of the spherical sulfur nanoparticle dispersion to the V2O5 nanoribbon dispersion is (1-4):1, preferably 2:

1.

9. The method for preparing a self-supporting nano-sulfur cathode material for lithium-sulfur batteries according to claim 5, characterized in that, In A4, the mass ratio of S@V2O5 core-shell structured nanoparticle solution to graphene dispersion is (3-10): 3, preferably 7:

3.

10. A lithium-sulfur battery, characterized in that, It includes the self-supporting nano-sulfur cathode material for lithium-sulfur batteries as described in any one of claims 1-4.

Images