A cathode material for a sulfur battery containing a graphene oxide composite and a preparation method thereof

Abstract

The present invention discloses a cathode material for a sulfur battery containing a graphene oxide composite and a preparation method thereof, which relates to the technical field of preparation of electrode materials; the cathode material for the sulfur battery containing the graphene oxide composite is composed of a host material loaded with selenium-doped cobalt sulfide, graphene oxide modified with polydopamine, and a zinc-based metal-organic framework composite coating material; after the host material loaded with Co nanoparticles is sulfided and selenized, the graphene oxide modified with polydopamine and the zinc-based metal-organic framework composite coating material form a coating layer on the surface of the host material loaded with selenium-doped cobalt sulfide, further enhancing the conductivity of the cathode material for the sulfur battery, improving the adsorption capacity and utilization rate of polysulfides, and at the same time providing sufficient buffer space for volume expansion, significantly enhancing the battery performance and cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode material preparation, and specifically refers to a sulfur battery cathode material containing graphene oxide composite and a preparation method thereof. Background Art

[0002] With the continuous development of science and technology, the demand for energy by humans is increasing day by day. However, fossil fuels, which are the main source of energy, are limited and non-renewable, and the processing and utilization of fossil fuels are accompanied by serious environmental pollution. Therefore, the development of new environmentally friendly and renewable energy sources has become a research hotspot in today's society; common new power energy mainly includes technologies such as photovoltaic power generation, hydropower generation, and wind power generation. However, the above power generation technologies will have a certain impact and pressure on the stability of the geographical system. Under the background of the great development of the new energy industry, in order to realize the application of renewable energy in daily life, the rechargeable battery system has become a key technology for the storage and use of renewable energy. Lithium-sulfur batteries have become emerging energy storage systems due to their high theoretical capacity, low cost, and environmental friendliness, and play an important role in promoting fields such as new energy electric vehicles and portable electronic devices.

[0003] A lithium-sulfur battery mainly consists of four parts: a cathode, an organic electrolyte, a separator, and a metallic lithium anode. Among them, the cathode is formed by compounding materials such as sulfur, a binder, and a conductive agent; during the working stage of the lithium-sulfur battery, charge storage and release are mainly achieved through the chemical reaction between the octasulfur ring (S8) existing inside the battery and lithium. Therefore, during the application process of the lithium-sulfur battery, stable charging / discharging conditions and a high energy density need to be satisfied. Under these conditions, higher requirements are put forward for the cathode material of the lithium-sulfur battery.

[0004] Currently, the following main problems exist in the prior art:

[0005] The conductivity of sulfur and polysulfides in the cathode material is poor, and there are volume changes and polysulfide shuttle effects during charge and discharge, which limit the utilization rate of polysulfides and reduce the battery performance and cycle stability. Summary of the Invention

[0006] In view of the above situation, to overcome the defects of the prior art, the present invention proposes a sulfur battery cathode material containing graphene oxide composite, which includes the following components in parts by weight: 40-60 parts of a host material loaded with selenium-doped cobalt sulfide composite material, and 10-20 parts of a composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework.

[0007] The host material includes the following components in parts by weight: 10-20 parts of transition metal carbide nanosheets, 20-30 parts of a composite material of porous polyimide and multi-walled carbon nanotubes, and 5-8 parts of cobalt nitrate hexahydrate.

[0008] The polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material comprises the following components in parts by weight: 5-10 parts of dopamine hydrochloride and 20-30 parts of graphene oxide and zinc-based metal-organic framework composite material.

[0009] The preparation method of the host material specifically comprises the following steps:

[0010] (1) Add 15.0 g of diphenyl sulfone and 0.1-0.2 g of multi-walled carbon nanotubes into a reaction kettle. Under nitrogen condition, control the kettle temperature at 130-150 °C and stir for 2-3 h. Then add 0.1-0.3 g of dimaleimide and react at 260-280 °C for 8-10 h. After the reaction ends, stop heating. When the temperature drops to 120 °C, transfer the reaction solution to an acetone solvent for filtration. The obtained crude product is subjected to Soxhlet extraction with acetone for 24 h, and then vacuum dried to obtain a porous polyimide and multi-walled carbon nanotube composite material. During the in-situ polymerization process, the multi-walled carbon nanotubes help the cross-linked polyimide polymer to uniformly adhere and grow on its surface, forming richer nanochannels, which is beneficial to the adsorption of polysulfides.

[0011] (2) Add 2.0-3.0 g of lithium fluoride into 40 mL of hydrochloric acid solution with a mass fraction of 30%. Stir in a water bath at 40 °C for 10-15 min, and then slowly add 1.0-2.0 g of titanium aluminum carbide. After complete addition, stir at 40 °C for 30-36 h. The mixed solution is centrifuged at 2500-3500 rpm for 5-10 min to remove the upper liquid. The precipitate is first washed 3-5 times with dilute hydrochloric acid with a mass fraction of 10%, and then repeatedly centrifuged and washed with deionized water until the pH is 6.0. The washed precipitate is added to 100 mL of deionized water and ultrasonicated in an ice bath for 0.5-1 h. The obtained colloidal solution is centrifuged at 4000-5000 rpm for 10-15 min, and the upper colloidal solution is taken and filtered into a film using a vacuum circulating water suction filter and dried to obtain transition metal carbide nanosheets. It has a large specific surface area and rich functional groups and can be used as a sulfur carrier. The chemical adsorption between the surface functional groups and sulfur can slow down the shedding and loss of sulfur. The high conductivity of the transition metal carbide helps to improve the electron transport of the sulfur cathode, enhance the rate performance and cycle stability of the battery. The flexibility of the transition metal carbide helps to alleviate the volume change of sulfur during charge and discharge and maintain the stability of the electrode structure.

[0012] (3) Disperse the porous polyimide and multi-walled carbon nanotube composite material described in step (1) in 50 mL of deionized water, then add the transition metal carbide nanosheets described in step (2), and ultrasonically treat for 1-2 h. Then add potassium hydroxide powder to the turbid liquid, stir for 2-3 h, centrifuge and wash the reaction product with deionized water 3-5 times. The precipitate is first freeze-dried. After removing the moisture, it is mixed evenly with cobalt nitrate hexahydrate powder, and then annealed in a nitrogen environment at 350-400 °C for 1-2 h to obtain the host material. The interlayer spacing of the transition metal carbide nanosheets is enlarged by the spontaneous insertion of potassium ions, providing conditions for the filling and insertion of the porous polyimide and multi-walled carbon nanotube composite material. The addition of the porous polyimide and multi-walled carbon nanotube composite material reduces the stacking of the nanosheets and forms a three-dimensional network structure. At the same time, Co 2+ is transformed into Co nanoparticles on the porous framework and evenly dispersed, enhancing the adsorption effect on polysulfides, reducing the volume change of the composite material during charge and discharge, and as a framework, it can also improve the conductivity of the positive electrode, which is beneficial to improving the battery performance and service life;

[0013] Preferably, in step (1), the multi-walled carbon nanotubes are amino-functionalized multi-walled carbon nanotubes, and the introduction of amino groups endows the multi-walled carbon nanotubes with chemical adsorption of sulfides;

[0014] Preferably, in step (3), the addition amount of potassium hydroxide powder is 2.0-2.5 g. Potassium hydroxide can remove a large amount of F and Cl functional groups on the transition metal carbide nanosheets, expose titanium oxide on the surface, and improve the chemical adsorption capacity for polysulfides.

[0015] The preparation method of the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material specifically includes the following steps:

[0016] a. Pour 50 - 100 mL of graphene oxide dispersion with a mass concentration of 2 mg / mL into 100 mL of N,N - dimethylformamide and 20 mL of methanol solution. Then add 0.8 g of zinc nitrate hexahydrate and 0.2 g of terephthalic acid. Ultrasonically treat for 5 - 6 h. Subsequently, place it in a high - pressure reactor and put it into a constant - temperature forced - air drying oven. React at a high temperature of 100 - 120 °C for 10 - 20 h. Cool to room temperature. Centrifuge the solution at a speed of 6000 - 8000 rpm for 5 - 10 min. Wash the precipitate with absolute ethanol by centrifugation until the supernatant becomes colorless. Collect the precipitate for drying treatment to obtain a graphene oxide and zinc - based metal - organic framework composite material. The cubic porous structure of the zinc - based metal - organic framework contains abundant micro - mesopores and a large pore volume. Composite with graphene oxide can alleviate the volume expansion phenomenon of the electrode during the cycling process, and also provides sufficient space and adsorption sites for the loading of sulfur, enhancing the adsorption performance. And zinc ions can serve as catalytic active sites to promote the redox reaction of polysulfides, accelerate the conversion process of polysulfides, and effectively improve the utilization rate of sulfur;

[0017] b. Add the graphene oxide and zinc - based metal - organic framework composite material described in step a into a Tris - HCl buffer solution with a pH of 8.5. Ultrasonically treat at 30 °C for 1 - 2 h. Then add dopamine hydrochloride and stir at 30 °C for 24 h. Centrifuge the mixed solution at a speed of 10000 - 11000 rpm for 5 - 10 min. Wash the precipitate with deionized water 3 - 5 times and dry to obtain a polydopamine - modified graphene oxide and zinc - based metal - organic framework composite coating material. Among them, the zinc - based metal - organic framework grows on the graphene oxide sheet structure, and at the same time, polydopamine is dispersed on its surface, optimizing the interface between the cathode material and the electrolyte, reducing the interface impedance, improving the conductivity and chemical activity of the coating material, enhancing the mechanical strength of the coating material, and reducing the volume change during charge and discharge;

[0018] Preferably, in step a, in the graphene oxide and zinc - based metal - organic framework composite material, the mass of graphene oxide accounts for 10 - 20% of the composite, which not only improves the dispersibility of graphene oxide but also ensures the hardness and toughness of the composite material, being beneficial to the coating effect.

[0019] The present invention also provides a preparation method for a sulfur battery cathode material containing a graphene oxide composite, which specifically includes the following steps:

[0020] S1. Mix 0.1 - 0.2 g of host material, 0.6 - 1.0 g of selenium powder, and 0.2 - 0.4 g of sulfur powder evenly, transfer them to a tubular furnace, heat up to 450 - 500 °C at a rate of 2 °C / min, and then keep the temperature for 2 - 3 h to obtain a host material-supported selenium-doped cobalt sulfide composite material. It has a rich pore structure. The Co nanoparticles on the host material are transformed into Se-doped CoS2, and a large number of anion vacancies are introduced. The loading of Co, CoSe2, and CoS2 nanoparticles is beneficial to the diffusion of Li + and the injection of molten S, provides more electrochemically active sites for redox reactions, effectively restricts the shuttle of polysulfides, enhances the electronic conductivity of the material, and obtains high capacity and excellent cycle stability;

[0021] S2. Add the host material-supported selenium-doped cobalt sulfide composite material described in step S1 into 150 mL of absolute ethanol, stir magnetically for 20 - 30 min, and ultrasonically treat for 1 - 2 h to be used as the solution to be encapsulated. Then add the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material into 50 mL of deionized water, ultrasonically treat for 4 - 5 h, and slowly drip it into the solution to be encapsulated as the coating solution while stirring magnetically. After the dripping is completed, put it into a water bath and heat up to 60 - 65 °C, heat for 1 - 2 h, and then freeze-dry to obtain a sulfur battery cathode material containing graphene oxide composite. The polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material form a coating protection layer on the host material-supported selenium-doped cobalt sulfide composite material, significantly improving the conductivity, further effectively preventing the shuttle effect of polysulfides, enhancing the adsorption and utilization rate of them. The multi-dimensional structure introduced by the loading and coating modification treatment also provides a large buffer space for the volume change during charge and discharge, which is beneficial to improving the cycle stability of the battery.

[0022] The beneficial effects obtained by the present invention are as follows:

[0023] After the host material loaded with Co nanoparticles is sulfided and selenized, the Co nanoparticles are transformed into Se-doped CoS2, which has a rich pore structure and S vacancies, facilitating the improvement of the electrical conductivity of the sulfur cathode, suppressing the shuttle of polysulfides and volume expansion. Then, a composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework is used to form a coating layer on the surface of the host material loaded with Se-doped cobalt sulfide composite material, further enhancing the electrical conductivity of the sulfur cathode material, improving the adsorption capacity and utilization rate of polysulfides, and at the same time providing sufficient buffer space for volume expansion, significantly enhancing the battery performance and cycle stability. In the host material, the cross-linked porous polyimide polymer is uniformly attached and grown on the surface of multi-walled carbon nanotubes, reducing the ineffective accumulation of the polymer and forming a more abundant nano-pore structure. On the premise that potassium ions expand the interlayer spacing of transition metal carbide nanosheets, the porous polyimide and multi-walled carbon nanotube composite material is filled and inserted to form a three-dimensional network structure with more pores. This structure can not only serve as a conductive network to ensure sufficient contact with the active material sulfur, reduce the impedance of the electrochemical reaction, and improve the electrical conductivity, but also rely on its excellent mechanical strength to maintain the stability of the structure, reduce the volume change during charge and discharge, and can also play the porous characteristics to provide more loading space for sulfur, improving the adsorption performance and utilization rate of sulfur. In the composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework, first, the high porosity of the zinc-based metal-organic framework material is combined with the lamellar structure of graphene oxide, providing more active sites, which is beneficial to enhancing the physical and chemical adsorption of polysulfides, effectively capturing polysulfides, and reducing their migration to the negative electrode. The electrical conductivity of graphene oxide compensates for the disadvantage of the insufficient electrical conductivity of the zinc-based metal-organic framework material, improving the electron transfer efficiency of the electrode. The addition of graphene oxide can prevent the structural collapse of the zinc-based metal-organic framework material and enhance the mechanical strength of the composite material. The pore structure of the zinc-based metal-organic framework material contributes to ion transport, while graphene oxide provides a conductive network, and the two cooperate to improve the electrochemical performance. Then, polydopamine is dispersed on the surface of the graphene oxide and zinc-based metal-organic framework composite material. The adhesion of polydopamine not only optimizes the interface between the cathode material and the electrolyte, reduces the interface impedance, and improves the battery performance, but also enhances the mechanical strength of the coating material and reduces the volume change during charge and discharge. The present invention uses a host material loaded with Se-doped cobalt sulfide composite material, a composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework to prepare a sulfur cathode material containing a graphene oxide composite, improving the electrical conductivity, suppressing the shuttle of polysulfides and volume expansion, and significantly enhancing the battery performance and cycle stability. Description of the Drawings

[0024] Figure 1It is a scanning electron microscope image, where (1) is a partial scanning electron microscope image of the sulfur battery cathode material containing graphene oxide composite prepared in Example 1 of the present invention, and (2) is a whole scanning electron microscope image of the sulfur battery cathode material containing graphene oxide composite prepared in Example 1 of the present invention;

[0025] Figure 2 It is a graph of charge transfer resistance results for Examples 1-4 and Comparative Examples 1-3 of the present invention;

[0026] Figure 3 It is a graph of discharge specific capacity retention rate results for Examples 1-4 and Comparative Examples 1-3 of the present invention;

[0027] Figure 4 It is a graph of the attenuation rate per cycle results for Examples 1-4 and Comparative Examples 1-3 of the present invention. Detailed implementation manners

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the present invention. The preferred implementation methods and materials described in the text are only for demonstration purposes and cannot limit the content of this application.

[0030] The experimental methods in the following embodiments are all conventional methods unless otherwise specified; the test materials used in the following embodiments are all obtained from commercial channels unless otherwise specified.

[0031] The sources of the reagents used in the examples are as follows:

[0032] Dimaleimide CAS No: 15209-14-0, brand Shanghai Chuangsai Technology Co., Ltd., product number CLS-HT0192;

[0033] Hydrochloric acid CAS No: 7647-01-0, brand Innochem, product number A04558;

[0034] Dopamine hydrochloride CAS No: 335081-04-4, brand Trc, product number D533787;

[0035] Tris-HCl buffer solution brand Krypton Road, product number CD434006-500mL;

[0036] Cobalt(II) nitrate hexahydrate, CAS No: 10026-22-9, Brand: Innochem, Article No: A80084;

[0037] Diphenyl sulfone, CAS No: 127-63-9, Brand: Innochem, Article No: A13136;

[0038] Multi-walled carbon nanotubes, CAS No: 308068-56-6, Brand: Innochem, Article No: A64674;

[0039] Acetone, CAS No: 67-64-1, Brand: Acros, Article No: 167645000;

[0040] Lithium fluoride, CAS No: 7789-24-4, Brand: Innochem, Article No: A08078;

[0041] Aluminum titanium carbide, CAS No: 196506-01-1, Brand: Innochem, Article No: A99238;

[0042] Potassium hydroxide, CAS No: 1310-58-3, Brand: Innochem, Article No: A13600;

[0043] Graphene oxide dispersion, CAS No: 1034343-98-0, Brand: Macklin, Article No: S992587-25ml;

[0044] N,N-Dimethylformamide, CAS No: 68-12-2, Brand: Innochem, Article No: A39494;

[0045] Sodium hydroxide, CAS No: 1310-73-2, Brand: Innochem, Article No: A36865;

[0046] Methanol, CAS No: 67-56-1, Brand: Innochem, Article No: A45780;

[0047] Zinc nitrate hexahydrate, CAS No: 10196-18-6, Brand: Acros, Article No: 211660050;

[0048] Terephthalic acid, CAS No: 100-21-0, Brand: Innochem, Article No: A68313;

[0049] Selenium powder, CAS No: 7782-49-2, Brand: Innochem, Article No: A01045;

[0050] Sulfur powder, CAS No: 7704-34-9, Brand: Aladdin, Article No: S106611-100g;

[0051] Absolute ethanol, CAS No: 64-17-5, brand Innochem, item number G00004.

[0052] Example 1

[0053] This example presents a sulfur battery cathode material containing graphene oxide composite, including the following components in parts by weight: 60 parts of host material loaded with selenium-doped cobalt sulfide composite, and 20 parts of poly-dopamine modified graphene oxide and zinc-based metal-organic framework composite coating material.

[0054] The host material includes the following components in parts by weight: 20 parts of transition metal carbide nanosheets, 20 parts of porous polyimide and multi-walled carbon nanotube composite, and 8 parts of cobalt nitrate hexahydrate.

[0055] The poly-dopamine modified graphene oxide and zinc-based metal-organic framework composite coating material includes the following components in parts by weight: 10 parts of dopamine hydrochloride, and 30 parts of graphene oxide and zinc-based metal-organic framework composite.

[0056] The preparation method of the host material specifically includes the following steps:

[0057] (1) Add 15.0 g of diphenyl sulfone and 0.2 g of multi-walled carbon nanotubes into the reaction kettle. The multi-walled carbon nanotubes are amino-functionalized multi-walled carbon nanotubes. The introduction of amino groups endows the multi-walled carbon nanotubes with chemical adsorption effect on sulfides. Under nitrogen condition, control the kettle temperature at 150 °C, stir for 3 h, add 0.3 g of dimaleimide, and react at 280 °C for 10 h. After the reaction is completed, stop heating. After cooling to 120 °C, transfer the reaction solution to acetone solvent for filtration. The obtained crude product is subjected to Soxhlet extraction with acetone for 24 h, and then vacuum dried to obtain the porous polyimide and multi-walled carbon nanotube composite. During the in-situ polymerization process, the multi-walled carbon nanotubes help the cross-linked polyimide polymer to uniformly adhere and grow on its surface, forming more abundant nanopores, which is beneficial to the adsorption of polysulfides;

[0058] (2) Add 3.0 g of lithium fluoride to 40 mL of hydrochloric acid solution with a mass fraction of 30%, stir in a water bath at 40 °C for 15 min, then slowly add 2.0 g of aluminum titanium carbide. After complete addition, stir at 40 °C for 36 h. Centrifuge the mixture at 3500 rpm for 10 min to remove the upper liquid. First, wash the precipitate 5 times with dilute hydrochloric acid with a mass fraction of 10%, and then repeatedly centrifuge and wash with deionized water until the pH is 6.0. Add the washed precipitate to 100 mL of deionized water and ultrasonicate in an ice bath for 1 h. Centrifuge the obtained colloidal solution at 5000 rpm for 15 min, and take the upper colloidal solution to filter it into a film using a vacuum circulating water suction filter, and dry it to obtain transition metal carbide nanosheets. It has a large specific surface area and abundant functional groups and can be used as a sulfur carrier. The chemical adsorption between the surface functional groups and sulfur can slow down the shedding and loss of sulfur. The high conductivity of the transition metal carbide helps to improve the electron transport of the sulfur cathode, enhance the rate performance and cycle stability of the battery. The flexibility of the transition metal carbide helps to alleviate the volume change of sulfur during charge and discharge and maintain the stability of the electrode structure;

[0059] (3) Disperse the porous polyimide and multi-walled carbon nanotube composite material described in step (1) in 50 mL of deionized water, then add the transition metal carbide nanosheets described in step (2), and ultrasonically treat for 2 h. Then add potassium hydroxide powder to the turbid liquid and stir for 3 h. The addition amount of potassium hydroxide powder is 2.5 g. Potassium hydroxide can remove a large number of F and Cl functional groups on the transition metal carbide nanosheets, expose titanium oxide on the surface, and improve the chemical adsorption capacity for polysulfides. Centrifuge and wash the reaction product 5 times with deionized water. First, freeze-dry the precipitate, mix it evenly with cobalt nitrate hexahydrate powder after removing the moisture, and then anneal it in a nitrogen environment at 400 °C for 2 h to obtain the host material. The interlayer spacing of the transition metal carbide nanosheets is expanded by the spontaneous insertion of potassium ions, providing conditions for the filling and insertion of the porous polyimide and multi-walled carbon nanotube composite material. The addition of the porous polyimide and multi-walled carbon nanotube composite material reduces the stacking of nanosheets and forms a three-dimensional network structure. At the same time, Co 2+ is transformed into Co nanoparticles on the porous framework and evenly dispersed, enhancing the adsorption of polysulfides, reducing the volume change of the composite material during charge and discharge, and as a framework, it can also improve the conductivity of the positive electrode, which is beneficial to improving the battery performance and service life.

[0060] A preparation method of a composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework specifically includes the following steps:

[0061] a. Pour 100 mL of graphene oxide dispersion with a mass concentration of 2 mg / mL into 100 mL of N,N-dimethylformamide and 20 mL of methanol solution. Then add 0.8 g of zinc nitrate hexahydrate and 0.2 g of terephthalic acid, and ultrasonically treat for 6 h. Subsequently, place it in a high-pressure reaction kettle and put it into a constant-temperature blast drying oven. React at a high temperature of 120 °C for 20 h, cool to room temperature, centrifuge the solution at a speed of 8000 rpm for 10 min, wash and centrifuge the precipitate with absolute ethanol until the supernatant becomes colorless, and collect the precipitate for drying treatment to obtain a graphene oxide and zinc-based organic framework composite material. In the graphene oxide and zinc-based organic framework composite material, the mass of graphene oxide accounts for 20% of the composite, which not only improves the dispersibility of graphene oxide but also ensures the hardness and toughness of the composite material, is beneficial to the coating effect. The cubic porous structure of the zinc-based organic framework contains abundant micro-mesopores and a large pore volume. Composite with graphene oxide can alleviate the volume expansion phenomenon of the electrode during the cycling process, and also provides sufficient space and adsorption sites for the loading of sulfur, enhancing the adsorption performance. And zinc ions can serve as catalytic active sites to promote the redox reaction of polysulfides and accelerate the conversion process of polysulfides, effectively improving the utilization rate of sulfur;

[0062] b. Add the graphene oxide and zinc-based organic framework composite material described in step a to a Tris-HCl buffer solution with a pH of 8.5, ultrasonically treat at 30 °C for 2 h, then add dopamine hydrochloride, and stir at 30 °C for 24 h. Centrifuge the mixed solution at a speed of 11000 rpm for 10 min, wash the precipitate 5 times with deionized water, and dry to obtain a polydopamine-modified graphene oxide and zinc-based organic framework composite coating material. Among them, the zinc-based organic framework grows on the graphene oxide sheet structure, and at the same time, polydopamine is dispersed on its surface, optimizing the interface between the cathode material and the electrolyte, reducing the interface impedance, improving the conductivity and chemical activity of the coating material, enhancing the mechanical strength of the coating material, and reducing the volume change during charge and discharge.

[0063] This embodiment provides a preparation method for a sulfur battery cathode material containing a graphene oxide composite, specifically including the following steps:

[0064] S1. Mix 0.2 g of host material, 1.0 g of selenium powder, and 0.4 g of sulfur powder evenly, transfer them to a tube furnace, heat up to 500 °C at a rate of 2 °C / min, and then keep warm for 3 h to obtain a host material-supported selenium-doped cobalt sulfide composite material with a rich pore structure. The Co nanoparticles on the host material are transformed into Se-doped CoS2, and a large number of anion vacancies are introduced at the same time. The loading of Co, CoSe2, and CoS2 nanoparticles is beneficial to Li +The diffusion of [substance] and the injection of molten S provide more electrochemically active sites for redox reactions, effectively restricting the shuttle of polysulfides, enhancing the electronic conductivity of the material, achieving high capacity and excellent cycle stability;

[0065] S2. Add the host material loaded with selenium-doped cobalt sulfide composite material described in step S1 into 150 mL of absolute ethanol, stir magnetically for 30 min, and ultrasonically treat for 2 h to be used as the solution to be encapsulated. Then, add the composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework into 50 mL of deionized water, ultrasonically treat for 5 h, and slowly drip it into the solution to be encapsulated while stirring magnetically. After the dripping is completed, place it in a water bath and heat it to 65 °C for 2 h, and then freeze-dry to obtain the cathode material for a sulfur battery containing a graphene oxide composite. The composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework forms a coating protection layer on the host material loaded with selenium-doped cobalt sulfide composite material, significantly improving the conductivity, further effectively preventing the shuttle effect of polysulfides, enhancing the adsorption effect and utilization rate of polysulfides. The multi-dimensional structure introduced by the modification treatment of loading and coating also provides a large buffer space for the volume change during charge and discharge, which is beneficial to improving the cycle stability of the battery.

[0066] In this example, the overall and local parts of the cathode material for a sulfur battery containing a graphene oxide composite prepared were scanned by electron microscopy to observe its microscopic morphology. Figure 1 (1) is the SEM image of the local part of the cathode material for a sulfur battery containing a graphene oxide composite prepared in Example 1 magnified 1000 times. Figure 1 (2) is the SEM image of the overall part of the cathode material for a sulfur battery containing a graphene oxide composite prepared in Example 1 magnified 100 times. As shown in the figure, the cathode material for a sulfur battery containing a graphene oxide composite prepared in this example shows a complete "dumpling-shaped" coating.

[0067] Example 2

[0068] This example presents a cathode material for a sulfur battery containing a graphene oxide composite, including the following components in parts by weight: 40 parts of the host material loaded with selenium-doped cobalt sulfide composite material, and 10 parts of the composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework.

[0069] The host material includes the following components in parts by weight: 10 parts of transition metal carbide nanosheets, 30 parts of a composite material of porous polyimide and multi-walled carbon nanotubes, and 5 parts of cobalt nitrate hexahydrate.

[0070] The composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework includes the following components in parts by weight: 5 parts of dopamine hydrochloride, and 20 parts of a composite material of graphene oxide and zinc-based metal-organic framework.

[0071] Preparation method of host material, specifically including the following steps:

[0072] (1) Add 15.0 g of diphenyl sulfone and 0.1 g of multi-walled carbon nanotubes into the reaction kettle. The multi-walled carbon nanotubes are amino-functionalized multi-walled carbon nanotubes. The introduction of amino groups endows the multi-walled carbon nanotubes with chemical adsorption effect on sulfides. Under nitrogen condition, control the kettle temperature at 130 °C, stir for 2 h, add 0.1 g of dimaleimide, and react at 260 °C for 8 h. After the reaction ends, stop heating. After cooling to 120 °C, transfer the reaction solution to acetone solvent for filtration. The obtained crude product is subjected to Soxhlet extraction with acetone for 24 h, and then dried under vacuum to obtain a composite material of porous polyimide and multi-walled carbon nanotubes. During the in-situ polymerization process, the multi-walled carbon nanotubes help the cross-linked polyimide polymer to uniformly adhere and grow on its surface, forming richer nanopores, which is beneficial to the adsorption of polysulfides;

[0073] (2) Add 2.0 g of lithium fluoride into 40 mL of hydrochloric acid solution with a mass fraction of 30%, stir in a water bath at 40 °C for 10 min, then slowly add 1.0 g of titanium aluminum carbide. After complete addition, stir at 40 °C for 30 h. The mixed solution is centrifuged at 2500 rpm for 5 min to remove the upper layer of liquid. The precipitate is first washed 3 times with dilute hydrochloric acid with a mass fraction of 10%, and then repeatedly centrifuged and washed with deionized water until the pH is 6.0. The washed precipitate is added to 100 mL of deionized water and ultrasonically treated in an ice bath for 0.5 h. The obtained colloidal solution is centrifuged at 4000 rpm for 10 min, and the upper colloidal solution is taken and filtered into a film using a vacuum circulating water suction filter and dried to obtain transition metal carbide nanosheets. It has a large specific surface area and rich functional groups, and can be used as a sulfur carrier. The chemical adsorption effect between the surface functional groups and sulfur can slow down the shedding and loss of sulfur. The high conductivity of transition metal carbides helps to improve the electron transport of sulfur cathodes, enhance the rate performance and cycle stability of the battery. The flexibility of transition metal carbides helps to relieve the volume change of sulfur during charge and discharge and maintain the stability of the electrode structure;

[0074] (3) Disperse the porous polyimide and multi-walled carbon nanotube composite material described in step (1) in 50 mL of deionized water, then add the transition metal carbide nanosheets described in step (2), and ultrasonically treat for 1 h. Then add potassium hydroxide powder to the turbid liquid and stir for 2 h. The addition amount of potassium hydroxide powder is 2.0 g. Potassium hydroxide can remove a large amount of F and Cl functional groups on the transition metal carbide nanosheets, expose titanium oxide on the surface, and improve the chemical adsorption capacity for polysulfides. Centrifuge and wash the reaction product 3 - 5 times with deionized water. First, freeze-dry the precipitate, remove the moisture, then mix it evenly with cobalt nitrate hexahydrate powder, and then anneal it in a nitrogen environment at 350 °C for 1 h to obtain the host material. The interlayer spacing of the transition metal carbide nanosheets is expanded by the spontaneous insertion of potassium ions, providing conditions for the filling and insertion of the porous polyimide and multi-walled carbon nanotube composite material. The addition of the porous polyimide and multi-walled carbon nanotube composite material reduces the stacking of nanosheets and forms a three-dimensional network structure. At the same time, Co 2+ is transformed into Co nanoparticles on the porous framework and uniformly dispersed, enhancing the adsorption of polysulfides, reducing the volume change of the composite material during charge and discharge, and as a framework, it can also improve the conductivity of the positive electrode, which is beneficial to improving the battery performance and service life.

[0075] Preparation method of a composite coating material of polydopamine-modified graphene oxide and zinc-based organic framework, specifically including the following steps:

[0076] a. Pour 50 mL of graphene oxide dispersion with a mass concentration of 2 mg / mL into 100 mL of N,N-dimethylformamide and 20 mL of methanol solution, then add 0.8 g of zinc nitrate hexahydrate and 0.2 g of terephthalic acid, ultrasonically treat for 5 h, then place it in a high-pressure reaction kettle, put it into a constant-temperature blast drying oven, and react at a high temperature of 100 °C for 10 h. Cool to room temperature, centrifuge the solution at a speed of 6000 rpm for 5 min, wash and centrifuge the precipitate with absolute ethanol until the supernatant becomes colorless, collect the precipitate and perform drying treatment to obtain the graphene oxide and zinc-based organic framework composite material. In the graphene oxide and zinc-based organic framework composite material, the mass of graphene oxide accounts for 10% of the composite, which not only improves the dispersion of graphene oxide but also ensures the hardness and toughness of the composite material, facilitating the coating effect. The cubic porous structure of the zinc-based organic framework contains abundant micro-mesopores and a large pore volume. Composite with graphene oxide can alleviate the volume expansion phenomenon of the electrode during the cycling process, and also provides sufficient space and adsorption sites for the loading of sulfur, enhancing the adsorption performance. Moreover, zinc ions can serve as catalytic active sites to promote the redox reaction of polysulfides and accelerate the conversion process of polysulfides, effectively improving the utilization rate of sulfur;

[0077] b. Add the graphene oxide and zinc-based metal-organic framework composite material described in step a into a Tris-HCl buffer solution with a pH of 8.5, sonicate for 1 h at 30 °C, then add dopamine hydrochloride, and stir at 30 °C for 24 h. Centrifuge the mixed solution at a speed of 10,000 rpm for 5 min, wash the precipitate with deionized water three times, and dry it to obtain a polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material. Among them, the zinc-based metal-organic framework grows on the graphene oxide sheet structure, and at the same time, polydopamine is dispersed on its surface, optimizing the interface between the cathode material and the electrolyte, reducing the interface impedance, improving the conductivity and chemical activity of the coating material, enhancing the mechanical strength of the coating material, and reducing the volume change during charge and discharge.

[0078] This example provides a preparation method for a sulfur battery cathode material containing a graphene oxide composite, which specifically includes the following steps:

[0079] S1. Mix 0.1 g of the host material, 0.6 g of selenium powder, and 0.2 g of sulfur powder evenly, transfer them to a tubular furnace, heat up to 450 °C at a rate of 2 °C / min, and then keep the temperature for 2 h to obtain a host material-supported selenium-doped cobalt sulfide composite material with a rich pore structure. The Co nanoparticles on the host material are transformed into Se-doped CoS2, and at the same time, a large number of anion vacancies are introduced. The loading of Co, CoSe2, and CoS2 nanoparticles is beneficial to the diffusion of Li + and the injection of molten S, providing more electrochemically active sites for the redox reaction, effectively restricting the shuttle of polysulfides, enhancing the electronic conductivity of the material, and obtaining high capacity and excellent cycle stability;

[0080] S2. Add the host material-supported selenium-doped cobalt sulfide composite material described in step S1 into 150 mL of absolute ethanol, stir magnetically for 20 min, and sonicate for 1 h for use as the solution to be encapsulated. Then add the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material into 50 mL of deionized water, sonicate for 4 h, and slowly drip it into the solution to be encapsulated as the coating solution while stirring magnetically. After the dripping is completed, place it in a water bath and heat up to 60 °C, heat for 1 h, and then freeze-dry to obtain a sulfur battery cathode material containing a graphene oxide composite. The polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material form a coating protection layer on the host material-supported selenium-doped cobalt sulfide composite material, significantly improving the conductivity, further effectively preventing the shuttle effect of polysulfides, enhancing the adsorption effect and utilization rate of polysulfides, and the multi-dimensional structure introduced by the loading and coating modification treatment also provides a large buffer space for the volume change during charge and discharge, which is beneficial to improving the cycle stability of the battery.

[0081] Example 3

[0082] This embodiment provides a cathode material for a sulfur battery containing a graphene oxide composite, which comprises the following components in parts by weight: 50 parts of a host material loaded with selenium-doped cobalt sulfide composite material, and 15 parts of a composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework.

[0083] The host material comprises the following components in parts by weight: 15 parts of transition metal carbide nanosheets, 25 parts of a composite material of porous polyimide and multi-walled carbon nanotubes, and 6.5 parts of cobalt nitrate hexahydrate.

[0084] The composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework comprises the following components in parts by weight: 7.5 parts of dopamine hydrochloride, and 25 parts of a composite material of graphene oxide and zinc-based metal-organic framework.

[0085] The preparation method of the host material specifically comprises the following steps:

[0086] (1) Add 15.0 g of diphenyl sulfone and 0.15 g of multi-walled carbon nanotubes to a reaction kettle. The multi-walled carbon nanotubes are amino-functionalized multi-walled carbon nanotubes. The introduction of amino groups endows the multi-walled carbon nanotubes with chemisorption of sulfides. Under nitrogen conditions, control the kettle temperature at 140 °C, stir for 2.5 h, add 0.2 g of dimaleimide, and react at 270 °C for 9 h. After the reaction is completed, stop heating. After cooling to 120 °C, transfer the reaction solution to an acetone solvent for filtration. The obtained crude product is subjected to Soxhlet extraction with acetone for 24 h, and then dried in vacuo to obtain a composite material of porous polyimide and multi-walled carbon nanotubes. During the in-situ polymerization process, the multi-walled carbon nanotubes contribute to the uniform attachment and growth of cross-linked polyimide polymers on their surfaces, forming richer nanopores, which is beneficial for the adsorption of polysulfides;

[0087] (2) Add 2.5 g of lithium fluoride to 40 mL of hydrochloric acid solution with a mass fraction of 30%, stir in a water bath at 40 °C for 12.5 min, then slowly add 1.5 g of aluminum titanium carbide. After complete addition, stir at 40 °C for 33 h. Centrifuge the mixed solution at 3000 rpm for 7.5 min to remove the upper liquid. The precipitate is first washed 4 times with dilute hydrochloric acid with a mass fraction of 10%, and then repeatedly centrifuged and washed with deionized water until the pH is 6.0. The washed precipitate is added to 100 mL of deionized water and ultrasonically treated in an ice bath for 0.75 h. The obtained colloidal solution is centrifuged at 4500 rpm for 12.5 min, and the upper colloidal solution is taken and filtered into a film using a vacuum circulating water suction filter and dried to obtain transition metal carbide nanosheets. It has a large specific surface area and rich functional groups and can be used as a sulfur carrier. The chemical adsorption between the surface functional groups and sulfur can slow down the shedding and loss of sulfur. The high conductivity of the transition metal carbide helps to improve the electron transport of the sulfur cathode and enhance the rate performance and cycle stability of the battery. The flexibility of the transition metal carbide helps to relieve the volume change of sulfur during charge and discharge and maintain the stability of the electrode structure;

[0088] (3) Disperse the porous polyimide and multi-walled carbon nanotube composite material described in step (1) in 50 mL of deionized water, then add the transition metal carbide nanosheets described in step (2), ultrasonically treat for 1.5 h, and then add potassium hydroxide powder to the turbid liquid and stir for 2.5 h. The addition amount of potassium hydroxide powder is 2.25 g. Potassium hydroxide can remove a large number of F and Cl functional groups on the transition metal carbide nanosheets, expose titanium oxide on the surface, and improve the chemical adsorption capacity for polysulfides. Centrifuge and wash the reaction product 4 times with deionized water. The precipitate is first freeze-dried, and after removing moisture, it is mixed evenly with cobalt nitrate hexahydrate powder, and then annealed at 375 °C in a nitrogen environment for 1.5 h to obtain a host material. The interlayer spacing of the transition metal carbide nanosheets is expanded by the spontaneous insertion of potassium ions, providing conditions for the filling and insertion of the porous polyimide and multi-walled carbon nanotube composite material. The addition of the porous polyimide and multi-walled carbon nanotube composite material reduces the stacking of nanosheets and forms a three-dimensional network structure. At the same time, Co 2+ is transformed into Co nanoparticles on the porous framework and uniformly dispersed, enhancing the adsorption of polysulfides, reducing the volume change of the composite material during charge and discharge, and as a framework, it can also improve the conductivity of the positive electrode, which is beneficial to improving the battery performance and service life.

[0089] Preparation method of poly-dopamine modified graphene oxide and zinc-based metal-organic framework composite coating material, specifically including the following steps:

[0090] a. Pour 75 mL of graphene oxide dispersion with a mass concentration of 2 mg / mL into 100 mL of N,N-dimethylformamide and 20 mL of methanol solution. Then add 0.8 g of zinc nitrate hexahydrate and 0.2 g of terephthalic acid, and ultrasonically treat for 5.5 h. Subsequently, place it in a high-pressure reaction kettle and put it into a constant-temperature blast drying oven. React at a high temperature of 110 °C for 15 h, cool to room temperature, centrifuge the solution at a speed of 7000 rpm for 7.5 min, wash the precipitate with absolute ethanol and centrifuge until the supernatant becomes colorless, collect the precipitate for drying treatment to obtain a graphene oxide and zinc-based organic framework composite material. In the graphene oxide and zinc-based organic framework composite material, the mass of graphene oxide accounts for 15% of the composite, which not only improves the dispersion of graphene oxide but also ensures the hardness and toughness of the composite material, is beneficial to the coating effect. The cubic porous structure of the zinc-based organic framework contains abundant micro-mesopores and a large pore volume. Compositing with graphene oxide can alleviate the volume expansion phenomenon of the electrode during the cycling process, and also provides sufficient space and adsorption sites for the loading of sulfur, enhancing the adsorption performance. And zinc ions can serve as catalytic active sites to promote the redox reaction of polysulfides, accelerate the conversion process of polysulfides, and effectively improve the utilization rate of sulfur;

[0091] b. Add the graphene oxide and zinc-based organic framework composite material described in step a to a Tris-HCl buffer solution with a pH of 8.5, ultrasonically treat at 30 °C for 1.5 h, then add dopamine hydrochloride, and stir at 30 °C for 24 h. Centrifuge the mixed solution at a speed of 10500 rpm for 7.5 min, wash the precipitate 4 times with deionized water, and dry to obtain a polydopamine-modified graphene oxide and zinc-based organic framework composite coating material. Among them, the zinc-based organic framework grows on the graphene oxide sheet structure, and at the same time, polydopamine is dispersed on its surface, optimizing the interface between the cathode material and the electrolyte, reducing the interface impedance, improving the conductivity and chemical activity of the coating material, enhancing the mechanical strength of the coating material, and reducing the volume change during charge and discharge.

[0092] This embodiment provides a preparation method for a sulfur battery cathode material containing a graphene oxide composite, specifically including the following steps:

[0093] S1. Mix 0.15 g of host material, 0.8 g of selenium powder, and 0.3 g of sulfur powder evenly, transfer them to a tube furnace, heat up to 475 °C at a rate of 2 °C / min, and then keep warm for 2.5 h to obtain a host material-supported selenium-doped cobalt sulfide composite material with a rich pore structure. The Co nanoparticles on the host material are transformed into Se-doped CoS2, and a large number of anion vacancies are introduced. The loading of Co, CoSe2, and CoS2 nanoparticles is beneficial to Li +The diffusion of S and the injection of molten S provide more electrochemical active sites for redox reactions, effectively restrict the shuttling of polysulfides, enhance the electronic conductivity of the material, and obtain high capacity and excellent cycle stability.

[0094] S2. Add the host material loaded with selenium-doped cobalt sulfide composite material described in step S1 to 150 mL of anhydrous ethanol, stir magnetically for 25 min, and ultrasonically treat for 1.5 h, and use it as a coating solution for standby. Then add polydopamine-modified graphene oxide and zinc-based organic framework composite coating material to 50 mL of deionized water, ultrasonicate for 4.5 h, and slowly drip it into the coating solution as a coating solution while stirring magnetically. After the dropwise addition is completed, put it into a water bath and heat it to 62.5° C., heat it for 1.5 h, and then freeze-dry it to obtain a sulfur battery positive electrode material containing graphene oxide composite. The polydopamine-modified graphene oxide and zinc-based organic framework composite coating material form a coating protective layer on the host material loaded with selenium-doped cobalt sulfide composite material, which significantly improves the conductivity, further effectively prevents the shuttle effect of polysulfides, and enhances the adsorption and utilization rate thereof. The multidimensional structure introduced by the modification treatment of loading and coating also provides a large buffer space for volume changes during charging and discharging, which is beneficial to improving the cycle stability of the battery.

[0095] Example 4

[0096] This embodiment proposes a sulfur battery positive electrode material containing a graphene oxide composite, comprising the following components in parts by weight: 40 parts of a host material loaded with selenium-doped cobalt sulfide composite material, and 20 parts of a polydopamine-modified graphene oxide and zinc-based organic framework composite coating material.

[0097] The host material comprises the following components in parts by weight: 10 parts of transition metal carbide nanosheets, 20 parts of porous polyimide and multi-walled carbon nanotube composite material, and 8 parts of cobalt nitrate hexahydrate.

[0098] The polydopamine-modified graphene oxide and zinc-based organic framework composite coating material comprises the following components in parts by weight: 10 parts of dopamine hydrochloride and 30 parts of graphene oxide and zinc-based organic framework composite material.

[0099] The preparation method of the host material specifically comprises the following steps:

[0100] (1) Add 15.0 g of diphenyl sulfone and 0.2 g of multi-walled carbon nanotubes into the reaction kettle. The multi-walled carbon nanotubes are amino-functionalized multi-walled carbon nanotubes. The introduction of amino groups endows the multi-walled carbon nanotubes with chemisorption of sulfides. Under nitrogen conditions, control the kettle temperature at -150 °C, stir for 2 h, add 0.3 g of dimaleimide, and control the reaction at 280 °C for 8 h. After the reaction is completed, stop heating. After cooling to 120 °C, transfer the reaction solution to acetone solvent for filtration. The obtained crude product is subjected to Soxhlet extraction with acetone for 24 h, and then dried in vacuo to obtain a porous polyimide and multi-walled carbon nanotube composite. During the in-situ polymerization process, the multi-walled carbon nanotubes help the cross-linked polyimide polymer to uniformly adhere and grow on its surface, forming richer nanopores, which is beneficial to the adsorption of polysulfides;

[0101] (2) Add 3.0 g of lithium fluoride to 40 mL of a hydrochloric acid solution with a mass fraction of 30%, stir in a water bath at 40 °C for 10 min, then slowly add 2.0 g of titanium aluminum carbide. After complete addition, stir at 40 °C for 30 h. The mixed solution is centrifuged at 3500 rpm for 5 min to remove the upper liquid. The precipitate is first washed 5 times with a 10% (mass fraction) dilute hydrochloric acid, and then repeatedly centrifuged and washed with deionized water until the pH is 6.0. The washed precipitate is added to 100 mL of deionized water and sonicated in an ice bath for 0.5 h. The obtained colloidal solution is centrifuged at 5000 rpm for 10 min, and the upper colloidal solution is taken and filtered into a film using a vacuum circulating water suction filter and dried to obtain transition metal carbide nanosheets. It has a large specific surface area and rich functional groups and can be used as a sulfur carrier. The chemisorption between the surface functional groups and sulfur can slow down the shedding and loss of sulfur. The high conductivity of the transition metal carbide helps to improve the electron transport of the sulfur cathode and enhance the rate performance and cycle stability of the battery. The flexibility of the transition metal carbide helps to relieve the volume change of sulfur during charge and discharge and maintain the stability of the electrode structure;

[0102] (3) Disperse the porous polyimide and multi-walled carbon nanotube composite material described in step (1) in 50 mL of deionized water, then add the transition metal carbide nanosheets described in step (2), and ultrasonically treat for 1 h. Then add potassium hydroxide powder to the turbid liquid and stir for 2 h. The addition amount of potassium hydroxide powder is 2.5 g. Potassium hydroxide can remove a large amount of F and Cl functional groups on the transition metal carbide nanosheets, expose titanium oxide on the surface, and improve the chemical adsorption capacity for polysulfides. Centrifuge and wash the reaction product 5 times with deionized water. First, freeze-dry the precipitate, remove the moisture, then mix it evenly with cobalt nitrate hexahydrate powder, and then anneal it in a nitrogen environment at 400 °C for 1 h to obtain the host material. The interlayer spacing of the transition metal carbide nanosheets is expanded by the spontaneous insertion of potassium ions, providing conditions for the filling and insertion of the porous polyimide and multi-walled carbon nanotube composite material. The addition of the porous polyimide and multi-walled carbon nanotube composite material reduces the stacking of the nanosheets and forms a three-dimensional network structure. At the same time, Co 2+ is transformed into Co nanoparticles on the porous framework and uniformly dispersed, enhancing the adsorption of polysulfides, reducing the volume change of the composite material during charge and discharge, and also improving the conductivity of the positive electrode as a framework, which is beneficial to improving the battery performance and service life.

[0103] Preparation method of a composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework, specifically including the following steps:

[0104] a. Pour 100 mL of a graphene oxide dispersion with a mass concentration of 2 mg / mL into 100 mL of N,N-dimethylformamide and 20 mL of methanol solution, then add 0.8 g of cobalt nitrate hexahydrate and 0.2 g of terephthalic acid, and ultrasonically treat for 5 h. Then place it in a high-pressure reaction kettle and put it into a constant-temperature blast drying oven. React at a high temperature of 120 °C for 10 h, cool to room temperature, centrifuge the solution at a speed of 8000 rpm for 5 min, wash and centrifuge the precipitate with absolute ethanol until the supernatant becomes colorless, and collect the precipitate for drying treatment to obtain a composite material of graphene oxide and zinc-based metal-organic framework. In the composite material of graphene oxide and zinc-based metal-organic framework, the mass of graphene oxide accounts for 20% of the composite, which not only improves the dispersibility of graphene oxide but also ensures the hardness and toughness of the composite material, which is beneficial to the coating effect. The cubic porous structure of the zinc-based metal-organic framework contains rich micro-mesopores and a large pore volume. Composite with graphene oxide can alleviate the volume expansion phenomenon of the electrode during cycling, and also provides sufficient space and adsorption sites for the loading of sulfur, enhancing the adsorption performance. And zinc ions can serve as catalytic active sites to promote the redox reaction of polysulfides and accelerate the conversion process of polysulfides, effectively improving the utilization rate of sulfur;

[0105] b. Add the graphene oxide and zinc-based metal-organic framework composite material described in step a into a Tris-HCl buffer solution with a pH of 8.5, sonicate for 1 h at 30 °C, then add dopamine hydrochloride, and stir at 30 °C for 24 h. Centrifuge the mixed solution at a speed of 11,000 rpm for 5 min, wash the precipitate 5 times with deionized water, and dry it to obtain a polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material. Among them, the zinc-based metal-organic framework grows on the graphene oxide sheet structure, and at the same time, polydopamine is dispersed on its surface, optimizing the interface between the cathode material and the electrolyte, reducing the interface impedance, improving the conductivity and chemical activity of the coating material, enhancing the mechanical strength of the coating material, and reducing the volume change during charge and discharge.

[0106] This example provides a method for preparing a sulfur battery cathode material containing a graphene oxide composite, which specifically includes the following steps:

[0107] S1. Mix 0.2 g of the host material, 1.0 g of selenium powder, and 0.4 g of sulfur powder evenly, transfer them to a tube furnace, heat up to 500 °C at a rate of 2 °C / min, and then keep the temperature for 2 h to obtain a host material-supported selenium-doped cobalt sulfide composite material with a rich pore structure. The Co nanoparticles on the host material are transformed into Se-doped CoS2, and at the same time, a large number of anion vacancies are introduced. The loading of Co, CoSe2, and CoS2 nanoparticles is beneficial to the diffusion of Li + and the injection of molten S, providing more electrochemically active sites for the redox reaction, effectively restricting the shuttle of polysulfides, enhancing the electronic conductivity of the material, and obtaining high capacity and excellent cycle stability;

[0108] S2. Add the host material-supported selenium-doped cobalt sulfide composite material described in step S1 into 150 mL of absolute ethanol, stir magnetically for 20 min, and sonicate for 1 h for use as the solution to be encapsulated. Then add the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material into 50 mL of deionized water, sonicate for 4 h, and slowly drip it into the solution to be encapsulated while stirring magnetically. After the dripping is completed, place it in a water bath and heat up to 65 °C for 1 h, and then freeze-dry to obtain a sulfur battery cathode material containing a graphene oxide composite. The polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material form a coating protection layer on the host material-supported selenium-doped cobalt sulfide composite material, significantly improving the conductivity, further effectively preventing the shuttle effect of polysulfides, enhancing the adsorption effect and utilization rate on it. The multi-dimensional structure introduced by the loading and coating modification treatment also provides a large buffer space for the volume change during charge and discharge, which is beneficial to improving the cycle stability of the battery.

[0109] Comparative Example 1

[0110] This comparative example provides a sulfur battery cathode material containing a graphene oxide composite. The difference from Example 1 is that the host material does not contain a porous polyimide and multi-walled carbon nanotube composite; the preparation method of the host material does not include step (1); the preparation method of the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material is the same as that of Example 1; the preparation method of the sulfur battery cathode material containing the graphene oxide composite is the same as that of Example 1.

[0111] Comparative Example 2

[0112] This comparative example provides a sulfur battery cathode material containing a graphene oxide composite. The difference from Example 1 is that the host material does not contain transition metal carbide nanosheets and cobalt nitrate hexahydrate; the preparation method of the host material does not include step (2), and cobalt nitrate hexahydrate is not added in step (3); the preparation method of the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material is the same as that of Example 1; the preparation method of the sulfur battery cathode material containing the graphene oxide composite is the same as that of Example 1.

[0113] Comparative Example 3

[0114] This comparative example provides a sulfur battery cathode material containing a graphene oxide composite. The difference from Example 1 is that the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material does not contain graphene oxide and dopamine hydrochloride; the preparation method of the host material is the same as that of Example 1; in step a of the preparation method of the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material, the graphene oxide dispersion is not added, and step b is not included; the preparation method of the sulfur battery cathode material containing the graphene oxide composite is the same as that of Example 1.

[0115] Experimental Example 1

[0116] Conductivity experiment

[0117] Test samples: The sulfur battery cathode materials containing graphene oxide composites prepared in Examples 1-4 and Comparative Examples 1-3.

[0118] Test method: Mix the test samples, Ketjen black, and PVDF in a mass ratio of 7:2:1 in NMP to form a slurry, coat it on carbon-coated aluminum foil, then dry it in a vacuum drying oven at 80 °C for 12 h, punch it into electrode sheets with a diameter of 12 mm using a punching machine, and finally separate the positive electrode and the lithium negative electrode with a Celgard 2400 membrane. Use a 1.0 M LITFSI (DOL / DME) solution containing 2% LiNO3 as the electrolyte to assemble a button-type LSBs; perform electrochemical impedance spectroscopy (EIS) tests on a CHI760E electrochemical workstation. By fitting and analyzing the EIS curve, the charge transfer resistance (Ω) is obtained. The smaller the charge transfer resistance, the better the conductivity.

[0119] Figure 2 Charge transfer resistance result diagrams for Examples 1-4 and Comparative Examples 1-3; as shown in the figure, the charge transfer resistances of Examples 1-4 are 45-56 Ω, indicating strong conductivity; the charge transfer resistances of Comparative Examples 1-3 are 70-86 Ω, indicating weak conductivity; the host material of Comparative Example 1 does not contain a porous polyimide and multi-walled carbon nanotube composite material, which cannot be inserted and filled between transition metal carbide nanosheets, increasing the stacking of nanosheets and unable to form a rich three-dimensional network structure, which is not conducive to maintaining sufficient contact of active substances and increases the impedance of the electrochemical reaction, resulting in weak conductivity; the host material of Comparative Example 2 does not contain transition metal carbide nanosheets and cobalt hexahydrate nitrate, which is not conducive to the dense continuity of the network structure and cannot be converted into Se-doped CoS2 through Co nanoparticles, which is not conducive to the sufficient and effective contact of active substances, resulting in weak conductivity; the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material of Comparative Example 3 does not contain graphene oxide and dopamine hydrochloride, and only the zinc-based metal-organic framework material with insufficient conductivity acts as the coating layer, resulting in weak conductivity.

[0120] Experimental Example 2

[0121] Rate performance experiment

[0122] Test samples: Sulfur battery cathode materials containing graphene oxide composites prepared in Examples 1-4 and Comparative Examples 1-3.

[0123] Test method: Mix the test samples, Ketjen black, and PVDF in a mass ratio of 7:2:1 in NMP to form a slurry and coat it on carbon-coated aluminum foil. Then, dry it in a vacuum drying oven at 80 °C for 12 h, punch it into electrode sheets with a diameter of 12 mm using a punching machine, and finally separate the positive electrode and lithium negative electrode with a Celgard 2400 membrane. Use a 1.0 M LiTFSI (DOL / DME) solution containing 2% LiNO3 as the electrolyte to assemble a button-type LSBs; due to the more serious shuttle effect of polysulfides under small current, resulting in rapid capacity decay, the rate performance test is selected at a positive electrode current density of 0.1 and 0.2 C to obtain the discharge specific capacity (mAh·g -1 ) and then calculate the discharge specific capacity retention rate (%) according to the ratio of the two.

[0124] Figure 3Graph of the discharge specific capacity retention rate for Examples 1-4 and Comparative Examples 1-3; as shown in the figure, the discharge specific capacity retention rate of Examples 1-4 is 92.3-95.5%, indicating that the shuttle effect of polysulfides is effectively reduced and the rate performance is better; the discharge specific capacity retention rate of Comparative Examples 1-3 is 78.6-85.2%, indicating that the shuttle effect of polysulfides cannot be effectively reduced and the rate performance is poor; the host material of Comparative Example 1 does not contain a porous polyimide and multi-walled carbon nanotube composite, and a more abundant pore structure cannot be formed, which is not conducive to the adsorption of polysulfides, resulting in the inability to effectively reduce the shuttle effect of polysulfides and poor rate performance; the host material of Comparative Example 2 does not contain transition metal carbide nanosheets and cobalt nitrate hexahydrate, reducing the carrier space of sulfur and also weakening the chemical adsorption of polysulfides, resulting in the inability to effectively reduce the shuttle effect of polysulfides and poor rate performance; the poly-dopamine modified graphene oxide and zinc-based metal-organic framework composite coating material of Comparative Example 3 does not contain graphene oxide and dopamine hydrochloride, which is not conducive to providing more active sites, thereby weakening the physical and chemical adsorption of polysulfides, resulting in the inability to effectively reduce the shuttle effect of polysulfides and poor rate performance.

[0125] Experimental Example 3

[0126] Cyclic stability experiment

[0127] Test samples: Cathode materials for sulfur batteries containing graphene oxide composites prepared in Examples 1-4 and Comparative Examples 1-3.

[0128] Test method: Mix the test samples, Ketjen black, and PVDF in a mass ratio of 7:2:1 in NMP to form a slurry and coat it on carbon-coated aluminum foil. Then, dry it in a vacuum drying oven at 80°C for 12 h, punch it into electrode sheets with a diameter of 12 mm using a punching machine, and finally separate the positive electrode and the lithium negative electrode with a Celgard 2400 membrane. Use a 1.0 M LiTFSI (DOL / DME) solution containing 2% LiNO3 as the electrolyte to assemble a coin-type LSBs; under a current density of 1C, perform constant current charge-discharge (GCD) tests, and calculate the decay rate (%) per cycle through the initial discharge specific capacity and the discharge specific capacity after 400 cycles.

[0129] Figure 4Graph of the per-cycle decay rate results for Examples 1-4 and Comparative Examples 1-3; as shown in the figure, the per-cycle decay rate of Examples 1-4 is 0.012-0.026%, indicating better cycle stability; the per-cycle decay rate of Comparative Examples 1-3 is 0.035-0.052%, indicating poor cycle stability; the host material of Comparative Example 1 does not contain a porous polyimide and multi-walled carbon nanotube composite material, and cannot fill and insert transition metal carbide nanosheets, which is not conducive to the stability of the structure, and thus is not conducive to reducing the volume change during charge and discharge, resulting in poor cycle stability; the host material of Comparative Example 2 does not contain transition metal carbide nanosheets and cobalt hexahydrate nitrate, and cannot form a rich pore structure and active sites, weakening the adsorption of polysulfides, and thus is not conducive to restricting the volume change of sulfur, resulting in poor cycle stability; the poly-dopamine modified graphene oxide and zinc-based metal-organic framework composite coating material of Comparative Example 3 does not contain graphene oxide and dopamine hydrochloride, and cannot prevent the structural collapse of the zinc-based metal-organic framework material, nor is it conducive to enhancing the mechanical strength of the coating material, increasing the volume change during charge and discharge, resulting in poor cycle stability.

[0130] The above experimental results show that the conductivity, rate performance, and cycle stability of Examples 1-4 of the present invention are significantly better than those of the samples of Comparative Examples 1-3. Among them, Example 1 using a host material loaded with a selenium-doped cobalt sulfide composite material and a poly-dopamine modified graphene oxide and zinc-based metal-organic framework composite coating material has stronger conductivity, better rate performance, and better cycle stability. After the host material loaded with Co nanoparticles is sulfided and selenized, the Co nanoparticles are converted into Se-doped CoS2, which has a rich pore structure and S vacancies, is conducive to improving the conductivity, inhibiting the shuttle and volume expansion of polysulfides. Then, the poly-dopamine modified graphene oxide and zinc-based metal-organic framework composite coating material forms a coating layer on the surface of the host material loaded with the selenium-doped cobalt sulfide composite material, further enhancing the conductivity of the sulfur battery cathode material, improving the adsorption capacity and utilization rate of polysulfides, and at the same time providing sufficient buffer space for volume expansion, significantly enhancing the battery performance and cycle stability.

[0131] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention.

[0132] The above describes the present invention and its embodiments. This description is not restrictive, and only one of the embodiments of the present invention is shown in the drawings. The actual application is not limited to this. In short, if those of ordinary skill in the art are inspired by it and design similar methods and embodiments without creative efforts without departing from the spirit of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A cathode material for a sulfur battery containing a graphene oxide composite, characterized in that: The sulfur battery cathode material containing graphene oxide composite includes the following components in parts by weight: 40-60 parts of a host material loaded with selenium-doped cobalt sulfide composite, and 10-20 parts of a composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework; the host material includes the following components in parts by weight: 10-20 parts of transition metal carbide nanosheets, 20-30 parts of a composite material of porous polyimide and multi-walled carbon nanotubes, and 5-8 parts of cobalt nitrate hexahydrate; the composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework includes the following components in parts by weight: 5-10 parts of dopamine hydrochloride, and 20-30 parts of a composite material of graphene oxide and zinc-based metal-organic framework.

2. A preparation method of a sulfur battery cathode material containing a graphene oxide composite according to claim 1, characterized in that: Specifically, it includes the following steps: S1. Mix 0.1-0.2 g of the host material, 0.6-1.0 g of selenium powder, and 0.2-0.4 g of sulfur powder evenly, transfer them to a tube furnace, heat up to 450-500 °C at a rate of 2 °C / min, and then keep the temperature for 2-3 h to obtain a host material loaded with selenium-doped cobalt sulfide composite; S2. Add the host material loaded with selenium-doped cobalt sulfide composite obtained in step S1 to 150 mL of absolute ethanol, stir magnetically for 20-30 min, and ultrasonically treat for 1-2 h to be used as the solution to be encapsulated. Then add the composite coating material of polydopamine-modified graphene oxide and zinc-based metal-organic framework to 50 mL of deionized water, ultrasonically treat for 4-5 h, and slowly drop it into the solution to be encapsulated as the coating solution while stirring magnetically. After the dropping is completed, place it in a water bath and heat up to 60-65 °C, heat for 1-2 h, and then freeze-dry to obtain the sulfur battery cathode material containing graphene oxide composite.

3. The preparation method of the sulfur battery cathode material of the graphene oxide composite according to claim 2, characterized in that: The preparation method of the host material specifically includes the following steps: (1) Add 15.0 g of diphenyl sulfone and 0.1-0.2 g of multi-walled carbon nanotubes to a reaction kettle. Under nitrogen conditions, control the kettle temperature at 130-150 °C, stir for 2-3 h, add 0.1-0.3 g of dimaleimide, and react at 260-280 °C for 8-10 h. After the reaction is completed, stop heating. After cooling to 120 °C, transfer the reaction solution to an acetone solvent for filtration. The obtained crude product is subjected to Soxhlet extraction with acetone for 24 h, and then vacuum-dried to obtain a composite material of porous polyimide and multi-walled carbon nanotubes; (2) Add 2.0 - 3.0 g of lithium fluoride into 40 mL of hydrochloric acid solution with a mass fraction of 30%, stir in a water bath at 40 °C for 10 - 15 min, then slowly add 1.0 - 2.0 g of aluminum titanium carbide. After complete addition, stir at 40 °C for 30 - 36 h. Centrifuge the mixed solution at 2500 - 3500 rpm for 5 - 10 min, remove the upper liquid. First, wash the precipitate with 10% dilute hydrochloric acid 3 - 5 times, and then repeatedly wash it with deionized water by centrifugation until the pH is 6.

0. Add the washed precipitate into 100 mL of deionized water, and ultrasonicate it in an ice bath for 0.5 - 1 h. Centrifuge the obtained colloidal solution at 4000 - 5000 rpm for 10 - 15 min, take the upper colloidal solution and filter it into a film using a vacuum circulating water suction filter, and dry it to obtain transition metal carbide nanosheets; (3) Disperse the porous polyimide and multi-walled carbon nanotube composite material described in step (1) in 50 mL of deionized water, then add the transition metal carbide nanosheets described in step (2), ultrasonically treat for 1 - 2 h, then add potassium hydroxide powder to the turbid solution, stir for 2 - 3 h, centrifuge and wash the reaction product with deionized water 3 - 5 times. First, freeze-dry the precipitate, after removing the moisture, mix it evenly with cobalt nitrate hexahydrate powder, and then anneal it in a nitrogen environment at 350 - 400 °C for 1 - 2 h to obtain the host material.

4. The preparation method of the sulfur battery cathode material of the graphene oxide composite according to claim 3, characterized in that: In step (1), the multi-walled carbon nanotubes are amino-functionalized multi-walled carbon nanotubes.

5. The preparation method of the sulfur battery cathode material containing graphene oxide composite according to claim 4, characterized in that: In step (3), the addition amount of potassium hydroxide powder is 2.0 - 2.5 g.

6. The preparation method of the sulfur battery cathode material containing graphene oxide composite according to claim 5, characterized in that: The preparation method of the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material specifically includes the following steps: a. Pour 50 - 100 mL of graphene oxide dispersion with a mass concentration of 2 mg / mL into 100 mL of N,N-dimethylformamide and 20 mL of methanol solution, then add 0.8 g of zinc nitrate hexahydrate and 0.2 g of terephthalic acid, ultrasonically treat for 5 - 6 h, then place it in a high-pressure reaction kettle, put it into a constant-temperature blast drying oven, and react at a high temperature of 100 - 120 °C for 10 - 20 h. Cool to room temperature, centrifuge the solution at 6000 - 8000 rpm for 5 - 10 min, wash the precipitate by centrifugation with absolute ethanol until the supernatant becomes colorless, collect the precipitate and perform drying treatment to obtain the graphene oxide and zinc-based metal-organic framework composite material; b. Add the graphene oxide and zinc-based metal-organic framework composite material described in step a into a Tris-HCl buffer solution with a pH of 8.5, ultrasonically treat at 30 °C for 1 - 2 h, then add dopamine hydrochloride, and stir at 30 °C for 24 h. Centrifuge the mixed solution at 10000 - 11000 rpm for 5 - 10 min, wash the precipitate with deionized water 3 - 5 times, and dry it to obtain the polydopamine-modified graphene oxide and zinc-based metal-organic framework composite coating material.

7. The preparation method of the sulfur battery cathode material containing graphene oxide composite according to claim 6, characterized in that: In step a, in the graphene oxide and zinc-based metal-organic framework composite material, the mass of graphene oxide accounts for 10 - 20% of the composite.

Images